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Coggins has been accepted towards fulfillment of the requirements for 1435;13:11— degree in E_nt. 0m0109y ‘I/ / v10! professor anew 0-7639 MS U i: an Aflirmative Action/Equal Opportunity Institution LIBRARY Michigan State University PLACE IN RETURN BOX to remove thie checkout from your record. TO AVOID FINES return on or baton die due. ll DATE DUE DATE DUE DATE DUE \ ~ ‘ ‘ ll 1__11 MSU le An Affirmetive ActiorVEquei Opportunlty Institution eana-ot 11 POTATO LEAFHOPPER (EMPOASCA FABAE) AND ALFALFA WEEVIL (HYPERA POSTICA) DENSITY AND DAMAGE IN BINARY MIXTURES OF ALFALFA AND FORAGE GRASSES By Margi L. Coggins A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Entomology 1991 ABSTRACT POTATO LEAF HOPPER (EMPOASCA FABAE) AND ALFALFA WEEVIL (HYPERA POST ICA) DENSITY AND DAMAGE IN BINARY MIXTURES OF ALFALFA AND FORAGE GRASSES By Margi L. Coggins Density and damage of potato leafhopper and alfalfa weevil in intercropped alfalfa/forage grass fields and in monoculture alfalfa fields were compared. In 1990, alfalfa weevil larval density (using sweep net sampling) and alfalfa tip damage was lower in fields intercropped with smooth brome, orchardgrass and timothy. On several sampling dates in 1989 and 1990, fewer potato leafhoppers (using suction sampling) were found in plots intercropped with brome and orchardgrass than in monoculture alfalfa. Potato leafhoppers were unable to reproduce on monocultures of smooth brome, orchardgrass, or timothy in the laboratory. Adult leafhoppers emigrated in higher numbers from caged pots of orchardgrass and smooth brome grass in both monocultures and mixtures with alfalfa than from alfalfa alone. Intercropping did not alter forage quality (crude protein, acid detergent fiber, and neutral detergent fiber) of alfalfa in any of the three harvests in 1990. ACKNOWLEDGEMENTS This work was supported, in part, by a grant from the Michigan Energy Conservation Program. Appreciation is extended to Scott Farm Seed Company and Great Lakes Hybrids, suppliers of seed used for these experiments. Thanks also to Kellogg Biological Station and its farm manager, Jim Bronson, for support. I am grateful to my committee members, Dr. D. Landis, Dr. M. Allen, Dr. J. Miller, and Dr. J .M. Scriber for advice. I would like to thank the "residents" in the forage lab of Oran Hesterrnan and Wally Moline for their assistance. Thank you to Mike Allen and his lab for teaching me forage quality analysis and giving me support. Jim Miller is noted and thanked as the originator of the "leaving assay' concept. Thanks also to his assistant, Trista Mowry, who rediscovered her father's cages for use in the leaving assay. A special thanks to my major advisor, Doug Landis, for his ideas and his patience. Thanks to Mike Haas and Joe Paling for field preparation. Thanks to Nancy Soule, Dan McMahon, Debra Addy, Anastasia Asongwed, Stephanie Wardell, Michael Ennis- McMillian, and my mother, Jo Crain, for data collection, suggestions, their sense of humor and their friendship. Finally, thank you to Jonathon DeNike for his assistance and affection. TABLE OF CONTENTS LIST OF TABLES ........................................................................................................ vi LIST OF FIGURES ....................................................................................................... ix CHAPTER 1: REVIEW OF LITERATURE ............................................................ 1 LIST OF REFERENCES .................................................................................... 1 2 CHAPTER 2: ALFALFA WEEVIL, HYPERA POSTICA, LARVAL DENSITY AND DAMAGE IN ALFALFA INTERCROPPED WITH FORAGE GRASSES ABSTRACT ........................................................................................................ 2 0 INTRODUCTION .............................................................................................. 2 1 METHODS .......................................................................................................... 2 4 Sampling and Analysis ................................................................... 2 7 RESULTS ............................................................................................................ 2 9 DISCUSSION ..................................................................................................... 4 5 LIST OF REFERENCES .................................................................................... 4 9 CHAPTER 3: POTATO LEAFHOPPER, EMPOASCA FABAE, POPULATION DYNAMICS AND DAMAGE IN ALFALFA/FORAGE GRASS MIXTURES ABSTRACT ........................................................................................................ 5 2 INTRODUCTION .............................................................................................. 5 4 METHODS ..................... ‘ ..................................................................................... 5 7 Field Sampling and Analysis. ...................................................... 6 0 Laboratory portion .......................................................................... 6 3 Reproduction and survival on grass ............................. 6 3 Leaving assay ......................................................................... 6 4 RESULTS ...................... 6 7 Field portion ....................................................................................... 6 7 l 9 8 9 ........................................................................................... 6 7 1 9 9 O ........................................................................................... 7 2 Laboratory studies ........................................................................... 9 0 Reproduction and Survival on grass ............................ 9 0 Leaving assay ......................................................................... 9 3 DISCUSSION ..................................................................................................... 9 6 LIST OF REFERENCES .................................................................................... 1 0 3 APPENDIX 1.1: RECORD OF DEPOSITION OF INSECT VOUCHER SPECIMEN S .................................................................................. l 0 5 TABLE 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 LIST OF TABLES Planting densities of alfalfa and three forage grasses, May 10, 1989, at Kellogg Biological Station. Chemicals applied to field at Kellogg Biological Station over course of study. Sampling types and dates on field at Kellogg Biological Station over course of study. Results of ANOVA treatment effects of first cutting biomass surveys, 1990. Treatment contrasts of grass portions of vegetation surveys in first cutting, 1990. Treatment contrasts of biomass surveys, alfalfa and weed portions, in first cutting. Treatment contrasts of alfalfa weevil larvae numbers in pure and mixed forage stands in 1990. Treatment contrasts of percent alfalfa weevil damage in pure and mixed forage stands on June 5, 1990. Results of regressions comparing biomass, alfalfa weevil numbers, and damage. Contrasts of alfalfa biomass fiber analysis treatments, June 6, 1990. vi PAGE 25 26 28 33 33 34 35 38 39 41 TABLE PAGE 3.1 Planting densities of alfalfa and three forage grasses, Male, 1989, at Kellogg Biological Station. 5 8 3.2 Chemicals applied to field at Kellogg Biological Station over course of study. , 5 9 3.3 Sampling types and dates on field at Kellogg Biological Station in 1989. 62 3.4 Sampling types and dates on field at Kellogg Biological Station in 1990.62 3.5 Treatment contrasts of potato leafhopper numbers in pure and mixed forage stands. 77 3.6 Results of ANOVA treatment effects of second and third cutting biomass surveys, 1990. 82 3.7 , Treatment contrasts of second cutting biomass surveys. 83 3.8 Contrasts of grass portions of biomass surveys in second and third cuttings. 84 3.9 Treatment contrasts of third cutting biomass surveys. 84 3.10 Results of regressions Comparing biomass against insect numbers for two sampling dates in July, 1990. 86 3.11 Surviving potato leafhopper adults and emerged nymphs during three weeks of exposure to adults to alfalfa and forage grass monocultures and binary mixtures. . 91 3.12 Replication of potato leafhopper reproduction experiment. 9 1 vii TABLE ' PAGE 3.13 Percent crude protein in plant matter after three weeks of potato leafhopper feeding (treatment) and in leafhopper-free controls. 92 “3.14 Percent of total adult potato leafhoppers trapped in each treatment, by replication. 94 viii LIST OF FIGURES FIGURE PAGE 2.1 Alfalfa weevil larvae density on four sampling dates. 31 2.2 Biomass survey results for first cutting, 1990. 32 2.3 Percentage of twenty randomly selected alfalfa tips damaged by alfalfa weevil larvae by first cutting, June 6, 1990. 37 2.4 Percent crude protein of alfalfa gathered in vegetation surveys on June 6, 1990. 42 2.5 Percent fiber (acid detergent [ADF] and neutral detergent [NDF] fiber) of alfalfa gathered in vegetation surveys on June 6, 1990. 43 2.6 Percent crude protein and fiber (acid detergent [ADF] and neutral detergent [NDF] fiber) of grass gathered in vegetation surveys on June 6, 1990. 44 3.1 Pop-bottle cage used for potato leafhopper reproduction and survival experiments. 66 3.2 Cage used for leaving assay experiments. 66 3.3 Potato leafhopper D-vac sampling on July 10, 1989. 70 3.4 Adult and nymphal potato leafhopper densities in 1989. 7 1 3.5 Adult potato leafhopper density in 1990 as determined by D-vac samples over two cuttings. 75 ix FIGURE PAGE 3.6 Potato leafhopper nymph density in 1990 as determined by D-vac samples over two cuttings. 7 6 3.7 Vegetation biomass from first three survey dates in second cutting period, 1990. 78 3.8 Vegetation biomass from last survey in second cutting period, 1990. 79 3.9 Vegetation biomass from first half of third cutting period, 1990. 80 3.10 .Vegetation biomass from second half of third cutting period, 1990. 81 3.11 Crude protein of alfalfa fraction of forage at second and third cutting. 87 3.12 Acid detergent fiber (ADF) and neutral detergent fiber (NDF) of alfalfa fraction of forage at second cutting. 8 8 3.13 Acid detergent fiber (ADF) and neutral detergent fiber (NDF) of alfalfa fraction of forage at third cutting. 89 3.14 Percentage of "escaped" potato leafhoppers after three days, averaged over five replications. 95 CHAPTER 1 REVIEW OF LITERATURE The potato leafhopper, Empoasca fabae (Harris) (Homoptera: ,Cicadellidae), is a serious pest of alfalfa, soybeans, beans (dry, edible, and fresh), potatoes and other crops in Michigan. Potato leafhoppers overwinter in the southern United States (Decker 1959) and migrate northward as adults in April, May, and June (Medler 1957). These adults are carried in warm air masses at elevations of 0.8 to 1.6 km (Glick 1939, 1960) and are deposited on the landscape with rains, at fronts and cooler air masses, and when exhausted or inactive (Wellington 1945, Pienkowski and Medler 1965). Storms most favorable for transport are typical in spring. They are characterized by high winds, rapid movement directly from the Mississippi Valley, ending in rain in the upper Midwest. The synoptic conditions that produce these patterns (high pressure to the east, low pressure to the west) are well known (Carlson et a1. 1991, Huff 1963, Pienkowski and Medler 1964). Potato leafhoppers are believed to be incapable of tolerating winter in the northern states where they feed. Decker and Cunningham (1967), after caging adults on alfalfa fields in fall, could find no surviving leafhoppers in spring. Also, potato leafhoppers cannot survive at temperatures below -15 degrees C (Decker and Maddox 1967). 2 Following migration, adults can breed on diverse interim host plants, such as oaks and honeysuckle (Gyrisco 1958). They then migrate to field crops where they oviposit. In alfalfa, eggs are laid in stem pith (Simonet and Pienkowski .1977), usually at night (Kieckhefer and Medler 1964). The average life span from egg to death as an adult is 33 days (DeLong 1938). The time required for eggs to hatch as nymphs is 136 _-|; 39.7 degree days (base 7.6 degrees C) (Simonet and Pienkowski 1980). Nymphs and adults feed on the phloem of host plants, leaving salivary sheath material in the phloem and occasionally xylem (Gyrisco 1958, Womak 1984). This sheath material causes interrupted photosynthate transport, leading to build-up in tissues distal to the feeding site (Smith and Poos 1931). Photosynthetic rates and, in turn, build up of carbohydrate reserves in the tap root, decline due to reduced transpiration rates (Poos and Johnson 1936, Davis and Wilson 1953, Wilson et al. 1955, Zaky 1981, Womak 1984, Shaw and Wilson 1986). Feeding traps higher levels of total‘ nonstructural carbohydrate in infested leaves (Flinn et al. 1990) and prevents elongation of stem intemodes (Oloumi-Sadeghi et al. 1988), resulting in a smaller plant. "Hopperbum," the visually observable result of the blockage and resultant damage, can be used as an indicator of infested and damaged alfalfa (Oloumi-Sadeghi et al. 1988). Feeding damage results in decreased forage dry weight and nitrogen content (Smith and Ellis 1983, Lamp et al. 1985, Flinn and Hower 1984, Kouskoulekas and Decker 1968). Why immigrants chose particular stands of host plants is not understood. Long distance immigrants tend to be female (Glick 1960); they appear better able to survive without food and water 3 during the long flight (Decker and Cunningham 1967). As the season progresses, in-field sex ratios shift, eventually reaching 1:1 by fall (Medler et al. 1966). Immigrants appear to cluster at field edges (Flinn et al. 1990) and elevated portions of the field (Kieckhefer and Medler 1966). Female potato leafhoppers may have a greater tendency to disperse out of alfalfa (Flinn et al. 1990). It is hypothesized by Flinn et al. (1990) that potato leaflloppers to go through three steps during spatial distribution. Long-distance immigrants land on alfalfa or nonhost plants as the cue for long distance flight ceases. Host-searching behavior begins, and short flights take the leafhoppers to alfalfa. When alfalfa is found the leafhoppers stop even the short flights and they accumulate at field edges (Flinn et al. 1990). Some researchers have found the presence of grass weeds reduces oviposition and increases flight of potato leafhoppers (Lamp et al. 1984, Smith 1987). The presence of nonhost plants, such as forage grasses, might prolong the flight of migrating leafhoppers and render the field unacceptable to potential immigrants. Currently, controls for potato leafhopper include insecticide sprays and cutting. To be effective, insecticides must be applied before nymphal populations are large enough to have caused yellowed leaves (hopperburn) (Womak 1984). Frequent cutting of alfalfa reduces the damage of potato leafhopper by killing the nymphs and killing or disturbing the adults (Simonet and Pienkowski 1979, Cuperus et al. 1986). Harvests which leave low stubble provide a poor recolonizing substrate for potato leafhoppers (Cuperus et al.1986). I 4 A second major pest of alfalfa in Michigan is the alfalfa weevil, Hypera postica (Gyllenhal), (Coleoptera: Curculionidae). This weevil was introduced from Europe and appeared first in Utah in 1904 (Titus 1910). By 1966, 41 states had established weevil populations (USDA 1966). Adult beetles chew holes in alfalfa stems and lay eggs in clusters of 2-25 within the hole, usually no more than seven to 10 cm above ground (Hamlin et al. 1943). When the eggs hatch, first instar larvae (0.5 mm long) feed inside the plants for three to four days, then climb to growing leaf buds at the tips of the plants to feed for the remainder of the first instar and part of the second (Titus , 1910). For the rest of their larval life, the weevils feed on leaves, leaving leaf veins and the lower epidermis untouched. This feeding gives infested fields a frosted appearance (Hamlin et al. 1943). Full- grown larvae are green with a white stripe down the middle of the back. They spin white cocoons, pupate and emerge as adults in two to three weeks. Adults which survive cutting remain active until July (Hower 1982). Most of these adults will migrate to sheltered areas to overwinter and reach sexual maturity the following spring (Landis and Haas 1.990). Alfalfa weevil adults apparently use humidity, vision, and olfaction to detect host plants (Meyer 1975, Meyer and Raffensperger 1974a, b, c). The adults are not strong flyers and usually fly only with the wind, but can travel as far as 136 km each year (Prokopy and Gyrisco 1965, Blickenstaff et al. 1972, Blickenstaff 1965). Weevils cannot distinguish alfalfa in chambers from empty controls when the air in both has been humidified (Meyer and Raffensperger 1974a). However, they "respond more actively" to 5 living alfalfa than to dead alfalfa, even when air currents are pulled away from the plants, suggesting the use of visual cues (Meyer and Raffensperger 1974c). However, adults cannot visually discriminate between alfalfa and red clover, oats, bluegrass, or beans (Meyer 1975). Although Meyer and Raffensperger minimize the importance of olfaction in weevil host plant orientation, adults do turn more frequently. when exposed to alfalfa leaf odor (Golik and Pienkowski 1969). A combination of all senses probably serves to get weevils to a planted field (humidity detection), then to move toward plants resembling alfalfa (vision), and finally to incite them to taste the plants (olfaction). Feeding and oviposition would then occur. Alfalfa weevils damage the first cutting of alfalfa (Hintz et al. 1976), but can also weaken the stand, limiting subsequent cuttings. Overwintering mortality of alfalfa can be increased due to weevil damage (Godfrey and Yeargan 1989), due to reduCtions in nonstructural root carbohydrates (Fick and Liu 1976) on which the plant. depends for regrowth and overwintering. Alfalfa weevil can be controlled with integrated pest management, including early harvests, pesticides, and introduced parasitoids M icroctonus aethiopoides (Loan)(Hymenoptera: Braconidae), BathypleCtes anurus (Thomson)(Hymenoptera: Braconidae) and Bathyplectes curculionis (Thomson)(Hymenoptera: Ichneumonidae) (Landis and Haas 1990). These three parasitoids are listed in order of importance in Michigan, but in‘ other states these and other parasitoids may perform differently; for example B. curculionis is reported to be more important in Illinois (Onstad and Shoemaker 1984). Areas with well- established parasitoid populations frequently have no need for 6 chemical control of alfalfa weevil (Day 1981). Fungal pathogens, such as Erynia phytonomi (Zygomycetes: Entomophthorales), can also be a major cause of mortality in weevils during maist springs (Goh et al. 1989). Fungal epizootics, which can thrive in wet springs, often occur after first-cutting alfalfa matures and after the weevil populations have peaked (Puttler et al. 1980, Brandenburg 1985, Nordin et al. 1983). Intercropping with forage grasses or allowing weeds into the sward is a potential method of managing alfalfa herbivores. The presence of grass weeds reduced potato leafhopper density (Lamp et al. 1984). Grass weeds or grass weed volatiles in alfalfa reduced female fecundity and increased flight (Smith 1987). The nymphs of the few eggs laid in grass weeds, especially yellow nutsedge (Cyperus esculentus L.), crabgrass (Digitaria sanguinalis (L.) Scop.), and foxtail (Setaria faberi Herrm), generally do not survive (Lamp et al. 1984). Since extracts of grass applied to alfalfa also reduced oviposition (Smith 1987). and increased flight, the presence of non-food biomass in an alfalfa-grass field is not the only deterrent to potato leafhoppers. Intercropping grass or weeds may also affect alfalfa weevil. Anecdotal evidence from alfalfa growers suggests weedy or grassy fields contain fewer potato leafhopper and alfalfa weevil. Titus noticed in 1910 that alfalfa fields in Summit County, Utah with "considerable" (sic) timothy seem to experience less alfalfa weevil damage. He noticed the timothy appeared to shade the alfalfa. Alfalfa weevils feed only on legumes, prefering alfalfa. They must taste or eat alfalfa to oviposit; other plants probably contain 7 oviposition deterrents (Byme 1969). Since alfalfa weevil must taste alfalfa before ovipositing, and they will not eat grass, intercrOpped grasses in- alfalfa fields could serve to mask food and oviposition sites, reducing alfalfa weevil numbers and damage. Buntin (1989) did not find grass weeds to alter alfalfa weevil defoliation of alfalfa, and grass root dry weight increased when alfalfa was removed by alfalfa. weevil, but this caged greenhouse experiment did not allow for choices or migration. Weevils use vision and odor to locate host plants, and thus could be distracted by grass odors, colors, or shapes. Finally, higher concentrations of preferred food resources exist in monocultures. Root's (1973) "resource concentration hypothesis" states that herbivores inhabiting monocultures of host plants will exhibit greater colonization rates, greater reproduction and longer tenure time as compared to the same herbivore inhabiting a diverse community. If greater concentrations 1 of food exist in monocultures, both potato leafhoppers and alfalfa weevil populations may be reduced in intercrops. The "enemies impact hypothesis" (Price 1984) may also serve as a partial explanation of why potato leafhoppers and alfalfa weevils may be less prevalent in intercropped alfalfa. Price's clarified version of the "enemies hypothesis" states that crop diversification creates an environment more favorable than monocultures for natural enemies of pests by providing additional resources. Nabid bugs, (especially Nabis roseipennis) a known predator of potato leafhopper, prefer to oviposit in grasses (Martinez and Pienkowski 1983, Mundinger 1922). Significantly more nabids were found in grassy alfalfa than in "uninfested" alfalfa in studies by 8 Barney, et al. (1984). The practical impact of nabids on potato leafhopper is questionable, however, because nabids prefer to eat pea aphids, Acrythosiphon pisum (Harris) (Homoptera: Aphididae), a fairly sessile creature, and they have not been shown to be an effective control agent of potato leafhopper (Rensner et al. 1983). Alfalfa, Medicago sativa L., is a popular forage crop because it produces hay more than once a year and it contains more nitrogen than most other field crops. In addition, because it fixes atmospheric nitrogen in underground nodules, it adds nitrogen to the soil. A stand of alfalfa can last four to six years, depending on fertility, soil, climate, and weeds or companion crops (Scheaffer and Marten 1986). Alfalfa has a crown and a tap root which stores nonstructural carbohydrates used to replenish photosynthetic tissue in times of defoliation, stress, and cutting (Hodgkinson 1969, Reynolds 1971, Chatterton et al. 1974, and Smith 1975). As a forage, alfalfa excels in providing nitrogen. However, too high of a percentage of crude protein in the diet of cattle can cause problems in reproduction, bloat, and waste, as more energy is used to excrete the additional urea created. Too much protein causes high surface tension in the rumen and forms bubbles which will not burst, causing bloat (Howarth 1975). A high rate of release of soluble protein from alfalfa is positiVely correlated with incidence of bloat (Howarth et al. 1978). A balance must be reached between degradable proteins, which feed rumen microbes, and undegradable proteins, which provide proteins directly to the cow. Adding grass to the cow's rations can increase efficiency by aiding in the formation of the rumen mat, which holds particles for microbe fermentation, and 9 by decreasing bloat by diluting soluble proteins (Howarth et al. 1978, Michael Allen, Animal Scientist, Michigan State University, personal communication). Alfalfa grown for grazing is often planted with a ' forage grass to reduce bloat potential. Weeds or grass mixed in the ration or grown with the alfalfa can reduce the problems mentioned above by adding fiber to the diet. Many annual weeds also supply nitrogen and other nutrients to the forage. Marten and Anderson (1975.) found that three common weeds were equivalent to alfalfa in nutrient composition and digestibility at early maturity: Pigweed (Amaranthus retroflexus), common lambsquarters (Chenopodium album), and common ragweed (Ambrosia artemisiifolia). Nine of the 12 weeds tested by Marten and Andersen contained more crude protein than oats and ten were more digestible. Dutt et al. (1979) determined that quackgrass (Agropyron repens) reduced digestibility and protein percentage in alfalfa forage. Milking cows fed alfalfa treated with the herbicide pronamide to control quackgrass had nearly 20% higher milk production than those fed weedy forage. The incidence of the problems of high nitrogen feed listed above, however, was not discussed. Also, dandelions grew in the place of the damaged quackgrass. Dandelions can eontain as much crude protein as alfalfa but are exceptionally high in potassium, they increase drying time in hay and create agronomic problems (Doll 1986). This performance of quackgrass in terms of adding fiber and indigestible matter to the forage is probably typical of grasses in alfalfa. Forage grasses, such as those planted with alfalfa in this 10 study, will also lower the highly digestible components, partly digestible components, and percent protein. But for the reasons listed earlier, this apparent decrease in forage quality may not be detrimental. Some weeds do decrease forage quality, milk production and taste, and palatability for cattle and goats. Temme et al. (1979) found Pennsylvania“ smartweed (Polygonum pensylvanicum), yellow foxtail (Setaria lutescens) and shepherd's purse (Capsella bursa- pastoris) were the most damaging to laboratory-determined forage quality. Yellow rocket (Barbarea vulgaris) is refused by cattle and goats and significantly reduced all qualitative parameters in alfalfa hay containing it (Dutt et al. 1982). Pure alfalfa is difficult and expensive to maintain and may not be profitable (Cosgrove and Barrett 1988). Seeding alfalfa with a companion crops is a recognized method for establishing alfalfa without herbicides. Goodwin and Morrison (1984) observed wheat companion seeding of alfalfa suppressed dry matter production of redroot pigweed and lambsquarters by more than 50%, night flowering catchfly by 75%, and wild oat and green foxtail by 60 to 70%. Other broadleaf weeds, however, were not significantly reduced. Also, companion cropping reduced light available to alfalfa seedlings and reduced second season regrowth by 50%. In Michigan, many farmers companion seed alfalfa with oats to provide early forage harvest, a‘s oats can be harvested before alfalfa (Temme ct al. 1979). Recently, studies have shown that the same benefits of an oat companion crop can be achieved by intercropping alfalfa with forage grasses (Brothers 1991, Schmidt 1991). 11 Adding grass to alfalfa may help outcompete weeds (Drolsom and Smith 1976) and should not add to hay drying time as with dandelion-infested hay (Doll 1985). Dutt et al. (1982) found that alfalfa forage with 29% weeds, including quackgrass, smooth brome, and orchardgrass, did not suffer reduced feeding value. Casler and Walgenbach (1990) found legume/forage grass mixtures suppressed weeds, aided in preventing erosion, and increased stand duration. The negative interactions of insects and weed pests may also- be improved with alfalfa-grass intercropping. Buntin (1989) reported that alfalfa weevil feeding on alfalfa regrowth following harvest allowed weeds to outcompete alfalfa in the second cutting. In addition, Berberet et al. (1987) found the combination of alfalfa weevil and weeds resulted in poor yield and stand retention. In this study, it is hypothesized that intercropping forage grasses into alfalfa stands will reduce insect pest damage. Since adding grass to alfalfa stands has been shown to suppress weeds, and if intercropping also helps control insects, these stands could produce greater quantities of good quality forage for longer duration than monoculture alfalfa. LIST OF REFERENCES Barney, R.J., W.O. Lamp, EJ. Armbrust, and G. Kapusta. 1984. Insect predator community and its response to weed management in spring-planted alfalfa. Protection Ecology 76:23-33. Berberet, R.C., J .F. Stritzke, A.K. Dowdy. 1987. Interactions of alfalfa weevil (Coleoptera: Curculionidae) and weeds in reducing yield and stand of alfalfa. J. Econ. EntOmol. 80(6):1306-1313. Blickenstaff, CC. 1965. Partial insterility of Eastern and Western US. strains of the alfalfa weevil. Ann. Entomol. Soc. Am. 58:523-6. Blickenstaff, C.C., J.L. Huggans, and R.W. Schroder. 1972. Biology and ecology of the alfalfa weevil, Hypera postica, in Maryland and New Jersey. 1961 to 1967. Ann. Entomol. Soc. Am. 65:336-49. Borror, D.J., D.M. DeLong, and C.A. Triplehom. 1981. An introduction to the study of insects, fifth edition. CBS College Publishing. Brandenburg, R.L. 1985. Impact of Erynia phytonomi (Zygomycetes: Entomophthorales), a fungal pathogen, on alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae) populations in Missouri. J. Econ. Entomol. 78: 460-462. Brothers, B. 1991. The effect of conventional and direct drill establishment of alfalfa on plant density, forage yield, and forage quality. M.S. thesis, Michigan State University, East Lansing. Buntin, GD. 1989. Competitive interactions of alfalfa and annual weeds as affected by alfalfa weevil (Coleoptera: Curculionidae) stubble defoliation. J. Entomol. Soc. 24(1):78-83. Byme, H.D. 1969. The oviposition response of the alfalfa weevil Hypera postica (Gyllenhal). Univ. of Maryland Ag. Exp. Station Bulletin A-160. Carlson, J.D., M.E. Whalon, D.A. Landis, and SH. Gage. 1991. Evidence for long-range transport of potato leafhopper into Michigan. Proc. Amer. Meteorol. Soc. Cont. on Biometeorology, Sept. 1991. 12 13 Casler, MD. and R.P. Walgenbach. 1990. Ground cover potential of forage grass cultivars mixed with alfalfa at divergent locations. Crop Sci. 30:825-831. Cosgrove, DR. and M. Barrett. 1988. Effects of weed control in established alfalfa (Medicago sativa) on forage yield and quality. Weed Sci. 35(4):564-567. Cuperus, G.W., C.G. Watrin, and EB. Radcliffe. 1986. Influence of post-harvest alfalfa stubble on potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae) J. Kansas Entomol. Soc. 59:246-252. Davis, R.L. and M.C. Wilson. 1953. Varietal tolerance of alfalfa to potato leafhopper. J. Econ. Entomol. 46:242-245. Day, W.H. 1981; Biological control of the alfalfa weevil in the Northeastern United States, pp. 361-374. In G.C. Papvizas (ed.), Biological control in crop production. Allanheld, Osmun, Totowa, NJ. Decker, G.C. 1959. Migration mechanisms of leaflloppers. Proc. North Central Branch Entomol. Soc. Amer. 14:11-12. Decker, G.C. and H.B. Cunningham. 1967. The mortality rate of the potato leafhopper and some related species when subjected to prolonged exposure at various temperatures. J. Econ. Entomol. 60:373-379. Decker, G.C. and J.V. Maddox. 1967. Cold-hardiness of Empoasca fabae and some related species. J. Econ; .Entomol. 60:1641- 1645. DeLong, D.M. 1938. Biological studies on the leafhopper Empoasca fabae as a bean pest. U.S. Dep. Agr. Tech. Bull. 618. Doll, JD. 1985. Forage weed management update. Proc. Wis. Forage Council 9:73-76. Doll, JD. 1986. Weed control in forage crops. Chap. 7 in "Forage management in the North". R. Buhla and R. Walgenbach. Kendall/Hunt Pub. Co., Dubuque, Iowa. 14 Drolsom, RN. and D. Smith. 1976. Adapting species for forage mixtures. pp. 223-232. In R.I. Papendick, et al. (ed.) Multiple cropping. ASA Spec. Pub]. 27. ASA, CSSA, and SSSA, Madison, WI. ' Dutt, T.E., R.G. Harvey, R.S. Fawcett, N.A. Jorgensen, H.J. Larsen, and D.A. Schlough. 1979. Forage quality and animal performance as influenced by quackgrass (Agropyron repens) control in alfalfa (Medicago sativa) with pronamide. Weed Sci. 27(1):127- 132. Dutt, T.E., R.G. Harvey, and R.S. Fawcett. 1982. Feed quality of hay containing perennial broadleaf weeds. Agron. J. 74:673-676. Fick, G.W. and B.W.Y. Liu. 1976. Alfalfa weevil effects on root reserves, development rate, and canopy structure of alfalfa. Agron. J. 68: 595-599. Flinn, P.W. and AA. Hower. 1984. Effects of density, stage, and sex of the potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae), on seedling alfalfa growth. Can. Entomol. 116:1543-1548. Glick, RA. 1939. The distribution of insects, spiders and mites in the air. U.S. Dep. Agr. Tech. Bull. 673. Glick, RA. 1960. Collecting insects by airplane, with special reference to the dispersal of the potato leafhopper. U.S. Dep. Agr. Tech. Bull. 1222: 1-16. ' Godfrey, L.D. and K.V. Yeargan. 1989. Effects of clover root curculio, alfalfa weevil (Coleoptera: Curculionidae), and soil-borne fungi on alfalfa stand density and longevity in Kentucky. J. Econ. Entomol. 82(6): 1749-1756. Goh, K.S., R.C. Berberet, L.J. Young, and KB. Conway. 1989. Mortality of Hypera postica (Coleoptera: Curculionidae) in Oklahoma caused by Erynia phytonomi (Zygomycetes: Entomophthorales). Environ. Entomol. 18(6): 964-969. 15 Golik, Z. and R.L. Pienkowski. 1969. The influence of temperature on host orientation by the alfalfa weevil, Hypera postica. Entomol. Exp. Appl. 12:133-138. Goodwin, M.S. and LN. Morrison. 1984. Effects of companion cropping on weed growth and alfalfa establishment. NCWCC Proc. 39:113-114. Gyrisco, G.G. 1958. Forage insects and their control. Ann. Rev. Entomol. 3:421-448. Hach, C.C., B.K. Bowden, A.B. Kopelove, S.V. Brayton. 1987. Method performance: More powerful peroxide Kjeldahl digestion method. J. Assoc. Off. Anal. Chem., 70(5): 783-787. Hamlin, J.C., W.C. McDuffie, F.V. Lieberman, R.W. Bunn. 1943. Prevention and control of alfalfa weevil damage. USDA Farmers Bulletin Number 1930. Hintz, T.R., M.C. Wilson, and EJ. Armbrust. 1976. Impact of alfalfa weevil larval feeding on the quality and yield of first cutting alfalfa. J. Econ. Entomol. 69: 749-54. Howarth, RE. 1975. A review of bloat in cattle. Can. Vet. J. 16:281- 294. . Howarth, R.E., B.P. Goplen, A.C. Fesser, and SA. Brandt. 1978. A pessible role for leaf cell rupture in legume pasture bloat. Crop Sci. 18:129-133. Hower, AA. 1982. Impact of alfalfa harvest on Microctonus aethiopoides and Microctonus colesi parasites of the alfalfa weevil Hypera postica. Final Rept. U.S. Dep. Agric. Coop. Agrmnt. 12-14-1001-1208. Huff, RA. 1963. Relation between leafhopper influxes and synoptic weather conditions. J. Appl. Meteorol. 2:39-43. Kieckhefer, R.W. and LT. Medler. 1964. Some environmental factors influencing oviposition by the potato leafhopper, Empoasca fabae. J. Econ. Entomol. 57(4):482-484. 16 Kouskoulekas, C.A., and G.C. Decker. 1966. The effect of temperature on the rate of development of the potato leafhopper, E mpoasca fabae (Homoptera: Cicadellidae). Ann. Entomol. Soc. Amer. 59(2):292-298. - Lamp, W.O., Barney, R.J., Armbrust, EL, and Kapusta, G. 1984. Selective weed control in spring-planted alfalfa: Effect on leafhoppers and planthoppers (Homoptera: Auchenorrhyncha), with emphasis on potato leafhopper. Environ. Entomol. ' l3(l):207-213. Lamp, W.C., S.J. Roberts, K.L. Steffey, and EL Armbrust. 1985. Impact of insecticide applications at various growth stages on potato leafhopper (Homoptera: Cicadellidae) abundance and crop damage. J. Econ. Entomol. 78:1393-1398. Landis, D. and M. Haas. 1990. Alfalfa weevil management. Extension Bulletin E-2242, May 1990. Cooperative Extension Service, Michigan State University, East Lansing, MI. Marten, G.C. and RN. Andersen. 1975. Forage nutritive value and palatability of 12 common annual weeds. Crop Sci. 15:821-827. Martinez, D.G., and R.L. Pienkowski. 1983. Comparative toxicities of several insecticides to an insect predator, a nonpest prey. species, and a pest prey species. J. Econ. Entomol. 76:933-935. Medler, J .T. 1941. The nature of injury to alfalfa caused by Empoasca fabae (Harris). Ann. Entomol. Soc. Amer. 34(2):439- 450. Medler, J .T. 1957. Migration of the potato leafhopper--a report on a cooperative study. J. Econ. Entomol. 50(4):493-497. Meyer, LR. 1975. Effective range and species specificity of host recognition in adult alfalfa weevils, Hypera postica. Ann. Entomol. Soc. Amer. 68(1):1-3. Meyer, JR. and EM. Raffensperger. 1974a. "Indirect-choice" olfactometer experiments on adult alfalfa weevils. Ann. Entomol. Soc. Amer. 67:135-6. 17 Meyer, LR. and E.M. Raffensperger. 1974b. Kinetic orientation. experiments on adult alfalfa weevils. Ann. Entomol. Soc. Amer. 67: 143-4. Meyer, LR. and E.M. Raffensperger. 1974c. The role of vision and olfaction in host plant recognition by the alfalfa weevil, H ypera postica. Ann. Entomol. Soc. Amer. 67:187-90. Nordin, G.L., G.C. Brown, and J.A. Millstein. 1983. Epizootic phenology of Erynia disease of the alfalfa weevil in central Kentucky. Environ. Entomol. 12: 1350-1355. Oloumi-Sadeghi, H., L.R. Zavaleta, SJ. Roberts, EJ. Armbrust, and G. Kapusta. 1988. Changes in morphological stage of development, canopy structure, and root nonstructural carbohydrate reserves of alfalfa following control of potato leafhopper (Homoptera: Cicadellidae) and weed populations. J. Econ. Entomol. 81(1): 368-375. Onstad, D.W. and C.A. Shoemaker. 1984. Management of alfalfa and the alfalfa weevil (Hypera postica): An example of systems analysis in forage production. Ag. Systems 14: 1-30. Pienkowski, R.L. and J.T. Medler. 1964. Synoptic weather conditions associated with long-range movement of the potato leafhopper, Empoasca fabae, into Wisconsin. Ann. Entomol. Soc. Amer. 57(5): 588-591. Price, P.W., 1984. Insect Ecology. Second edition. John Wiley & Sons, New York, NY, 607 pp. Prokopy, R.J., and G.G. Gyrisco. 1965. Diel flight activity of migrating alfalfa weevils, Hypera postica (Coleoptera: Curculionidae). Ann. Entomol. Soc. Am. 58:642-7. Poos, F.W. and H.W. Johnson. 1936. Injury to alfalfa and red clover by the potato leafhopper. J. Econ. Entomol. 29(2):325-331. Puttler, B., D.L. Hostetter, S.H. Long, and A.A. Borski, Jr. 1980. Seasonal incidence of the fungus Entomophtora phytonomi infecting H. postica larvae in central Missouri. J. Invertebr; Pathol. 35: 99-100. 18 Rensner, P.E., W.O. Lamp, R.J. Barney, and EJ. Armbrust. 1983. Feeding tests of Nabis roseipennis (Hemiptera: Nabidae) on potato leafllopper, Empoasca fabae (Homoptera: Cicadellidae), and their movement into spring-planted alfalfa. J. Kan. Entomol. Soc. 56:446-450. Root, RB. 1973. Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassi ca oleracea). Ecol. Monogr., 43:95-124. Scheaffer, CC. and G.C. Marten. 1986. Producing quality alfalfa - a systems approach. 17th Ann. Alfalfa Improvement Conf., Lafayette, Indiana. pp. 30-39. Schmidt, LR. 1991. Alternative methods of alfalfa establishment. M.S. thesis, Michigan State University, East Lansing. Shaw, M.C. and M.C. Wilson. 1986. The potato leafhopper: scourge of leaf protein and root carbohydrate too, pp. 152-160 in Proceedings, 16th National Alfalfa Symposium, March 5-6, 1986. Purdue University, Fort Wayne, Indiana. Simonet, DE. and R.L. Pienkowski. 1977. Sampling and distribution of potato leafhopper eggs in alfalfa stems. Ann. Entomol. Soc. Amer. 70:933-936. Simonet, DE. and R.L. Pienkowski. 1979. Impact of alfalfa harvest on potato leafhopper populations with emphasis on nymphal survival. J. Econ. Entomol. 72:428-431. Simonet, DE. and R.L. Pienkowski. 1980. Temperature effect on development and morphometrics of the potato leafhopper. Environ. Entomol. 9:798-800. Smith, RF. and F.W. Poos. 1931. The feeding habits of some leafhoppers of the genus Empoasca. J. Agric. Res. 43:267-284. Smith, L.M. 1987. Mechanisms by which grass reduces potato leafllo'pper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), abundance in alfalfa. Ph.D. dissertation, University of Illinois, Urbana-Champaign. 1 9 Smith, S.M. and CR. Ellis. 1983. Economic importance of insects on regrowth of established alfalfa fields in Ontario. Can. Entomol. 115:859-968. Temme, D.G, R.G. Harvey, R.S. Fawcett, and A.W. Young. 1979. Effects of annual weed control on alfalfa forage quality. Agron. J. 71:51-54. - Titus, E.G. 1910. The alfalfa leaf weevil. Utah Ag. College Experiment Station Bulletin Number 110, September. U.S.D.A. 1966. Plant Pest Control Division. Coop. Econ. Ins. Rep. 16: 241. Watkins, K.L., T.L. Veum, G.F. Krause. 1987. Total nitrogen determination of various sample types: A comparison of the Hach, Kjeltec, and Kjeldahl methods. Assoc. Off. Anal. Chem., 70(3): 410-412. Wellington, W.G. 1945. Conditions governing the distribution of insects in the free atmosphere. Can. Entomol. 77:7-15, 21-28, 44-49. Wilson, M.C., R.L. Davis and G.G. Williams. 1955. Multiple effects of leafhopper infestation on irrigated and non-irrigated alfalfa. J. Econ. Entomol. 48:323-326. Womak, CL. 1984. Reduction in photosynthetic and transpiration rates of alfalfa caused by potato leafhopper (Homoptera: Cicadellidae) infestations. J. Econ. Entomol. 77:508-513. Zaky, S.H.F.M. 1981. Damage potential of potato leafhopper nymphs, Empoasca fabae (Harris), on established stand alfalfa. Ph.D. dissertation, The Pennsylvania State Univ., University Park. CHAPTER 2 ALFALFA WEEVIL, HYPERA POSTICA, LARVAL DENSITY AND DAMAGE IN ALFALFA INTERCROPPED WITH FORAGE GRASSES ABSTRACT The effect of alfalfa (Medicago sativa L.) intercropped with three forage grass species on alfalfa weevil numbers, damage, and plant biomass was determined in a randomized complete block design field experiment. Eight treatments consisting of alfalfa alone (18 and 14.6 kg/ha') and in mixtures with the forage grasses: smooth brome grass (Bromus enermis Leyss.), orchardgrass (Dactylis glomerata 1.), and timothy (Phleum pratense L.). Each grass species was intercropped with alfalfa (14.6 kg/ha) at two seeding rates. Weekly insect sampling showed significantly (ng.05 using two way ANOVA and contrasts) more alfalfa weevil larvae in alfalfa monocultures than in alfalfa-forage grass mixtures on two sampling dates (immediately prior to and at first cutting). Alfalfa weevil damage was also greater in alfalfa monocultures than in four out of six mixtures at harvest. Weevil density was not correlated with alfalfa, grass, or total plant biomass density. Intercropping forage grasses shows promise for reducing alfalfa weevil damage and producing long-lasting stands of high-quality forage. 20 INTRODUCTION Alfalfa weevil, Hypera postica (Gyllenhal) is a serious pest of first-cutting alfalfa in Michigan. The weevil's feeding removes leaf tissue, giving the field a silvery appearance and reducing the quantity and quality of alfalfa harvested (Hamlin et al. 1943). Alfalfa weevil feeding on regrowth following cutting hinders alfalfa's ability to compete with weeds (Buntin 1989) and can reduce subsequent yields (Edwards et al. 1978). The weevil can be managed _ using integrated pest management techniques, including cultural, chemical, and biological controls. Timely cutting of hay (early to mid-bud stage) is recommended - as the primary method for limiting weevil damage. In combination with the introduced parasitoids, Microctonus aethiopoides ' (Loan)(Hymenoptera: Braconidae), Bathyplectes anurus (Thomson), and Bathyplectes curculiOnis (Thomson)(Hymenoptera: Ichneumonidae), these two management practices largely control weevil populations. In Michigan, M. aethiopoides, a parasitoid of adults, is probably the primary controlling parasitoid, followed by the larval parasitoid, B. anurus (Landis and Haas 1990). Insecticides are used when these methods fail to provide adequate suppression of weevil populations. An' additional cultural method of managing alfalfa weevil may be through intercropping alfalfa with forage grasses. Forage grass/legume mixtures are commonly grown for beef and horse feed 21 22 and have other well-known advantages including erosion control, weed control, and increased stand lOngevity (Drolsom and Smith 1976). The effect of such mixtures on alfalfa weevil, however, is not known. Alfalfa weevil feeds only on legumes and prefers alfalfa. Titus (1910) noticed alfalfa and timothy intercrop fields in Summit County, Utah had less alfalfa weevil damage than in other fields. He believed this was due to shading of the alfalfa by the taller timothy. Anecdotal evidence from Michigan producers also indicates that alfalfa Weevil damage is lower in fields with a grass intercrop or grass weeds, but rigorous testing of the effect on pests of intercropped forage grasses has not been conducted. Intercropping may reduce the concentration of food available to alfalfa weevil. Root's (1973) "resource concentration hypothesis" states that herbivores inhabiting monocultures of host plants will exhibit greater colonization rates, greater reproduction and longer tenure time as compared to the same herbivore inhabiting a diverse community. If greater concentrations of food exist in monocultures, alfalfa weevil populations may be reduced in intercrops. In addition, alfalfa weevils use vision and olfaction to orient to alfalfa (Meyer 1975, Meyer and Raffensperger 1974a, b, c, Golik and Pienkowski 1969). They must taste or eat alfalfa to oviposit as other plants probably contain oviposition deterrents (Byrne 1969). After feeding on alfalfa tips and leaves in the early spring, full- grown larvae spin white cocoons, pupate and emerge as adults in two to three weeks (Titus 1910). In Michigan, most of these adults will migrate to sheltered areas to overwinter (Landis and Haas 1990). In 23 spring, they reach sexual maturity, move back into alfalfa fields, and oviposit. The effects of intercropping on weevils might be mainifested in differences in numbers of eggs, larvae, or recolonizing adults, and altered feeding damage. It is possible that intercropping grasses could interrupt the life cycle of the weevil at four important junctions: feeding, recolonization, oviposition, and larval development. Here, only the overall effect of lifecycle interruption, using density and damage as indicators, was studied. In this study, the effect of intercropping stands of alfalfa with three common, cool-weather forage grasses, smooth brome (Bromus enermis Leyss.), orchardgrass (Dactylis glomerata I.), and timothy (Phleum pratense L.), on alfalfa weevil density and damage was investigated. If intercropping these grasses reduces alfalfa weevil damage, this technique could reduce pesticide usage and lower the cost of producing high quality forage. METHODS Field preparation. A 1.0 hectare plot (Kalamazoo sandy loam) on the Kellogg Biological Station, Hickory Comets, Michigan, was selected for this field study. The field was previously in corn and soybeans, over- seeded with various legumes. For several years prior, . the field was in alfalfa. In the fall prior to planting, the field was limed (4482 kg/ha on November 3, 1988), and chisel plowed. No further amendments were called for by the soil test for establishing alfalfa. The following spring, the field was disked (April 28, 1989), field- cultivated (May 1), and cultipacked to prepare a seed bed (May 8). Two levels 0f alfalfa (cultivar 'Big Ten'), orchardgrass (cultivar 'Potomac'), timothy, and smooth brome grass (cultivar 'VNS') were planted in eight treatments with five replications in a randomized complete block design on May 10, 1989(Table 2.1). The grasses were obtained from Scott Farm Seed Company, Mechanicsburg, Ohio, and the alfalfa from Great Lakes Hybrids, Ovid, Michigan. Each treatment plot was 9.88 m by 12.16 m with borders and edges planted in low density (14.6 kg/ha) alfalfa. Five replications of eight treatments were arranged in a randomized complete block design. In the spring following establishment, potassium fertilizer (0-0-60, 258 kg/ha on April 24, 1990) was applied to the entire field as recommended by soil test results. Post-emergence herbicides were used as needed to control broadleaf weeds in all treatments and to remove weed grasses from alfalfa monocultures (Table 2.2). 24 Table 2.1. 25 Planting densities of alfalfa and three forage grasses, May 10, 1989, at Kellogg Biological Station. TREATMENT _ GRASS ALF ALFA NUMBER TREATMENT PLANTED PLANTED _k_g_/ha (lb/A) _k_g_/ha (lb/A) 1 alfalfa 2 alfalfa 3 alfalfa 4 alfalfa 5 alfalfa 6 alfalfa 7 alfalfa 8 alfalfa (alfalfa alone-high) none 18 (16) (alfalfa alone-low) none 14.6 (13) and brome (brome-high) 5.6 (5.0) 14.6 (13) and brome (brome-low) 2.8 (2.5) 14.6 (13) and orchard (orchard-high) 1.1 (1.0) 14.6 (13) and orchard (orchard-low) . 0.6 (0.5) 14.6 (13) and timothy (timothy-high) 4.5 (4.0) 14.6 (13) and timothy (timothy-low) 2.2 (2.0) 14.6 (13) 26 Table 2.2. Chemicals applied to field at Kellogg Biological Station field over course of study. DATE TARGET PEST CHEMICALS AND RATES 1006 3. 1939 quackgrass1 Roundup® 33% applied With (isopropylamine IOPCWiCk on salt of quackgrass. Did- not glyphosphatc complete field and 41%) rain immediately followed. ropewick, entire field June 6, 1989 quackgrass Roundup® 33% June 16, 1989 broadleaves, primarily lambsquarters2 and pigweed3 Butyrac® (2,4-D) backpack sprayer, 2 qts/Acre entire field ropewick, non-plot areas June 28, 1989 quackgrass Roundup® 33% backpack sprayer, pint/Acre (plus applied to alfalfa crop oil and 28% monoculture plots urea ammonium (treatments 1 & 2) May 13, 1990 quackgrass, Poast® 1 other grasses nitrate) June 21, 1990 potato Cygon® backpack sprayer, leafhopper4 (dimethoate) 1 on leafhopper pint/Acre ’ exclusion subplots only July 17, 1990 potato Cygon®l backpack sprayer, leafhopper pint/Acre on new exclusion subplots 1Agropyron repens 2Chenopodium album . 3Amaranthus retroflexus 4Empoasca fabae 27 Sampling and Analysis. From May 2, 1990 until June 6, 1990, alfalfa weevil density was estimated using Sweep sampling (10 sweeps per plot) (Table 2.3). Sweeps were taken using the "pendulum" sweep technique (net 37 cm diameter). Both adults and larvae were counted, however- adult numbers were too, low to analyze statistically. Numbers of larvae in each instar were determined on the June 6 sampling date by examining head capsule diameter. Alfalfa weevil larvae damage was assessed on June 6, the day prior to cutting. Twenty alfalfa tips were randomly selected in each plot, examined for holes and other signs of weevil feeding damage, and designated damaged or undamaged. The tips in each category were totalled and percent damage in each plot was calculated. Between May 19 and June 6, 1990, plots were sampled weekly to determine biomass of alfalfa, planted grass, and weeds (Table 2.3). Quadrats of 1/16 meter square area were randomly tossed into a plot and the vegetation within the quadrat was clipped, removed and sorted into groups consisting of alfalfa, planted grasses, and weeds. Sorted material was dried, weighed, and ground. The effect of alfalfa weevil feeding on alfalfa and grass quality was analyzed by the Hach procedure (Hach et al. 1987, Watkins et a1. 1987) to determine nitrogen content. Acid detergent fiber and neutral detergent fiber procedures were performed to determine total fiber content (Van Soest and Wine 1967). All dependent variables (damage, insect density, plant bio- mass) were analyzed using two-way ANOVA (Systat, Evanston, IL). Significant treatment effects (pg 0.05) were further explored using . 28 planned comparisons (contrasts). Contrasts used to compare differences in insect numbers, and biomass (alfalfa, weed, and total) were high rate alfalfa against low rate alfalfa, both alfalfa monocultures together against all mixtures combined, and low rate of alfalfa against each individual intercrop treatment. The low alfalfa rate was used to compare because each mixture was planted with alfalfa at the low rate. Contrasts used to compare grass biomass were the treatment with the most grass against all other mixtures, and high rate of' each grass against the low rate of the same grass fOr each grass. Differences in biomass and forage quality between sprayed and unsprayed areas were tested with t-tests. Correlations between each of biomass and damage, and larvae numbers were determine. Table 2.3. Sampling types and dates on field at Kellogg Biological Station in 1990. Sampling type Date Larval sweep Vegetation Larval damage Harvest May 2 X . May 9 X 'May 18 X May 19 X May 23 X May 25 X May 31 X June 2 X June 6 X X X June 7 X RESULTS Alfalfa weevil surveys performed on May 2 and May 9 revealed almost no alfalfa weevil larvae and are not presented in further analysis. On May 18, alfalfa weevil numbers were low [under 0.5 per sweep (Figure 2.1)], with no significant differences in alfalfa weevil numbers between treatments. Total forage biomass on May 19 was fairly uniform across treatments and not significantly different (Table 2.4). Alfalfa biomass was also uniform with no significant differenCes between treatments, however treatment 3 (brome at the high rate) had numerically the lowest amount of alfalfa and significantly the most grass (Figure 2.2, Table 2.5). There was significantly more weed biomass in the alfalfa monocultures than in the intercrops except treatment 6 (orchardgrass at the low rate) (Table 2.6). On May 23, the alfalfa weevil larval population began to rise (Figure 2.1). The high-rate alfalfa monoculture had the most weevil larvae and the high—rate brome and orchard mixtures had the least, however, differences were not significant. The vegetation survey for May 25 showed the high-rate of brome mixture had the highest total biomass, and lowest alfalfa biomass, but these differences were not significant (Figure 2.2). The high brome mixture did have significantly more grass biomass than in all other mixtures (Table 2.5). The difference in weed biomass seen one week earlier disappeared as the mixtures yielded more weeds. 29 30 By May 30, the numbers of weevil larvae in the alfalfa monocultures (both seeding rates) were significantly greater than in any of the mixtures (Figure 2.1, Table 2.7). The number of weevils in mixtures rose uniformly; numbers in the high rates of brome and orchard were still the lowest. The biomass survey taken on June 2 (Figure 2.2) showed no significant differences in grass biomass. Alfalfa did differ significantly, however, as the high brome treatment had less alfalfa than in the low alfalfa monoculture (Table 2.6). The low rate of alfalfa“ were compared with the intercrops because the planting rate of alfalfa was the same as in the mixtures. ’ On June 6, the day before cutting, alfalfa weevils in the alfalfa monocultures continued to be more numerous than in the mixtures. The number of weevils between the two monoculture treatments was not significantlydifferent (Table 2.7), but weevils were significantly less numerous in all six mixtures than in alfalfa monocropped at the low rate. The amounts of alfalfa in the mixture treatments varied, but not between the two alfalfa monocultures (Figure 2.2). Alfalfa biomass in the two alfalfa monocultures was significantly greater than in the mixtures (Table 2.6). Alfalfa biomass in the low rate alfalfa monoculture was significantly greater than in all mixtures except the orchardgrass treatments (p=0.060 for orchard at the high rate contrasted against alfalfa monocropped at the low rate, p=0.065 for low orchard contrasted to low alfalfa). 31 50 ' . -----o---- alfalone htgh x0 m i ----- O ----- alf alone low "x, 3 —O— alf-brome high "x, '. g 40 - —O— alf-brome low x’x """"" m —{j— alf-orch high ,,/ ........ 3 ' + alf-orch low £2". E 30 - fik— alf'tim high ’I”’Ino : + alf-tim low ' f a 6.: e h 20 ' 0 .2 E :3 s: 10 ' . 5-18 5-23 5-30 6-6 Date of alfalfa weevil survey, 1990 Figure ' 2.1. Alfalfa weevil larvae density per treatment on four sampling dates; ten sweeps per replication, five replications per treatment. 32 May 19, 1990 Biomass (gm/0.16 square m) June 2, 1990 Biomass ll \\\\\\\ (gm/0.16 square m) \ \ \ \ \ I \ \ TREATMENT l=alfalfa alone 3=alfalfa-brome 5=alfalfa-orchard 7=alfalfa-timothy Treatment high high high high 1990 May 25, June 6, 1990 III/I’ll: \\\\\\\\: II/zlrlu 1 2 3 4 5 6 7 8 TREATMENT legend 2=alfalfa alone 4=alfalfa-brome 6=alfalfa-orchard 8=alfalfa-timothy low low low low Figure 2.2. Biomass survey results for first cutting, 1990. Biomass equals vegetation within one 1/16th meter quadrat per replication, averaged over replications. 33 Table 2.4. Results of ANOVA treatment effects on biomass from first cutting vegetation surveys, 1990. ANOVA for grass portions excluded monoculture treatments. p valuesa DATE TOTAL ALFALFA GRASS WEEDS May 19 n s n s 0027* 0001" May 25 n s n s 0.003“ n 3 June 2 ns 0.007M ns 0.016** June 6 ' ns 0.002“ ns ns Table 2.5. Treatment contrasts of grass biomass portions of vegetation surveys in first cutting, 1990. p valuesa Contrasts May 19 May 25 Brome high vs. other mixtures 0.006" <0.001*** Brome high vs. brome low 0.020* 0001*" Orchard high vs. orchard low 0029* ns Timothy high vs. timothy 10W. ns ns aTreatments are considered significantly different by ANOVA and contrasts if p g 0.05. *p value 5 0.05 **p value 5 0.01 ***p value 5 0.001 Table 2.6. 34 Treatment contrasts of biomass surveys, alfalfa and weed portions, in first cutting. p values21 Contrasts May 19 June 2 June 2 June 6 weeds alfalfa weeds alfalfa Alfalfa high vs. rest <0.001*** 0.001" 0.010" 0.001*** Monocultures vs. rest <0.001*** 0.003" 0.002" <0.001*** alfalfa low vs. all mixtures 0.003“ ns ns 0.001*** alfalfa low vs. brome high . 0.004" 0.027* 0.014* 0.005" alfalfa low vs. brome low 0.005" ns ns 0.027*' alfalfa low vs. orchard high 0029* ns ns ns alfalfa low vs. orchard low ns ns ns ns alfalfa low vs. timothy high 0.003“ ns ns 0.001*** alfalfa low vs. timothy low ns ns ns 0.003?" aTreatments are considered significantly different by ANOVA and contrasts if p g 0.05. *p value 5 0.05 **p value 5 0.01 ***p value 5 0.001 35 Table 2.7. Treatment contrasts of alfalfa weevil larvae numbers in pure and mixed forage stands in 1990. p Valuesa Contrasts May 30b June 6 ANOVA treatment effect <0.001*** 0.001*** Alfalfa high vs. alfalfa low ns ns Alfalfa alone (both) vs. all <0.001*** <0.001*** mixtures Alfalfa low vs. Brome high <0.001*** <0.001*** Alfalfa low vs. Brome low 0.008“ 0.007“ Alfalfa lOw vs. Orchardthigh <0.001*** 0.002“ Alfalfa low vs. Orchard low 0.026* 0.002" Alfalfa low vs. Timothy high 0.005“ 0.004" Alfalfa low vs. Timothy low 0.003" 0.002** aNumbers of alfalfa weevil larvae in different treatments are considered significantly different by ANOVA and contrasts where p s 0.05. b No significant differences between treatments were found on the first four sampling dates, May 2, May 9, May 18, and May 23. *p value 5 0.05 **p value _<_ 0.01 ***p value _<_ 0.001 36 The damage estimate taken 'on June 6 resembled the weevil larvae survey and alfalfa biomass survey for the same date (Figure 2.3). The alfalfa monocultures together were significantly more damaged than the mixtures as a whole (Table 2.8), but when comparing each mixture against alfalfa at the low rate, alfalfa intercropped with brome and orchard at the low rates sustained damage comparable to alfalfa alone (low rate). The least damaged treatment was the low rate of timothy (Figure 2.3). This treatment also had one of the lowest amounts of grass (Figure 2.2). The percentage of larvae in each instar for this date was not significantly different across treatments, suggesting that grass presence did not alter development rates and/or sampling effectiveness. Alfalfa biomass at the earliest vegetation survey date (May 19) was not strongly correlated with alfalfa weevil density at harvest (r2: 0.176) (Table 2.9). The strongest correlation, damage at harvest (June 6) against alfalfa weevil at the same date was not high (r2=0.415). Grass biomass on May 19 was also not strongly correlated with weevil density or damage at harvest (r2=0.356 and 0.028), nor was total biomass at May 19 (at harvest, with weevil density r2=0.064, damage r2=0.067). It appears that biomass partitioning early in the season does not directly affect weevil numbers and damage later. Likewise, plant proportions at harvest do not seem to predict weevil numbers and damage. This reduced the possibility of any effect on alfalfa weevil abundance due only to plant biomass. 37 Percent damaged alfalfa tips 1 2 3 4 5 6 7 8 TREATMENT Treatment legend 1=alfalfa alone high 2=alfalfa alone low 3=alfalfa-brome high 4=alfalfa-brome low 5=alfalfa-orchard high 6=alfalfa-orchard low 7=alfalfa-timothy high 8=alfalfa~timothy low Figure 2.3. Percentage of twenty randomly selected alfalfa tips damaged by alfalfa weevil larvae by first cutting, June 6, 1990. Error bars are standard error of the mean. 38 _Table 2.8. Treatment contrasts of percent alfalfa weevil damage in pure and mixed forage stands on June 6, 1990. ANOVAs and Contrasts p valuesa ANOVA treatment effect 0.006“ Alfalfa high vs. alfalfa low ns Alfalfa alone (both) vs. all <0.001*** mixtures Alfalfa low vs. Brome high 0.019* Alfalfa low vs. Brome low ns Alfalfa low vs. Orchard high 0.037* Alfalfa low vs. Orchard low ns Alfalfa low vs. Timothy high 0.005” Alfalfa low vs. Timothy low 0.001*** aNumbers of alfalfa weevil larvae in different treatments are considered significantly different by ANOVA and contrasts where p g 0.05. - *p value _<_ 0.05 **p value _<_ 0.01 ***p value 5 0.001 39 Table 2.9. Results of regressions comparing biomass, alfalfa weevil numbers, and damage. X vs. Y r2 May 19 plant data forage biomass vs. 5-19 weevil numbers 0.002 forage biomass vs. 6-6 weevil numbers 0.064 forage biomass vs. 6-6 damage 0.067 alfalfa biomass vs. 6-6 weevil numbers 0.176 grass biomass vs. 6-6 weevil numbers 0.356 grass biomass vs. 6-6 damage 0.028 June 6 plant data forage biomass vs. 6-6 damage 0.044 alfalfa biomass vs. 6-6 weevil numbers 0.241 grass biomass vs. 6-6 damage 0.073 grass biomass vs. 6-6 weevil numbers 0.270 damage vs. 6-6 weevil numbers 0.415 The vegetation surveys were similar across sampling dates. Brome grass was the dominant grass in early spring and appeared to compete with alfalfa (Figure 2.2). With regard to the alfalfa planting rates, one point became clear: the amount of alfalfa between the alfalfa-alone treatments differed significantly on only one date, June 2, and the number of insects between the two treatments never 40 differed significantly. The biomass of weeds in this second year alfalfa field was not very high, but'again it was never different between the two alfalfa-alone treatments. On most dates, weed biomass in the alfalfa-alone treatments was greater than in the intercropped treatments, significantly on May 19. Total biomass in the first cutting was not significantly different between treatments. Vegetation biomass from harvest surveys. was analyzed for Kjeldahl nitrogen as an indicator of forage quality. Forages with high protein are of better quality than those with low protein. There were no significant differences found between any treatments at first cutting (Figure 2.4). Significant differences were found fOr acid detergent fiber (ADF) and neutral detergent fiber (NDF). Forages with high fiber percentages are of lower quality than those with low fiber. Table 2.10 shows fiber content in alfalfa portions of low rates of orchard and timothy differ significantly from the high rates of those grasses. The high rate of orchard has more fiber than the low rate of orchard, but the high rate of timothy has less fiber than the low rate of timothy. There were no significant differences in the fiber percentages between the alfalfa monocultures or the brome treatments. There were some differences, however, between the results of the two fibers (Figure 2.5). Alfalfa in treatment 8, the alfalfa- timothy low treatment had the highest percentage of ADP and NDF, and the highest nitrogen content (Figure 2.4). This treatment had the lowest percentage of larval feeding damage (Figure 2.3). On both protein and fiber analyses, alfalfa in treatment 6 (alfalfa-orchard. low) was of highest quality, with the lowest fiber 41 fractions and the highest protein. The rest of the treatments are not as consistent across quality tests. The quality of the grasses in the treatments was also measured. There were no significant differences between nitrogen content of the grasses (ANOVA p=0.166), and likewise with fiber fractions (ADF p=0.073, NDF p=0.067) (Figure 2.6). Table 2.10. Contrasts of alfalfa biomass fiber analysis treatments, June 6, 1990. p valuesa Contrast and AN OVA ADF NDF ANOVA treatment effect 0.018 0.010 Monocultures vs. mixtures ns ns Alfalfa high vs. alfalfa low ns ns Brome high vs. brome low ns ns Orchard high vs. orchard low 0.001*** 0.002** Timothy high vs. timothy low 0.037* 0.005** a Treatments are considered significantly different by ANOVA and contrasts where p g 0.05. *p value 5 0.05 **p value _<_ 0.01 ***p value _<_ 0.001 42 30 Percent - crude protein 1 2 3 4 5 6 7 8 TREATMENT Treatment legend 1=alfalfa alone high 2=alfalfa alone low 3=alfalfa-brome high 4=alfalfa-brome low 5=alfalfa~orchard high 6=alfalfa-orchard low 7=alfalfa-timothy high 8=alfalfa-timothy low Figure 2.4. Percent crude protein of alfalfa gathered in vegetation ’ surveys on June 6, 1990. Error bars are standard error of the mean. 43 44444444444444444444444444444444 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ I’llIIIIIIIIIIIIIIIIllill’lll’li \\\\\\\\\\\\\\\\\\\\ ““\“““\\\““‘\\“‘\‘\\‘ III/II’IIIIIIIIIIIII(I’ll/III \\\\\\\\\\\\\\\\\\\\\\\\\\\\\ III/I’ll I [I’ll/llIII/IIIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\ IIIIIIIIIII IIIIIIIIIII 44444444444444444444444444444444 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ I’ll/II’IIIIIIIIIt’ll/IIIIIIIIII \\\\\\\\\\ \ \\\ \\\\\\\\\\\\\ (I’ll/Ill!IIIIIIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ III/IIIIIIIII(I’ll/IIIIIIIIIII IIIIIIIIIIIIIIIIIIIll/1111’!!! \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ III/IIIIIIIII Ill/IIIIIIIIIII \\t\4\t\t\t\4\4\t\t\ \l\t\4\t\4\t\t\t\t\ \t\t\4\ \t\t\4\t\l\ IIIIIIIIIIIIIIIIII/I’IIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ V‘“V“‘\\\\\V\‘\V‘V\\\‘\‘\\N\‘ III/IIIIIIIIIII’IIIII/IIIIIIIII \\\\.\\\\\\\\\\\\\\\\\\\\\\\\\\\ I’ll/III!!!I’ll/IIIIIIIIIIIIIII .35: «:3th TREATMENT legend Treatment low alfalfa alone alfalfa alfalfa 2 4 lgh hig alfalfa alone h alfalfa- alfalfa l 3 5 7 0W 1 brome h. brome orchard h 0W -orchard l 6 8 igh low alfalfa-timothy lgh thy h -timo alfalfa Percent fiber (acid detergent [ADF] and neutral detergent Figure 2.5. 1990. [NDF] fiber) of alfalfa gathered in vegetation surveys on June 6, Error bars are standard error of the mean. 44 8 Percent crude protein 3 l so I-I \ x 3 1*: 1*: H 3:: 5°“ :2; :1; If .. 31 3‘3 ‘3‘ a 1:1 :I :l‘ 3 40‘ $1 ‘Z "3‘ h 1" \I ‘1 g: . ,1, z, :5 I ADF 1‘3 ‘3 v NDF 20" 1:1 :1 :1: 0‘ (:1 :I :I: ' 3 4 5 6 7 8 TREATMENT Treatment legend 3=alfalfa-brome high 4=alfalfa-brome low 5=alfalfa-orchard high 6=alfalfa-orchard low 7=alfalfa-timothy high 8=alfalfa-timothy low Figure 2.6. Percent crude protein and fiber (acid detergent [ADF] and neutral detergent [NDF] fiber) of grass gathered in vegetation surveys on June 6, 1990. Error bars are standard error of the mean. DISCUSSION In this study, alfalfa intercropped with forage grasses contained significantly fewer alfalfa weevil larvae than alfalfa monocultures. These differences did not emerge until May 23 and were not significant until May 30. The rapid increase in grass biomass and concurrently grass height during this period raised some questions about sampling artifacts. First, grass emerging above the alfalfa canopy shaded larval feeding sites in alfalfa tips. If shading altered the microclimate enough to reduce weevil developmental rates, larval development may be retarded in intercropped plots. It is known that sweep sampling in alfalfa consistently underestimates the number of early instars (Higgins et al. 1991). Thus, if larvae in intercropped plots were less developed on average, a consistent bias may have occurred. This possibility was examined by looking at the age structure of larvae from sweeps of all plots on June 6. Since the age structures were not significantly different, it is unlikely that this could explain the results. A second potential artifact of grass height could be a reduction in sweeping efficiency in these plots. Alfalfa in monocultures was approximately 40 cm tall but grass height was up to 150 cm tall. No direct tests of sweeping efficiency were made. However, the stem samples collected to determine percent damage paralleled the results of larval sweep samples and would not be influenced by grass height. Planting intercrops appears to reduce alfalfa biomass within first cutting. Other researchers, however, have found mixtures to 45 46 produce more total biomass than monocultures (Chamblee and Collins 1988). In later cuttings of the same plots in this study, the mixtures did produce greater harvests than the monocultures. The high rate of brome grass continually produced the most grass of any of the mixtures. Determining composition of orchardgrass plots proved challenging. The tussock (clump) growth pattern of orchardgrass, and a quadrat size which was similar to tussock size, resulted in entire quadrats filled or devoid of orchardgrass. This resulted in the variance of orchardgrass measurement being somewhat higher than other grasses on June 2, and on three dates in later cuttings. Because the other grasses also had high variances at times, quadrat sampling probably did not unduly bias the orchardgrass surveys. Increasing quadrat number or size might increase accuracy of the survey and decrease variability between replications. I The plant biomass present on May 19 did not seem to influence later weevil numbers or damage. Grass and alfalfa biomass, both early in spring and at harvest, was not correlated with weevil density or damage, nor was total forage biomass (Table 2.9). This reduced the possibility of any effect on alfalfa weevil abundance due only to plant biomass. However, the combination of plants could have created different odor plumes than pure alfalfa, as detected by colonizing insects, and may have elicited a different response by the insect. Stanton (1983) described decreasing olfactory attractiveness of hypothetical intercropped patches. Golik and Pienkowski (1969) showed alfalfa leaf odor more than doubled turning rates of hungry adult alfalfa weevils in an arena. If pure alfalfa odor incites weevils to cease flying like it directs kinetic orientation on land, a masked or 47 altered odor plume could result in insects failing to detect alfalfa and continuing flight over "hidden" alfalfa fields. Once the insects are cued to land in an intercropped plot, the amount of grass they encounter could impair oviposition. Weevils must taste alfalfa to oviposit (Byrne 1969); it is possible repeatedly tasting grass could trigger flight or delay oviposition. A study directly investigating the choices made by recolonizing and ovipositing females would further clarify the behavior of weevils in intercrops and explain the lowered numbers we found. ‘ Forage quality parameters did not show significant differences between most treatments, suggesting that these forage quality tests are not sensitive enough to measure differences caused by alfalfa weevil feeding. Some aspect of the crude protein could be flawed as protein is higher than expected for late first cutting alfalfa with 40 to 50 percent fiber (National Research Council 1982), but as all treatments are consistent, it is valid to compare treatments. The fiber data for treatment 8 (timothy at the low rate) alfalfa indicates a low quality forage, but the protein data indicates the best quality of all the treatments. This date had the loweSt percentage of visual damage, and it would be reasonable to have the highest percentage of crude protein. It is not reasonable, however, to also have the highest percentage of fiber. This could be an isolated incident, as the other treatments do correspond in general. The forage quality parameters measure different aspects of quality, and it is likely alfalfa weevil feeding, by removing plant matter rather than sucking plant juices, does not alter protein greatly but does increase fiber content. Insect feeding has been shown to increase plant quality in 48 some plants by causing a compensatiOn response (Owen 1980, Owen and Wiegert 1976), but examining this aspect is beyond the scope of this study. Alfalfa is a popular forage crop because it produces hay more than once a year, it contains more nitrogen than most other field crops, and, because it fixes atmospheric nitrogen in underground nodules, it adds nitrogen to the soil. Because alfalfa is so high in protein, it can cause bloat in animals feeding on it (Howarth 1975). Alfalfa grown for grazing is often planted with a forage grass to reduce bloat. Total crude protein in the feed decreases when grass is added, decreasing the quality parameters of the feed (Van Soest 1982), but this may not be detrimental because of the resulting bloat protection. Planting mixtures could lead to more forage and less potential for bloat. Adding grass to alfalfa may help outcompete weeds (Drolsom and Smith 1976), prevent erosion, and increase stand duration (Casler and Walgenbach 1990). In this study, intercropping forage grasses into alfalfa stands reduced insect pest damage and weeds. Since adding grass to alfalfa stands has been shown to suppress weeds, and intercropping here helped control alfalfa weevil, intercropped stands could produce greater quantities of good quality forage for longer duration than monoculture alfalfa. For monocultures, planting the low rate could be more profitable than planting the high rate of alfalfa. Intercropping smooth brome grass at the high rate appeared to limit alfalfa weevil numbers and damage more than other mixtures while providing the most total biomass. LIST OF REFERENCES Berberet, R.C., J.F. Stritzke, A.K. Dowdy. 1987. Interactions of alfalfa weevil (Coleoptera: Curculionidae) and weeds in reducing yield and stand of alfalfa. J. Econ. Entomol. 80(6):1306-1313. Buntin, GD. 1989. Competitive interactions of alfalfa and annual weeds as affected by alfalfa weevil (Coleoptera: Curculionidae) stubble defoliation. J. Entomol.Soc. 24(1):78-83. ' Byme, H.D. 1969. The oviposition response of the alfalfa weevil Hypera postica (Gyllenhal). Univ. of Maryland Ag. Exp. Station Bulletin A-160. ' Casler, MD. and R.P. Walgenbach. 1990. Ground cover potential of forage grass cultivars mixed with alfalfa at divergent locations. Crop Sci. 30:825-831. Chamblee, BS. and M. Collins. 1988. Relationships with other species in a mixture. p. 439-461. In A.A. Hanson et al. (ed.) Alfalfa and alfalfa improvement. Agronomy Monogr. 29, ASA, Madison, ‘ WI. ‘ Drolsom, RN. and D. Smith. 1976. Adapting species for forage mixtures. pp. 223-232. In R.I. Papendick, et al. (ed.) Multiple cropping. ASA Spec. Publ. 27. ASA, CSSA, and SSSA, Madison, WI. Edwards, C.R., R.I. Abrams, M.J. AndersOn, B.D. Blair, C.M. Christiansen, J.K. Evans, J.M. Ferris, B.J. Hankins, T.N. Jordan, R.W. Meyer, M.C. Shurtleff, R.E. Stuckey, J.L. Wedberg and W.W. Witt. 1978. Alfalfa weevil, pp. 91-93. In Alfalfa: A guide to production and integrated pest management in the Midwest. North Central Reg. Ext. Publ. 113, West Lafayette, IN. Golik, Z. and R.L. Pienkowski. 1969. The influence of temperature on host orientation by the alfalfa weevil, Hypera postica. Entomol. Exp. Appl. 12:133-138. 49 50 Hach, C.C., B.K. Bowden, A.B. Kopelove, S.V. Brayton. 1987. Method performance: More powerful peroxide Kjeldahl digestion method. J. Assoc. Off. Anal. Chem., 70(5): 783-787. Hamlin, J.C., W.C. McDuffie, F.V. Lieberman, R.W. Bunn. 1943. Prevention and control of alfalfa weevil damage. USDA Farmers Bulletin Number 1930. Higgins, R.A., M.E. Rice, S.L. Blodgett, and TJ. Gibb. 1991. Alfalfa stem-removal methods and their efficiency in predicting actual numbers of alfalfa weevil larvae (Coleoptera: Curculionidae). J. Econ. Entomol. 84(2). 650- 655. Howarth, RE. 1975. A review of bloat in cattle. Can. Vet. J. 16:281- 294. Howarth, R.E., B.P. Goplen, A.C. Fesser, and S.A. Brandt. 1978. A possible role for leaf cell rupture in legume pasture bloat. Crop Sci. 18:129-133. ‘ Landis, D. and M. Haas. 1990. Alfalfa weevil management. Extension Bulletin E-2242, May 1990. C00perative Extension Service, Michigan State University, East Lansing, MI. Meyer, J .R. 1975. ‘ Effective range and species specificity of host recognition in adult alfalfa weevils, Hypera postica. Ann. Entomol. Soc. Amer. 68(1):1-3. Meyer, LR. and E.M. Raffensperger. 1974a. "Indirect-choice" olfactometer experiments on adult alfalfa weevils. Ann. Entomol. Soc. Amer. 67:135-6. Meyer, JR. and E.M. Raffensperger. 1974b. Kinetic orientation experiments on adult alfalfa weevils. Ann. Entomol. Soc. Amer. 67:143-4. Meyer, JR. and E.M. Raffensperger. 1974c. The role of vision and olfaction in host plant recognition by the alfalfa weevil, Hypera postica. Ann. Entomol. Soc. Amer. 67:187-90. National Research Council, Subcommittee on feed composition. 1982. Nutritional data for United States and Canadian feeds, Third Revision. National Academy Press, Washington, DC. 51 Owen, DP. 1980. How plants may benefit from the animals that eat them. Oikos 35:230-235. Owen, BF. and R.G. Wiegert. 1976. Do consumers maximize plant fitness? Oikos 27: 488-492. Root, R.B. 1973. Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassica oleracea). Ecol. Monogr., 43:95-124. Scheaffer, CC. and G.C. Marten. 1986. Producing quality alfalfa - a systems approach. 17th Ann. Alfalfa Improvement Conf., Lafayette, Indiana. pp. 30-39.- Stanton, ML. 1983. Spatial patterns in the plant community and their effects upon‘ insect search in Herbivorous Insects, Sami Ahmad, ed. 'Academic Press, New York, pp.125-157. Titus, E.G. 1910. The alfalfa leaf weevil. Utah Ag. College Experiment Station Bulletin Number 110, September. Van Soest, PJ. 1982. Nutritional ecology of the ruminant. O & B Books, Corvallis, OR. Van Soest, PJ. and RH. Wine. 1967. Use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell-wall constituents. J. Assoc. Off. Anal. Chem. 50:50-55. Watkins, K.L., T.L. Veum, G.F. Krause. 1987. Total nitrogen determination of various sample types: A comparison of the Hach, Kjeltec, and Kjeldahl methods. Assoc. Off. Anal. Chem., 70(3): 410-412. CHAPTER 3 POTATO LEAFHOPPER, EMPOASCA FABAE, POPULATION DYNAMICS AND DAMAGE IN ALFALFA/FORAGE GRASS MIXTURES ABSTRACT Potato leafhopper (Empoasca fabae) (Harris) numbers and damage in alfalfa/forage grass binary mixtures were determined in a field experiment. Treatments consisting of alfalfa alone (14.6 kg/ha and 18 kg/ha) and in mixtures with three forage grasses were planted. The grasses, smooth bromegrass (Bromus enermis Leyss.), orchardgrass (Dactylis glomerata 1.), and timothy (Phleum pratense L.), were each planted at two seeding rates with 14.6 kg/ha of alfalfa. There was an overall trend for more adult leafhoppers to be present in alfalfa monocultures, however, this was significant on only one of 12 dates sampled in 1990. Reduced potato leafhopper nymph density in many mixtures occurred on two dates, one immediately prior to and one following second cutting. In laboratory experiments, adult potato leafhoppers were found to be, able to survive but not reproduce on smooth brome, timothy, or orchardgrass monocultures, indicating that the presence of grass in alfalfa plantings may delay or inhibit oviposition by 52 53 potato leafhoppers. In a laboratory assay measuring emigration, leafhoppers left alfalfa-grass mixtures (alfalfa-brome, alfalfa- orchardgrass) significantly more than from alfalfa monocultures. INTRODUCTION Potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), is a serious pest of alfalfa, soybeans, dry beans, potatoes and other crops in Michigan. This insect cannot survive midwestern winters and each year must migrate from the gulf states in late spring (Decker. and Cunningham 1967). Typically the first cutting alfalfa crop receives little leafhopper damage, however, new seedings and the second and third cuttings of alfalfa frequently sustain serious damage. Phloem feeding by potato leafhoppers on alfalfa results in visual symptoms termed "hopperburn", decreased dry weight yield and decreased crude protein content (Smith and Ellis 1983, Lamp et al. 1985, Flinn and Hower 1984, Kouskoulekas and Decker 1968). The feeding traps higher levels of total nonstructural carbohydrate in infested leaves (Flinn et al. 1990). The feeding of potato leafhoppers also prevents elongation of stem intemodes (Oloumi-Sadeghi et al. 1988), resulting in stunted plants. Currently, controls for potato leafhopper include insecticide. sprays and timely cutting. An additional method of managing potato leafhopper may be cultivating non-host plants (grass or weeds) with alfalfa. Potato leafhopper adults can survive but cannot reproduce on smooth brome, orchardgrass or timothy (Coggins, this volume). The presence of grass weeds in alfalfa has been reported to reduce potato leafhopper density (Lamp et al. 1984). Grass weeds or grass- weed volatiles reduce oocytes and eggs laid per female in alfalfa and 54 55 increase flight activity (Smith 1987). Since extracts of grass applied to alfalfa also reduce oviposition (Smith 1987) and increase flight, the presence of non-food biomass in an alfalfa-grass field is not the only deterrent to potato leafhoppers. Some Michigan alfalfa growers have noticed reduced potato leafhopper damage in weedy and grassy alfalfa fields but testing the effect of intercropped forage grasses on ’ pests has not previously been conducted. Although some studies of potato leafhopper movement have been performed, why immigrants chose to move into particular stands of host plants is not understood. Long distance immigrants tend to be female (Glick 1960); they appear to be better able to survive without food and water during the long flight (Decker and Cunningham 1967). As the season progresses, in-field sex ratios change, eventually reaching 1:1 by fall (Medler et a1 1966). Immigrants appear to cluster at field edges (Flinn et al. 1990) and elevated portions of the field (Kieckhefer and Medler 1966), with female leafhoppers having a greater tendency to disperse out of alfalfa (Flinn et al. 1990). Flinn, Hower and Taylor (1990) believe potato leafhoppers to go through three steps during spatial distribution: long-distance immigrants land on alfalfa or nonhost plants as the cue for long distance flight ceases, host-searching behavior begins, and short flights take the leafhoppers to alfalfa. Apparently, when alfalfa is found the leafhoppers cease even short flights, causing accumulation at field edges (Flinn et al. 1990). If leafhoppers discriminate between fields of pure alfalfa and alfalfa mixed with nonhosts, intercropping alfalfa could alter these patterns. Furthermore, if the presence of grass weeds reduces oviposition and 56 increases flight of potato leafhoppers (Lamp et al. 1984, Smith 1987), the presence of nonhost plants could render the field less acceptable to potential immigrants. Prior to the current emphasis on alfalfa monoculture, producers in Michigan typically grew alfalfa/grass mixtures. Mixtures have certain positive agronomic characteristics including weed t suppression, increased stand persistence, increased resistance to lodging, decreased drying time of cut forage, and decreased potential for causing bloat in cattle (Casler and Walgenbach 1990, Howarth et al. 1978). These mixtures, although not typically as high in crude protein as alfalfa monocultures, provide an acceptable forage for many classes of animals. Dutt et al. (1982) found that alfalfa forage with 29% weeds, including quackgrass, smooth brome, and orchardgrass, did not suffer reduced feeding value for cattle. New varieties of forage grasses, improved production practices, and the potential to reduce insect damage have caused renewed interest in the production of alfalfa/forage grass mixtures. The objectives of the field portion of this study were to. investigate the effect of intercropping stands of alfalfa with three common, cool-weather forage grasses, smooth brome (Bromus enermis Leyss.), orchardgrass (Dactylis glomerata 1.), and timothy (Phleum pratense L.), on potato leafhopper density and damage. The laboratory objectives were to determine if potato leafhoppers could survive and reproduce on the forage grasses listed above, and to analyze emigration attempts from alfalfa, alfalfa/forage grass mixtures, and nonhosts (grass monocultures and soil). METHODS Field Studies. A 1.0 hectare plot (Kalamazoo sandy loam) on the Kellogg Biological Station, Hickory Comets, Michigan, was selected for this field study. The field was previously in corn and soybeans, over- seeded with various legumes. For several years prior, the field was in alfalfa. In the fall prior to planting, the field was limed (4482 kg/ha on November 3, 1988), and chisel plowed. No further amendments were called for by the soil test for establishing alfalfa. The following spring, the field was disked (April 28, 1989), field- cultivated (May 1), and cultipacked to prepare a seed bed (May 8). Two levels of alfalfa (cultivar 'Big Ten'), orchardgrass (cultivar 'Potomac'), timothy, and smooth brome grass (cultivar 'VNS') were planted in eight treatments with five replications in a randomized complete block design on May 10, 1989 (Table 3.1). The grasses were obtained from Scott Farm Seed Company, Mechanicsburg, Ohio, and the alfalfa from Great Lakes Hybrids, Ovid, Michigan. Each treatment plot was 9.88 m by 12.16 m with borders and edges planted in low density (14.6 kg/ha) alfalfa. In the spring following establishment, potassium fertilizer (0-0-60, 258 kg/ha on, April 24, 1990) was applied to the entire field as recommended by soil test results. Post-emergence herbicides were used as needed to control broadleaf weeds in all treatments and to remove weed grasses from alfalfa monOcultures (Table 3.2). 57 Table 3.1. 58 Planting densities of alfalfa and three forage grasses, May 10, 1989, at Kellogg Biological Station. TREATMENT GRASS ALFALFA NUMBER TREATMENT PLANTED PLANTED _kg/ha (lb/A) _kg/ha (lb/A) l alfalfa (alfalfa alone-high) none. 18 (16) 2 alfalfa (alfalfa alone-low) none 14.6 (13) 3 alfalfa and brome (brome-high) 5.6 (5.0) 14.6 (13) 4 alfalfa and brome (brome-low) 2.8 (2.5) 14.6 (13) 5 alfalfa and orchard (orchard-high) 1.1 (1.0) 14.6 (13) 6 alfalfa and orchard (orchard-low) 0.6 (0.5) 14.6 (13) 7 alfalfa and timothy (timothy-high) 4.5 (4.0) 14.6 (13) 8 alfalfa and timothy (timothy-low) 2.2 (2.0) 14.6 (13) 59 Table 3.2. Chemicals applied to field at Kellogg Biological Station field over course of study. . DATE TARGETPEST COMMENTS RATES June 3. 1939 quackgrassl Roundup® 33% applied With (iSOpropylamine IOPCWiCk on salt of ‘ quackgrass. Did- not glyphosphatc complete field and 41%) rain immediately June 6, 1989 quackgrass June 16, 1989 broadleaves, primarily Roundup® 33% Butyrac® (2,4—D) 2 qts/Acre lambsquarters2 and pigweed3 June 28, 1989 quackgrass May 13, 1990 quackgrass, other grasses June 21,1990 potato leafhopper4 July 17, 1990 potato leafhopper lAgropyron repens Roundup® 33% Poast® 1 pint/Acre (plus crop oil and 28% urea ammonium nitrate) Cygon® (dimethoate) 1 pint/ Acre Cygon® 1 pint/Acre followed. . ropewick, entire field backpack sprayer, entire field ropewick, non-plot areas backpack sprayer, applied to alfalfa monoculture plots (treatments ,1 & 2) backpack sprayer, on leafhopper exclusion subplots only backpack sprayer, on new exclusion subplots 2Chenopodium album 3Amaranthus retroflexus 4Empoasca fabae . 6 0 Field Sampling and Analysis. In July 1989, after- establishing the plots, preliminary insect sampling using a D-vac® (D-.vac vacuum insect net, Riverside, California) and biomass sampling was done. The D-vac procedure was similar to that described in Flinn et al. (1990), except here researchers walked in a zigzag pattern while taking 10 suctions per plot (10 suctions = 0.9 m2 per plot). For biomass sampling in this study, counting stems within five l/l6 meter quadrats was attempted (July 26), {but proved too time-consuming. Quadrat harvests (August 10) provided the most information in the least amount of time, and this method was chosen for 1990 vegetation surveys. Quadrats of 1/16 meter were randomly tossed into a plot and the vegetation within the quadrat was clipped, removed and sorted by vegetation type (alfalfa, planted grass, weed). Sorted material was dried and weighed. Weights were compared on a per quadrat basis for statistical analysis. Between May 30 and August 13, 1990, weekly insect D-vac samples were used to assess potato leafhopper density (Table 3.3). ’ Between May 19 and August 13, 1990, plots were sampled weekly to determine biomass of alfalfa, planted grass, and weeds. Numbers of quadrats per plot varied with plant height (more quadrats on dates with little vegetation). Sorted material was dried, weighed, and ground with a Wiley mill (1 mm screen) and then with a Udy mill (1 mm screen). Vegetation biomass from harvest surveys was analyzed for Kjeldahl nitrogen as an indicator of forage quality (Hach et al. 1987, Watkins et al. 1987). Acid detergent fiber and neutral detergent fiber procedures were, performed at harvests to determine 61 total fiber content (Van Soest and Wine 1967). These measurements were used to compare potato leafhopper feeding damage on alfalfa and grass forage quality between treatments. To compare insect- infested plants to non-infested controls, subplots were sprayed with C‘ygon® (dimethoate, American Cyanamid) insecticide using a backpack sprayer (Table 3.2). Vegetation samples from these areas were also collected (as above), and analyzed for forage quality. It was hypothesized that feeding damage would be greatest in monoculture alfalfa, less in intercropped plots, and least in insecticide treated subplots. All dependent variables (plant biomass, plant quality, insect numbers) were analyzed using two-way ANOVA (Systat, Evanston, IL). Significant treatment effects (p5. 0.05) were further explored using planned comparisons (contrasts). Contrasts used were high rate alfalfa against low rate alfalfa, both alfalfa monocultures together against all mixtures combined, and low. rate of alfalfa against each mixture treatment individually. This contrast schedule was used to compare differences in insect numbers, and alfalfa, weed, and total biomass. The low alfalfa rate was used to compare because each mixture was planted with alfalfa at the low rate. Contrasts used to compare grass biomass were the treatment with the most grass against all other mixtures, and high rate of each grass against the low rate of the same grass for each grass. Differences in biomass and forage quality between sprayed and unsprayed areas were tested with t-tests. Correlations were determined between alfalfa and grass biomass, and potato leafhopper nymphs and adults. 62 Table 3.3. Sampling types and dates on field at Kellogg Biological Station in 1989. _ sapling typ Date Insect Vegetation Harvest July 10 x July 13 x July 24 x July 26 ' counted stems August 1 x August 8 x August 10 destructive August 17 x Table 3.4. Sampling types and dates on field at Kellogg Biological Station in 1990. Date hday June June June June June June June June 30 2 5 6 7 12 1'7 18 25 ‘July 1 July 9 July 11 July 16 July 23 July 24 July 30 August 7 August 13 August 14 Sagmplin type H Insect Vegetation Harvest X X N X X >1 X X X X X X X X X X X X 63 Laboratory portion Reproduction and survival on grass In a preliminary experiment, three species of grass (brome, timothy and orchardgrass) in alfalfa-grass mixtures were planted, five grass plants with five alfalfa plants. Pots were 32 ounce food containers (Sweetheart Cup Company, Chicago, IL) and soil was Baccto® Professional planting mix (Michigan Peat Company, Houston, TX). Monocultures of 10 plants each of alfalfa and each grass were also planted. -When the plants were approximately six weeks old, three unsexed adult potato leafhoppers were placed in each pot and caged with a pop-bottle cage (Figure 3.1). Cages were made from clean, plastic two-liter soda bottles with tops cut off and holes cut in the side. Holes were covered with saran screening (0.23 mm mesh, Chicopee Manufacturing Company, New Brunswick, NJ). The open end was placed over the pot and taped securely. Adult leafhoppers were gathered from a laboratory culture originally collected on alfalfa and reared on fava beans (Vicia fava L., long pod, improved; Harris Seeds, Rochester, NY). As a control, three potato leafhoppers were placed on barren soil in a pot. After three weeks of potato leafhopper infestation, the. plant matter was harvested, dried, weighed, and analyzed for crude protein. This experiment was repeated eight months later, using only monocultures of alfalfa, brome and orchardgrass with ten plants each. Timothy did not thrive in greenhouse conditions and was not used in this or future laboratory experiments. Plants of heterogeneous age and width within each pot (same as previous experiment) were used to control for the possibility of egg 64 desiccation due only to the thinness of young grass. Whereas the preliminary experiment was unreplicated, in ' the second run, five replications of each monoculture were used. The number of potato leafhoppers was increased to six in each caged pot including both males and females. Plant quality was not analyzed for this experiment. Leaving assay In a second laboratory study, movement from alfalfa, alfalfa- forage grass mixtures, and nonhosts were measured by trapping leafhoppers at the only exit of a cage. Flats of eight-week-old alfalfa, brome, and orchardgrass plants were carefully dug from a new seeding at Kellogg Biological Station, Hickory Comets, Michigan. Twenty plants for monocultures and ten plants each, alfalfa and grass, for treatment mixtures were transferred to clay pots (12 cm tall, 12 cm top diameter) and allowed to grow. Plants were watered, fertilized (10-20-20) and clipped regularly as needed. Treatments were bare moist soil, alfalfa alone, brome alone, orchardgrass alone, alfalfa-brome, and alfalfa-orchard. Pots with similar biomass, height, and plant condition were selected, caged and subjected to 20-30 adult potato leafhoppers (same number of leafhoppers were, used within replications). Sex ratios of potato leafhopper used were estimated by collecting, killing and sexing a randomly selected subset of leafhoppers gathered at the same time as the experimental insects. Insects were gently blown into the cages and the cages were transferred to temperature and light controlled environmental chambers (I-35 series, Percival Manufacturing Company, Boone, IOwa) for four days. Cages, cylinders of wood and saran screening, 65 were designed to fit snugly on top of pots leaving only a 3 cm diameter hole at the top (Figure 3.2). Daylight in the chamber lasted 14 hours at 26 ° C, and nights were ten hours at 19 0 C. Dawn and dusk were simulated by keeping one set of lights on for two hours in the morning and four hours in the evening. For the rest of the "day," two sets of lights were on. Moonlight was approximated by a foil- covered night-light lit above the cages at all times (including night when all other lights were off). Insects emigrating through the 3 cm diameter hole were caught in diet cups (Fill-Rite Corporation, Newark, New Jersey) sprayed with Tangletrap® (The Tanglefoot Company, Grand Rapids, Michigan) attached above the hole. Leafhoppers leaving the arena were counted at 6 pm and 10 pm the first night of each replicate, and at 8 am and 6 pm the next two. At 8 am of the fourth day, the cages were emptied of leafhoppers and the plant matter was clipped and dried to compare biomass. During each replication, sticky cups were replaced every 24 hours and the captives sexed. Cups were allowed to dry for 5-12 hours after spraying to dissipate Tangletrap® odors. Insect numbers were totalled for each treatment in each replication, percentages transformed using the arcsin square root transformation, and compared using two-way ANOVA and contrasts. ' Figure 3.1. Pop-bottle cage used for potato leafhopper reproduction and survival experiments. Screened areas are holes covered with saran screening. -— 220m _— trap coated inside with Tangletrap® 3 cm hole on top 32.5 cm wooden frame and saran screen clay pot Figure 3.2. Cage used for leaving assay experiments. RESULTS Field portion 1 98 9 Lack of selective pre-emergence herbicides for use in mixed plots led us to attempt to establish; the entire test without herbicides. As expected from a spring planting, the field had moderate weed pressure. Following crop and weed emergence, treatment with a selective post-emergence herbicide (Buctril®) removed the broadleaf weeds effectively, however, patches of quackgrass (Agropyron repens) remained. These were suppressed in alfalfa monocultures using Poast® (a selective post-emergence grass herbicide), but could not be removed from the mixed plots in this fashion without harming the forage grasses. In mixed plots when quackgrass emerged about the crop canopy, a rope-wick applicator was used to achieve partial control (Table 3.2). Threecuttings were planned for the establishing alfalfa stand as per typical agronomic practice, however, only two were taken. The first cutting was July 13, 1989, 64 days following seeding. The second cutting was taken on August 17. The forage grasses grew very slowly in this establishment year, generally evident only as a part of the crop understory. Following cutting, the mixed plots were noticeably more green than the alfalfa monoculture plots. The low growth habit of the grasses at this time allowed more grass biomass to escape cutting compared to the taller alfalfa. 67 68 The biomass surveys supported these observations. There were no differences in grass biomass in either the stem or the destructive harvest surveys, and the. treatments had less grass biomass than alfalfa. Both surveys showed significantly more alfalfa in the alfalfa-high monoculture than in low monoculture and in all other treatments (contrast p=0.002 for low vs. high monoculture stems, p=0.011 for low vs. high monoculture biomass, and p<0.001 for high monoculture vs. all other treatments for both stems and destructive sampling). The stem count revealed no differences between the low rate of alfalfa and the mixtures. The destructive harvest had significantly more alfalfa in alfalfa-low treatments than in brome-low and timothy-low (contrast p=0.029 and 0.016). Spring storms, particularly on May 29, 1989, brought large numbers of migrating potato leafhoppers into Michigan. These leafhoppers infested the establishing alfalfa and caused considerable hopperburn and stunting. Three days prior to first cutting, July 10, 1989, the high rate of pure alfalfa contained significantly (p<0.001) higher numbers of adult leafhoppers than all intercropped treatments, except alfalfa mixed with orchardgrass at the low rate (Figure 3.3). Nymph numbers were not significantly different between treatments. During the regrowth of second cutting, there were no significant treatment differences detected in leafhopper numbers. On July 18, there was a trend for higher leafhopper numbers (adults and' nymphs combined) on alfalfa monoculture and alfalfa-timothy intercrops, and low leafhopper numbers on alfalfa-brome treatments (Figure 3.4). On July 24, adult numbers declined in many plots while 69 nymph numbers increased. On August 1, total. leafhopper numbers (adults and nymphs combined) in alfalfa monocultures tended to be higher than any of the intercropped treatments. By August 8, adult leafhopper numbers had declined noticeably in all treatments While nymph numbers generally rose slightly. The sudden drop in adult numbers was likely due to an epizootic of Zoophthora radicans (Brefeld) Batko, a fungal pathogen of potato leafhopper. Cool, wet conditions in the previous weeks are believed to have triggered the epizootic which was widespread across lower Michigan. 70 E] PLH adults _* 1 2.2.0:» .22: 22:3 mod :8 .2. 1.5 I PLH nymphs . , IIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\ rlll/lll/IIIIIIII IIIIIIIII \\\\\\\\\\\\\ III/IIIIIII/II \NkkkNNkaKkN 4444444444444 s s s s s s \ s s s s \ s x s I I I I I I I I I I I I I I I I I I I I I I I I \ \rsrxr\r\r\r\r\»\r\r\r\r\r\r\r\r\r\r\r\r\rmr III/IIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\ III/IIIIIIIIIIIIIII Ill/IIIIIIIIIIII \\\\\\\\\\\\\\\\ IIIIIIIIIIIIIIII \NthNNKkKNNKKN TREATMENT IIIIIIIIIIIIIIIIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ IIIIIIIIIIIIIIIIIIIIIIIIIIIIII \\\\\\.\\\\\\\\\\\\\\\\\\\\\\Nhr legend Treatment alfalfa alone high alfalfa alone low 2: 1: WW wmm 1 my earns th 0cm rrol bot . . a new...” 111 mmm 111 333 === 468 .nh h.m..e.m.e .wahh h My cam... th 0cm ft... .00.... . . my am... I'll mmm 111 333 === 357 Treatment 1 (*) contained significantly more adults (p=0.05 or less by ANOVA) than any other treatment except 6. Error bars are Figure 3.3. Potato leafhopper (PLH) D-vac sampling on July 10, 1989. ‘standard error of the mean. 71 a 5 so so =3 . . 3 W July 18. 1989 '0 ‘ July 24. 1939 5 701 704 O . r E n "‘ m d e « i g m E m I g. i 1 4° 40-1 3 . 0 fl . ”I: I C , ‘ 3 fl 4“; _ ”'1 I : '- l .3 I a. 10 i g I153 3" E 10 I ’ -.’:1: :7. ’ =5 0 . , . o l . a. 1 2 a ‘ 5 3 7 . 1 2 a 4 s e 7 e PLH NYMPHS PLH ADULTS Q C s a “u 0 i a .04 August 1, 1989 .0. August 8, 1989 0.! 70' 10-1 C E 1 .2 '° ”1 g a: s . ~ \ 0 II 3. . : p o w- s s: 5 s s u 20- x \j " \ s a. 10‘ s s: 1 . \ \ 5 I a 1 2 3 4 5 6 7 B o 1 3 4 5 6 7 TREATMENT TREATMENT Treatment legend 1=alfalfa alone high 2=alfalfa alone low 3=alfalfa-brome high 4=alfalfa-brome low S=alfalfa-orchard high 6=alfalfa-orchard low 7=alfalfa-timotlry high 8=alfalfa-timothy low Figure 3.4. Adult and nymphal potato leafhopper densities in 1989. Error bars are standard error of the mean, and no significant differences exist between treatments on any date. 72 1 9 9 0 For the first half of second cutting, June 11 through June 25, adult potato leafhopper numbers rose uniformly as I a group, with no significant differences between treatments (Figure 3.5). Nymph numbers did not increase during this time (Figure 3.6). On-June 18,- there were significantly more weeds in the alfalfa monocultures than in the other treatments (Figure 3.7, Tables 3.6 and 3.7). On June 25, there was significantly more alfalfa and total biomass in the monocultures than in the mixtures (Figure 3.7, Tables 3.6 and 3.7). On July 1, 1990, numbers of potato leafhopper adults were significantly greater in the alfalfa alone-low treatment than in. brome mixtures (both high and low rates) and in the high rate of orchard mixture (Figure 3.5, Table 3.5). In addition, there were more adults in the alfalfa alone-high treatment than in all other treatments, but no contrasts against this treatment were made. Nymph numbers began to increase on July 1 (Figure 3.6) There was significantly more alfalfa biomass in the monocultures than in the mixtures on July 1 (contrast p< 0.001) (Figure 3.7, Table 3.7). On July 9, there were no significant differences in adult numbers among treatments. The highest numbers were found in low orchard mixtures and the lowest in high orchard mixtures. Nymph numbers showed a significant treatment ANOVA, however, none of our standard contrasts were significant. Numerically more leafhoppers were found in low orchard mixtures and the least in high plantings of all three grasses. Brome at the low rate had more nymphs than brome at the high rate and orchard-low had more than 73 orchard-high (Figure 3.6). Timothy-low also had more nymphs than timothy-high, but here the difference was not significant (p=0.061). There were no significant differences between alfalfa biomass on July 9. (Table 3.6), but there was less alfalfa in the brome-high and orchard-high treatments than in the other mixtures and in the monocultures (Figure 3.7). The alfalfa biomass was fairly. uniform across the other treatments. There was significantly more grass in the brome-high and orchard-high treatments when contrasted against the timothy-high treatment (p=0.022 and 0.001 respectively), but there was no difference between brome and orchard biomass. These differences were more pronounced in the controlled (sprayed) subplots. Immediately following second cutting, there were significant differences in nymph abundance on July 16. Orchard-low and both timothy rates contained more nymphs than the other treatments (Table 3.5, Figure 3.6). Adult numbers on this date were low and did' not differ, similar to What occurred after first cutting as well (Figure 3.5). No biomass survey was conducted on this date. On July 23, nymph numbers decreased from the previous date (Figure 3.6). Adult numbers increased slightly, with no separation between treatments. Alfalfa biomass on July 24 was uniform (Table 3.6), but orchardgrass in both treatments was significantly greater than the other grasses (p<0.001, Table 3.8). Brome and timothy treatments contained comparable biomass. These differences were not present in the controlled portion (Figure 3.8). Adult leafhopper numbers rose by July 30. The two alfalfa monoculture treatments had the highest adult numbers and both 74 orchard mixtures had the lowest (Figure 3.5). Nymph numbers remained low (Figures 3.4). All fractions of the vegetation biomass survey were comparable (Table 3.6, Figure 3.8). On August 7, both adults and nymph numbers rose, but with no differences between treatments (Figures 3.4 and 3.5). ‘Alfalfa alone- high had the most adults while orchard-high again had the least. There was more alfalfa in the alfalfa-high monoculture on August 6 than in most 0f the treatments, except 7 (timothy-high), but this difference was not seen in the controlled portion (Figure 3.10, Table 3.6). ' At the third cutting harvest date, August 13, nymph numbers in most of the treatments again declined, but adult numbers rose (Figures 3.4 and 3.5). There were nearly two times more leafhopper adults in the alfalfa high-rate monoculture than in the orchard-high treatment, but this difference was not significant (ANOVA p=0.357). This second year alfalfa field had few weeds. On most dates, there were more weeds in the alfalfa alone treatments than in the intercropped treatments (significantly more on July 24). Biomass generally did not differ significantly between the sprayed and unsprayed subplots. - On two dates, however, contradictory differences were found. On July 30, there was more alfalfa in the sprayed subplot of the low rate monoculture than in the unsprayed (t-test p=0.037). On August 13, there was more alfalfa in the unsprayed subplot of the brome-high treatment (t-test p=0.018) 75 . .538 on. .«o .85.... Ewes... 2a $338032 .nwE 328052.... we. :3: 0:2. 33:8 £385: mm. .332 we. 52—3: 55 958...... on. :o .953 Stm image”. 03. .30 338... 92rd mn 358.80.. 8 com. 5 53:2. Samoa—.32 0.309 .33.. .m.m oSmE ...c_v 19 go. 5...... 3.. 5...... luqll 525...... '1' 5.... 5...... llfll 8. 5...... lair 5e. 6...... '0'. so... 6...... .IT 5.... 5...... lil 3352...... lull .8 3.53.... .lelu .8 so... .52.... IT 5.... .52.... III. .5. 8...... Iol no... 25...... 1 .el 1 .8. 25...... lol 5.... 8...... .. .el .. unsung. 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Bo. 3.5.... m5 .5 ..8566 *266 m5. .5 .5 Be. 0585 ..> Bo. 5.25.... 3.86 .386 56.66 3.366 .5 m5 .5 5w... 0588 .m> 3o. 56.5.... *NN66 .686 .1866 2.1666 .5 m5 .5 8.5.5.5. :5 .m> Be. 0.25.... 3......666v ***_66.6v ***_66.6v ***.66.6v 32666 555.666 .1866 .m0. .m> 8.5.3.8552 *uwioodv 5.1.56.6V *smood *smood fwmcod 1.1666 ***~8.6V .8. .m> cm... 5.23;. 5.25.... .58. 500 500 .58. 5:8... .58. 5:56... .6003 . .35.. . .35.. . 3.: . .25.. mm 055a mm 055m .2 05.... 322.500 5.03.? a . .3025. .3583 w5...50 65000. .8 822.80 805.80.... .56 035... 84 Table 3.8. Contrasts of grass portions of biomass surveys in second and third cutting. ‘ p valuesa Contrasts July 9 con July 24 grass grass Brome high vs. other mixtures 0.009" ns Orchard high vs. other mixtures 0.009" 0.026* Brome high vs. brome low 0.026* ns Orchard high vs. orchard low 0.0ll* ns Timothy high vs. timothy low ns ns Both brome vs. both orchard ns 0.001*** Both orchard Vs. both timothy ns <0.001*** Both brome vs. both timothy 0.022* ns Table 3.9. Treatment contrasts of third cutting biomass surveys. p values21 Contrasts July 24 July 24 August 6 August 13 weedsb con weeds alfalfa con weeds Alfalfa high vs. rest ns 0.001*** 0.003“ ns Monocultures vs. rest ns 0.001*** 0.004** 0.004** alfalfa low vs. all mixtures ns ns ns <0.001*** alfalfa low vs. brome high 0.017* ns ns 0.001*** alfalfa low vs. brome low ns ns ns ~ 0.001*** alfalfa low vs. orchard high ns ns ns 0.001*** alfalfa low vs. orchard low ns ns ns 0.007“ alfalfa low vs. timothy high ns ns ns ns alfalfa low vs. timothy low ns ns ns 0.003** aTreatments are considered significantly different by ANOVA and contrasts if p g 0.05. bBrome high vs. all other treatments p<0.00l *p value _<_ 0.05 **p value 5 0.01 ***p value _<_ 0.001 85 Forage quality There were no significant differences found in percent crude protein in alfalfa portions between any treatments on any date, either within insect controlled or non-controlled areas, or between them (Figure 3.11). Percent protein in alfalfa varied from about 22 percent to 26 percent. Differences in grass quality, in terms of both fiber and protein, could not be detected for second and third cuttings as replications were combined for chemical analysis. Protein varied in the grass portions of vegetation biomass samples from about 9 percent crude protein to 14 percent. No particular grass tended to be of higher quality than another. On July 9, the alfalfa from the insect controlled areas had a greater percentage of protein (numerically) than that from the non-controlled areas (Figure 3.10). On August 13, the situation was reversed, except for treatment 1, the high rate alfalfa monoculture. Protein percentages of alfalfa in non-controlled treatment 8 of August 13 were close to significantly greater (t-test p=0.055) than the alfalfa in the controlled area. Alfalfa fiber percentages varied from 26 to 33 percent ADF and 33 to 41 percent NDF. Grass fiber percentages varied between 30 and 35 percent ADF and 54 to 64 percent NDF. Fiber percentage of alfalfa increased somewhat from second cutting to third for both sprayed and unsprayed subplots (Figure 3.12 and 3.13). There were no significant differences between any treatments on either date. On July 9, fiber percentages were not different between sprayed and unsprayed subplots also (Figure 3.12). On August 13, the ADF and NDF percentages of the alfalfa in the unsprayed subplots of treatment 1 (alfalfa-high monoculture) were significantly greater 86 than in the sprayed subplots, t-test p=0.024 for ADF and 0.006 for NDF (Figure 3.13). This indicates lower quality in the unsprayed ' alfalfa, and is substantiated by slightly less protein in the unsprayed alfalfa, although here the difference is not significant (Figure 3.11). Regression results Regression lines for graphs of grass or biomass against leafhopper numbers showed no correlation (for July biomass dates, against July adults, r 2 tended to be below 0.2). The amount of grass or alfalfa cannot predict the number of leafhoppers in the same treatment. Table 3.10. Results of regressions comparing biomass against insect numbers for two sampling dates in July, 1990. 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