The Control of Annual Grasses in Sugar Beets
PROCEEDINGS—EIGHTH GENERAL MEETING 125
experiment stations in 1953) compared to the sodium salt of TCA. Sodium TCA is Cl3CCOONa. Sodium dalapon is CH3Cl2CCOONa. Except for the substitution of a methyl group for a chlorine atom on the No. 2 carbon, these compounds are the same. Yet TCA can be absorbed through the roots only whereas dalapon is absorbed through both leaves and roots. Dalapon has been found by results of single oral acute experiments to be less toxic to warm-blooded animals than table salt. T h e sodium salt, which will be the first formulation to be marketed, is readily soluble in water.
At the rates required for annual grass control, contact burn usually does not occur; however, it may develop on the margins of both broad- leaves and grasses under conditions of high temperature. T h e killing action on grasses is first manifested 2 to 3 weeks after spraying as necrosis of blade margins, which gradually progresses downward to the crown of the plant in 7 weeks. This is the time usually required for ultimate kill, although young seedling grasses may succumb in 3 to 4 weeks.
One of the first crops considered for selective treatments with this chemical was sugar beets. T h e first applications were made in the summer of 1952 to beets in various growth stages where watergrass was a problem.
Observations of these plots indicated the following: 1. T h e dosage for control of grasses was in the range of 3 to 6 pounds per acre. 2. Although the beet top growth was suppressed for a few weeks, at harvest time there were no observable differences between the treated and untreated plots.
With this encouragement, plans for the 1953 season were made to con- firm the findings of our 1952 work and in addition to determine: 1. Effect of dalapon on the yield of beets. 2. Optimum volume rate. 3. Relation- ship of growth stage of grasses to dosage. 4. Effect of environmental con- ditions such as temperature and soil moisture.
T h e yield plots were uniform beets which received normal culture including good non-chemical weed control. Applications were made at two growth stages—just after thinning and about 5 weeks later—both as sep- arate and repeat sprays. One experiment was applied to beets in the 2-leaf stage with the second and repeat sprays after thinning. Two or three samples per plot were collected for sucrose analysis and processed by the appropriate company laboratories.
T h e dosage required for control of watergrass under conditions favor- able to the action of dalapon is in the range of 3 to 5 pounds sodium salt per acre, as shown in Table 1.
T h e dosage rates specified are based on excellent wetting (film type) of grass blades. It has been found that dalapon is much more efficient with
T a b l e 1.—Control o f Watergrass i n Sugar Beets w i t h D a l a p o n . S o d i u m d a l a p o n Estimated °f0 control
lbs. per acre E x p t . 1 E x p t . 2
— — —
3.5 96
4.7 9 2 93 7.0 99
In T a b l e 2 we c a n see t h a t t h e c o n t r o l s at g i v e n dosages a r e essentially e q u a l a t t h r e e g r o w t h stages i r o m s e e d l i n g t o s t o o l i n g . E x p e r i m e n t s 1 a n d 2 w e r e i m m e d i a t e l y a d j a c e n t ; 3 was in a n o t h e r field b u t in all t h r e e t h e beets, a n d c o n s e q u e n t l y t h e grasses, w e r e m a i n t a i n e d i n g o o d g r o w t h d u r i n g t h e season. T h e i n f o r m a t i o n o n t e m p e r a t u r e s shows t h a t over this r a n g e t h e r e is no a p p a r e n t difference in t h e c o n t r o l of grasses.
Table 2.—Effect of Temperature and Size of Grass on Control with Sodium Dalapon.
T h e influence o f soil m o i s t u r e o n c o n t r o l was i n d i c a t e d i n a n e x p e r i - m e n t in w h i c h , at t h e t i m e of t h e first a p p l i c a t i o n a n d for a few days after- wards, t h e g r o w e r w i t h h e l d i r r i g a t i o n t o r e t a r d t h e g r o w t h o f t h e grass.
T h i s was effective in r e d u c i n g t h e vigor of t h e grass. Very p o o r c o n t r o l w i t h d a l a p o n o c c u r r e d , w h i c h m a y h a v e b e e n because t h e grasses w e r e u n d e r m o i s t u r e stress.
R e s u l t s o f tests t o d e t e r m i n e t h e o p t i m u m v o l u m e r a t e for d a l a p o n sprays r e v e a l e d no differences in t h e r a n g e of 100 to 12.5 g p a , as s h o w n i n T a b l e 3 . I n selecting t h e r a t e o f s u r f a c t a n t t o b e used i n t h e v o l u m e r a t e tests, it was d e c i d e d to use an i n t e r m e d i a t e scale b e t w e e n p e r c e n t solu- t i o n a n d c o n s t a n t a m o u n t p e r acre.
126 A M E R I C A N S O C I E T Y O F SUGAR B E E T T E C H N O L O G I S T S
a g o o d s u r f a c t a n t . C u r v e s ( F i g u r e 1) h a v e b e e n d r a w n for a n o t h e r ex- p e r i m e n t , w h i c h show t h e i m p r o v e m e n t in a c t i o n of d a l a p o n at a given dosage p e r acre w i t h g o o d w e t t i n g a c t i o n after 27 days.
F i g u r e 1.—Effect of s u r f a c t a n t s on a c t i o n of d a l a p o n .
P R O C E E D I N G S — E I G H T H G E N E R A L M E E T I N G 127 Table 3.—A Comparison of Volume Rates Using Dalapon in Grass Contol.
T h e degree to which the beets will recover from dalapon treatments appears to be a function of time to harvest. Therefore, it may be advan- tageous to allow as much time as possible after treatment before digging the crop. Beets in seedling stage are not more sensitive than at later periods.
Although the work reported here in connection with sugar beets is concerned with only water grass (Echinochloa crusgalli) , research on other projects indicates that a wide variety of annual grasses, both winter and summer, can be controlled with the dosages of dalapon specified above.
Factors relating to environment, surfactants, volume rates, etc., appear to apply as well to these other species.
T h e influence of environmental factors such as temperature, soil and air moisture and soil fertility appears to be important because they influence the growth conditions of the grasses. It seems reasonable that translocation and assimilation would be faster and more effective when the plant is growing vigorously, as is found with 2,4-D on broadleaved plants. There-
T h e r e s u l t s o f s t u d i e s t o d e t e r m i n e w h e t h e r d a l a p o n i n f l u e n c e s t h e y i e l d o f s u g a r b e e t s a r e s u m m a r i z e d i n T a b l e 4 . I t i s r e a d i l y s e e n t h a t s u c r o s e p e r c e n t a g e i s n o t affected b y a n y o f t h e s e t r e a t m e n t s . N e i t h e r d o e s t h e w e t t i n g a g e n t i n f l u e n c e a n y o f t h e r e s u l t s . T h e r e f o r e , t h e o n l y con- s i d e r a t i o n is t h e effect of d a l a p o n on t h e size of t h e b e e t s . A n a l y s e s of v a r i a n g e o f t h e s e d a t a i n d i c a t e t h a t t h e f o l l o w i n g t r e a t m e n t s m a y r e d u c e s u g a r b e e t y i e l d s s i g n i f i c a n t l y ; 1 . R a t e s o v e r 4 p o u n d s s o d i u m d a l a p o n p e r a c r e . 2 . R e p e a t a p p l i c a t i o n s o f 4 p o u n d s o r m o r e p e r a c r e e a c h t i m e .
Table 4.—Effect of Sodium Dalapon on Yield of Sugar Beets.
128 A M E R I C A N S O C I E T Y O F SUGAR B E E T T E C H N O L O G I S T S
fore, i t m a y b e d e s i r a b l e t o a p p l y d a l a p o n d u r i n g p e r i o d s o f v i g o r o u s grass g r o w t h . I f soil m o i s t u r e i s a d e q u a t e a n d o t h e r e n v i r o n m e n t a l factors a r e favorable, g r o w t h is m o s t r a p i d from s e e d l i n g to early s t o o l i n g of t h e grass.
Practices w h i c h m a i n t a i n t h e beets i n g o o d g r o w i n g c o n d i t i o n w o u l d favor t h e grass a s well, s o t h e c u l t u r a l o p e r a t i o n s w o u l d n o t n e e d t o b e c h a n g e d t o a c c o m m o d a t e t h e d a l a p o n a p p l i c a t i o n .
U n d o u b t e d l y a p p l i c a t i o n s s h o u l d n o t b e m a d e a few days before o r after b l o c k i n g a n d t h i n n i n g b e c a u s e o f t h e stress this d i s t u r b a n c e places o n t h e y o u n g beets.
A l t h o u g h o b s e r v a t i o n s t o d a t e i n d i c a t e t h a t t e m p e r a t u r e does n o t in- fluence a c t i o n o f d a l a p o n e x c e p t t o cause m a r g i n a l leaf b u r n i n h o t w e a t h e r , it is q u i t e possible t h a t a t e m p e r a t u r e stress m a y r e d u c e t h e c o n t r o l .
T h e yield d a t a i n d i c a t e t h a t care will h a v e t o b e exercised i n a p p l y - i n g d a l a p o n to sugar beets. Since these w e r e o v e r a l l sprays, it is difficult t o d e t e r m i n e w h e t h e r d a l a p o n i s a b s o r b e d b y t h e b e e t m o r e r e a d i l y t h r o u g h t h e leaves o r t h e r o o t s . Surface i r r i g a t i o n following a p p l i c a t i o n w o u l d carry c h e m i c a l o n t h e soil surface i n t o t h e r o o t z o n e easily. H o w e v e r , i n t h e first t w o e x p e r i m e n t s , t h e b e e t leaves at t h e second a p p l i c a t i o n f o r m e d a n e a r l y c o m p l e t e c a n o p y over t h e soil surface. T h e r e f o r e , since m o s t of t h e spray p r o b a b l y r e m a i n e d o n t h e leaves, a n d t h e yields a t this t i m e w e r e r e d u c e d a s m u c h a s o r m o r e t h a n e a r l i e r t r e a t m e n t s , i t c a n b e a s s u m e d t h a t d a l a p o n is a b s o r b e d t h r o u g h b e e t foliage in sufficient a m o u n t s to affect g r o w t h .
A l t h o u g h d a l a p o n i s u n d o u b t e d l y a b s o r b e d t h r o u g h t h e foliage o f beets, i t was e v i d e n t t h a t yields w e r e e q u a l w h e t h e r o r n o t a w e t t i n g a g e n t was i n c l u d e d i n t h e sprays. U n d o u b t e d l y , this i s because p l a i n w a t e r carriers s p r e a d r e a d i l y over t h e b e e t leaves a n d t h e w e t t i n g a g e n t does n o t de- cidedly e n h a n c e e i t h e r t h e s p r e a d i n g o r p e n e t r a t i n g q u a l i t i e s o f t h e d a l a p o n s o l u t i o n . T h e r e f o r e , since i t h a s b e e n s h o w n t h a t g o o d surface active a g e n t s i m p r o v e t h e a c t i o n of d a l a p o n on grasses, it is d e s i r a b l e to use a g o o d w e t t i n g spray for this a p p l i c a t i o n .
Because of t h e r e d u c t i o n in yield w i t h o v e r 4 p o u n d s of d a l a p o n p e r acre, it b e c o m e s d e s i r a b l e to c o n s i d e r t h e effect of t r e a t m e n t s u s i n g 2 to 4 p o u n d s . F i g u r e 1 shows t h a t g o o d c o n t r o l is possible w i t h dosages of 3 p o u n d s p e r acre. T w o p o u n d s p e r acre c o u l d b e q u i t e effective i n r e l i e v i n g t h e s t r a i n o n t h e t h i n n i n g crew. W h e r e l a t e r g e r m i n a t i o n o f grasses i s likely, a timely a p p l i c a t i o n of 3 p o u n d s of d a l a p o n to t h e l a t e r c r o p of grass m a y benefit t h e beets m o r e t h a n a n e a r l i e r t r e a t m e n t . I t i s p o s s i b l e t h a t t r e a t m e n t o f s e e d l i n g grass a t sub-lethal b u t g r o w t h r e t a r d i n g r a t e s followed by sprays of l e t h a l dosages on r e g r o w t h of t h e grass w o u l d p r o v i d e effective c o n t r o l a n d still n o t r e d u c e t h e b e e t yield.
O t h e r possibilities o f r e d u c i n g t h e effect d a l a p o n m i g h t h a v e o n t h e c r o p i n c l u d e p l a c e d sprays. T h e b e e t s a r e s h i e l d e d a n d / o r t h e spray di- r e c t e d to c o n t a c t o n l y as m u c h of t h e b e e t p l a n t s as is necessary to cover t h e grasses a d e q u a t e l y . G o o d a p p l i c a t i o n t e c h n i q u e s a r e always i m p o r t a n t a n d h e r e , i n a d d i t i o n t o t h e types o f s p r a y i n g m e n t i o n e d a b o v e , i t i s desir- a b l e t o a t t e m p t t h e b e s t possible coverage o f t h e weeds. R e a s o n a b l y f i n e sprays u s u a l l y a c c o m p l i s h this p u r p o s e best.
PROCEEDINGS—EIGHTH GENERAL MEETING 129 Conclusions reached from data available are as follows:
1. Dosage of 3 to 4 pounds sodium dalapon per acre was required for control of watergrass. (Research is necessary on other grasses.)
2. When grasses were growing well, dosage required was same from seedling to early stooling stage.
3. Above dosage rates assume excellent wetting of grasses.
4. Maximum effect of dalapon on grasses required 6 to 8 weeks.
5. Severe soil moisture stress reduced grass control.
6. Temperature in range of 55° F. to 100° F. had no effect on control.
7. Controls were same for volume rates from 100 to 12.5 gpa.
8. Addition of surfactant did not affect yield.
9. Sucrose percentage was not affected by dalapon at 2 to 7 pounds per acre.
10. Yields were reduced by sodium dalapon applied as follows:
a. More than 4 pounds per acre.
b. More than one application of 4 pounds or more per acre.
Much more research is necessary before dalapon can be recommended to control grasses in sugar beets. Some of these projects are as follows:
1. Effect of sodium dalapon at 2 to 4 pounds per acre on yield. (Higher rates may be desirable in some areas.)
2. Use of placed and shielded sprays.
3. Relationship of volume rate to control and yields.
4. Influence of various times between treatment and harvest.
5. More data on effects of environmental factors, particularly growth stresses on control and yield.
6. More data on value of repeat sprays to control:
a. T h e first crop of grass to be treated.
b. Succeeding germinations of grasses.
7. Effect of dalapon in the soil on germinating beet seedlings.
8. Presence or absence of dalapon residue in soil and crop at harvest.
9. Differences of beet varieties in response to dalapon.
10. Best types of surfactants.
Dalapon will be recommended in 1954 only for non-crop grass control.
It will be marketed as the sodium salt with some wetting agent added. Under some circumstances this may be insufficient to provide the best wetting and additional surfactants will be desirable. Experimental formulations of sodium dalapon without wetting agent will be available for research purposes.
Literature Cited
(1) Dalapon Bulletins Nos. 1 and 22, T h e Dow Chemical Company.