Efficacy of Preplant/Postemergence Weeding Systems on Sugarbeet, 1968-72 1
E. F. SULLIVAN 2
Efficacy of Preplant/Postemergence Weeding
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Materials and Methods
T h e studies were c o n d u c t e d i n n o r t h e r n C o l o r a d o d u r i n g 1968- 72. T h e soil was a clay loam with 1.4 p e r c e n t o r g a n i c m a t t e r a n d a pH of 7.5. F u r r o w or ditch irrigation s u p p l e m e n t e d n a t u r a l precipitation each year.
Artificial weed mixtures were sown in soil in a 7-inch b a n d simul- taneously with planting the c r o p . T h e major weeds t h a t e m e r g e d in the u n t r e a t e d controls were r e d r o o t pigweed (Amaranthus retroflexus L.), kochia (Kochia scoparia L. Schrad.), g r e e n foxtail (Setaria viridis L.
Beauv.), foxtail millet (5. italaca), a n d b a r n y a r d g r a s s (Echinochloa crus- galli L. Beauv.). T h e primary m i n o r weeds were c o m m o n l a m b s q u a r - ters (Chenopodium album L.), black n i g h t s h a d e (Solanum nigrum L.) a n d s h e p h e r d s p u r s e {Capsella bursa-pastoris L. Medic). M o n o g e r m s u g a r b e e t seed were sown at nine seeds p e r foot of row at o n e inch soil d e p t h .
T h e chemicals evaluated were cycloate; d a l a p o n ; 2,ethoxy-2, 3 - d i h y d r o - 3 , 3-dimethyl-5-benzofuranol m e t h a n e s u l p h o n a t e (NC- 8438); p h e n m e d i p h a m ; p h e n m e d i p h a m + Ethyl m - h y d r o x y c a r b a n i - late carbanilate ( p h e n m e d i p h a m 475); a n d pyrazon. T h e y were ap- plied p r e p l a n t a n d p o s t e m e r g e n c e alone, in m i x t u r e , a n d in p r e p l a n t / p o s t e m e r g e n c e sequences.
P r e p l a n t herbicides were i n c o r p o r a t e d at t h e 1.5 inch d e p t h with a p o w e r tiller simultaneously with c r o p planting, which o c c u r r e d in early to mid-April each year. Postplant herbicides w e r e foliar-applied at early species maturity stages, mainly cotyledonary to 2-4 trueleaf stages, in early to late May. A four week delay o c c u r r e d between p r e - plant a n d p o s t e m e r g e n c e applications when herbicides were applied in sequence. Herbicide applications were m a d e at fixed a n d logarith- mic dosages in 14.1 gpa in a 7-inch b a n d over t h e row. U n d e r logarith- mic establishment, t h e r a t e r e a c h e d half-dosage at 23.5 feet in a 2-row by 100-foot plot. T h e t r a c t o r - m o u n t e d sprayer o p e r a t e d at 2.25 m p h at 32 psi with ES-4 nozzle tips. Plot size m e a s u r e d 6 rows spaced 22 inches a p a r t by 30 feet in t h e constant rate plots.
All t r e a t m e n t s w e r e placed in r a n d o m i z e d complete blocks with two replications a n d four replications for the logarithmic a n d fixed dosage trials, respectively. Plant counts were m a d e a p p r o x i m a t e l y five weeks after soil application a n d two weeks after foliar application, alone or in sequence. Observations were taken at a place in each logarithmic row estimated to have the highest p e r c e n t a g e weed control with t h e least c r o p injury (optimal response), a n d on the four inner- most rows of each fixed-dosage plot within a q u a d r a t e which m e a s u r e d 3 inches by 48 inches. Visual estimates of seedling beet r e t a r d a t i o n a n d t r e a t m e n t persistence were m a d e .
Data obtained were analyzed statistically by c o m p u t e r , a n d t h e results a r e r e p o r t e d as p e r c e n t a g e s of t h e u n t r e a t e d controls.
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R e s u l t s and D i s c u s s i o n
Weed control from cycloate
Cycloate, a p p l i e d p r e p l a n t at 3.25 or 3.5 lb/A d u r i n g 1968-72, r e s u l t e d i n 7 5 p e r c e n t a v e r a g e w e e d c o n t r o l . R e d r o o t p i g w e e d a n d small s e e d e d grass c o n t r o l r a n g e d f r o m 8 0 - 8 8 p e r c e n t , w h e r e a s kochia was t o l e r a n t (Tables 1 a n d 2). C r o p s e e d l i n g vigor a n d p r e - t h i n n i n g s t a n d w e r e u n a f f e c t e d by t r e a t m e n t .
Schweizer a n d W e a t h e r s p o o n (23) a n d Wicks a n d A n d e r s o n (32) h a v e r e p o r t e d similar results with cycloate. Earlier (1962-66), Sullivan (26) r e p o r t e d t h e ineffectiveness o f cycloate for k o c h i a c o n t r o l , a l t h o u g h g r a s s a n d s u s c e p t i b l e b r o a d l e a f w e e d s w e r e c o n t r o l l e d satisfactorily.
Weed control from NC-8438
T h e c a n d i d a t e , N C - 8 4 3 8 , a p p l i e d p r e p l a n t i n 1971-72 gave 9 0 p e r c e n t a g e points a v e r a g e weed c o n t r o l ( T a b l e s 1 a n d 2). R e d r o o t pigweed a n d grass c o n t r o l r a n g e d from 9 4 t o 9 8 p e r c e n t o f t h e u n - t r e a t e d . N C - 8 4 3 8 greatly i m p r o v e d kochia c o n t r o l w h e n c o m p a r e d t o t h e c o n t r o l o b t a i n e d with cycloate.
Pfeiffer a n d H o l m e s (21), r e p o r t i n g o n p r o p r i e t a r y trials i n m a n y c o u n t r i e s , r e v e a l e d t h a t N C - 8 4 3 8 h a d s h o w n g o o d c o n t r o l o f a n n u a l grasses a n d m a n y b r o a d l e a f w e e d s , i n c l u d i n g r e d r o o t pitweed a n d c o m m o n l a m b s q u a r t e r s . S u g a r b e e t s h o w e d a h i g h t o l e r a n c e to N C - 8 4 3 8 . T h e s e c o m p r e h e n s i v e d a t a w e r e o b t a i n e d p r i m a r i l y i n 1972, a n d they a r e c o n f i r m e d by findings in this r e p o r t (Tables 1 a n d 2). In a d d i t i o n , field o b s e r v a t i o n s h a v e i n d i c a t e d t h a t N C - 8 4 3 8 h e r b i - cidal activity has persisted l o n g e n o u g h to c o n t r o l l a t e - e m e r g i n g w e e d s , often b e y o n d t h i n n i n g .
Weed control from phenmedipham
P o s t e m e r g e n c e applications o f p h e n m e d i p h a m c o n t r o l l e d kochia a n d grass, a l t h o u g h r e d r o o t p i g w e e d was t o l e r a n t (Tables 1 a n d 2).
C r o p injury was m i n i m a l d u r i n g f i v e application years. P r i o r evalua- tion o f p h e n m e d i p h a m h a d revealed s o m e c o n t r o l o f kochia (31).
Weed control from cycloate/phenmedipham sequence
P r e l i m i n a r y 1968 trail results from this s e q u e n c e w e r e r e p o r t e d by Scott a n d B a t e m a n (24) a n d by Sullivan (28).
Results o b t a i n e d f r o m seven trials, established d u r i n g 1968-72, indicate almost c o m p l e t e weed c o n t r o l from cycloate a p p l i e d p r e p l a n t followed by p h e n m e d i p h a m a p p l i e d p o s t e m e r g e n c e ( T a b l e s 1 a n d 2).
N e v e r t h e l e s s , c o m p u t a t i o n s reveal t h a t 9 5 p e r c e n t w e e d r e d u c t i o n
1Averages for redroot pigweed, kochia, common lambsquarters, black nightshade and shepherdspurse.
2Averages for foxtails and barnyardgrass.
Table 1.—Response of sugarbeet to preplant and postemergence herbicides alone and in sequences applied at fixed dosages, 1968-72.
Table 2.—Response of sugarbeet to preplant and postemergence herbicides alone and in sequences applied at logarithmic dosages, 1968-72.
1Citowett surfactant added to pyrazon + dalapon.
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permits 2.5 weeds to survive w h e n 50 weeds p e r s q u a r e foot exist before t r e a t m e n t . U n d e r a m o r e n o r m a l weed p o p u l a t i o n density of 25 representative weeds, a single weed would r e m a i n for each 10 feet of row within the row area e x p o s e d to n o r m a l cultivation.
It is interesting to n o t e that t h e c y c l o a t e / p h e n m e d i p h a m s e q u e n c e was r e c o m m e n d e d for grower use in C o l o r a d o with cycloate applied at r e d u c e d dosages in 1970 (27). Bray (7) a n d Short (25), a m o n g o t h e r workers, have shown that p r e e m e r g e n c e herbicide d o s a g e may be r e d u c e d by 25 p e r c e n t when followed by p h e n m e d i p h a m .
Schweizer a n d W e a t h e r s p o o n (23) a n d N o r r i s a n d O r r (20) h a d r e p o r t e d that weed control from t h e s t a n d a r d system cycloate/pyrazon + d a l a p o n was insufficient to p r o v i d e c r o p protection until t h i n n i n g time. Data shown in Table 2 a n d elsewhere (28, 30, 32) for pyrazon + d a l a p o n a n d the cycloate sequence reveal this inadequacy in semi-arid regions, particularly on kochia a n d r e d r o o t pigweed. In practice, t h e c y c l o a t e / p h e n m e d i p h a m sequence has p r o v e n s u p e r i o r , particularly w h e n sugarbeet is machine t h i n n e d .
Early work in E u r o p e has shown the practical effectiveness of c o m p l e m e n t a r y t r e a t m e n t s , including p h e n m e d i p h a m . For e x a m p l e , research on pyrazon or l e n a c i l / p h e n m e d i p h a m , c h l o r o p r o p h a m + p r o p h a m 4- f e n u r o n / p h e n m e d i p h a m , a n d p y r a z o n + d i a l l a t e / p h e n m e d i p h a m has commercial acceptance (2, 6, 12, 13, 14).
C u r r e n t work (5, 11, 15, 17, 25, 30) on diallate or lenacil/phen- m e d i p h a m , cycloate + l e n a c i l / p h e n m e d i p h a m , p y r a z o n + T C A / pyrazon + p h e n m e d i p h a m , d i a l l a t e / p y r a z o n / p h e n m e d i p h a m shows p r o m i s e .
Weed control from NC-8438/phenmedipham and other new systems In 1971-72, complete weed control was obtained from several herbicide sequences containing NC-8438 applied in split application with p r e p l a n t a n d postplant herbicides at n o r m a l dosages (Table 1).
In particular, kochia was chemically controlled, which h e r e t o f o r e was impossible with o t h e r herbicides a n d chemical w e e d i n g systems. T h i s favorable control was caused by t h e c o m p l e m e n t a r y effect o b t a i n e d from c o m b i n i n g N C - 8 4 3 8 a n d p h e n m e d i p h a m in timed s e q u e n c e . Each chemical alone provided 75-80 p e r c e n t control of kochia (Table 1).
S u g a r b e e t h a d a high tolerance for these p r o m i s i n g sequences, except for s o m e t e m p o r a r y seedling r e t a r d a t i o n which was soon over- c o m e . Field observations showed that chemical w e e d i n g persistence r e m a i n e d active until the c r o p canopy covered the rows, a n d t h e N C - 8438 sequences h a d no adverse affects on c r o p yield or s u g a r c o n t e n t . Similar studies, applied at logarithmic doses, gave similar results on r e d r o o t pigweed a n d grass, a l t h o u g h kochia control was s o m e w h a t
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less ( T a b l e 2). A p p a r e n t l y , d o s a g e a n d r e s p o n s e is m o r e critically r e l a t e d on hard-to-kill species s u c h as kochia. T h e r e f o r e , in practice it a p p e a r s p r u d e n t — e s p e c i a l l y in surface i r r i g a t e d r e g i o n s — t o r e c o m - m e n d s e q u e n c e d o s a g e s t h a t e n s u r e kill o f t h e less susceptible species, w h e t h e r o r n o t s o m e slight c r o p injury o c c u r s i n practice.
P o s t e m e r g e n c e weed c o n t r o l f r o m N C - 8 4 3 8 + p h e n m e d i p h a m a n d its p o s t p l a n t u s a g e , especially in split a p p l i c a t i o n with N C - 8 4 3 8 a p p l i e d p r e p l a n t , gave p r o m i s i n g results ( T a b l e 2).
Summary and C o n c l u s i o n s
P r o g r e s s i v e s t u d i e s c o n d u c t e d o n c h e m i c a l w e e d i n g systems d u r i n g 1968-72 indicate that cycloate a n d N C - 8 4 3 8 / N C - 8 4 3 8 a n d p h e n m e d i p h a m herbicides a r e c o m p l e m e n t a r y w h e n a p p l i e d i n se- q u e n c e s . C h e m i c a l w e e d i n g systems c o n t a i n i n g N C - 8 4 3 8 a n d p h e n - m e d i p h a m s u r p a s s e d t h o s e consisting of cycloate, p y r a z o n + d a l a p o n , a n d p h e n m e d i p h a m .
T h e s e studies suggest that early c h e m i c a l p e r s i s t a n c e from d u a l h e r b i c i d e application, at c o m p a r a t i v e l y low d o s a g e i n p u t s w i t h o u t s u p p l e m e n t a l tillage, a n d c r o p c o m p e t i t i o n f o r m s t h e a d v a n c e design for chemical w e e d i n g o n s u g a r b e e t . F u t u r e w e e d i n g systems m u s t p r o v i d e technical simplicity in practice, c o m p l e t e reliability, a n d a r e d u c t i o n in p r o d u c t i o n costs.
A c k n o w l e d g m e n t s
A p p r e c i a t i o n is e x p r e s s e d to P. J. D e c k e r , T. L. Dollerschell, L. K. Fagala, T. R. O ' H a r e , D. R. R a d e m a c h e r , a n d C. G. Ross for field assistance in c o n d u c t i n g these e x p e r i m e n t s .
A c k n o w l e d g m e n t i s d u e B A S F W y a n d o t t e C o r p o r a t i o n , Dow C h e m i c a l C o m p a n y , F i s o n s C o r p o r a t i o n , N o r - A m A g r i c u l t u r a l P r o d u c t s , Inc., a n d t h e Stauffer C h e m i c a l C o m p a n y for s u p p l y i n g t h e h e r b i c i d e s u s e d in t h e s e studies.
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