10 Deposition of Chemical and Biological Agents in Conifers JOHN W. BARRY
Downloaded by TUFTS UNIV on June 4, 2018 | https://pubs.acs.org Publication Date: January 16, 1984 | doi: 10.1021/bk-1984-0238.ch010
U.S. Department of Agriculture, Forest Service, Forest Pest Management, Davis, CA 95616
Accounting for aerially released pesticides involves techniques for sampling and assessing pesticide drops within and below the canopy. The USDA Forest Service (FS) in its effort to account for pesticide sprays has supported research to quantify deposition in the canopy, on foliage, and beneath the tree. This paper reviews results of several FS aerial spray projects. Field methods included spray deposit sampling with cards and assessing foliage for presence of pesticide drops and tracers. Results show that conifers are relatively efficient collectors of spray drops and that deposits decrease from the upper to the lower crown. The majority of drops observed on coniferous foliage are below 60 μm in diameter. Results indicate that recovery of spray is influenced by application rate, drop size, tree species, and density of foliage. The ban on the c h l o r i n a t e d hydrocarbon p e s t i c i d e s during the e a r l y 1970 s r e s u l t e d i n a search f o r methods t o improve t h e efficiency of aerial application of pesticides to forests. I t soon became apparent that the use o f l e s s p e r s i s t e n t chemical and b i o l o g i c a l agents t o c o n t r o l d e f o l i a t o r s such as the tussock moth and spruce budworm, would r e q u i r e a higher degree o f a p p l i c a t i o n p r e c i s i o n than p r e v i o u s l y had been p r a c t i c e d . Candidate agents required more a t t e n t i o n t o a p p l i c a t i o n t i m i n g , atmospheric c o n d i t i o n s , and the t a r g e t ' s p h y s i c a l and b e h a v i o r a l c h a r a c t e r i s t i c s . Bnphasis was given t o developing methods which would increase p e s t i c i d e deposit on the t a r g e t . Concurrent with the need t o improve a e r i a l a p p l i c a t i o n , needs have been expressed f o r techniques which w i l l a s s i s t i n accounting f o r p e s t i c i d e s released over f o r e s t s . While a t o t a l accountancy or mass balance o f a e r i a l l y released spray may be an unattainable g o a l , 90 percent accountancy may be a t t a i n a b l e . f
This chapter not subject to U.S. copyright. Published 1984, American Chemical Society
Garner and Harvey; Chemical and Biological Controls in Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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CHEMICAL AND
BIOLOGICAL CONTROLS IN FORESTRY
Accountancy i s a complex process as i t i n c l u d e s the e n t i r e tank m i x — c a r r i e r , d i l u t e n t , adjuvant and the a c t i v e i n g r e d i e n t . The f o r e s t pest manager has a need f o r i n f o r m a t i o n on how much spray reaches the t r e e crown and the f o r e s t f l o o r , or d r i f t s o f f the t a r g e t . Understanding i n t e r a c t i o n o f spray w i t h i n the t r e e crown, q u a n t i f y i n g the c o l l e c t i o n o f drops by f o l i a g e elements, and determining how much spray d e p o s i t s on the f o r e s t f l o o r are part o f the accountancy process. Consistent w i t h the concern to improve the e f f i c i e n c y o f a e r i a l a p p l i c a t i o n there has been an attempt over the past 20 years to determine where spray drops d e p o s i t i n c o n i f e r o u s f o r e s t s . Researchers such as H u r t i g et a l . (JO $ Snowden et a l . ( 2 ) , Thompson et a l . (3.) » Barry e t a l . ( 4 ) , Joyce et a l . (5.) • Armstrong and Yule ( 6 ) , and Sundaram ÇH have reported on the d e p o s i t of p e s t i c i d e drops on c o n i f e r s . Himel and Moore (8), reported t h a t the highest m o r t a l i t y o f western spruce bud worm was caused by p a r t i c l e s l e s s than 50 m i n diameter. Their work prompted others t o look at what was being deposited d i r e c t l y on t a r g e t f o l l o w i n g c o n v e n t i o n a l a p p l i c a t i o n methods. These and s i m i l i a r s t u d i e s have helped to provide us an understanding o f the behavior and d e p o s i t i o n o f spray drops i n c o n i f e r o u s f o r e s t s . The r a t i o n a l e f o r these s t u d i e s i s based on the assumption t h a t once we have determined what i s deposited i n t r e e s , steps can be taken to apply the proper number and s i z e range o f drops t o achieve r e s u l t s . Safe, e f f e c t i v e , and economical a p p l i c a t i o n s are dependent upon i n f o r m a t i o n generated by such s t u d i e s . Several f a c t o r s are known to i n f l u e n c e d e p o s i t i o n o f drops on f o l i a g e and i n s e c t s . These i n c l u d e drop s i z e , wind speed, t a r g e t shape and s i z e , d e n s i t y and type o f f o l i a g e , and v e l o c i t y o f the f a l l i n g drops. Other f a c t o r s have a l e s s defined r o l e such as the microenvironment surrounding the t a r g e t , p h y s i c a l and chemical aspects o f the drops, and c h a r a c t e r i s t i c s o f the t a r g e t s u r f a c e , i n c l u d i n g i t s e l e c t r i c a l charge (9). Research i s needed to understand the c o n t r i b u t i o n o f these f a c t o r s t o drop d e p o s i t i o n , i m p a c t i o n , and r e t e n t i o n on f o l i a g e . This paper reviews o b s e r v a t i o n s on the d e p o s i t i o n o f spray drops on t r e e s , f o l i a g e , and the f l o o r o f c o n i f e r o u s f o r e s t s . The data presented provides some i n s i g h t i n t o our knowledge o f spray behavior i n c o n i f e r o u s f o r e s t s .
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f
D e p o s i t i o n on F o r e s t F l o o r The f i l t r a t i o n o f drops by c o n i f e r o u s f o l i a g e has a pronounced a f f e c t on what reaches the f o r e s t f l o o r . Maksymiuk (10) suggested t h a t ground samplers should be placed three or more t r e e h e i g h t s from the nearest t r e e to avoid f i l t e r i n g o f drops. T y p i c a l l y as p a r t o f the spray cloud descends to the ground a f t e r r e l e a s e , i t descends at an angle due to wind. In the absence o f wind the spray tends to descend p e r p e n d i c u l a r l y w i t h the smaller drops expanding l a t e r a l l y . Our observations i n d i c a t e t h a t under
Garner and Harvey; Chemical and Biological Controls in Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
Downloaded by TUFTS UNIV on June 4, 2018 | https://pubs.acs.org Publication Date: January 16, 1984 | doi: 10.1021/bk-1984-0238.ch010
10.
BARRY
Deposition of Agents in Conifers
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low wind v e l o c i t i e s (
