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I4OM004. .h 4 . , . .. -. . . . 44. ..tttalllnznfif4n?v4'4 . 4. I “4.... 4.445.434 4344.44.43: . 4 .. . -444 . “.Iloflfi VQOad 4" of... t; ....h 4 4. I _ 4 . o . :0414 0. 4a .. t. ..(41 4.. 4. . 4.4..- ....4 ...- 4,... ..444. .443. 4445.34.44.04: 44 .4.! 14:”. 4&4? 4r. _. _ .. .... . ‘4 4 .....4. ‘14. 4 . 4 440.4419.‘. . Sufi]! 1-dv-3f3-‘¥$M'-va“‘ ' a v 19’ ha.» .42. ...» a p... . 1 .fl. . .. 3. . a. v .3 w + , “...”. $ ‘4 a . 9a ... . I ‘ . A ‘ . u.“ ( . .7. . \ r1; r I 36.2.1}; L; none & sous' 00K BINDER? " n“? H“ B Y BINDER: ' ngr “mum:- - Jaqfiq y,_, l... Q, if. ”1“.“ h» v ~4 MAJ-An]. -.|..'~4’.-m..in-I‘Jl\ . 'r . -. “~' . -‘ v ... A r . ~ ICAICIJQTQH .; in ft“? J J . Univcrs: r, y r m '7‘" r w ., rsu. 0 W757 {34 m 2 E w“ mofliflO? ABSTRACT FACTORS AFFECTING THE FEASIBILITY OF ULTRAHIGH FREQUENCY ELECTROMAGNETIC ENERGY FOR SOIL PEST CONTROL By Robert Patrick Rice Jr. Available methods for the control of a variety of soil pests affecting minor acreage crops are often inadequate. These studies were initiated to determine if selected weeds, insects, and nematodes could be controlled with UHF energy (2450 t 20 MHz) and to determine factors which affect the efficiency of UHF energy for control of these pests. Field tests were conducted at three geographically different locations on three soil types to test the effectiveness of UHF energy for both preemergence and postemergence weed control, and control of sugarbeet cyst nematodes (Heterodera schactii), root-lesion nematodes (Pratylenchus penetrans), and onion maggots (Hylema antiqua). Excellent season long weed control was obtained with levels from 671 - 1000 joules/cmz. The specific energy rate required depended on soil type, seedbed preparation and weed species present. Higher rates were required on muck soils and fresh seedbeds. All rates tested provided weed control equal or superior to standard herbicides. Robert Patrick Rice Jr. Quackgrass was not controlled at any of the rates tested. Nematode and onion maggot populations were reduced at all levels tested although control diminished with increasing soil depth. LD50 levels were determined for imbibed and non—imbibed seeds of several different species. The LD of non-imbibed black medic 50 (Medicagg_lupulina L.) occurred at 183 joules/cc, barnyardgrass (Echinochloa crusjgalli (L.) Beauv.) at 160 joules/cc, common purslane (Portulaca oleracea L.) at 139 joules/cc, and redroot pigweed (Amaranthus retroflexus L.) at 125 joules/cc. After the seeds imbibed water for 24 hours the LD declined to 80 joules/cc for 50 common purslane, 117 joules/cc for barnyardgrass, and 161 joules/cc for black medic, but did not decline for redroot pigweed. When seed- soil mixtures were treated, greatest toxicity occurred with the higher moisture levels in muck and clay loam soils with least toxicity oc- curring in a dry loamy sand soil. Attenuation by dry soil occurred with all types tested but was greatest with a sandy loam soil. Increasing power greatly reduced exposure time necessary for kill of seeds. Less energy was required to kill seeds as the soil temperature was increased from -20 to +18 C. FACTORS AFFECTING THE FEASIBILITY OF ULTRAHIGH FREQUENCY ELECTROMAGNETIC ENERGY FOR SOIL PEST CONTROL By Robert Patrick Rice Jr. A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1974 This thesis is dedicated to my parents, Jane and Bob who have been a constant source of encouragement in all of my endeavors. ii ACKNOWLEDGMENTS The author expresses appreciation to Dr. A. R. Putnam for guidance during the conduct of the research and assistance in editing the manuscript. Appreciation is also expressed to the members of my guidance committee, Dr. S. K. Ries and Dr. G. W. Bird. A special thanks is extended to Kei Erlandson for her invaluable assistance during the laboratory phase of this study. Appreciation is also expressed to Paul Love and Amos Lockwood for technical assistance and to Rose Magistro for typing assistance. The assistance of Dr. J. R. Wayland and Oceanography International Inc. is also gratefully acknowledged. LIST OF TABLES . . . LIST OF FIGURES . . INTRODUCTION . . . . CHAPTER 1: CHAPTER 2: Abstract . . . . Introduction . . TABLE OF CONTENTS Materials and Methods . Results and Discussion Literature Cited CHAPTER 3: Abstract . . . . Introduction . . Materials and Methods . Results and Discussion Literature Cited. LIST OF REFERENCES LITERATURE REVIEW iv EFFECTIVENESS OF UHF OF SEVERAL SOIL PESTS 0F WEED SEEDS ENERGY FOR CONTROL SOME FACTORS AFFECTING EFFICIENCY OF ENERGY FOR CONTROL Page . vi ll . 15 22 . 23 . 23 25 . 26 31 . 48 . 49 LIST OF TABLES CHAPTER 2 1. Description of weed control tests with UHF electro- magnetic energy on stale seedbeds, newly prepared seed- beds, and quackgrass sod 2. Weed control with UHF electromagnetic energy on a newly prepared seedbed (Fox sandy loam) 3. Weed control with UHF electromagnetic energy on a newly prepared seedbed (Miami loam) 4. Weed control with UHF electromagnetic energy on a newly prepared seedbed (Houghton muck) 5. Weed control with UHF electromagnetic energy on a stale seedbed 6. Quackgrass control with UHF electromagnetic energy 7. Control of Pratylenchus penetrans and Heterodera schactii with UHF electromagnetic energy at two depths of each of two soil types 8. Toxicity of UHF energy to onion maggot pupae CHAPTER 3 1. Moisture content of seeds of 4 weed species 2. Effects of UHF energy on radicle growth of barnyardgrass 3. Reflectivity characteristics of Houghton muck soil (H20 initial 3 49%) Page 16 l6 l7 l8 19 20 20 26 36 36 LIST OF FIGURES CHAPTER 2 1. Mobile microwave field application device Top--Frontal view Bottom-—Closeup view of horn applicator CHAPTER 3 l. 2. Schematic diagram of the waveguide of a UHF laboratory treatment apparatus Effects of increasing UHF energy on the germination of non-imbibed seeds of 4 weed species Effects of increasing UHF energy on the germination of 4 weed species imbibed for 24 hours Attenuation of UHF energy by dry soil of three types as indicated by corn germination Effects of UHF energy on germination of barnyardgrass when seeds were mixed with soil (6 g) of 3 soil types and 2 moisture levels A. Houghton muck (49% and 552 H O) B. Bellefontaine loamy sand (3% and 20% H20) C. Miami loam (7.42 and 242 H20) Effects of varying the field intensity and duration of treatment when total energy remains constant on germination of barnyardgrass at 5 total energy levels Effects of initial soil-seed temperature on the efficiency of UHF energy for controlling germination of barnyardgrass vi Page 12 28 33 35 39 41 44 46 INTRODUCTION In an age of increasing demands for food and a growing concern for the environment, increased use of pesticides has in- creased yield and quality of crops. Concern about the environment has prompted restrictive legislative controls which make the develop- ment and use of pesticides more costly. These two factors work against each other, and have renewed the interest in physical and biological methods of controlling pests. It has been estimated that weeds result in a greater depres- sion of crop yields than either insects or diseases (8). Weeds compete with crops for water, light, and nutrients and may suppress crops directly through alle10pathic exudates (10). By eliminating weed competition, yields can be significantly increased. Weeds are controlled by cultural methods such as cultivation, fallowing, crop rotations, or by the use of herbicides. Dependence on herb- icides for minor acreage crops has several disadvantages. The high cost of registration does not justify the effort to develop herbicides for many fruit, vegetable, and ornamental crops. This makes it difficult for growers to obtain acceptable weed control with the use of federally approved methods. Another problem associated with herbicides is that organic matter adsorbs and inactivates many of them making high rates necessary on soils such as peats and mucks. As a result of these and other problems such as herbicide residues and drift, alternative weed management techniques must be explored. The use of ultrahigh frequency electromagnetic energy is one of the physical weed control measures being investigated. Apparently it will not require EPA registration and may provide effective pest control on organic soils while being free from drift and residue problems. Commercial use of UHF energy depends on the ability of micro- wave energy to compete with current pest control practices on an energy consumption and cost per acre basis. Since efficiency is of utmost importance, the objective of this research is to ascertain the factors which affect the efficiency of UHF energy in controlling weeds. CHAPTER 1 LITERATURE REVIEW Microwaves (UHF energy) are the portions of the electromagnetic spectrum.which fall between lower frequency radiowaves and higher frequency infrared waves. The basic properties of electromagnetic waves apply to microwaves. Microwaves travel at the speed of light and for each wavelength there is a corresponding frequency (F) obtained by dividing the velocity (c) of light by the wavelength (A). F a cVA The use of microwaves in the United States is controlled by the Federal Communications Commission which has designated four frequencies for non-communications use. These are 915 megacycles per second (mc/sec), 2450 mc/sec, 5800 mc/sec, and 22125 mc/sec. Penetration of microwaves into organic compounds is greatest at lower frequencies, resulting in 915 mc/sec and 2450 mc/sec being of greatest interest for pest control (4). As frequencies decrease, the quantity of energy contained in the wave also decreases. Although lower frequency waves penetrate deeper into a substance than higher energy waves, they do not contain as much energy. Therefore, 2450 mc/sec is of particular interest because of its adequate penetration char— acteristics coupled with reasonably high energy capacity. Microwaves are produced either by magnetron or klystron tubes. Unlike an ordinary vacuum tube which contains two fixed poles, an anode and a diode, a magnetron is a cylindrical diode having resonant cavities which act as the anode. The klystron is a vacuum tube 3 4 in which an electron beam is alternately accelerated and decelerated to produce oscillations which deliver pulsating energy to a cavity resonator. After microwaves are produced, they travel through metal waveguides to their point of use. The size of the waveguide is precisely determined by the particular microwave frequency. At 2450 mc/sec, the waveguide must be exactly 9.26 x 5.46 cm.with walls at least 0.20 cm thick. If waveguides are correctly proportioned, the waves will be directed along the guide with a minimum of reflection. This will allow a uniform distribution of waves and prevent "hot spots" which are common in cavity type chambers due to the reflection from cavity walls and the resulting unequal distribution of energy. As a result of these variations, data obtained from treatments in a cavity will differ substantially from that obtained from wave- guide treatments. Since present methods of field application of microwaves employ waveguides with horn type applicators, data obtained from waveguide treatments will be most applicable to field conditions. Microwaves are capable of producing many and varied effects on substances which enter the field. A primary effect is that of heating. Heating involves the loss of energy from the microwave to the heated substance. This phenomenon is referred to as loss. High loss materials are those which readily absorb UHF energy to produce heat; conversely, low loss materials are those which either reflect the waves (e. g. metals) or allow them to pass through (e.g. silica) with little or no energy absorption. Several factors influence the dielectric characteristics of plant materials, such as moisture content of the tissue, water of hydration of molecules particularly proteins, and presence of interfaces between tissues of different dielectric properties. Moisture content is important 5 in determining the loss characteristics of a particular tissue in that high moisture in a tissue will cause minimum penetration but maximum absorption. On the molecular level, hydrated molecules absorb energy faster than molecules with a lower water content. The presence of interfaces between tissues of different dielectric properties is important because the electromagnetic waves may be reflected from the interface causing the lossy tissue to be exposed to both direct and reflected waves. Copson (3) indicated that when animal fat is superimposed over muscle tissue, energy is trans- mitted through the fat, reflected at the muscle interface and absorbed by the fat. This phenomenon may further account for localized effects of microwaves. Microwaves affect biological systems in a variety of ways. The most obvious are those resulting from heating of the tissue. Heat may cause a disruption of cells by denaturing proteins or causing chemical or physical changes in other cell constituents. Because different types of molecules differ in their dielectric loss properties, heating of biological tissues must occur in a non-uniform fashion. Since energy absorbed by the cell cytOplasm, for example, must eventually cross the plasmalemma, it seems that a very high thermal gradient would exist across the membrane (12). In plant cells, a temperature differential of only 0.01 C corresponds to an osmotic pressure of 1.32 atm (9). A change of this magnitude would certainly affect the physiological processes of the cell. Van Everdingen found that at 3000 MHz, microwaves cause a change in the optical activity of starch and glycogens and cause precipitation in starch solutions. It was possible in this case to obtain Optimal 6 conditions for microwave interaction by altering the viscosity of the solution rather than by changing the frequency (16). Suspensions of materials may also be affected by the imposition of an electro- magnetic field. Microwaves can cause such things as colloidal particles, blood cells and droplets to allign themselves into formations known as "pearl chains" (14). Presumably molecular orientation of dipoles of the supporting medium must occur before "pearl chains" can be formed. The physiological significance of this allignment is not clear, except that the particles concerned would be redistrib- uted (4). Another non—thermal cellular effect exerted by microwaves is that of altering the electrical prOperties of the plasmalemma. ‘The cell membrane naturally exhibits such properties as separation of electrical potentials and capacitance. Frequencies in the microwave range may induce a loss in functional integrity of the cell membrane, leaving the cell to act essentially as a protein- electrolyte solution. In tests on mesquite and bean seeds in a microwave chamber, mortality of seeds was thought to be due to non—thermal effects (20). Davis 23 51. in tests conducted in a microwave cavity (2450 i 20 MHz), found that susceptibility of seeds is positively cor- related with increasing moisture content, mass of seed, volume per seed, and energy absorbed per seed. Susceptibility is negatively correlated with ether soluble lipid content 0.8 ). Selectivity also occurs between species, in that low levels of energy effectively control some while others are unharmed by similiar levels (5). In field tests, Wayland g£_al, found that at a fixed energy level increased power levels can be substituted for exposure time in the 7 100 to 1200 W range (19). Field tests have also shown that appli- cations of 1200 joules/cm2 of microwave energy provided preemergence control of London rocket (Sisymbrium irio L.), Japanese millet (Echinochloa frumentacea (Roxb.) Link), ridgeseed euphorbia (Euphorbia glyphosperma Engelm.), redroot pigweed (Amaranthus retroflexus L.), and annual sunflower (Helianthus annuus L.) when applied directly to both wet and dry soils. Control of common purslane (Portulaca oleracea L.) required 2400 joules/cmz. These same energy levels applied to dry soil prior to planting increased muskmelon (Cucumis Eglg_L.) plant size at 4 weeks and increased yield in irrigated soils of Texas (12). Vela 35 31. reported that herbicidal and insecticidal rates of UHF energy had no effect on soil microorganisms such as heterotrophic bacteria, spores, fungi, and actinomycetes (l7). CHAPTER 2 EFFECTIVENESS 0F UHF ENERGY FOR CONTROL OF SEVERAL SOIL PESTS ABSTRACT Available methods for the control of soil pests affecting minor acreage crops often are inadequate. The purpose of this study was to determine if selected weeds, insects, and nematodes could be effectively controlled with UHF energy (2450 i 20 MHz). Varying rates of UHF energy (621 - 1856 joules/cmz) were applied to three geographically different newly prepared seedbeds, a stale seedbed, and a quackgrass sod to assess preemergence and postemergence weed control. Excellent season-long control of annual weeds was obtained with energy levels from 671-1000 joules/cmz. The specific energy rate required depended on soil type, seedbed preparation, and weed species present. Higher rates were required for newly prepared seedbeds and muck soils. All rates tested produced annual weed control equal or superior to standard herbicides. Quackgrass was not controlled at any of the rates tested. Onion maggot (Hylema antiqua) pupae, sugarbeet cyst nematodes (Heterodera schactii), and root-lesion nematodes (Pratylenchus penetrans) were placed in 100 cc nylon sacks, buried at 5 and 10 cm depths, and treated with UHF energy (673 - 1480 joules/cmz). Nematode and onion maggot population densities were substantially reduced at all energy levels tested although control diminished with increasing soil depths. 9 INTRODUCTION Soil-borne organisms including weed seeds, nematodes, insects, and fungi all have the potential to seriously reduce crop growth and yield. At present independent control practices and pesticides are usually employed for each of these pests. Each pesticide requires registration on the particular cr0p and pest, and each is subject to individual or interacting problems of adsorption, inactivation, persistance, etc. Techniques designed to control more than one of the soil—borne organisms harmful to crops would greatly reduce the quantities of fungicides, nematicides, herbicides, and insecticides used. Broad spectrum soil fumigants are used in certain high value crops to non-selectively control many soil-borne weed seeds, insects, nematodes, fungi and bacteria. Fumigants such as methyl bromide (CH3Br), carbon disulfide (C82), and chloropicrin (CCl N02) are quite effective 3 in controlling soil pests; however, their use requires utmost caution, they are expensive, and they may kill beneficial microorganisms allowing toxic ammonia levels to accumulate in the soil (4). In addition, chemical fumigants require EPA registration and must be allowed to dissapate from the soil before planting of crops (4). A pest control method which would perform on a variety of soil types and would not require EPA registration certainly could offer additional advantages for minor acreage crops. Wayland st 31. found that seeds of wheat and radish buried in a sandy loam were susceptible to UHF (2450 i 20 MHz) exposure. Wheat seeds were more susceptible than radish seeds which was attributed 10 largely to their differences in mass (7). In field tests at several different locations, Wayland gt_§l, found that effective preemergence weed control could be obtained at energy/area levels of between 80 and 160 joules/ cm2 (7). Menges controlled London rocket (Sisymbrium irio L.), Japanese millet (Echinochloa frumentacea (Roxb.) Link), ridgeseed euphorbia (Euphorbia glyptosperma (Engelm.), redroot pigweed (Amaranthus retroflexus L.), and annual sunflower (Helianthus annuus L.) with field applications of 1200 joules/cm2 of UHF energy regardless of soil moisture content on a sandy loam soil (5). 0n dry soil, 2400 joules/cm2 was required to control common purslane (Portulaca oleracea L.). On similar soils, cantaloupe (Cucumis melos L.) yields were increased after preplant applications of 1200 and 4800 joules/cmz. This was attributed to a reduction in weed competition and reniform nematode (Rotylenchus reniformis) populations (5). Field and laboratory studies indicate that UHF energy can control a wide spectrum of soil pests. The purpose of this investigation was to determine if important weeds, nematodes, and insects could be controlled by UHF energy applied in the field on a variety of soil types. 11 MATERIALS AND METHODS UHF energy (2450 i 20 MHz) was applied to the soil by a mobile microwave generating device (Figure 1). It consisted of a gas powered 60 hz electrical generator which provided power to four 1.5 KW microwave generators each containing a magnetron tube. A control panel provided adjustment of microwave power and readings of forward and reflected power. Microwaves were guided through four flexible wave guides to a 20.3 cm square horn type applicator which skimmed over the soil surface. .A pyroceram plate with a dielectric constant between soil and air covered the applicator serving mainly as a barrier against the entry of soil into the radiator. The generators were mounted on a trailer which was propelled by means of a variable speed winch. Efficacy of Microwaves for Weed Control. Newly prepared seedbeds at three different locations with three different soil types (Table l) were treated with UHF energy at three energy levels, a standard herbicide, and hand weeded control. Different energy levels were obtained by altering the speed of the applicator. In all cases the soil surface was dry at time of application. Plot size was 6.1 m x .2 m and each treatment was replicated three times in a randomized block design. Observations included visual weed control ratings at 30 or 45 days and weed density counts after 60 days. A stale seedbed (prepared 3 weeks earlier) was treated with UHF energy at varying rates, a standard herbicide and a control. An adjacent area containing a severe infestation of quackgrass was also similarly treated but with a plot size of 6.1 m x .4 m. The design was a randomized block 12 Figure 1.--Mobile microwave field application device. Tap--Frontal view bottom--Closeup view of horn applicator 14 muosuo A.ooom A.Av NH wfiamcwawmwm maumuHManv mmauwnouo omuma NOH A.q moowuoao mowasupomv oooamuan doaaoo Ram nouumo pontoon smouw xosa ocunwsom goo: am: A.A ms>ao>ooo ssoowxwomv uoonsxoan vaa3 Bo m an moxoawouuon manusmumaahmooom mmmmwwmmmv vooauwnam maso>a>mooom so m Auoaoona .U.A A.onv Honmx scammmumv vumumaa mafia so m A.>=oom A.Av mooamu oouwmouwdv mmuuwxomov Bo ma Tamflflw mmwmmmmmmmwv mumuumaomnasa soaaoo so m .az .msaaon:< A.A «Haomwmaaouuo camounasmom A.qv mcomww ooummomwahwoaum mmmmwwwmmv vooauuoam aaoo>ahmsaom NOH A.>:mom A.Av mcomou nouhmoumoHo vow «ma A.UQ A.Av unsung monouuomv somhfldo humon Non .Hz .moaauu=< A3903 A.Av wasnom waoamunomonv vooaxadw non Ouwaou wonvoom amouw suoa human wow Bush nownoz muonuo nma A.A unmaaaano Edofiommv mmmumnouw3 um nouooo nouaowom A.A moomuoao womaauuomv onwamuam soaaoo Rom Honaooso pontoon amoum smog Hana: ounuaoOfiuuom pm: moaooem woos unasflaoa mono nowunfiuouov ouwm mama Hwom soauwooq .vom mmouwxoaso can .mvonvoou consaoua hasoo .mvonvoou mason so hwuooo oauoowmaouuooao mm: nous uumou Houuooo U003 mo ooauawuomooII.H wands 15 with three replications on the stale seedbed and two on the quack- grass sod. Observations included visual ratings at 30, 45, and 60 days and weed density counts 90 days after treatment. Efficacy of Microwaves for Insect and Nematode Control. The potential of UHF energy for control of onion maggots (Hylema antiqua), sugarbeet cyst nematodes (Heterodera schachtii) and root-lesion nematodes (Pratylenchus penetrans) was determined. Ten pupae of onion maggots were placed in cheesecloth sacks and'buried at 5 and 10 cm depths in a Miami loam soil. The soil was then treated with UHF energy at two rates. The treatments were replicated three times. After treatment the sacks were removed to the laboratory where the number of adults which emerged after 30 days were recorded. Soils containing the sugarbeet cyst nematodes or the root-lesion nematodes were placed in 100 cc nylon sacks and buried in Fox sandy loam and Houghton muck soils at 5 and 10 cm prior to treatment with microwaves at two energy levels. The treatments were replicated five times at each location. Sacks containing sugarbeet cyst nematodes had an initial population density (Pi) of 64 cysts/100 cc of soil, while sacks containing the root-lesion nematodes had a P of 52 adults/100 cc 1 of soil. After treatment the sacks were collected and stored for 60 days at 12.5 C prior to assay by the centrifuge flotation technique. RESULTS AND DISCUSSION Efficacy of Microwaves for Weed Control. Treatment of newly prepared seedbeds with UHF energy provided weed control equal to or better than the standard herbicide treatment in all cases (Tables 2,3,4). 16 Control generally improved as energy levels were increased. Since crops were under a great deal of stress from weeds impinging on the treated area from outside of the plot, meaningful yield data were not obtained. Crop injury did not occur with any treatment and cucumbers appeared to grow better in UHF treated plots than in hand weeded plots. Weed control in UHF treated plots remained acceptable throughout the duration of the growing season. Table 2.—-Weed control with UHF electromagnetic energy on a newly prepared seedbed (Fox sandy loam). Treatment joules/cm2 Weed Control Ratings Weeds/2 ft2 or lb/A 30 days 45 days (60 days) UHF energy 621 8.0a 5.3a 5.1 UHF energy 891 9.03 6.0ab 4.0 UHF energy 1389 9.0a 8.7c 1.5 diphenamid 5 5.0b 5.3a 6 2 Weeded check - 9.0a 7.0bc 4.2 Means with a column followed by identical letters are not significently different by Tukey's HSD test at the 5% level. Table 3.--Weed control with UHF electromagnetic energy on a newly prepared seedbed (Miami loam). Treatment joules/cm2 Weed Control Ratings Weeds/2 ft2 or lb/A 45 days (60 days) UHF energy 671 7.3a 3.5a UHF energy 854 8.3a 1.5a UHF energy 1376 9 .0 a 0.5a chloramben (methylester) 2 6.7b 1-38 Weedy check - 0.0c 13.0c Means within a column followed by identical letters are not significently different by Tukey's HSD test at the 5% level. 17 Table 4.--Weed control with UHF electromagnetic energy on a newly prepared seedbed (Houghton muck). Treatment joules/cm2 Weed Control Rating Weeds/2 ft2 or lb/A 30 days (60 days) UHF energy 879 5.7ab 4.5a UHF energy 1000 7.3bc 1.8a UHF energy 1480 9.0c 0.2a linuron 2 5.7ab ll.5b Weedy check - 4.7a 17.0b Means within a column followed by identical letters are not significently different by Tukey's HSD test at the 5% level. On Fox sandy loam, red clover was generally the first species to appear in plots treated with the lower energy levels. This may indicate that red clover seed is resistant to UHF energy at levels up to 891 joules/cm2 on this soil type. Flixweed and hoary allysum emerged sporadically in all plots regardless of energy level applied. Since these species can behave as biennials or perennials, regrowth may have occurred from underground vegetative organs. 0n the Miami loam and Houghton muck soils, common purslane was the only species to consistently emerge in UHF treated plots; however, common purslane was the dominant species present at both locations so that no conclusion can be drawn concerning relative resistance to microwaves on these soils. Germination of seeds in the plots cannot necessarily be attributed to seeds which escaped treatment since the plots were narrow and could have been contaminated by seeds blown in from adjacent untreated areas. It appears that the energy required to kill weed seeds is somewhat less on sandy loams and loam soils than on muck soils. Definite comparisions are difficult to make since different weed species were present at each location. .18 On the stale seedbed, all UHF energy levels tested caused immediate loss of turgor and apparent death of emerged weeds (Table 5). Little or no regrowth occurred during the entire season, and after 90 days all UHF treated plots still exhibited commercially acceptable weed control. Table 5.-—Weed control with UHF electromagnetic energy on a stale seedbed Treatment joules/cm2 Weed Control Ratings Weeds/2 ft2 or lb/A 30 days 45 days 60 days (90 days) UHF energy 771 9.0a 8.0a 9.0a 0.7 UHF energy 926 9.0a 9.03 9.7a 1.0 UHF energy 1856 9.0a 9.0a 9.3a 0.7 diphenamid + paraquat 5 +0.5 5.3b 0.7b 2.7b 17.7 Weeded check - 9.03 9.0a 6.3c 16.3 Means within a column followed by identical letters are not significently different by Tukey's HSD test at the 5% level. UHF treatment of stale seedbeds appears particularly promising due to the comparative ease of kill of emerged weeds and imbibed seeds (4). With this system, there should be a high percentage of seeds which have either germinated or imbibed water. Seeds capable of germination are primarily those viable seeds located within 1.3 cm of the soil surface. If soil disturbance is minimal, few new seeds should be introduced into this germination zone (4). Besides requiring less energy, stale seedbed treatments would allow the grower more flexibility since treatment date would not be as critical as where treatment must occur immediately after soil preparation and prior to planting. 19 Treatment of quackgrass at two energy levels tested resulted in immediate death of shoots. Rhizomes were apparently not harmed, as vigorous regrowth occurred within thirty days (Table 6). The translocated herbicide glyphosate gave excellent season long control. UHF energy may be feasible for perennial weed control only at higher rates or as spot treatments. Table 6.--Quackgrass control with UHF electromagnetic energy Treatment joules/cm2 Quackgrass Control Rating or lb/A 15 days 60 days UHF energy 502 8.53 4.03 UHF energy 952 5.0b 0.0b glyphosate 2 10.03 10.0c check - 0.0c 0.0b Means within a column followed by identical letters are not significently different by Tukey's HSD test at the 5% level. Efficacy of Microwaves for Insect and Nematode Control. UHF treatment at 1480 joules/cm2 reduced final population densities (Pf) of root-lesion nematodes to non-detectable levels at both depths in mineral and muck soils. It is highly probable that UHF treatment at 879 joules/cm2 reduced the Pf of root-lesion nematodes at both depths of each soil; however, natural mortality in nontreated soil was not determined. UHF treatment with 1480 joules/cm2 reduced the Pf of sugarbeet cyst nematodes in muck soil at a 5 cm soil depth, but not at the 10 cm soil depth. It is highly probable that UHF treatment at an energy level of 879 joules/cm2 reduced population densities of the sugarbeet cyst nematode at both depths in mineral 20 soil, however, natural mortality levels in nontreated soil were not measured (Table 7). Table 7.--Control of Pratylenchus penetrans and Heterodera schachtii with UHF electromagnetic energy at two depths of each of two soil types. Energy Nematodes recoveredgper sack joules/cm2 Root—lesion nematode Sugarbeet cyst nematode Muck soil Mineral soil Muck soili/ Mineral soili/ 5 cm 10 cm 5 cm 10 cm 5 cm 10 cm 5 cm 10 cm 879 1.8 1.2 1.6 1.8 136 241 15.2 4.6 1000 0.0 0.6 5.2 0.2 207 93 14.0 9.0 1480 0.0 0.0 0.0 0.0 18 105 15.0 16.6 l-/Surviviors are primarily larvae 2/ -Surviviors are primarily cysts. (A cyst contains 250-300 larvae) Onion maggot pupae were eradicated at the highest energy level at the two depths tested while populations were reduced at the lower level (Table 8). Table 8.--Toxicity of UHF energy to onion maggot pupae. Energy ' Adults Emerged (Z) joules/cm2 5 cm 10 cm 0 100 100 673 0 73 832 0 0 21 These data indicate that microwaves have excellent potential for nematode and soil insect control. The energy levels necessary for weed control may also effectively control certain insect and nematode p0pu13tions. Discussion. UHF energy has the potential to control several major soil pests. The shortage and high cost of energy may be a major obstacle to development of microwave applicators for pest control. Major expenses associated with microwave usage will include fuel, equipment (either purchased or leased), and labor. At 800 joules/cmz, using a 40% efficient gas powered generator and an 80% efficient magnetron tube, approximately 64 gallons of gasoline per acre would be required to treat 0.3 m bands 1.0 m apart for wave generation alone (1, 3, 6,). Additional power will be required to supply drive motors. In high value crops where soil fumigation is used, UHF energy will be able to compete most effectively. In these crops, costs of fumigation to control weeds, nematodes, fungi, and soil insects generally range from $400 to $600 per acre for a tarped commercial application. In order for microwave energy to be competitive for pest control, application devices must be engineered which will use energy efficiently and will be capable of generating high intensity microwaves that can be applied rapidly. Costs can be further reduced by manipulation of soil conditions and application techniques so that energy requirements can be minimized. A thorough understanding of the factors which affect the efficiency of UHF energy is imperative for UHF energy to be used effectively for pest control. 22 LITERATURE CITED Baumeister, Theodore. 1967. Standard Handbook for Mechanical Engineers. McGraw Hill Book Co. New York. Davis, F. S., J. R. Wayland, and M. G. Merkle. 1971. Ultrahigh frequency electromagnetic fields for weed control: Phyto- toxicity and selectivity. Science 173:535-537. Fink, Donald B. 1968. Standard Handbook for Electrical Engineers. McGraw Hill Book Co. New York. 8:45. Klingman, Glenn C. 1961. Weed Control as 3 Science. John Wiley and Sons, Inc. New York. pp. 272. Menges, Robert M. Ultrahigh frequency (UHF) electromagnetic energy for weed control in vegetables. Weslaco, Texas. Unpublished. Pimental, David, L. E. Hurd, A. C. Bellotti, M. J. Forster, I. N. Oka, O. D. Sholes, R. J. Whitman. 1973. Food production and the energy crisis. Science 182:443-448. Wayland, J. R., F. S. Davis, and M. G. Merkle. Toxicity of an UHF device to plant seeds in soil. Texas A&M University. Unpublished. - Wayland, J. R., F. S. Davis, R. M. Menges, C. Robinson, and M. G. Merkle. Pre-emergence control of unwanted vegetation by use of UHF electromagnetic fields. Texas A&M University. Unpublished. CHAPTER 3 SOME FACTORS AFFECTING EFFICIENCY OF UHF ENERGY FOR CONTROL OF WEED SEEDS ABSTRACT The potential of ultrahigh frequency electromagnetic energy as an alternative weed control method is being investigated. These studies were initiated to determine methods of maximizing the efficiency of UHF energy on weed seeds. Imbibed and non-imbibed seeds of several different species were treated with UHF electromagnetic energy at varying intensities and for various periods of time. In addition, soil type and moisture influences on phytotoxicity were evaluated. Soil attenuation was measured by inserting a three cm thick soil plug into the wave- guide in front of the target seeds. After treatment, seeds were germinated in an incubator at 27 C to determine viability. The LD50 of nonimbibed black medic (Medicago lupulina L.)occurred at 183 joules/cc, barnyardgrass (Echinochloa crusfigalli (L.) Beauv.) at 160 joules/cc, common purslane (Portulaca oleracea L.) at 139 joules/cc, and redroot pigweed (Amaranthus retroflexus L.) at 125 joules/cc. After the seeds had imbibed water for 24 hours the LD50 declined to 80 joules/cc for common purslane, 117 joules/cc for barnyardgrass, and 161 joules/cc for black medic, but did not decline for redroot pigweed. When seed-soil mixtures were treated, greatest toxicity occurred with the higher moisture levels in muck and clay loam soils with least toxicity occurring in a dry loamy 23 24 sand soil. Attenuation by dry soil occurred with all types tested but was greatest with Bellefontaine loamy sand. Increasing the power greatly reduced the time of exposure necessary to kill barn- yardgrass seeds but not that necessary to kill corn seeds (gggflmgyg'L.). Less energy was required to kill seeds as the soil temperature was increased from -20 to +18 C. 25 INTRODUCTION For UHF energy to be used as a weed control tool, the factors which affect the efficacy of the process must be understood. An understanding of these factors will allow weed control with the least amount of energy. One of the greatest obstacles to the widespread use of UHF energy to control weeds is the high cost of treatment. By manipulating equipment and field conditions so that seeds can be killed at maximum efficiency, significant cost reductions could be obtained. In tests conducted in a microwave cavity, Wayland gt 31. found that seeds of broadleaf bean (Phaseolus vulgaris L.) and mesquite (Prosopis glandulosa Torr) were more easily killed after they had imbibed water. Wayland also found that lethal effects of microwaves in plant tissue were not due to average temperature increases but to either selective heating or non-thermal effects C5). Davis 35 31. reported that in a microwave chamber, UHF phytotoxicity is increased in imbibed seeds and young plants and that soil partially attenuates the UHF field but is not opaque to it (2.3)- Due to differences in wave patterns and non uniformity of the field in a cavity, results from cavity treatments may not be directly applicable to those obtained with horn type applicators (l). The objective of this investigation was to study methods for maximizing the efficiency of UHF energy for the control of weed seeds. 26 MATERIALS AND METHODS All tests were conducted with a 1.5 KW microwave generator. Microwaves were produced by a magnetron tube and channeled through 3 metal wave guide. Treatments were made in a quartz test tube which was placed directly into the wave guide (Figure 1). In all cases reflected radiation was minimal. At the distal end of the waveguide, UHF energy was absorbed by water flowing through 3 cooling chamber separated from the waveguide by a ceramic plate. Power was regulated by a control panel which enabled adjustment of power in the range of 0 to 1500 W. The control panel also housed a gauge which measured forward and reflected power. Lethal dose determinations. Laboratory tests were conducted to determine the lethal dosages of UHF energy for non-imbibed and imbibed seeds of several different species (Table 1). Table l.--Moisture content of seeds of 4 weed species. % H00 Common name Scientific name non-imbibed imbibed Barnyardgrass Echinochloa crusfigglli (L.) 12.6 54.6 Beauv. Common purslane Portulaca oleracea L. 13.5 49.5 Redroot pigweed Amaranthus retroflexus L. 13.3 51.6 Black medic Medicago lupulina L. 13.6 ---- Moisture content was determined by drying seeds in an oven for one 27 Figure l.—-Schem3tic diagram of the waveguide of a UHF laboratory treatment apparatus. 28 ($2 ._.Zm<zm<<