”E“ Jlllllllllllllllllllllllilllllllllll'llllllllllll ” mm! 3 1293 00083 9443 Michigan @tate University This is to certify that the thesis entitled A Comparison of Cultural, Biological, and Chemical Control of Pieris Rapae (L.) On Cabbage and Cauliflower presented by Resham Bahadvr Thapa has been accepted towards fulfillment of the requirements for M.Sci. degree in Biological Sciences Ml. Major progssor February 24, 1983 Date 0-7639 MS U is an Aflirmativc Action/Equal Opportunity Institution MSU RETURNING MATERIALS: Place in book drop to remove this checkout from LIBRARIE . a; your record. FINES will be charged if book is returned after the date stamped below. 'H-‘d" 031*!" f ) )4 3" L9? \Je" S“) A COMPARISON OF CULTURAL, BIOLOGICAL, AND CHEMICAL CONTROL OF PIERIS RAPAE (L.) ON CABBAGE AND CAULIFLOWER By Resham B. Thapa A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Entomology I982 ABSTRACT A COMPARISON OF CULTURAL, BIOLOGICAL, AND CHEMICAL CONTROL OF PIERIS RAPAE (L.) ON CABBAGE AND CAULIFLOWER BY Resham B. Thapa Cultural, biological, and chemical controls of Pieris algae (L) were tested. On cabbage, Bacillus thurigqiensis (B.t.) Berliner provided good control of E. M (92% control and 97% damage reduction). It also gave the highest yield. A mixture of malathion and carbaryl gave very good control and also produced better yield than the other treatments except B.t. On cauliflower, B.t. and the chemical treatment provided 96% and 99% damage reduction, respectively. On both cabbage and cauliflower, chemical treatment based on economic thresholds and weekly sampling was less effective than either B.t. or the weekly insecticide treatment. Hand removal was the least effective on both cabbage and cauliflower, and would not be economical in controlling E. rapae in the U.S. DEDICATION This thesis is dedicated to my mother. 11' ACKNOWLEDGMENTS I express a deep sense of gratitude to my major professors, Dr. Ed Grafius and Dr. Fred W. Stehr, for their guidance and valuable suggestions during the period of my study and thesis preparation. Sincere thanks are due to Dr. Robert F. Ruppel, member of my guidance committee, for providing helpful suggestions. Equal thanks are due to Dr. Glenn R. Dudderar and Dr. Mark Whalon for serving as guidance committee members. Special thanks to Dr. Charles E. Cress, Ms. Tressa Hugh, and Mr. Ken Dimoff for their personal help in computer and data analysis. Sincere thanks to Ms. Liz Morrow who has been especially helpful throughout the period of this study. My sincere thanks to Mr. Netra Bahadur Basnyat, former Dean IAAS/Ram- pur, and Dr. Rex E. Ray, former MUCIA Team Leader IAAS/Rampur, for arranging this program opportunity and granting my study leave for Michigan State University. A grateful thanks is extended to Dr. Darrell F. Fienup, Ms. Ardell Ward, and Ms. Ann Halm, MUCIA/Nepal project, at Michigan State University for their great patience and kindness in providing me necessary support throughout my study period. Special thanks to Dr. Fanindra P. Neupane and Dr. Harry C. Bittenbender whose friendly suggestions and inspirations helped me very much in my field research. I am grateful to Ms. Glenna E. Ray and family for their help and support on all occasions. Equal thanks are due to Dr. George Axinn and Ms. Nancy Axinn m for their timely inspiration. Also sincere thanks to the faculty members and staff of the Entomology Department, Michigan State University, who made this period a beneficial learning experience for me. Invaluable gratefulness is expressed to my friends, Mr. Fred Warner, Mr. Dave Prokrym, and Mr. Lee Eavy, who made my stay enjoyable, interesting, and rewarding. Sincere thanks and appreciation to Ms. Susan Battenfield for her special effort undertaken in making sure this manuscript was finished on time. My heartfelt appreciation and deep regard to my wife, Krishna, and sons, Sagar and Suman, for their constant love, understanding, and sacrifices given to me for the study period. iv TABLE OF CONTENTS Lists of Tables ......................... vii Lists of Figures ......................... 1x I. Introduction ........................ 1 II. Management ........................ 8 I. Cultural ........................ 8 2. Biological ....................... 9 3. Chemical ....................... 10 4. Threshold ....................... 11 Ill. Objectives ......................... 11 IV. Materials and Methods ................... 13 I:I Hand removal ..................... 14 |:2 Bacillus thuringiensis .................. 14 I:3 Chemicals ....................... 14 I:4 Threshold ....................... 14 I:5 Control ........................ 16 2 Observations ...................... 16 2:I Insect counts ...................... 16 2:2 Feeding damage .................... 16 2:3 Predators and parasitoid counts .............. 17 2:4 Yield records ...................... 17 2:5 Adult activity (counts) .................. 17 2:6 Weather records .................... 17 V. Results and Discussion .................... 18 I:I Pier is rapae eggs on cabbage ............... 18 |:2 Pieris rapae eggs on cauliflower .............. 18 2:I Pieris rapae larvae on cabbage .............. 18 2:2 Pieris rapae larvae on cauliflower ............. 21 3 Pieris rapae adult activity in field ............ 21 4:I Predator activity on cabbage ............... 27 4:2 Predator activity on cauliflower ............. 27 5:I Parasitoid activity on cabbage .............. 27 5:2 Parasitoid activity on cauliflower ............. 27 6:| Hol es on cabbage .................... 30 6:2 Holes on cauliflower ................... 30 TABLE OF CONTENTS, continued 7=| Yield in cabbage ..................... 37 7:2 Yield in cauliflower ,,,,,,,,,,,,,,,,,,, 37 VI. Cost-benefit Analysis of Different Control Measures on Cabbage . . 37 VII. Other Insect Pests ...................... 43 IX. Summary and Conclusion ................... 47 BIBLIOGRAPHY .......................... 49 APPENDICES ........................... 60 vi LIST OF TABLES Table I. Mean Pieris rapae eggs and larvae/plant on cabbage ....... 19 2. Mean Pieris rapae eggs and larvae/plant on cauliflower ..... 22 3. Mean Pieris rapae larvae (small equivalents)/plant treatment X date interaction on cabbage ........... 23 4. Mean Pieris rapae larvae (small equivalents)/plant treatment X date interaction on cauliflower .......... 24 5. Mean predators and parasitoids/plant during growing season on cabbage ..................... 28 6. Mean predators and parasitoids/plant during growing season on cauliflower .................... 29 7. Pieris rapae and damage reduction on cabbage ,,,,,,,,, 31 8. Effect of treatments on damage reduction on cabbage ..... 32 9. Mean numbers of holes (small equivalents)/plant, treatment X date interaction on cabbage ........... 33 IO. Effect of treatments on damage reduction and yield on cauliflower ........................ 34 ll. Mean numbers of holes (small equivalents)/plant on cauliflower ........................ 35 l2. Cabbage yield by grades .................. 38 I3. Marketable cabbage yield under U.S. and Nepal condi- tions ..... . ..................... 39 I4. Treatment cost dollars/acre on cabbage ........... 41 I5. Marginal net return/acre on cabbage ............. 42 I6. Cabbage Ioopers (small larvae equivalents), aphids, and whiteflies on cabbage x number/plant ............ 45 vii LIST OF TABLES, continued I7. Cabbage Ioopers (small larvae equivalents), aphids, and whiteflies on cauliflower x number/plant ............ 46 Appendix I. Cabbage and cauliflower world production ....... 60 Appendix 2. Cabbage and cauliflower production and value in Michigan .................. 61 Appendix 3. Essential amino acid content in vegetables ....... 62 Appendix 4. Vitamin content in cabbage and cauliflower ....... 53 Appendix 5. Nutritional values of cabbage and cauliflower ...... 64 Appendix 6. Amount and dollar value of B.t. at the farmer level ....................... 65 Appendix 7. Parasitic insects introduced as biological control agents of arthropod pests on cole crops ....................... 66 viii LIST OF FIGURES Figure I. Individual plot design .................... 15 2. Pieris rapae eggs on cabbage ................. 20 3. Pieris rapae larvae (small equivalents)/plant on cabbage ......................... 25 4. Adult butterflies on field .................. 26 5. Holes (small equivalents)/plant on cabbage ,,,,,,,,,,, 36 ix INTRODUCTION The family cruciferae includes many important vegetables and weeds worldwide. The most important species and varieties are cabbage (Brassica oleracea var. capitata L.), cauliflower (Brassica oleracea var. botrxtis L.), brussel sprouts (Brassica oleracea var. gemifera DC.), broccoli (Brassica oleracea var. italica Plenck), kholrabi (Brassica oleracea var. caulorapa DC.), turnip (Brassica campestris L. ssp. rapifera (metzg) Sinsk), mustard (Brassica campestris L.), and radish (Raphanus sativus L.) as well as many weed species, such as yellow rocket (Barbarea vulgaris R. Br.), hoary alysum (Berteroa incana L.), indian mustard (m L.) and black mustard (Brassica m L.). Cabbage and cauliflower are two of the major vegetables among crucifers. They originated on the coast of England and Wales, the Channel Islands and Southern Europe. An Arab writer in the twelfth century mentioned "Flowering Syrian Cabbage," today called cauliflower, growing at the eastern end of the Mediterranean Sea (McDonald I97I). Perhaps the original home was the Island of Rhodes and its cultivation spread from the Mediterranean region throughout Europe. Both cabbage and cauliflower are the leading vegetable crops in many countries of the world (McCollum I975). They are grown as spring and summer vegetables in temperate climates and winter vegetables in the tropics. In Nepal, they are major winter vegetables. Cabbage and cauliflower world production figures are given in Appendix I (FAO I980). In the U.S., the annual return from fresh market cabbage is 40-60 million dollars, from I56,000 to I95,000 acres of land (Mack et aI. I956). Cabbage ranked ninth in acreage and seventh in value among 22 principle vegetable- growing states in I973. In I977, total harvest of I0|,920 acres valued at about $l2 million (McCollum I980). New York ranked first in cabbage production for sauerkraut with I979 total harvest of 3402.6 acres valued at $2.54 million (Anonymous I979). Among cabbage-producing states, Michigan ranks eleventh for its $3,229,000 cabbage crop. In l98l, 2,900 acres of commercial cabbage yielded 46,400 cwt (hundred-weight) for fresh market and processing (Michigan Food Facts I982). About 90% of the cabbage produced goes to the fresh market. Generally, 32,000 to 35,000 acres of cauliflower are grown annually. It ranked eighth in acreage and sixth in value among vegetable-growing states in I977. The Michigan cauliflower crop almost doubled in I98I (Appendix 2), ranking seventh nationally. Cabbage has long been thought to have medicinal value (McDonald I97I). For example, in Rome every illness had just one remedy-cabbage: crushed cabbage for wounds and dislocated joints, raw cabbage for gout, cabbage juice for deafness, and cooked cabbage for warts and weak eyes. Cabbage was also used to prevent drunkenness. Cabbage md cauliflower play an important role in nutrition in developing countries. Their nutritional value as greens claims priority among the first foods of infants as their diet needs to be supplemented (Oomen and Grubben I977). In developing countries, where animal sources of protein are very expensive, vegetables are available and dependable sources of protein. Legumes and other vegetables are the only affordable and readily available source of many required nutrients for vegetarians. Duckworth (I966) listed the quantities of amino acids in vegetable crops. Of the 20 different amino acids, eight are essential ones that must be provided in the diet. The remaining l2 amino acids can be synthesized in the body. The essential amino acids present in leafy and other vegetables are given in Appendix 3 (Duckworth I966, in Arthey I975). Cabbage and cauliflower contain much sulfur, and when eaten row are rich in vitamins A, B, and C (Appendix 4). Vitamin C alone is 30-60 mg/I00 gm cabbage and, even after storage or fermentation, it is high compared to that of most vegetables. They are also rich in iron and calcium. In addition, raw cabbage provides needed roughage to the diet (Becker and Dickson I982) (Appendix 5). Grading of cabbage and cauliflower is done on the basis of maturity, color, head size, and condition. Kramer and Twigg (I970) classified quality character- istics of cabbage and cauliflower into: I. Quantitative - including yield and net weight. 2. l_-l_i_d_de_n_ - including nutritional value and 3. _S_e;n§c_>_rx - including appearance (color, size, flavor and texture). In the U.S., the Food and Drug Administration controls the quality of various agricultural products. The Agricultural Marketing Service has defined the required qualitative as well as quantitative characteristics for cabbage and cauliflower (CF R I982). The Runciman Committee (I957) reported the horticul- tural marketing that stressed the importance of acceptability. Quality is one of the most important aspects in marketing cabbage and cauliflower in developed countries such as the U.S.A., Europe, and the U.K. (Arthey I975). However, there are no market standards for these vegetables in developing countries, such as Nepal or India. Simple visual inspection is given at the time of harvest to separate severely damaged heads. Outer leaves are removed from solid heads giving a better appearance and convenience in handling. Quality control and market price are often directly related. There- fore, even some improvement in quality standards in developing countries would result in better prices for producers and better produce to consumers. Twenty-one different orders of insects, including 92 families and I86 genera, occur in cabbage field (Weives and Chiang I973). At least 60 species of invertebrates (insects, mites, and gastropods) are injurious to cabbage and cauliflower (Safaryan I972). Diseases, nematodes, and weeds also affect cabbage and cauliflower production. The primary insect pests in Michigan are the cabbage maggot (Hylemya (= Delia) brassicae Bouche), imported cabbage worm (Pieris rcpae L.), cabbage looper (Trichgalusia Qi Hbr.), and diamondback moth (Plutella xylostella L.). Other insects may also cause considerable damage. As a result of insect pest attacks, yield and/or market value may be reduced. Of the major insect pests, E. rapae is the most important one (Cass I96l, Pimentel I96I, Hirata I963, Prasad I963, Weires and Chiang I973). 399$ E. m is widely distributed throughout the world (Commonwealth of Entomology I952). It is more common than B. brassicae (L) in Rumania (Niculescu I963). In Australia and New Zealand, Bartholemeu (I9I I) reported only the presence of E. Elms. Shapiro (I975) calculated 4% loss of a dozen crops throughout its world range. In the USSR, E. Ego: and _P_. brassicae both are common and cause up to 50% loss in white cabbage (Voltukhov I975). In the Krasnador region in the USSR, E. rapae caused more damage than B. brassicae. I. Oviposition The female lays eggs individually over the host plant leaves, 70% of which are laid on the lower leaf surface (Harcourt, I962, I969). She prefers large but not too old plants (Jones and Ives I979). Richard (I940) reported that the adult female lays 300-400 eggs. Generally she deposits eggs on uninfested hosts or ones with low infestation. There is a significant correlation between the density of eggs and larvae of E. [9_pc1_e(Prasad I96I). Border rows tend to have a higher density of eggs. This is the function of host discovery (Harcourt I962, I969). The eggs hatch in 5-7 days (Demin I965). Egg biology is referred to Hinton (I982). Ovipositional preference is the most important factor determining the susceptibility of cabbage to E. {2293 (Latheef and Irwin I979). Plant size, age and varietal characteristics significantly affect egg laying. Mustard glucosides serve as a larval feeding stimulant and also as an adult ovipositional stimulant. Rainey (I936) reported that E. r3293 prefered mustard glucosides and presented the glucoside content of 24 cruciferous varieties. Radcliffe and Chapman (I966) tested varietal resistancy of cabbage to E. m oviposition preferences. Red cabbage variety was least susceptible to early season oviposition. Chalfant and Brett (I967) studied 37 cabbage varieties and found Mammoth Red Rock and Savoy Perfection Drumhead were the most resistant varieties. Copenhagen Market 36 and Stein's Flat Dutch proved highly susceptible. Leaf water content is another phenotypic characteristic associated with oviposition by E. gpa_e (Wolfson I980). Terofol (I965) concluded, on the basis of tests of 50 food plants, that E. rapae and E. brassicae had similar preferences. 2- Ems _P_. £9203 larvae are voracious feeders. They feed on the lower epidermis just after hatching and slowly move to the central part. In general, larvae feed from 8 a.m. to 4 p.m. but are most active from noon to 4 p.m. (Stepanova I962). However, on warm days, they may feed from 4 a.m. to noon and 4 p.m. to midnight. They do not migrate except at very high densities (Harcourt I96I). Larval development starts at 50°F. Growth rate is limited by availability of nitrogen in the food plants (Slansky and Fenny I977). Larvae adjust their feeding rate to maximize the nitrogen accumulation rate, since amino acids are necessary for the development and growth of immature stages (Abdel Mageed I973). Weather and natural enemies are the major mortality factors for the larvae. Harcourt (I966) reported 3 natural mortality periods for E. [gag in early and late cabbage: l. Between hatching and second moult (primarily rainfall). 2. Third instar to fifth instars (primarily predators and parasitoids). 3. Pupal stage (primarily parasitoids). Hirta (I963) reported 50% mortality in the egg or first instars and 50% of the surviving larvae failed to pupate. Late transplanted cabbage may suffer more damage than early transplant- ed ones (Prasad I962). Late season infestation reduced weights of marketable heads by I25, I42, and 539 gm/plant, infested at 4, 7, and 9 weeks, respectively, with two larvae/plant. Jackson and Scott (I980) found a highly negative correlation between larval numbers and yield. 3. Pupae and Diapause The pupal period lasts 8-I4 days. Long daily photoperiod and high temperature result in continuous development (Matinyan I966). Pupae enter diapause after exposure of larvae to photoperiods of less than ll hours/day (Barker I963, Barker et al. I963, Baker and Cohen I965). However, there is variation in the incidence of diapause in different geographic locations. Pupae may overwinter on tree trunks, fences, plant remains, or other vegetation (Stepanova I962, Baker et al. I963, Demin I965). 4. Adult Activity Adults emerge in spring from overwintering pupae (Southerland I966). Generally, they have 3 generations in a year (Harcourt I96I, Kelsey I964), but may have as many as 6-8 generations (Oatman I966, Avidov and Harpaz I969, Saunders I982). Adults can fly Ila-3 miles a day and flying speed is 3-6 miles an hour. They prefer to fly I5 cm above the vegetation (Nikolaus I974). Predators and Parasitoids of E. m I. Predators About 26 species of birds feed on pierids. Weires and Chiang (I973) reported seven different species of birds occurring in cabbage fields. However, only English sparrow (Passer domesticus L.) was common. Dempster (I967, I969) reported I2 different arthropod predators including five species from Coleoptera alone. Among the predators, the most important were Harpolus rufipes (Dig) and Phalangium opilio (L.). Feltwell (I982) reports seven species of Hymenoptera and Hemiptera, and three species of Diptera predaceous on pierids. Some species of Orthoptera, Heteroptera, and Dermaptera also are predaceous on pierid larvae. Pimentel (I96l) rpeorted spiders as very effective predators of E. rapae. 2. Parasitoids Parasitoids are more host-specific than predators (Stehr I975). Both primary and secondary (hyperparasitoids) are known from E. [9293. A few species are facultative hyperparasitoids, attacking both the host and its primary parasitoids. Both solitary and gregarious parasitoids attack E. m. Apanteles rubecula (Marshall) is an early solitary endoparasitoid of E. rapae larvae (Puttler et al. I970). Trichogramma evanescens (Westwood) attacks E. rapae eggs (Parker I970). A very common gregarious larval parasitoid of _P_. rapae is Apanteles glomeratus (L), which can be reared easily in the laboratory (David and Gardiner I952, Gardiner I978). Parker (I970) reported A. glomeratus as a major factor keeping E. m population at low levels. It parasitizes all stages of E. m, but develops best on first and second instars (Moisecva I960). Ho (I962) reported only 0.33% larval parasitism by A. glomeratus. There are about 45 Apanteles larvae/host (Moss I933). High rates of A. glomeratus parasitism on E. rapae suppress tachinid parasitoids (Bisset I934). Management I. Cultural Various pest management options have been used in cabbage and cauliflow- er to reduce damage in terms of quality and quantity. Some of the oldest practices, still in use today, are methods in which numbers are reduced through cultural practices (Watson I979, Sill I982). In the USSR, cultural methods have been used to increase the effectiveness of natural enemies (Ennis I979). In the Philippines, tomato grown close to cabbage provides good control for diamond- back moth (Sill I982). Trap crop or decoy crop is used to control the club root of cabbage incited by Plasmodiophora brassicae (MacFarlane I952). The trap crop induces the resting fungal spores to germinate but is actually resistant to fungus. lntercropping with repellent crops or enhancer crops has been successful in reducing damage on cabbage and cauliflower (Hart I979, Brewer and Ball I978). Direct traditional cultural practices have been used by farmers for many years. Handpicking of pests is even today practiced in backyard gardens. Cultural practices also have been used in combination with chemical treatment. This practice may be less profitable for the short term; however, in the long run, it may be far more advantageous when considering the side effects of chemical use alone (Watson I979). 2. Biological Some very serious pests have been managed by biological methods using natural enemies. Many predators feed on pierids, including various species of birds, spiders, and many orders of insects (Marshall I909, Collenette I935, Witherby et al. I938, Michel I947, Speyer I956, Gyory and Reichart I965, Singh et al. I976). Cole crop insect parasitoids are listed in Appendix 7 (Pimentel I98I). The use of microbial control has developed into a more important part of biological control in recent years. The over I000 microbes known are probably only a part of the total number of pathogens infecting insects (Maddox I975). The National Academy of Science list of insect pathogens (I969) includes 90 species of bacteria, 260 species of virus and rickettsiae, 460 species of fungi and 255 species of protozoa. Although the first record of the use of microbes for 10 insect control was in the eighteenth century, much of the work was carried out by the middle of the nineteenth century (Feltwell I982). Among bacteria that infect insects, the best known is Bacillus thuringiensis var. thuringiensis Berliner (B.t.). B.t. was first discovered in diseased silkworms by a Japanese scientist in I902. It was rediscovered in I9l5 by the German scientist Berliner, in the province of Thuringia. The resting spore of B.t. produces a proteinaceous endotoxin, toxic to lepidopterous caterpillars but with little or no effect on other species (Krieg and Herbs I963). Its production by American companies has grown to over 900 metric tons (2 million lbs.) per year, including 375 isolates. The advantages of B.t. are: I. There is no chemical residue problem. 2. It is somewhat specific and not hazardous to many beneficial insects or humans. 3. Commercial preparation can be made easily and economically. 4. Low doses can suffice in control work. 5. It is compatible with most insecticides and application techniques. 3. Chemical Insecticides were apparently used before recorded history. F ronk (l_n Pfadt l97l) noted that sulfur was used by the Greeks against pests about 3000 years ago md the Romans used asphalt fumes to rid their vineyards of insect pests. The Chinese used arsenic compounds against garden pests before 900 AD. Before the l9405, only 2 major categories of insecticides (inorganic and botanical) were used. Paris green (arsenical) was the first insecticide to be used on a large scale in the U.S. After the discovery of DDT by Paul Miller in I939, a 11 revolution in insecticide control occurred, with the majority (about 90%) of currently used pesticides being synthetic organics. 4. Threshold Stern (I959) proposed the terms "Economic injury level" and "Economic threshold level." Economic injury level refers to the density of a particular pest species that will cause a loss equal to the cost of an insect control measure. Economic threshold is a density of insect species lower than the economic injury level. It is the pest level where something must be done to avoid reaching the economic injury level. Plant damage is expressed as visible foliage damage to leaves, fruits, or both. According to these terms, insects are of 2 types: economic and non- economic. Non-economic species are always below the economic threshold. Of many species in a particular crop, only a few occur at densities above the economic injury level, where control measures should be considered. (bjectives The main objective of this study was to compare different control methods in terms of effectiveness, costs and benefits. The goal was to select an economically desirable combination of control methods for managing cabbage worm complexes in Michigan. In addition, since cabbage worm complexes are prevalent in many countries where cabbage and cauliflower are grown, this study may supply basic information for using management tools in other countries. Nepal is primarily an agro-based country where 93% of the people are dependent on agriculture (TRAS No. I4, I980). Legumes and vegetables are the main source of protein in Nepal. Since cabbage and cauliflower are major winter 12 vegetables, pest management is very important to protect these crops. Serious cabbage worm complex problems occur in government research farms and farmers' fields. For example, the cabbage crop was totally destroyed on a farm in Rampur due to severe attacks of insect pests and nematodes (Tereda, IAAS/Rampur, I978). It was not possible to go there and study this problem in Nepal due to the short time and costs. This study in Michigan will provide problem-oriented information for Nepal where: Farmers are unaware of the potential problems of toxic chemicals. Only I9% of the total population are literate, including government officials, teachers, students, and workers. Most of the farmers can hardly read or write. Therefore, they are not aware of serious hazards of using chemicals such as insecticides, herbicides, and fungicides. Farmers have little experience in chemical use and handling. They are aware of the fact that insect pests and diseases are serious problems in vegetable production, but pest management is largely unknown. It is important here to focus on the safe use of chemicals for pest management. In addition, the use of safe chemicals will reduce problems by lowering the adverse effects on the crop and the environment. Kitchen gardening is common in Nepal; hence, the potential adverse effects on house pets, animals, and humans is high when pesticides are used because of the everyday close contact with them. There are no cold storage facilities for vegetables in Nepal. Many fresh green vegetables may lose their flavor, have their color fade, and undergo rapid decay due to lack of storage facilities. Therefore, 13 daily fresh vegetable selling and consumption as well as everyday fresh-picked vegetable uses by farmers is a common practice in Nepal. For this reason, chemicals with no waiting days or minimum waiting days after application have advantages over chemicals with long waiting days. Materials and Methods This experiment was conducted at the M.S.U. Department of Entomology, Collins Road Farm. The field was selected on the basis of soil type and irrigation availability for growing cabbage and cauliflower (Anonymous I982). The plot (Fig. I) was follow in I980. During the summer of I977, the plot had been planted in potatoes for Colorado potato beetle study. The same plot was used in a small plot vegetable study during I978 and I979 with various vegetable crops. Cabbbage and cauliflower were planted for experimental study in summer, l98l. Fertilizer (Anonymous I970, Warnke and Christenson I98l), irrigation (Kaoli and DeVera I977, Vitosh I977), weed control (Barrett and Meggitt I983, Zandstra and Putnam I983), and maggot control (Wells I979, Graflus et al. I98I, Lyon et al. I98I) were done as recommended. Cabbage (var. sanibel) and cauliflower (var. self-blanche) were used in this study. Minge (I968) summarizes varietal characteristics. Self-blanche variety was a self-wrapping variety from M.S.U. (Honma I973) and sanibel from Wisconsin (Williams and Walker I968). Cabbage and cauliflower seeds were sown in vermiculite in the green house on May 20 and watered as needed. Six week old seedlings were transplanted into the field on June 30. A plot consisted of 48 plants spaced one foot apart in 6 14 rows (3 rows cabbage and 3 rows cauliflower) with 2.5 ft between rows (Fig. I). A uniform walking space of 4 feet was left between each plot. Plots were arranged in a randomized block design. The center 4 rows of each plot were treated, leaving one border row on each side to reduce the border effect and provide sources of beneficial insects. There were five treatments including a control. Each treatment was replicated four times. Treatments consisted of: I. Hand removal (0 traditional cultural practice). Hand removal of larvae on cabbage and cauliflower was done weekly. Larvae were removed or smashed on the leaves. No chemical or synthetic biological treatments were used. 2. Bacillus thurifiiensis (B.t.) (biological method of pest management). Bacillus thuringiensis (Dipel) was sprayed at 72 lb. per acre weekly until the crop was harvested. Spraying was done with a low volume 3 gallon (I 2 liter) backpack sprayer. Spray drift or border effect was mini- mized with the guard rows, and by selecting spray time for low wind velocity and optimal wind direction (perpendicular to the rows). Each plant in the center 4 rows was covered evenly. 3. Chemicals (chemical method of pest control). The safest available insecticides, malathion and carbaryl, were used in this treatment. They were applied at a rate of 2 pt./A and Ill: Ib./A, respectively, in approximately I25 gal. water/A. Treatments were applied weekly. 4. Threshold spray (threshold level of pest management). The same concentration of malathion and carbaryl were used in this treatment. Treatment was applied when the population exceeded an average of one larva per plant. 15 I 15 t A O O X X X 0 O X X X 0 O X X X 0 O X X X N O O X X X 0 O X X X 0 O X X X C O X X X l Figure 1. Individual plot Cabbage (O) and Cauliflower (X). 16 Control (untreated). This was provided to compare the above 4 treatments as well as to observe the pest population trend during the growing season on late cabbage and cauliflower. The following observations on the center 4 rows in each plot were recorded weekly: Insect counts. The number of eggs, small (Ist, 2nd instars), medium (mostly 3rd, a few 4th), and large (4th, 5th instars) larvae per plant in each plot were recorded weekly. E. rapae was the major pest. A few cabbage Ioopers (Trichoplusia fl) were observed during the growing period. Aphids and white fly numbers were also recorded. The abundance of other insect pests was extremely low. Diamondback moth (Plutella xylostella) was not observed during the study. For E. brassicae, a European relative, large larvae consume about I0 times as much as small larvae and medium larvae consume about 5 times as much (Chlondy I967). Larval numbers of E. M were converted into small larva equivalents using these factors, and converted into insect degree days (Ruppel I982). This made it easier to compare treatments like chemical and 8.1. in which only small larvae were present, with the controls and hand removal, where larval size varied. Feedigg damage. Holes per plant were recorded weekly. The size of hole is important to plant recovery. Also, hole size is related to the size of the larva. Holes were recorded as small (less than 7 mm) and large (greater than 7 mm). Fifty leaf samples were collected from mid-season growing plants and small and large holes measured on 17 them, gave the average ratio of I:I0. Large holes were converted into small hole equivalents for comparison between treatments. Only small holes were observed in the chemical and B.t. treatments. Predators and parasitoid counts: In the weekly observations, predators were counted in each plot. Cocoon number of the gregarious braconid, Apanteles glomeratus, was counted. Tachinids were present in very low numbers and were not quantitatively sampled. Yield records. Cabbage and cauliflower yields were recorded at harvest. Cabbage heads were graded into 4 categories: i. A grade. No holes, no insects, no frass. ii. B grade. Wrapper leaves with a few small holes, no insects, no frass. iii. Cgrade. Wrapper and I-2 inner leaves with small holes, no insects, no frass. iv. Dgrade. Wrapper and more than 2 inner leaves with holes (small or large), presence of frass and insect larvae. Cauliflower was harvested almost 3 weeks later than cabbage. No insects or frass were observed in the heads at either of the two harvest dates. All heads were marketable. Adult activiLy. Pherocon Ic* traps with commerical pheromone caps (Zoecon Corp.) were set up next to the field for cabbage looper adult monitoring. Counts of E. [3% adults active in the experimental area were made each week before noon. Weather records. Weather data was recorded at the M.S.U. Horticul- ture Farm, 2 km south of the Entomology Farm. Temperature data 18 were converted into degree days using a base 50°F and the technique of Baskerville and Emin (I969). Results and Discussion I. EGGS I. Pieris rapae (L) eggs on cabbage: Eggs were first observed on cabbage leaves on July 3|, 0 month after transplanting, but they must have been present in small numbers earlier since larvae were first found a week earlier. Early cabbage in an adjacent plot was already infested by E. [2% larvae. The mean egg number ranged from 0.58 to 0.84 per plant in the control and the chemical treatments, respectively (Table I). There were no significant differences in mean numbers of eggs per plant in any treatments. However, block differences occurred. Lower egg numbers were observed in the central blocks. Differences in egg numbers were observed between dates during the growing season. The highest numbers of eggs were observed on August 6, approximately six weeks after transplanting (Fig. 2). The early and late egg laying trends for each treatment were similar. 2. Pieris rapae eggs on cauliflower: Similar results were found in cauliflower. However, the highest egg numbers occurred on hand removal treatment (0.53) and fewest eggs on control (00.4) and differences were not statistically significant (Table 2). More eggs were laid per plant on cabbage than on cauliflower, in agreement with the results of Hart (I979). Il. LARVAE I. Pieris rapae larvae on cabbage: Cabbage was not infested by first generation E. rapae, as the plants were transplanted in late June. Second 19 Table 1 Mean Pieris rapae eggs and larvae (small equivalents)/ plant on cabbage averaged for all sampling dates.1 Treatment Eggs (smtilvzgvt.) chemical 0.84 a 0.04 a threshold 0.73 a 0.43 a control 0.58 a 4.30 c hand removal 0.22 a 3.61 b Bt 0.80 a 0.34 a 1Means followed by the same letter are not significantly different (P > 0.05) by SNK test. CUMULATIVE NUMBERS OF EGGS/PLANT 20 lO- Chemical Hand removal 8 ._. B.t. hreshold 6 -+ g-Control 4 —-4 2 ‘fi 0 l l l T* ‘7 1300 1500 1700 1900 2100 2300 DEGREE DAYS (Base 50°F.) Figure 2. g: rapae eggs on cabbage. 21 generation E. m larvae were first noticed in the third week of July (Table 3). Peak numbers were observed in the middle of August. The mean density of _P_. m larvae (small equivalents) ranged from 0.04 to 4.30 per plant in chemical treatment and control, respectively, during the growing season. Larval density in the control plots was significantly higher than in the other treatments. Chemical, threshold, and B.t. treatment did not differ from each other (Table I). Treatment and date interaction showed significant differences between dates and treatments (Table 3). The mean E. M larval density (small equivalent) for each date and treatment was converted into insect degree days and plotted against degree days DDSOOF (Ruppel I982). A sigmoid trend was observed in hand removal and control while the rest of treatments did not show such a trend (Fig. 3). The chemical treatment reduced insect degree days to the lowest level. 2. Pieris rapae larvae on cauliflower: Similar results were observed for cauliflower as occurred on cabbage. The mean larval number (small equivalent) per plant during the growing season ranged from 0.02 in chemical to 2.62 in hand removal treatment (Table 2). Mean larval densities were lower in cauliflower than in cabbage. Date x treatment interaction was similar to results for cabbage (Table 4). III. ADULTS E. M adult activity on field: Butterflies were observed on the day of transplanting of cabbage and cauliflower. Their number peaked on July 3|, 0 month after transplanting (Fig. 4). Thereafter, I3. E293 adults decreased, and no adults were observed after the third week of September. 22 Table 2 Mean Pieris rapae eggs and larvae/ plant on cauliflower averaged for all sampling dates.1 Treatment Eggs (smallvggvt.) chemical 0.45a 0.02a threshold 0.43a 0.23a control 0.40a 2.17b hand removal 0.53a 2.62b Bt 0.49a 0.13a 1Means followed by the same letter are not significantly different (P > 0.05) by SNK test. 23 Table 3 Mean Pieris rapae Larvae (small equivalents) / Plant 1 During the Growing Season on Cabbage. Date 7/24 7/31 8/6 8/14 8/21 8/29 9/6 rt. chemical 0.0Aa 0.14Aa 0.19Aa 0.03Aa 0.02Aa 0.03Aa 0.0Aa threshold 0.0Aa 0.59Aa 0.33Ba 2.4SCa 0.063a 0.27Aa 0.55Aa control 0.27Ac 2.25Ac 8.95Ab 18.52Aa 10.40Ab 2.03Ac 0.5 Ac hand removal 0.5 Ab 3.23Ab 8.47Aa 10.89Ba 8.73Aa 2.94Ab 1.33Ab Bt 0.0Aa 0.33Aa 1.13Ba 1.03Ca 0.8lBa 0.14Aa 0.0 Aa 1 Means followed by the same letter (capital in row and small in column) are not significantly different (P > 0.05) by Tukey's multiple range test. 24 Table 4 Mean Pieris rapae Larvae (small equitalents) / Plant during the growing season on cauliflower.l Date 7/24 7/31 8/6 8/14 8/21 8/29 9/6 rt. chemical 0.0Aa 0.06Aa 0.09Az 0.02Aa 0.0Aa 0.03Aa 0.0Aa threshold 0.39Aa 0.06Aa 1.39ABa 0.0 Ba 0.25Ba 0.64Ba 0.0 Aa check 0.14Ad 0.61Acd 3.31ABc 9.81Aa 6.7 Ab 2.69Bcd 0.89Acd hand removal 0.23Ad 0.80Ad 4.09Abc 7.98Aa 8.06Aa 6.28Aab 2.09Acd Bt 0.02Aa 0.17Aa 0.75Ba 0.39Ba 0.22Ba 0.0 Ba 0.0 Aa 1Means followed by the same letter (capital in rows and small in columns) are not significantly different (P > 0.05) by Tukey's multiple range test. CUMULATIVE INSECT DEGREE DAYS 6000 4500 3000 1500 1300 25 .a-Control Hand removal I 1500 B.t. Threshold e—————-* ’ Ch ' I l l I l 1700 1900 2100 2300 2500 O DEGREE DAYS(Base 50 F.) Figure 3. P. rapae larvae(small equivalents)on cabbage. 26 .eflmfla c. mwfiflmumoosb pager .v masons mmmzmsamm _ amoosa _ some A.m om mmmmvmwca mmmomo ooo~ o coma OONH oom A _ _ 0 To GEIAHESBO SLTDGV JO HHBWON 27 IV. PREDATORS l. Predator activity on cabbage: The first coccinellid predator was observed on July 30. Coccinellid and Chrysopa spp. were observed feeding on aphids on cabbage leaves. Very low numbers of predators were observed, ranging from 0.002 to 0.0I2 per plant in chemical and hand removal, respectively (Table 5). Perhaps the low number of predators in cabbage was due to the low aphid populations which were present during the growing period (0.38 to .74 per plant in chemical and B.t., respectively). Predator numbers were slightly higher on B.t. and hand removal treatments than chemical and threshold treatments. 2. Predator activity on cauliflower: They occurred the same time as in cabbage, and results were similar to results in cabbage (Table 6). Similar numbers of predators were present on cauliflower than on cabbage (0.004/plant in chemical treatment to 0.0I2/plant in hand removal treatments). IV. PARASITOIDS l. Parasitoid activity on cabbage: Apanteles cocoons were noticed early in the first week of August and adult Apanteles were first observed on August I0. Most parasitoids observed in this study were Apanteles llomeratus, ranging from 5-50 per affected host. A few larvae were parasitized by tachinid flies; generally three emerged per affected pupa. Mean percent parasitism ranged from 3.85 in chemical treatment to 0.84 in hand removal (Table 5). Parasitoids in B.t. treatment were lower than hand removal or control, probably due to the the low number of hosts rather than an adverse effects of the B.t. treatment. 2. Parasitoid activity on cauliflower: Pimilar parasitoid activity on cauliflower was similar to that on cabbage (Table 6). Percent parasitism ranged 28 Table 5 Predators and parasitoids / plant during growing season on cabbageJ Mean numbers of Mean numbers of Treatment predators/ parasitisized % Parasitism plant larvae/plant1 chemical 0.002 0.002a 3.85 threshold 0.005 0.003a 0.86 control 0.011 0.040b 2.55 hand removal 0.012 0.011a 0.84 Bt 0.008 0.005a 1.35 1Means followed by the same letter are not significantly different (P >0.05) by SNK test. 29 Table 6 Predators and parasitoids / plant during growing season on cauliflower. Treatment Prgdgfigrs/ paugggiis$:ed % Parasitism larvae/plant1 chemical 0.004 0.0 a 0 a threshold 0.007 0.0 a 0 a control 0.010 0.014b 2.25b hand removal 0.012 0.008a 0.86b Bt 0.008 0.004a 3.03a 1Means followed by the same letter are not significantly different (P > 0.05) by SNK test. 30 from 3.03 in B.t. treatment to 0.86 in hand removal. There were no parasitoids observed in chemical and threshold treatments. Parasitoid numbers were slightly lower in cauliflower than in cabbage. Vl. DAMAGE l. Holes on cabbage: Chemical and B.t. treatments provided the best control in terms of damage reduction. B.t. provided a 92% reduction of E. Lgpg larvae and 97% damage reduction and 2-3 times as many marketable heads compared with the control on cabbage (Table 7). Chemical treatment reduced both E. mpg; larvae and damage by 99% (Table 7). The mean number of holes (small equivalent) ranged from 0.22 to 43.69 in chemical and control, respective- ly (Fig. 5). Hand removal was significantly better than control. Both hand removal and control were significantly worse, in terms of damage reduction, than the other treatments. Chemical, critical, and B.t. treatment did not differ significantly from each other. Analysis of date x treatment interaction showed no differences between dates and treatment for B.t. and chemical treatment. The other treatments differed significantly from each other (Table 9). 2. Holes on cauliflower: Similar results occurred in cauliflower (Table ID). The mean number of holes was lower in cauliflower than in cabbage in the respective treatments, as the result of E. ms ovipositional preference for cabbage. Treatment x date interaction showed no differences between B.t. and chemical treatments. The rest of the treatments differed significantly between dates (Table I l). 31 Table 7 E, rapae and damage reduction in cabbage. Treatment Larval reduction % Damage Reduction % chemical 99.0 99.5 threshold 90.1 82.5 hand removal 16.0 52.3 Bt 92.0 97.5 32 Table 8 Effect of treatments on damage reduction on cabbage. Treatment Holes/Plant1 Marketable Heads (in %) (small equivalents) U.S. Nepal chemical 0.22 a 90.62 96.9 threshold 7.69 a 57.1 76.2 control 43.69 c 30.5 44.1 hand removal 20.83 b 36.5 60.3 Bt 1.10 a 96.9 100.0 lMeans followed by the same letter are not significantly different (P > 0.05) by SNK test.. 2Some heads not marketable due to small size. 33 Table 9 Mean Number of Holes (small equivalents)/Plant on Cabbage.1 ‘\ Date 7/24 7/31 8/6 8/14 8/21 8/29 9/6 Trt. chemical 0.17Aa 0.37Ca 0.78Ca 0.19Ca 0.58Ca 0.128a 0.0 Aa threshold 8.66Ab 3.64Cb 32.028a 3.0 Cb 6.050b 16.53Ba 6.73Ab Check 15.64Ae 48.25Ad 87.52Ab 141.0 Aa 69.03Ac 55.95Acd 4.48Ae hand removal .9.33Ac 28.97Bb 46.00Ba 60.44Ba 46.698a 13.47Bbc 3.44Ac Bt 0.70Aa 2.2 Ca 3.39Ca 2.950a 1.39Ca 0.36Ba 0.0 Aa 1 Means followed by the same letter (capital in rows and small in columns) are not significantly different (P > 0.05) by Tukey's multiple range test. 34 Table 10 Effect of treatments on damage reduction and yield for cauliflower Treatment (small]::£§iglzits) Yield (cwt/A) chemical 0.17 a 237 a threshold 2.57 b 264 a control 13.70 c 257 a hand removal 12.94 c 260 a Bt 0.62 a 300 a 1Means followed by the same letter are not significantly different (P > 0.05) by SNK test. 35 Table 11 Mean Number of Holes (small equivalents)/Plant on Cauliflower.1 Date 7/24 7/31 8/6 8/14 8/21 8/29 9/6 Trt. chemical 0.0 Aa 0.22Ba 0.41Ca 0.56Ba 0.7 Ba 0.16Ca 0.0 Ba threshold 1.67Ab 0.92Bb 11.83Ba 0.73Bb 1.398b 13.8Ba 0.6 Bb check 1.94Ae 14.77Ad 34.27Ab 42.39Aa 38.41Aab 24.17Ac 8.52Ad hand 1.59Ae 9.95Ad 33.22Ab 39.67Aab 44.03Aa 20.67ABc 6.11ABde removal Bt 0.37Aa 1.53Ba 2.44Ca 1.84Ba 1.06Ba 0.33Ca 0.0 Ba 1 Means followed by the same letters (capital in rows and small in columns) are not significantly different (P > 0.05) by Tukey's multiple range test. 36 .mmmnnmo co “mucoam>flsvo HHmEmvmmHom .m wusmflm Tao om 038 $25 mmmomo omHN ommH oth ommH Omma FIIIIIIIII _ llllll HMUMEUSU I'll-III _ II o u o m ”HO—km much. IIIIII‘\I\\|\I Hm>OEou can: Houucoo omaa OOH ooN 00m oov oom .LNV'Id/SE'IOH JO SHSBWON HAILV'IDWDD 37 VI. YIELDS I. Yield in cabbage: Qualitative or marketable grades of cabbage were separated for U.S. and Nepal conditions (Table l2). B.t. was the best treatment, producing the highest U.S. marketable yield. However, it did not differ statistically with chemical treatment in U.S. or Nepal market condition. Hand removal was the least effective treatment, producing very low marketable heads under U.S. conditions. The U.S. marketable grade yields averaged from I38 cwt/A to 607 cwt/A in hand removal and B.t. treatment, respectively. However, under Nepal market conditions, yields ranged from 240 cwt/A in control to 63I cwt/A in B.t. treatment (Table I3). Threshold treatment produced slightly lower marketable yields than chemical treatment under Nepal conditions. 2. Yield in cauliflower: First harvest of cauliflower was three weeks later than cabbage and second harvest a month later. E. gpgg larval populations were extremely low due to cold weather. Also, cauliflower was less preferred for oviposition. Therefore, all cauliflower heads escaped damage or contamination and all heads were marketable. No significant difference in yield was found between the treatments, although B.t. treatment produced slightly higher yields than the rest of the treatments (Table I0). VIII. Cost-benefit analysis of different control measures on cabbage. The threshold of larvae on cabbage has been suggested as 0'I cabbage looper larvae/plant (Green I972), I-3 damage rating (Shelton et al. I982), I-2 holes/plant (Chalfant et al. I979), and I-4 head damage rating (Simonet and Morisak I982). Andolaro et al. (I982) suggested threshold level on the basis of larval units such as 0'8, I'0, I'6, and 2’5 for early preheading, late preheading, 38 Table 12 Cabbage yield by grade.1 U.S. marketable Nepal marketable Total Treatment (A) (A+B) (A+B+C) (A+B+C+D) chemical 44.25b 46.10b 48.975b 51.075a threshold 20.225a 25.70a 39.30b 50.175a control 12.125a 16.975b 21.40a 54.850a hand removal 6.225a 12.475a 24.475a 49.125a Bt 46.275b 55.80b 57.9250 57.925a 1Pounds per plot, means followed by the same letters are not significantly different (P > 0.05). 39 Table 13 Marketable Cabbage Yield1 U.S. marketable . Nepal marketable Treatment cwt/A $ value cwt/A $ value chemical 502 3494 533 1455 threshold 294 2046 449 1223 control 188 1308 240 653 hand removal 138 960 271 739 Bt 607 4225 631 1720 1Dollar value based on 1981 market price for U.S. and 1974-76 for Nepal. 40 early head formation, and late head formation, respectively. Hoy (I982) provided codes I-5 for damage rating and larval number per plant on the basis of his sampling technique for cabbage. Studies have been done on plant growth stages of cabbage, as well as cabbage insect biology. These two critical factors are important means for optimizing sampling and for making control decisions (Chalfant et al. I979, Harcourt I962 and I969, Ladd et al. I98I, Green I972, Shepard I973, Simonet and Morisak I982). The same data still has to be worked out under Nepal conditions based on market standard requirement. The benefit/cost ratio and net benefit (benefit minus cost) approaches are two common criteria for choosing the best method for pest management (Howitt and Edens I979). Headley (I972) discussed the economics of pest management as functions of productivity in pest control. The economics of production lie in achieving maximum net return per unit produced. The difference in yield with and without control measure is the marginal benefit of the control method. Treatment costs and yield recorded at harvest for each treatment are given in Table I3 and I4. The market value of cabbage at harvest was calculated for U.S. marketable grades (Table I3). C and D grade did not meet U.S. market standards. Grades A, B, and C are easily marketable in Nepal. Market value is given in Table I3. Prices for insecticides are estimated for U.S. and Nepal conditions (Table I4). B.t. and chemical treatments gave higher marketable yields in both U.S. and Nepal market conditions. B.t. was the best control method for U.S. as well as Nepal conditions on the basis of economic analysis (Table l5). It gave the highest net return ($2802 and $999 under U.S. and Nepal conditions, respective- 41 Table 14 Treatment Cost dollars / acre.1 Treatment U.S. Nepal chemical 60 33 threshold 32 14 hand removal 175 17 Bt 115 68 lPrice calculation based on 1981, labor and chemical costs for U.S., and 1972-76 farming book Rapti model farm. 42 Table 15 Marginal Return/Acre.1 (marginal revenue - marginal cost) Treatment U.S. Nepal chemical 2126 769 threshold 706 556 hand removal -523 69 Bt 2802 999 1Value in dollars. 43 ly). B.t. exceeded the net return of the chemical treatment by $676 under U.S. and $230 under Nepal conditions. The second best alternative in both the U.S. and Nepal was the chemical treatment. Chemical treatment gave a slightly higher net dollar value compared to the threshold treatment in Nepal marketable yields, but much higher net return under U.S. conditions. This difference was due to grade standard differences between Nepal and the U.S. Economic thresholds are related to the marketable yield produced; therefore, different grade standards for different countries may alter economic thresholds. In this study, treatments and sampling were done on a weekly basis. [3. m densities were far above economic threshold levels on certain dates. The peak period coincided with the critical heading of cabbage which resulted in reduced cabbage head quality, thereby reducing marketable yields. Hand removal was the least effective method and was not profitable at all under U.S. conditions. In fact, marketable yield and net return were less than the control. Under Nepal market conditions, hand removal gave some net return. It would also provide some employment to farmers. However, it is only practical in small-scale production. Other cultural practices, such as the use of wood ashes, companion crops, and lntercropping, may be better alternatives to this method (Brewer and Ball I978, Ives I978, York and Guin I98I). IX. Other insect pests. Pieris rapae was the most important pest in this study. Other insect pests may also have severe effects on cabbage and cauliflower when they are abundant. In this study, cabbage looper, cabbage aphids, and white flies were also monitored. 44 Many authors have reported cabbage looper as a major pest in cabbage (Kennedy and Putnam I976, Wyman and Oatman I977 in California; Creighton and McFadden I975 in South Carolina; Hostettler et al. I979 in Columbia, South America). Similarly, severe injury has been reported on cabbage and broccoli from aphids (Oatman and Planter I969, Kennedy and Oatman I976). White flies can cause considerable damage when present in large numbers. There were few cabbage Ioopers observed (Tables l6 and I7). Simonet and Morisak (I982) also observed large numbers of E. BEE and only a few cabbage Ioopers on cabbage in Ohio. Cabbage Ioopers were first found in early July and continued to late September. Cabbage Ioopers (small larval equivalents) during the growing season are given in Tables I6 and I7. Aphid populations were also low. Mean numbers per plant were very low throughout the growing season (Tables l6 and I7). Densities did not differ between cabbage and cauliflower and never reached damaging levels. Chemical and threshold treatments were significantly better than the other treatments in reducing aphid populations in cabbage. However, only chemical treatment was better than the others in cauliflower (Table I7). Whiteflies can cause considerable damage when present in large numbers. However, they were present only in low numbers and therefore did not differ between treatments. Means per plant averaged during the growing period ranged from 0.37 to 0.5I in chemical and control, respectively, on cabbage (Table I6). Numbers were slightly higher on cauliflower, possibly because of the long growing period (Table I7). 45 Table 16 Cabbage l00pers (small larvae equivalents), aphids, and whiteflies on cabbage 2 number / plant.1 Treatment (small gazisglents) Aphids Whiteflies chemical 0.02a 0.38a 0.37a threshold 0.15bc 0.54b 0.46a control 0.34d 0.71c 0.51a hand removal 0.21c 0.68c 0.46a Bt 0.06ab 0.74c 0.47a 1Means followed by the common letters are not significantly different (P > 0.05) by SNK test. 46 Table 17 Cabbage Ioopers (small larvae equivalents), aphids, and whiteflies 0n cauliflower x number / plant.l Treatment (small :2:¥3§1ents> Aphids Whiteflies chemical 0.01a 0.30a 0.48a threshold 0.03a 0.49b 0.60a control 0.14a 0.62b 0.67a hand removal 0.07a 0.56b 0.51a Bt 0.01a 0.64b 0.70a 1Means followed by the common letters are not significantly different (P > 0.05) by SNK test. 47 Summary and Conclusions Cultural, biological, and chemical methods were compared for the control of E. m (L.) on cabbage and cauliflower. Bacillus thurinflnsis (Berliner) provided excellent control of E. m (L.) with 92% larval reduction and 97% damage reduction on cabbage. It provided the highest marginal returns: 4I9 cwt/A increase due to treatment for the U.S. market conditions, and 360 cwt/A increase for Nepal market conditions. B.t. was also the best method on the basis of cost benefit analysis with $2802 and $999 net benefit, respectively, under U.S. and Nepal conditions. In addition, B.t. can be used by farmers without any harmful effects on beneficial insects (honey bees, predators, parasitoids) or human health. The combination of malathion and carbaryl also provided excellent control with 99% E. M larval reduction and 99% damage reduction on cabbage. It provided marginal returns of 3I4 cwt/A and 293 cwt/A under U.S. and Nepal market conditions, respectively (slightly less than the B.t. treatment). The threshold spray provided 90% reduction of E. M larvae and 82% damage reduction. It was better under Nepal market conditions (209 cwt/A increase) than under U.S. conditions (l06 cwt/A increase due to treatment). This difference was due to the differences in grading in U.S. and Nepal. Hand control provided only I6% larval reduction of E. gage, with 52% damage reduction. it was not affordable under U.S. conditions, being more expensive and providing unsatisfactory control. It produced a 3| cwt/A yield increase under Nepal market condition. It would provide some employment for workers under Nepal conditions. However, the only possibility of using this method for E. 5:23 control is in kitchen gardens, farmers using their leisure hours, or in places where no alternative methods are available. 48 On the basis of overall effect on E. M control, damage reduction, marketable yield increases, and the economic analysis, Bacillus thuringiensis (Berliner) was the best control measure on cabbage. The malathion and carbaryl mixture was the second best method. Hand removal resulted in high costs and the least control obtained. It did not produce sufficient U.S. grade cabbage increases to cover labor costs. Threshold sprays did not produce enough marketable cabbage because sampling was not done frequently enough to treat before damage occurred. More frequent sampling is needed on cabbage beginning with pre-heading stages (Simonet and Morisak I982). This study shows that B.t. is the best method for E. m management. Use of the B.t. program in Nepal will provide the following benefits: I. It eliminates the potential problem of toxicity and poisoning to beneficial insects, animals, growers, and consumers. 2. Even the least experienced farmer can handle it easily. Insecticide and herbicide handling is more critical. 3. B.t. facilitates daily fresh vegetable consumption due to no time limit from spray to harvest. 4. B.t. solves the problem of poisoning and toxic effects on household pets, animals, and human beings. 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E-433, Coop. Ext. Serv. MSU. I98 p. 60 Appendix 1 Cabbage and Cauliflower World Production for 1980 (FAD 1981). Area harvested (1000 HA) Yield (1000 MT) Region Cabbage Cauliflower Cabbage Cauliflower World 1628 341 35139 4535 Africa 25 7 640 146 N. 0. America‘ 95 23 1847 264 U.S.A. 72 17 1551 195 South America 23 5 571 73 Asia 783 176 15401 1746 Europe 320 126 8032 2183 Oceania 5 4 109 114 USSR 377* 2* 8540* 9* *Data estimated. 1 includes Antigua, Barbados, Bermuda, Canada, Costa Rica, Cuba, Dominican Republic, El Salvador, Guadelope, Guatemala, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Puerto Rico, Trinidad Tab. and USA. 61 Appendix 2 Vegetable production and value in Michigan (Michigan Dept. of Ag. 1982). Crop Year Acres Production Price Value of Planted Harvested Per Total Received Production Acre (1,000 (Dollars/ (1,000 (cwt) cwt) cwt) Dollars) Cabbage 1977 3,600 3,200 164 526 6:28 3,302 1979 3,300 3,000 163 489 6.56 3,207 1981 3,200 2,900 160 464 6.96 3.229 Cauliflower 1977 1,100 1,000 50 50 16.60 831 1979 1,200 1,100 70 77 27.70 2,132 1981 1,200 1,000 62 62 37.90 2,350 62 Appendix 3 Essential amino acid contents in vegetables (Duckworth 1960). Amounts gm/100 gm protein Leafy Vegetables Other Vegetables Lysine 3.1 - 7.5 1.5 - 5.8 Methionine 0.9 - 2. 0.5 - 2.6 Tryptophan 0.9 - 2.1 0.6 - 1.6 Leucine 3.7 - 9.3 2.7 —11.9 Isoleucine 2.4 - 6.3 1.5 - 5.1 Phenylalanine 1.9 - 6.4 1 4 - 4.5 Threonine 2.2 - 5.5 1.5 - 5.0 Valine 1.8 - 7.1 2.2 - 6.4 63 Appendix 4 Vitamin Content in Cabbage and Cauliflower (Lorenz and Maynard 1980). Amounts/100 gm Vegetable Vit A Thiamin Riboflavin Niacin Ascorbic Acid (IU) (m9) (mg) (mg) (mg) Common Cabbage 130 0.05 0.05 0.3 47 Savoy Cabbage 200 0.05 0.08 0.3 55 Cauliflower 60 0.11 0.15 0.7 78 64 maN mH H.H cm mm N.m ~.o N.N KN Hm cage-capscu a mom NN m.o am am c.e N.o e.N em mm a mummw a mmm ON e.o am we e.m ~.o m.H am No acmuuww Amev Amev Amev Amev Amev AEmV Asmv Asmv Apmuxv any x oz ma a no mumcuzgoacmu pea campoca amcmcm imam: so ooH\aec=ae< .Aowmfi UmehmZ Ocm Ncwgot: Lm30F$wpzwo Ucm mmmnnmu $0 mm:_.0> chowuwc—HJZ m xwecmaa< 65 Appendix 6 Amount and dollar value of BT used at the farm level (USDA 1976). 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