Enhanced Biodegradation of Pesticides in the ... - ACS Publications

Chapter 15

Evaluation of Some Methods for Coping with Enhanced Biodegradation of Soil Insecticides 1

2

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 24, 2016 | http://pubs.acs.org Publication Date: May 3, 1990 | doi: 10.1021/bk-1990-0426.ch015

A. S. Felsot and J. J. Tollefson 1

Center for Economic Entomology, Illinois Natural History Survey, 607 East Peabody Drive, Champaign,IL61820 Department of Entomology, Iowa State University, Ames, IA 50011 2

Several proposed strategies for either preventing or circumventing enhanced biodegradation of corn rootworm s o i l insecticides have been studied i n Iowa and I l l i n o i s . Operational strategies included cultivation-time treatments, suppression of adults, and insecticide rotations; a technological strategy was the use of controlledrelease formulations. In 9 of 13 f i e l d experiments, carbofuran (2,3-dihydro-2,2dimethyl-7-benzofuranyl methylcarbamate) applied at c u l t i v a t i o n prevented root damage better than when applied at planting. Root damage following adult control with carbaryl (1-naphthyl methylcarbamate) the preceding season was less than or similar to root damage following the use of s o i l insecticides, which suggested that corn rootworms could be controlled without use of a s o i l insecticide. Cultivation-time treatments and adulticiding depended on accurate timing of insecticide applications. Under laboratory conditions, rotations of carbofuran with isofenphos (1-methylethyl 2-[[ethoxy[(1methylethyl)amino] phosphinothioyl]-oxy] benzoate) slowed the rate of metabolism of carbofuran but did not prevent the development of enhanced biodegradation. In the f i e l d , the results of rotations of carbofuran with fonofos (O-ethyl S-phenyl ethylphosphonodithioate) or terbufos (S-[tert-butylthio)methyl]O,O-diethyl phosphorodithioate) were inconclusive. Multiyear treatments of fonofos resulted in enhanced biodegradation, but its rate of degradation was slowed by rotations with carbofuran or terbufos. When carbofuran was applied as a controlledrelease formulation, its degradation was 0097-6156/90/0426-0192S06.50/0 © 1990 American Chemical Society

Racke and Coats; Enhanced Biodegradation of Pesticides in the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

15.

FELSOT & TOLLEFSON

Coping with Soil Insecticide Degradation

193


s i g n i f i c a n t l y slowed compared to the commercial sand granule; however, efficacy i n the f i e l d was not improved. In t h e U n i t e d S t a t e s , t h e g r e a t e s t p r o p o r t i o n o f i n s e c t i c i d e s a r e u s e d on c o r n b y v i r t u e o f t h e v a s t a c r e a g e s d e v o t e d t o p r o d u c t i o n (1). Most o f t h e i n s e c t i c i d e s are applied at planting time t o control root a n d s e e d l i n g f e e d i n g damage b y soil insects, especially the western and n o r t h e r n corn rootworm (Diabrotica v i r g i f e r a a n d R. b a r b e r i , r e s p e c t i v e l y ) a n d t h e b l a c k cutworm ( A g r o t i s i p s i l o n ) . Because s o i l i n s e c t i c i d e s a r e applied long before the insect pest appears, chemical p e r s i s t e n c e and b i o a v a i l a b i l i t y i s c r i t i c a l t o s u c c e s s f u l r e d u c t i o n o f p o t e n t i a l l y damaging p o p u l a t i o n levels. Although a myriad o f environmental and b i o l o g i c a l factors interact t o affect the ultimate bioactivity of a s o i l insecticide (Z,l) , t h e e f f e c t o f e n h a n c e d b i o d é g r a d a t i o n o n e f f i c a c y o f c r o p p r o t e c t i o n h a s r e c e i v e d much a t t e n t i o n i n t h e 1980's . W i t h few r e l i a b l e c o r n rootworm (CRW) i n s e c t i c i d e s o n the m a r k e t , t h e p r e s s u r e t o u s e t h e same p r o d u c t y e a r a f t e r year has i n c r e a s e d over t h e l a s t decade. The enhanced biodégradation o f the methyl carbamate i n s e c t i c i d e s , such as carbofuran and t r i m e t h a c a r b (7-10), and t h e o r g a n o p h o s p h i n o t h i o a t ei n s e c t i c i d e , isofenphos (11-13) i s w e l l known a n d h a s b e e n l i n k e d t o c r o p protection failures (£,14.) . E n h a n c e d b i o d é g r a d a t i o n o f the organophosphorus s o i l i n s e c t i c i d e s , fonofos, terbufos, and c h l o r p y r i f o s has been suggested i n s e v e r a l r e p o r t s (15-17), b u t l i t t l e d a t a has been g e n e r a t e d t o d e f i n i t i v e l y determine the s u s c e p t i b i l i t y of these compounds t o m i c r o b i a l a d a p t a t i o n s . With the assumption t h a t c h e m i c a l c o n t r o l o f c o r n r o o t w o r m f e e d i n g damage will r e m a i n t h e p r e d o m i n a n t management s t r a t e g y i n c o n t i n u o u s corn f i e l d s over t h e next decade, i t i s important t o d e v e l o p b e s t management p r a c t i c e s f o r t h e l o n g - t e r m u s e o f the registered soil insecticides. P a r t o f t h e l o n g - t e r m management s t r a t e g y w o u l d be a v o i d i n g t h e development o f enhanced biodégradation, b e c a u s e t h i s phenomenon c a n s i g n i f i c a n t l y affect insecticide efficacy. Another p o s s i b i l i t y i s employing methods t h a t c i r c u m v e n t enhanced biodégradation a f t e r i t has d e v e l o p e d . The t e c h n i q u e s a v a i l a b l e a n d p r o p o s e d f o r coping with t h e adverse e f f e c t s o f enhanced biodégradation, which can be c l a s s i f i e d as e i t h e r o p e r a t i o n a l o r t e c h n o l o g i c a l , have been d i s c u s s e d elsewhere (£). B r i e f l y , operational s t r a t e g i e s f o r coping w i t h e n h a n c e d b i o d é g r a d a t i o n r e l y on management t e c h n i q u e s b a s e d on b i o l o g i c a l p r i n c i p l e s whereas t e c h n o l g i c a l strategies require alterations i n formulation chemistry or structural chemistry of the insecticide. The o p e r a t i o n a l alternatives include conservation of pesticides (e.g., use



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ENHANCED BIODEGRADATION OF PESTICIDES IN T H E ENVIRONMENT

o f i n t e g r a t e d p e s t m a n a g e m e n t [IPM] s t r a t e g i e s such as s c o u t i n g f o l l o w e d by c o n t r o l , i f n e c e s s a r y , t o r e d u c e economic i n f e s t a t i o n s ) , crop r o t a t i o n (e.g., corn/soybeans), proper c a l i b r a t i o n of a p p l i c a t i o n equipment, a l t e r e d t i m i n g o f a p p l i c a t i o n s (use o f cultivation-time t r e a t m e n t s when l a r v a e a r e a c t i v e l y f e e d i n g ) , and c h e m i c a l r o t a t i o n s (use o f a c h e m i c a l every other year or at longer i n t e r v a l s ) . The t e c h n o l o g i c a l a l t e r n a t i v e s i n c l u d e extenders and i n h i b i t o r s (to delay b i o d é g r a d a t i o n ) , new formulation technology (e.g., c o n t r o l l e d r e l e a s e ) , and d i r e c t e d c h e m i s t r y (synthesis of insecticides possessing higher t o x i c i t i e s i n s o i l ) . Few o f t h e p r o p o s e d m a n a g e m e n t s t r a t e g i e s h a v e b e e n e x p e r i m e n t a l l y i n v e s t i g a t e d . The o b j e c t i v e o f t h i s p a p e r is to present results of previously unpublished e x p e r i m e n t s t h a t have e v a l u a t e d s e v e r a l p r o p o s e d s t r a t e g i e s f o r coping with enhanced biodégradation of soil i n s e c t i c i d e s u s e d t o c o n t r o l CRW, namely, c u l t i v a t i o n - t i m e treatments as o p p o s e d t o p l a n t i n g - t i m e treatments, s u p p r e s s i o n of a d u l t s t o prevent e g g - l a y i n g and larval damage t h e f o l l o w i n g s p r i n g , c h e m i c a l r o t a t i o n s , and controlled-release formulations. Experimental

Design

Cultivation-Time Treatments. Compared t o a p p l y i n g an i n s e c t i c i d e a m o n t h o r m o r e b e f o r e CRW eggs hatch, c u l t i v a t i o n - t i m e a p p l i c a t i o n would expose a c t i v e l y f e e d i n g l a r v a e t o a much h i g h e r d o s e o f i n s e c t i c i d e . I n Iowa, a p p l i c a t i o n s of i n s e c t i c i d e s at c u l t i v a t i o n time have been r o u t i n e l y compared w i t h a p p l i c a t i o n s a t p l a n t i n g - t i m e s i n c e 1975, r e s u l t i n g i n a t o t a l o f 19 e x p e r i m e n t s a c r o s s the state. T h e e x p e r i m e n t a l d e s i g n i n a l l e x p e r i m e n t s was a randomized complete block with four r e p l i c a t i o n s . T r e a t m e n t u n i t s w e r e s i n g l e r o w s , 11 t o 15 m l o n g d e p e n d i n g on t h e l o c a t i o n . The l i k e l i h o o d o f h a v i n g a c o r n r o o t w o r m i n f e s t a t i o n was i n c r e a s e d by either s e l e c t i n g s i t e s t h a t had a documented i n f e s t a t i o n o f CRW or by p l a n t i n g a " t r a p c r o p " . A trap crop c o n s i s t e d of corn p l a n t e d l a t e r than normal during the previous season to p r o v i d e a f o o d s o u r c e t h a t a t t r a c t e d and accumulated o v i p o s i t i n g f e m a l e b e e t l e s w h i l e s u r r o u n d i n g f i e l d s were senescing. C u l t i v a t i o n treatments of carbofuran (Furadan 15G, 1.12 k g Α Ι / h a ) w e r e made f o u r t o s i x w e e k s a f t e r p l a n t i n g , when CRW l a r v a e were a c t i v e l y f e e d i n g on c o r n r o o t s . P l a s t i c tubes, p o s i t i o n e d d i r e c t l y i n front of the c u l t i v a t o r sweeps, d i r e c t e d t h e i n s e c t i c i d e t o b o t h s i d e s o f t h e c o r n r o w w h e r e s o i l was t h r o w n o v e r t h e g r a n u l e s t o effect incorporation. For planting-time applications, F u r a d a n 15G ( 1 . 1 2 k g Α Ι / h a ) was p l a c e d i n a n 18-cm band i n f r o n t o f t h e f i r m i n g wheels and i n c o r p o r a t e d w i t h a d r a g chain.


15.

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195


I n s e c t i c i d e e f f i c a c y was e v a l u a t e d b y d i g g i n g five r o o t s f r o m e a c h t r e a t e d row a n d u n t r e a t e d row i n m i d t o late July a f t e r the majority o f l a r v a l feeding had occurred. T h e s o i l was r e m o v e d u s i n g a n a i r - p r e s s u r i z e d w a t e r s p r a y , a n d t h e f e e d i n g d a m a g e was r a t e d u s i n g t h e Iowa 1 t o 6 r a t i n g s c a l e where 1 = n o t o m i n o r a n d 6 = s e v e r e damage ( 1 £ ) . To d e t e r m i n e i f a p p l y i n g a n i n s e c t i c i d e a t c u l t i v a t i o n circumvented enhanced biodégradation, t h e root damage r a t i n g s o f t h e f i v e r o o t s f r o m a n e x p e r i m e n t a l u n i t ( i . e . , each t r e a t e d and untreated row) were a v e r a g e d . The most commonly a c c e p t e d e c o n o m i c t h r e s h o l d ( i . e . , when l o s s e s d u e t o damage e q u a l t h e c o s t o f c o n t r o l , i n t h i s c a s e i n s e c t i c i d e c o s t ) f o r r o o t r a t i n g s i s b e t w e e n 2.5 a n d 3.0 (1£) . I n a d d i t i o n r o o t damage i n t h e u n t r e a t e d area m u s t e x c e e d 3.0 b e f o r e d i f f e r e n c e s b e t w e e n i n s e c t i c i d e t r e a t m e n t s w i l l become a p p a r e n t . F o r t h e s e two r e a s o n s , s i x e x p e r i m e n t s t h a t h a d r o o t r a t i n g s o f 3.0 o r l e s s i n t h e u n t r e a t e d a r e a s were d e l e t e d from f u r t h e r consideration. T r e a t m e n t m e a n s i n t h e r e m a i n i n g 13 e x p e r i m e n t s were a n a l y z e d u s i n g a n a l y s i s o f v a r i a n c e t e c h n i q u e s (2Ώ.) . D u n c a n ' s m u l t i p l e r a n g e t e s t (21) was u s e d t o s e p a r a t e t h e t r e a t m e n t means. A d u l t S u p p r e s s i o n t o P r e v e n t L a r v a l Damage. Another o p e r a t i o n a l s t r a t e g y f o rcoping w i t h enhanced biodégradation would be c o n t r o l l i n g a d u l t s r a t h e r than l a r v a e s o t h a t t h e i n s e c t i c i d e s d o n o t come i n t o c o n t a c t with the s o i l . I f f e m a l e b e e t l e numbers c o u l d be s u f f i c i e n t l y reduced during the egg-laying period (i.e., d u r i n g A u g u s t ) , a d a m a g i n g p o p u l a t i o n o f CRW l a r v a e should not develop t h e f o l l o w i n g season. To t e s t t h i s hypothesis, s i x C R W - i n f e s t e d c o r n f i e l d s i n Iowa d u r i n g 1977 w e r e c h o s e n . An u l t r a - l o w volume a p p l i c a t i o n o f c a r b a r y l ( S e v i n 4 - O i l ) a t t h e r a t e o f a p p r o x i m a t e l y 2.5 L/ha a n d c o n t a i n i n g 1.12 k g A I w a s a e r i a l l y a p p l i e d t o h a l f o f each f i e l d and t h e remainder l e f t untreated. The a d u l t i c i d e s p r a y s w e r e a p p l i e d t o a f i e l d when b e e t l e c o u n t s r e a c h e d one b e e t l e p e r p l a n t a n d 10% o f t h e f e m a l e s were g r a v i d . D u r i n g 1 9 7 8 t h e d e s i g n was m o d i f i e d t o e v a l u a t e t i m i n g o f a d u l t i c i d e s t o determine i fa longer beetle-free p e r i o d would improve subsequent root p r o t e c t i o n and t o compare a d u l t s u p p r e s s i o n with the preventative use o f s o i l i n s e c t i c i d e s a p p l i e d a t p l a n t i n g t h e subsequent year. Two t i m i n g s a n d m u l t i p l e a p p l i c a t i o n s o f c a r b a r y l w e r e a c h i e v e d b y d i v i d i n g f o u r Iowa c o r n f i e l d s i n h a l f a n d t r e a t i n g one s i d e with a b r o a d c a s t a e r i a l a p p l i c a t i o n . T r e a t m e n t s w e r e a p p l i e d when b e e t l e n u m b e r s r e a c h e d o n e b e e t l e p e r p l a n t a n d 10% o f t h e f e m a l e s were g r a v i d . When b e e t l e numbers r e c o v e r e d t o 0.5 b e e t l e s p e r p l a n t , t h e f i e l d was d i v i d e d a g a i n p e r p e n d i c u l a r to the first d i v i s i o n and one-half was t r e a t e d . The p r o t o c o l f o r i n s e c t i c i d e a p p l i c a t i o n divided t h e f i e l d s i n t o quadrants,



196


where one q u a d r a n t r e c e i v e d an e a r l y s p r a y , one quadrant r e c e i v e d a l a t e spray, the t h i r d quadrant received both an e a r l y and l a t e spray, and t h e f i n a l quadrant r e c e i v e d no treatment. The f o l l o w i n g s e a s o n (1979), t h e farmers applied t h e i r s o i l i n s e c t i c i d e of choice to the f i e l d s at planting. T h e y were a s k e d t o l e a v e two s t r i p s a c r o s s t h e f i e l d , one i n e a c h h a l f , u n t r e a t e d w i t h t h e soil insecticide. E a c h s t r i p b i s e c t e d two q u a d r a n t s p r o v i d i n g s o i l i n s e c t i c i d e t r e a t e d and u n t r e a t e d a r e a s i n a l l f o u r adult suppression treatments. The e x p e r i m e n t was repeated d u r i n g 1979 i n t h r e e Iowa c o r n f i e l d s . E f f i c a c y of the a d u l t i c i d e a n d l a r v i c i d e t r e a t m e n t s was e v a l u a t e d b y d i g g i n g 10 r o o t s a t e a c h o f f i v e s i t e s i n a l l t r e a t m e n t s . T h e d a m a g e was r a t e d as p r e v i o u s l y d e s c r i b e d . Laboratory E v a l u a t i o n of Chemical Rotations. I t was h y p o t h e s i z e d t h a t use o f a s o i l i n s e c t i c i d e e v e r y o t h e r year might slow the development o f enhanced biodégradation. To t e s t t h i s h y p o t h e s i s u n d e r l a b o r a t o r y conditions, the e f f e c t of r o t a t i o n s of carbofuran with i s o f e n p h o s was s t u d i e d u s i n g methods d e s c r i b e d by Dzantor and F e l s o t (JLQ) . O v e r a p e r i o d o f 181 d a y s 5 k g soil ( F l a n a g a n s i l t l o a m , T a b l e I) i n i n d i v i d u a l b u c k e t s was p r e t r e a t e d i n t h r e e 2-month c y c l e s w i t h g r a n u l a r c a r b o f u r a n ( F u r a d a n 15G), i s o f e n p h o s (Amaze 2 0 G ) , an a l t e r n a t i o n b e t w e e n c a r o b u r a n and i s o f e n p h o s , o r no insecticide (Table I I ) . Following the t h i r d pretreatment c y c l e , s o i l was removed and t r e a t e d w i t h t e c h n i c a l carbofuran to monitor chemical p e r s i s t e n c e . Another batch o f s o i l was p l a c e d i n b i o m e t e r f l a s k s (22) a n d t r e a t e d with C - c a r b o n y l - l a b e l e d c a r b o f u r a n (FMC Corp., radiochemical purity=93%) to monitor production of C02. 1 4

1 4

F i e l d E v a l u a t i o n of Chemical Rotations. D u r i n g 1985-1988, experiments were c o n d u c t e d a t t h e U n i v . o f 111. Northwest I l l i n o i s A g r i c u l t u r a l Research and Development C e n t e r near Monmouth, I l l i n o i s . A s i n g l e 2 - a c r e f i e l d was u s e d over the 4 years of research. T h e s o i l was a M u s c a t i n e silt l o a m a n d t h e s l o p e was ^ 2 % ( s o i l 69, T a b l e I ) . The c r o p p i n g h i s t o r y p r i o r t o 1985 w a s : s o y b e a n s , 1980-82; wheat, 1983; c o r n , 1984. No s o i l i n s e c t i c i d e h a d b e e n u s e d f o r a t l e a s t t h r e e y e a r s p r i o r t o 1985. Chlorpyrifos ( L o r s b a n 4E) was u s e d f o r a d u l t c o r n r o o t w o r m c o n t r o l during 1984. T h e e n t i r e f i e l d was d i v i d e d i n t o f o u r r e p l i c a t e blocks. E a c h b l o c k was r a n d o m l y a s s i g n e d 22 insecticide and check t r e a t m e n t s (Table I I I ) . Each treatment c o n s i s t e d o f f o u r 20-m l o n g rows o f c o r n . Blocks and t r e a t m e n t rows were s e p a r a t e d f r o m one a n o t h e r by u n t r e a t e d c o r n rows, w h i c h s e r v e d as b u f f e r zones. The p l o t was c h i s e l - p l o w e d d u r i n g t h e f a l l a n d fieldc u l t i v a t e d i n the spring. A l l t i l l a g e o p e r a t i o n s were


15.

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Table

197

C h a r a c t e r i s t i c s o f S o i l s Used i n S t u d i e s o f Chemical Rotation and Controlled-Release Formulations

Texture silt loam

pH

% Org. Carbon

7. 0

3.5

carbofuran

clay

loam

6. 5

1.8

WestvillePecatonica

phorate

silt

loam

6. 1

1.1

46

PlanoProctor

carbofuran, terbufos

clay

loam

5. 7

1.5

52

Drummer Catlin

mixed, UI exp'tl. plot

silty c l a y loam

4. 6

1.9

69

Muscatine

none p r i o r t o 1985

silt

5. 7

2.5

S o i l Type o r Assoication Flanagan

Insecticides Used

29

AndresReddick

44

Code 11


I.


Table

II.

Days o f Incubation 53 75 53 Code

none, UI borrow p i t

loam

Experimental Design f o r T e s t i n g t h e E f f e c t s o f I n s e c t i c i d e R o t a t i o n on P e r s i s t e n c e o f Carbofuran Insecticide P r e t r e a t m e n t Regime i n B u c k e t No. 1 4 5 2 3 isofen. none isofen. carb. carb. isofen. none isofen. carb. carb. isofen. none isofen. carb. carb. NI Ill CCC ICI CIC

conducted along the north-south axis t o avoid contamination o f adjacent treatments with s o i l . Alachlor ( L a s s o 4 E C ) h e r b i c i d e was a p p l i e d p r e e m e r g e n c e a t a r a t e o f 2.8 k g Α Ι / h a d u r i n g a l l y e a r s , a n d a t r a z i n e was a l s o u s e d d u r i n g 1988. The i n s e c t i c i d e s were a p p l i e d d u r i n g p l a n t i n g i n a n 18-cm b a n d o v e r t h e f u r r o w a n d i n c o r p o r a t e d w i t h s p r i n g tines. The i n s e c t i c i d e s , which were a p p l i e d a t a r a t e o f 1.12 k g Α Ι / h a , i n c l u d e d t e r b u f o s ( C o u n t e r 1 5 G ) , f o n o f o s (Dyfonate 20G), and carbofuran (Furadan 15G). The sequence o f m u l t i - y e a r and r o t a t i o n a l treatments i s shown i n T a b l e I I I . By 1988, t h e f o l l o w i n g h i s t o r i e s h a d b e e n established: (1) t w o , t h r e e , a n d f o u r y e a r s o f c o n t i n u o u s use o f a product; (2) f i r s t y e a r u s e o f a p r o d u c t o n previously untreated plots; (3) a l l c o m b i n a t i o n s o f t w o


198

ENHANCED BIODEGRADATION O F PESTICIDES IN T H E ENVIRONMENT

Table


Insecticide Counter

III.

1985 C

Insecticide

treatments

and coding

Insecticide History Year 1987 1986 CC UC FC DC

CCC UCC UUC CFC CDC

cue

a

1988 CCCC UCCC UUCC UUUC FCFC DCDC

Dyfonate

D

DD UD FD CD

DDD UDD UUD DCD DFD DUD

DDDD UDDD UUDD UUUD CDCD FDFD

Furadan

F

FF UF CF DF

FFF UFF UUF FCF FDF FUF

FFFF UFFF UUFF UUUF CFCF DFDF

Untreated

U

UU CU DU FU

UUU

UUUU CUCU DUDU FUFU

a

Letters i n each

i n each code r e p r e s e n t i n s e c t i c i d e succeeding year.

treatments

chemical rotations over a four year period. During each year o f t h e study, untreated p l o t s served as c o n t r o l s f o r r o o t - f e e d i n g damage. R o o t damage r a t i n g s were measured d u r i n g J u l y , and y i e l d s were d e t e r m i n e d b y m a c h i n e - h a r v e s t i n g i n October. D u r i n g 1987 a n d 1988 s o i l s a m p l e s were c o l l e c t e d for b i o l o g i c a l and chemical assay. Immediately following a p p l i c a t i o n a n d a p p r o x i m a t e l y 1.5 m o n t h s l a t e r , f o u r soil c o r e s (5-cm d i a m . χ 10-cm l o n g ) were r a n d o m l y collected f r o m between t h e s e c o n d a n d t h i r d row o f e a c h t r e a t m e n t replicate (n=88 s a m p l e s / d a y ) . The c o r e s from an i n d i v i d u a l t r e a t m e n t were b u l k e d t o g e t h e r a n d s i e v e d t h r o u g h a 3-mm s c r e e n . Two 2 5 - g a l i q u o t s f r o m e a c h p l o t w e r e w e i g h e d i n t o 125-mL p l a s t i c c u p s a n d f r o z e n u n t i l b i o a s s a y e d b y p r e v i o u s l y d e s c r i b e d m e t h o d s (1,22.) . T h e r e m a i n d e r o f t h e s o i l was f r o z e n u n t i l e x t r a c t e d f o r quantitative analysis. F o r s t a t i s t i c a l a n a l y s e s , d a t a were g r o u p e d b y i n s e c t i c i d e t r e a t m e n t d u r i n g 1987 a n d 1988 a n d a n a l y z e d b y


15.



199


t h e SAS G e n e r a l L i n e a r Means P r o d e c u r e (2Û). I f the a n a l y i s o f v a r i a n c e was s i g n i f i c a n t ( p < 0.1) t h a n t h e mean r o o t r a t i n g s o r i n s e c t i c i d e c o n c e n t r a t i o n s w e r e s e p a r a t e d b y D u n c a n ' s m u l t i p l e r a n g e t e s t a t ρ < 0.1 (2Ώ.) . Laboratory Testing of Controlled-Release Formulations. Two t y p e s o f c a r b o f u r a n f o r m u l a t i o n s w e r e t e s t e d , a gypsum-based r o l l - c o m p a c t e d g r a n u l e manufactured by Union Carbide ( R e s . T r i a n g l e P k . , N. C a r o l i n a ) a n d a p r o p r i e t a r y c o n t r o l l e d - r e l e a s e g r a n u l e m a n u f a c t u r e d b y S i e r r a Chem. Co. ( M i l p i t a s , C A ) . T h e p e r s i s t e n c e o f c a r b o f u r a n when a p p l i e d a s a gypsum g r a n u l e ( 1 5 % A I ) was c o m p a r e d t o t h e p e r s i s t e n c e o f t h e c o m m e r c i a l s a n d - b a s e d g r a n u l e (FMC C o r p , P r i n c e t o n , N J ) . S o i l 29 ( T a b l e I ) , w h i c h was r e p o r t e d t o b e c o n d i t i o n e d f o r e n h a n c e d b i o d é g r a d a t i o n (£) was w e i g h e d ( 5 0 g o v e n - d r y w e i g h t ) i n t o i n d i v i d u a l flasks a n d s p i k e d w i t h 0.01 g o f g r a n u l e s t o g i v e a n o m i n a l c o n c e n t r a t i o n o f 30 ppm. S o i l w a s a d j u s t e d t o 4 0 % o f MHC a n d i n c u b a t e d a t 2 5 ° C . f o r u p t o 63 d a y s . Triplicate f l a s k s were removed p e r i o d i c a l l y f o r a n a l y s i s o f carbofuran. In a second l a b o r a t o r y experiment, t h e c h e m i c a l p e r s i s t e n c e o f c a r b o f u r a n a p p l i e d a s F u r a d a n 10G ( t h e commercial sand-coated granule) and 2 S i e r r a controlledr e l e a s e c a r b o f u r a n f o r m u l a t i o n s ( s a m p l e s n o . 3 2 - 4 7 - 2 , 9.1% A I a n d 3 2 - 4 8 - 2 , 9.7% A I ) w e r e m o n i t o r e d f o r two months i n t h r e e s o i l t y p e s , n o . 2 9 , 4 6, a n d 44 ( T a b l e I ) . Threeh u n d r e d f o r t y - o n e grams (300 g o v e n - d r y w e i g h t ) o f e a c h s o i l were w e i g h e d i n t o g l a s s b o t t l e s a n d f o r t i f i e d with 1.5 g o f o n e o f t h e t h r e e f o r m u l a t i o n s . The a c t u a l r a t e s o f a p p l i c a t i o n w e r e 4 5 5 ppm ( n o . 3 2 - 4 7 - 2 ) , 4 8 5 ppm ( n o . 3 2 - 4 8 - 2 ) , a n d 5 0 0 ppm ( F u r a d a n 1 0 G ) . T h e s o i l s w e r e t h o r o u g h l y m i x e d a n d a d j u s t e d t o 2 5 % o f MHC. The b o t t l e s were s e a l e d w i t h P a r a f i l m a n d i n c u b a t e d a t 25°C. At b i w e e k l y i n t e r v a l s , 20-g r e p l i c a t e s o f each s o i l were removed f o r q u a n t i t a t i v e a n a l y s i s o f c a r b o f u r a n . F i e l d Testing o f Controlled-Release Formulations. The e f f i c a c y o f two a d d i t i o n a l S i e r r a c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s ( n o . 3 2 - 4 5 - 2 , 8 . 9 % A I ; n o . 4 1 - 4 - 2 , 9.3% A I ) was t e s t e d i n t h e f i e l d d u r i n g t h e summer o f 1 9 8 2 i n K a n k a k e e C o . ( s o i l 29) a n d C h a m p a i g n C o . ( s o i l 52) I L . T h e S i e r r a f o r m u l a t i o n s w e r e a p p l i e d a t t h e r a t e o f 1.12 a n d 2.24 k g Α Ι / h a i n a n 1 8 - c m b a n d o v e r t h e r o w a n d l i g h t l y incorporated with a drag chain. The p l o t s c o n s i s t e d o f o n e 15.2-m l o n g r o w o f c o r n r e p l i c a t e d 4 t i m e s i n a r a n d o m block design. The c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s were c o m p a r e d t o t h e c o m m e r c i a l F u r a d a n 15G f o r m u l a t i o n a n d a n u n t r e a t e d check. I n m i d - J u l y , 5 c o r n r o o t s were randomly sampled from each r e p l i c a t e and r a t e d f o rrootworm f e e d i n g d a m a g e (IB.) . S o i l s a m p l e s w e r e c o l l e c t e d f o r c a r b o f u r a n a n a l y s i s immediately a f t e r a p p l i c a t i o n a n d 1 month l a t e r .



200


A n a l y t i c a l Methods. F o r a l l e x p e r i m e n t s , c a r b o f u r a n was e x t r a c t e d from s o i l by s l u r r y i n g with water and mixing w i t h e t h y l a c e t a t e (24.) . T h e e x t r a c t i o n was normally repeated twice, but s o i l s from t h e c o n t r o l l e d r e l e a s e e x p e r i m e n t s were e x t r a c t e d t h r e e t i m e s . For the f i e l d studies of the controlled-release formulations, the e x t r a c t s were p a s s e d t h r o u g h a 10-g F l o r i s i l column a n d e l u t e d w i t h 50 mL o f 3 0 % a c e t o n e i n h e x a n e t o s e p a r a t e atrazine. Carbofuran c o n c e n t r a t i o n was d e t e r m i n e d b y g a s chromatography employing s e v e r a l d i f f e r e n t columns. For laboratory and f i e l d studies o f c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s , c a r b o f u r a n was a n a l y z e d o n a 6 0 - c m o r 45.7cm, r e s p e c t i v e l y , g l a s s c o l u m n ( 0 . 2 mm i . d . ) o f 5% O V - 2 2 5 and d e t e c t e d by a P a c k a r d n i t r o g e n - p h o s p h o r u s d e t e c t o r . C o l u m n t e m p e r a t u r e was i s o t h e r m a l a t 1 7 0 ° o r 1 8 5 ° C , a n d t h e d e t e c t o r a n d i n j e c t o r were h e l d a t 250°C. For the r o t a t i o n s t u d i e s , t h e G L C c o l u m n was 90 cm l o n g χ 0.2 cm i . d . a n d p a c k e d w i t h 5% A p i e z o n + 0 . 1 2 5 % DEGS a s d e s c r i b e d b y F e l s o t e t a l . (21). Isofenphos, fonofos, and terbufos were e x t r a c t e d a n d a n a l y z e d as d e s c r i b e d b y F e l s o t e t a l . (25-26). Results

and Discussion

Cultivation-Time Studies. I n n i n e o f t h e 13 e x p e r i m e n t s a n a l y z e d , t h e r e was l e s s r o o t d a m a g e w h e n c a r b o f u r a n was a p p l i e d d u r i n g c u l t i v a t i o n t h a n when a p p l i e d d u r i n g p l a n t i n g ( d a t a n o t shown), a l t h o u g h a l l r o o t damage r a t i n g s were l e s s t h a n t h e e c o n o m i c t h r e s h o l d o f 3.0. In t h r e e o f t h e 13 e x p e r i m e n t s , c a r b o f u r a n a p p l i e d a t p l a n t i n g time d i d not provide acceptable c o n t r o l , i . e . , r o o t d a m a g e r a t i n g s w e r e g r e a t e r t h a n 3.0 ( T a b l e I V ) . B e c a u s e t h e t w o Ames l o c a t i o n s h a d b e e n i n c o m m e r c i a l c o r n p r o d u c t i o n and had r e c e i v e d a p l a n t i n g - t i m e banded a p p l i c a t i o n o f c a r b o f u r a n two o f t h e p r e c e d i n g f o u r y e a r s , i t was a s s u m e d t h a t t h e f i e l d s w e r e c o n d i t i o n e d f o r enhanced biodégradation. T h e N e w e l l l o c a t i o n was a t e s t p l o t s i t e a n d o n l y a few rows h a d r e c e i v e d a c a r b o f u r a n a p p l i c a t i o n i n a l t e r n a t e y e a r s , b u t i t seemed t h a t t h e s o i l was a l s o c o n d i t i o n e d f o r e n h a n c e d b i o d é g r a d a t i o n . In g e n e r a l , p o o r e f f i c a c y o f c a r b o f u r a n due t o enhanced biodégradation c o u l d be c i r c u m v e n t e d by a p p l y i n g c a r b o f u r a n a t a t i m e when t h e l a r v a e w e r e a c t i v e l y feeding. A d u l t S u p p r e s s i o n t o P r e v e n t L a r v a l Damage. T h e 1977 a d u l t i c i d e treatments r e d u c e d r o o t damage d u r i n g t h e subsequent year i n a l l s i x f i e l d s (Table V ) . In o n l y one field ( M e a d F a r m ) was t h e 1 9 7 8 r o o t d a m a g e economically significant. The p r e v i o u s y e a r ' s a d u l t i c i d e treatment, h o w e v e r , d i d p r o v i d e g o o d s u p p r e s s i o n o f l a r v a l damage i n this field.


15.

FELSOT & TOLLEFSON

Table

IV.


201

A v e r a g e Root-Damage R a t i n g s i n Iowa C o r n f i e l d s Treated with Carbofuran Applied During P l a n t i n g and Cultivation 3

Time Year

of Application

Untreated Planting 4.52 b Newell 3.00 a 3.70 a 4.00 c Ames 2.25 a 3.05 b 3.75 a Ames 2.65 a 3.30 a M e a n s w i t h i n a r o w f o l l o w e d b y t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a c c o r d i n g t o Duncan's M u l t i p l e R a n g e T e s t ( p £ 0.05) . Location

Cultivation

1976 1983 1985


a

Table

V.

A v e r a g e Root-Damage R a t i n g s i n Iowa C o r n f i e l d s Following A d u l t i c i d i n g t h e Preceding Year t o S u p p r e s s A d u l t C o r n Rootworm P o p u l a t i o n s Root

Location Ranshau Farm Grevengoed Farm Goode Farm Mead Farm Hahn F a r m P e r k i n s Farm

A p p l i c a t i o n Date J u l y 24 J u l y 24 July 29 J u l y 30 August 1 A u g u s t 10

Damage R a t i n g No A d u l t i c i d e 1.8 2.0 2.4 4.4 2.3 2.7

Adulticide 1.5 1.7 2.2 2.3 2.2 2.4

In t h e 1978 a n d 1979 e x p e r i m e n t s (Table VI), t h e root damage r a t i n g c o r r e s p o n d i n g t o n o a d u l t i c i d e / n o s o i l i n s e c t i c i d e r e p r e s e n t e d t h e r o o t damage when n o i n s e c t i c i d e s were used. The r a t i n g c o r r e s p o n d i n g t o no a d u l t i c i d e / s o i l insecticide represented the root p r o t e c t i o n provided by t h e s o i l i n s e c t i c i d e alone a t p l a n t i n g and s e r v e d as a r e f e r e n c e p o i n t f o ra s s e s s i n g t h e efficacy of adulticide treatments. D u r i n g 1978 two o f t h e f o u r f i e l d s s p r a y e d ( t h e P a y s e n a n d H a r k s e n f a r m s ) h a d e c o n o m i c r o o t damage t h e year f o l l o w i n g t h e a d u l t i c i d e a p p l i c a t i o n s (i.e., root r a t i n g s £ 3.0 i n t h e n o a d u l t i c i d e / n o s o i l insecticide treatment). A l l b u t one o f t h e a d u l t i c i d e treatments provided s u f f i c i e n t suppression o f egg laying t o avoid e c o n o m i c r o o t damage t h e f o l l o w i n g y e a r . In t h e Paysen f i e l d , t h e J u l y 28 a p p l i c a t i o n o f a n a d u l t i c i d e reduced t h e s u b s e q u e n t damage, b u t n o t t o t h e a c c e p t a b l e l e v e l o f 3.0. W h i l e t h e s u b s e q u e n t r o o t damage i n t h e r e s t o f t h e a d u l t i c i d e t r e a t m e n t s was s l i g h t l y g r e a t e r t h a n a s o i l i n s e c t i c i d e a l o n e , i t was b e l o w t h e e c o n o m i c l e v e l . In f a c t , c o n t r o l was s u f f i c i e n t l y g o o d t h a t t h e a d d i t i o n o f a planting-time s o i l i n s e c t i c i d e t h e f o l l o w i n g year only improved root p r o t e c t i o n s l i g h t l y .


202


Table

VI.

Comparison o f A d u l t i c i d e Applied t h e Preceding Year with S o i l I n s e c t i c i d e s Applied During Planting f o r Protection from Corn Rootworm L a r v a l Damage i n I o w a


Root Location and A d u l t i c i d e Treatment 1978 Seesor Farm J u l y 14 t r e a t m e n t J u l y 28 t r e a t m e n t early + l a t e treatment no a d u l t i c i d e

Damage

No S o i l Insecticide

Rating Soil Insecticide

2.5 2.6 2.0 2.7

2.0 2.0 1.5 1.9

Paysen Farm J u l y 16 t r e a m e n t J u l y 28 t r e a t m e n t early + l a t e treatment no a d u l t i c i d e

2.4 3.8 2.4 4.3

2.4 1.9 1.8 2.1

B a r r Farm J u l y 14 t r e a m e n t August 2 treatment early + l a t e treatment no a d u l t i c i d e

2.6 2.4 1.7 —

— — 1.8

Harksen Farm J u l y 19 t r e a m e n t A u g u s t 10 t r e a t m e n t early + l a t e treatment no a d u l t i c i d e

2.2 2.0 2.0 3.4

1.9 1.7 1.7 1.7

1979 O s t e r Farm J u l y 28 t r e a t m e n t no a d u l t i c i d e

2.2 2.1

1.9 2.6

Harksen Farm J u l y 28 t r e a t m e n t no a d u l t i c i d e

2.2 2.7

1.8 2.3

Shaffer Farm J u l y 30 t r e a m e n t August 2 treatment early + l a t e treatment no a d u l t i c i d e

1.9 — 1.6 2.2

1.8 — 1.4 1.7

The s u b s e q u e n t y e a r ' s r o o t damage i n a l l t h r e e f i e l d s t h a t r e c e i v e d a n a d u l t i c i d e i n 1 9 7 9 was b e l o w e c o n o m i c levels. Under t h e l i g h t i n f e s t a t i o n s , t h e p r e v e n t i o n o f l a r v a l damage b y t h e a d u l t i c i d e s p r a y s e q u a l l e d t h e planting-time application of soil insecticides. Although


15.



203


c a r b o f u r a n d e g r a d a t i o n was n o t c h a r a c t e r i z e d f o l l o w i n g t r e a t m e n t , t h e d a t a s u g g e s t e d t h a t l a r v a l damage c o u l d b e s u c c e s s f u l l y c o n t r o l l e d without a s o i l i n s e c t i c i d e i f t h e a d u l t p o p u l a t i o n was s u p p r e s s e d t h e p r e c e d i n g y e a r . The s u c c e s s o f such a s t r a t e y would be h i g h l y dependent on s c o u t i n g t e c h n i q u e s t o d e t e r m i n e when b e e t l e n u m b e r s h a d r e a c h e d an economic t h r e s h o l d . Laboratory T e s t i n g o f Chemical Rotations. Carbofuran d e g r a d e d most s l o w l y i n p r e t r e a t m e n t s o f NI a n d I I I (Figure 1 ) . T h e e s t i m a t e d 50% d i s a p p e a r a n c e t i m e (DT50%) b a s e d o n t h e e v o l u t i o n o f r a d i o l a b e l e d CO2 was 2 2 - 2 4 days. In s o i l p r e t r e a t e d three times with carbofuran, D T 5 0 % d r o p p e d t o 5 d a y s ( F i g u r e 1 ) , a n d a f t e r 42 d a y s o n l y 7% o f t h e i n i t i a l l y r e c o v e r e d c a r b o f u r a n r e m a i n e d . When c a r b o f u r a n was a l t e r n a t e d w i t h i s o f e n p h o s , t h e D T 5 0 % was 8 d a y s f o r t h e C I C r o t a t i o n a n d 12 d a y s f o r t h e I C I r o t a t i o n (21-23% r e c o v e r y o f c a r b o f u r a n b a s e d on c h e m i c a l a s s a y s ) . C a r b o f u r a n b i o d é g r a d a t i o n was s t i l l e n h a n c e d i n p r e t r e a t m e n t s w i t h i n s e c t i c i d e r o t a t i o n when c o m p a r e d t o p r e t r e a t m e n t s w i t h o u t c a r b o f u r a n , b u t t h e p e r s i s t e n c e was lengthened r e l a t i v e t o the pretreatments with carbofuran alone. F i e l d T e s t i n g o f Chemical Rotations. D u r i n g 1987 a n d 1 9 8 8 , c h e m i c a l a s s a y o f s o i l s a p p r o x i m a t e l y 1.5 m o n t h s a f t e r a p p l i c a t i o n was u s e d a s a b e n c h m a r k f o r d e t e r m i n i n g i f m u l t i - y e a r u s e o f an i n s e c t i c i d e r e s u l t e d i n enhanced biodégradation. T h i s time p e r i o d s h o u l d have c o i n c i d e d w i t h a c t i v e f e e d i n g by corn rootworm l a r v a e , and t h e r e f o r e , e f f e c t i v e i n s e c t c o n t r o l was e x p e c t e d t o c o i n c i d e w i t h i n s e c t i c i d e r e s i d u e s t h a t were a t l e a s t a s high as published concentration-response estimates 22.) . L a b o r a t o r y b i o a s s a y s , r o o t damage r a t i n g s , a n d y i e l d s w e r e used t o assess t h e e f f e c t o f m u l t i - y e a r treatments and r o t a t i o n s on i n s e c t i c i d e efficacy. Recovery o f terbufos and t o x i c metabolites during 1987 a n d 1988 d i d n o t d i f f e r s i g n i f i c a n t l y among a n y i n s e c t i c i d e treatment h i s t o r y (Table V I I , V I I I ) . P e r c e n t a g e m o r t a l i t y d i d n o t d i f f e r among t r e a t m e n t s , b u t t h e m o r t a l i t y i n a l l t r e a t m e n t s was n o t i c e a b l y l o w e r d u r i n g 1987 t h a n d u r i n g 1988, e v e n t h o u g h t h e s o i l s were a b o u t 40% d r i e r i n 1988 (a d r o u g h t y e a r ) t h a n i n 1 9 8 7 . T h i s d i s c r e p a n c y c a n b e a t t r i b u t e d t o t h e much l o w e r r e c o v e r i e s d u r i n g 1987 o f p a r e n t t e r b u f o s ( d a t a n o t shown), w h i c h i s more t o x i c t h a n i t s m e t a b o l i t e s (27-28). R o o t damage r a t i n g s were b e l o w t h e e c o n o m i c t h r e s h o l d o f 3.0 i n a l l t r e a t m e n t s , a n d y i e l d s d i d n o t d i f f e r s i g n i f i c a n t l y from one a n o t h e r n o r from t h e u n t r e a t e d check. D u r i n g 1987, t h e h i g h e s t c o n c e n t r a t i o n s o f f o n o f o s w e r e r e c o v e r e d f r o m t h e f i r s t y e a r (UUD) a n d r o t a t i o n a l treatments (DFD, DCD, D U D ) , a n d t h e l o w e s t c o n c e n t r a t i o n s



204


were r e c o v e r e d from t h e t h r e e - y e a r t r e a t m e n t (DDD) (p £ 0.055, T a b l e V I I ) . These d a t a s u g g e s t e d t h e development o f enhanced biodégradation. The t r e n d i n r e s i d u e r e c o v e r y was more d e f i n i t i v e o f enhanced b i o d é g r a d a t i o n d u r i n g 1988 when 42 days a f t e r a p p l i c a t i o n n e a r l y 3 t o 5 t i m e s a s much D y f o n a t e was r e c o v e r e d from f i r s t - y e a r (UUUD) a n d r o t a t i o n a l (CDCD, FDFD) t r e a t m e n t s as from m u l t i - y e a r (DDDD, UDDD, UUDD) t r e a t m e n t s (ρ ^ 0.001, T a b l e V I I I ) . The p a t t e r n i n p e r c e n t a g e m o r t a l i t y d u r i n g 1987 d i d n o t r e f l e c t t h e o c c u r r e n c e o f enhanced b i o d é g r a d a t i o n (ρ < 0.478) b e c a u s e f o n o f o s c o n c e n t r a t i o n s were s t i l l a t l e a s t e q u a l t o o r g r e a t e r t h a n t h e p u b l i s h e d LC95 (1.88 ± 0.43) f o r t h i r d i n s t a r s o u t h e r n CRW (22.) . I n 1988 m o r t a l i t y was lower i n m u l t i - y e a r treatments than i n f i r s t - y e a r o r r o t a t i o n a l t r e a t m e n t s (p < 0.077). The n u m e r i c a l t r e n d i n r o o t damage r a t i n g s d u r i n g 1988 r e f l e c t e d t h e e v i d e n c e f o r enhanced b i o d é g r a d a t i o n t h a t was o b s e r v e d i n t h e c h e m i c a l and b i o l o g i c a l a s s a y s . Y i e l d s d i d not d i f f e r s i g n i f i c a n t l y among f o n o f o s t r e a t m e n t s n o r from t h e u n t r e a t e d check. In a l l t r e a t m e n t s d u r i n g 1987, n e a r l y 90% o f t h e a p p l i e d c a r b o f u r a n d e g r a d e d w i t h i n 45 d a y s . The t h r e e y e a r c a r b o f u r a n t r e a t m e n t (FFF) h a d t h e l o w e s t r e s i d u e s , t h e l o w e s t m o r t a l i t y , and t h e h i g h e s t r o o t damage r a t i n g s ( T a b l e V I I ) . These d a t a p r o v i d e o n l y weak e v i d e n c e f o r enhanced biodégradation, however, b e c a u s e i n s e c t i c i d e r e c o v e r y i n t h e t w o - y e a r F u r a d a n t r e a t m e n t s (UFF, FUF) d i d n o t d i f f e r s i g n i f i c a n t l y from t h e f i r s t - y e a r t r e a t m e n t (UUF) n o r from t h e r o t a t i o n a l t r e a t m e n t s (FCF, FDF, F U F ) . D u r i n g 1988, t h e l a c k o f s i g n i f i c a n t d i f f e r e n c e s i n r e s i d u e r e c o v e r y among t r e a t m e n t s ( T a b l e V I I I ) may have r e f l e c t e d the influence of the very dry s o i l s during the drought. The b i o a s s a y s i n 1988 showed a s i g n i f i c a n t d i f f e r e n c e between f o u r - y e a r and f i r s t - y e a r t r e a t m e n t s although the i n s e c t i c i d e residues d i d not d i f f e r . I n t e r e s t i n g l y , r o o t damage r a t i n g s a l s o r e f l e c t e d t h e t r e n d o f t h e b i o a s s a y s (Table V I I I ) . Neither percentage m o r t a l i t y n o r r o o t damage r a t i n g s f o r t h e r o t a t i o n a l t r e a t m e n t s (CFCF, DFDF) d i f f e r e d s i g n i f i c a n t l y from t h a t for the multi-year treatments. As p r e v i o u s l y o b s e r v e d f o r t e r b u f o s and f o n f o f o s , y i e l d s d i d not d i f f e r s i g n i f i c a n t l y among t r e a t m e n t s . Of t h e t h r e e i n s e c t i c i d e s s t u d i e d , enhanced b i o d é g r a d a t i o n has been d e f i n i t i v e l y a s s o c i a t e d w i t h repeated a p p l i c a t i o n s o f carbofuran (£). In our s t u d i e s , t h e c h e m i c a l a s s a y d a t a from 1987 o n l y weakly s u g g e s t e d t h e development o f enhanced biodégradation, a n d t h e d a t a from 1988 i n d i c a t e d t h a t biodégradation r a t e was n o t a f f e c t e d by m u l t i - y e a r c a r b o f u r a n treatments. Since a s e v e r e d r o u g h t o c c u r r e d i n 1988, a l a c k o f s o i l m o i s t u r e may have s l o w e d t h e r a t e o f c a r b o f u r a n d e g r a d a t i o n . Chapman e t a l . (22.) a n d H a r r i s e t a l . (1£) n o t e d t h a t t h e


15.

FELSOT & TOLLEFSON

Coping with Soil insecticide Degradation


100

Days After Application Figure

1.

14

1 4

R e c o v e r y o f CC>2 f r o m C-carbonyl-labeled c a r b o f u r a n i n s o i l 11 p r e t r e a t e d w i t h carbofuran, isofenphos, or rotations o f carbofuran and isofenphos. See t e x t f o r treatment codes.

degradation o f carbofuran i n s o i l e x h i b i t i n g enhanced b i o d é g r a d a t i o n w a s v e r y s l o w when m o i s t u r e c o n t e n t was low. I n c o n t r a s t t o t h e c h e m i c a l a s s a y d a t a , r o o t damage r a t i n g s and bioassays o f s o i l s from c a r b o f u r a n - t r e a t e d p l o t s s t r o n g l y suggested enhanced biodégradation. The c o m p a r a t i v e l y h i g h m o r t a l i t i e s d u r i n g 1 9 8 7 may b e attributed t o the recovery of residues at levels s t i l l c l o s e t o t h e L C 9 5 f o r s o u t h e r n CRW i n s o i l s o f s i m i l a r s o i l organic carbon content (i.e., 0 . 3 8 - 0 . 4 8 ppm, [2.]) coupled with adequate s o i l moisture. The d i s c r e p a n c y b e t w e e n t h e c h e m i c a l a n d b i o l o g i c a l a s s a y s d u r i n g 1 9 8 8 may be a t t r i b u t e d t o v e r y l o w s o i l m o i s t u r e t h a t c o u l d i n h i b i t t h e a b s o r p t i o n o f t h e i n s e c t i c i d e s b y t h e l a r v a e (2) i n


205

206


Table

VII.

E f f e c t o f f i r s t - y e a r use, m u l t i - y e a r use r o t a t i o n s on e f f i c a c y a n d p e r s i s t e n c e o f i n s e c t i c i d e s d u r i n g 1987 a t M o n m o u t h , I L 45


Treatment

3

Yield (bu)

U

131. 8

CCC UCC UUC CFC CDC

137. 148. 134. 136. 134. 139. 0.

days a f t e r a p p l i c a t i o n Concentration (ppm)

Percent Mortality 1 8 .,1

0. 0 0 0

7 6 .,3 8 6 .,3 7 0 .,0 8 7 .,5 8 1 . ,3 7 0 .,0 0,.925

1.,552 1.,581 1.,767 1.,766 2.,194 1.,948 0.,813

1 0 0 4 0 0 665

2 2 2 2 2 2 0

.65 .70 .20 .60 .35 .25 .298

Ρ

Enhanced Biodegradation of Pesticides in the ... - ACS Publications

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