O R I N A. H I L L S , F. H. H A R R I E S , AND A. C. VALCARCE2
C o n t r o l of the beet leafhopper is essential on susceptible varieties of sugar beets grown for seed in the Southwest. T h i s was originally accom- plished with a pyrethrum-in-oil spray (1)3, b u t D D T has b e e n the accepted m e t h o d since it became available in 1945 (2) . D D T r e m a i n s active for some time on the larger plants, killing l e a l h o p p e r s t h a t may move into the field after a p p l i c a t i o n . However, control is m o r e difficult on cotyledon a n d two-leaf beets because of lack of sufficient foliage to h o l d the insect- icides. Seedlings are also m o r e susceptible to curly top t h a n the larger p l a n t s . R e c e n t research has, therefore, been directed toward the develop- m e n t of better m e t h o d s for controlling the beet l e a f h o p p e r on these seed- ling beets.4. T h i s work is still in progress a n d the results p r e s e n t e d in this p a p e r should be considered a progress r e p o r t .
In the last few years several systemic insecticides have passed the ex- p e r i m e n t a l stage a n d are on the m a r k e t . P r o b a b l y the o n e best k n o w n is D e m e t o n (in. Systox) . T h e s e insecticides e n t e r the circulatory system of the p l a n t , causing the juices to be toxic to certain insects. T h e insecticide may be i n t r o d u c e d i n t o the soil with the irrigation water or a p p l i e d as a foliage spray. R e c e n t tests at P h o e n i x , Arizona, have also shown t h a t some of these insecticides are effective for considerable time if the seed is treated before p l a n t i n g .
Greenhouse Tests
In the Salt R i v e r Valley of Arizona, sugar beets grown for seed are p l a n t e d in late August or September. In a n t i c i p a t i o n of field-plot experi- ments, tests were m a d e in the g r e e n h o u s e d u r i n g the s p r i n g a n d summer on sugar beets grown in pots or flats.
Insecticides i n c l u d e d in these studies were the p h o s p h o r o u s compounds, D e m e t o n , Schradan, a n d A m e r i c a n C y a n a m i d 3911 a n d 12008. Emulsions of these materials were tested as soil drenches a n d p r e p l a n t i n g seed treat- ments. Dusts, p r e p a r e d by American C y a n a m i d to c o n t a i n 50 percent of 3911 or 12008 on p o w d e r e d carbon, were also tested as seed coatings. The dosages for seed t r e a t m e n t were calculated on the basis of 15 p o u n d s of seed p e r acre.
Soil Applications.
T h e first of these tests was with soil drenches. P o t t e d p l a n t s were irri- gated with water c o n t a i n i n g various insecticides a n d later leafhoppers were confined on the leaves in a special type of leaf cage. Each cage contained o n e leaf on which 10 leafhoppers were confined for 24 hours. Treatments were at the a p p r o x i m a t e rates of 8 a n d 16 p o u n d s of t h e active ingredient p e r acre. T h e e i g h t - p o u n d r a t e was a d e q u a t e , a n d no a d d i t i o n a l benefit was i n d i c a t e d for the h i g h e r dosage. As shown in Figure 1, b o t h American
1 In cooperation with the Arizona Agricultural Experiment Station.
2 Entomologists, Entomology Research Branch, A.R.S., U. S. Department of Agriculture, Phoenix, Arizona.
3 Numbers in parentheses refer to literature cited.
4 T h e beet plots on which these experiments were conducted were furnished by the West- ern Seed Production Corporation.
VOL. IX, No. 2, JULY 1956 125 Gyanamid 3911 and 12008 killed practically all the leafhoppers caged on the plants throughout the experiment, whereas the effectiveness of Demeton d r o p p e d off rapidly after about 20 days, but was superior to Schradan.
Seed T r e a t m e n t .
Tests were also made to determine the effectiveness of seed treatment in the control of leafhoppers on seedling plants. In one test the seed was soaked for 30 minutes in one-percent emulsions of the same materials used in the soil-drench tests. O n e leafhopper per plant was caged on 25 plants receiving each treatment when the beets were in the four-leaf stage. All the treatments gave good leafhopper control, as shown by the following mortalities:
In a n o t h e r test, the seed was coated with carbon dusts impregnated to contain 50 percent of American Cyanamid 12008 or 3911. By tumbling
1 2 6 J O U R N A L OF T H E A. S. S. B. T.
in a revolving d r u m for 15 m i n u t e s , a p p r o x i m a t e l y 1.1 ounces of the im- p r e g n a t e d dust could be m a d e to a d h e r e to o n e p o u n d of seed T h e s e seeds were p l a n t e d in six-inch pots a n d all leafhoppers, caged on the p l a n t s 35 days later, died in 24 hours.
Some of the p l a n t s from treated seed showed growth abnormalities, therefore, a series of tests was m a d e to d e t e r m i n e the p l a n t tolerance of these materials. Seed was treated with various a m o u n t s of 12008 or 3911 in 50 p e r c e n t carbon dusts or various emulsion d i l u t i o n s . T h e emulsions were first used as seed soaks, by which the seed was soaked for 30 minutes in emulsions c o n t a i n i n g 0.5, 1, a n d 5 p e r c e n t of the insecticide. T h e r e was some indication t h a t the five-percent emulsion reduced the viability of the seed and also caused a high p e r c e n t a g e of a b n o r m a l plants. O w i n g to difficulties in t r e a t m e n t a n d h a n d l i n g of the wet seed, this m e t h o d was soon a b a n d o n e d . It was found t h a t a t h o r o u g h d i s t r i b u t i o n of l i q u i d materials could be o b t a i n e d in a revolving d r u m m i x e r by using only e n o u g h water to d a m p e n the seed (1 gallon to 15 p o u n d s of seed) a n d the q u a n t i t y of t h e active i n g r e d i e n t a p p l i e d to t h e seed could be m o r e accurately deter- m i n e d . A l t h o u g h the seed was n o t so wet as w h e n treated by the soak m e t h o d , there was still the p r o b l e m of drying it before p l a n t t i n g .
Since the previous tests h a d shown the two materials to be equally effective against t h e leafhopper, only 12008 was used in the m o r e concen- trated emulsions. T r e a t m e n t s were m a d e at rates of 1/4, 1/2, 1, a n d 2 pounds to 15 p o u n d s of seed. At 14 p o u n d , the viability of the seed was satisfactory a n d p l a n t s a p p e a r e d n o r m a l , except for a slight c u p p i n g of some of the cotyledons shortly after emergence. At 1/2 p o u n d , seed viability was con- siderably r e d u c e d a n d at 1 a n d 2 p o u n d s , n o n e of t h e seeds germinated.
It was therefore concluded, t h a t by this m e t h o d , any dosage above 14 pound to 15 p o u n d s of seed was n o t safe.
Plant-tolerance tests with carbon dusts i m p r e g n a t e d to c o n t a i n 50 p e r c e n t of American C y a n a m i d 12008 or 3911 were m a d e at 1/8,, 1/4, 1/2, 3/4, a n d 1 p o u n d of the active i n g r e d i e n t on 15 p o u n d s of seed. Viability of the seed was unaffected up to 3/4 p o u n d , b u t materially r e d u c e d at the 1-pound rate. No a b n o r m a l p l a n t s resulted from the 1/8- or 1/4-pound treat- m e n t , b u t a p p r o x i m a t e l y one-third of the p l a n t s a p p e a r e d a b n o r m a l in the 14-pound t r e a t m e n t a n d from 63 to 100 p e r c e n t in t h e 3/4- a n d 1-pound t r e a t m e n t s . T h e a b n o r m a l i t i e s in the 1/2-pound t r e a t m e n t seemed to be confined to the cotyledon a n d two-leaf stages a n d as the p l a n t s developed these symptoms d i s a p p e a r e d .
Field Tests
In t h e fall of 1955, field tests with t r e a t e d beet seed were m a d e on a series of small plots a n d also on two five-acre plots. T h e rates used on the five-acre plots were w i t h i n t h e r a n g e considered safe from t h e greenhouse tests, b u t in some of the small plots, they were somewhat higher, although no adverse effects developed.
Small Plots.
T h e s e plots consisted of four rows of beets 35 feet long. T h e seeds were treated with American C y a n a m i d 12008 or 3911 in t h r e e ways: (A) in 50-percent i m p r e g n a t e d c a r b o n dust, (B) in emulsions at t h e r a t e of one gallon to 15 p o u n d s of seed, a n d (C) in an emulsion spray directed into t h e seed row before the seeds were covered. Special e q u i p m e n t was con-
V O L . IX, N o . 2, J U L Y 1956 127
T h e results are given in T a b l e 1. At the two-leaf stage, some mortality was indicated for most of the treatments. Seed treated with the 50-percent carbon dusts produced better results than did seed treated with the emulsions.
Good results were also indicated from spraying directly into the seed row, b u t two p o u n d s of the active ingredient were required to produce: about the same results as were obtained with 1/2 p o u n d when applied in carbon dust on the seed. By the time the plants had reached the four-leaf stage, considerable toxicity to the leafhoppers was lost, b u t there were still some mortalities due to treatment. These data indicate that, after the two-leaf stage, the effectiveness of the treatment rapidly declines.
Large Plots.
T w o five-acre plots of seed beets were planted with treated seed on a commercial field. A beet variety resistant to curly top was chosen, so that .leafhopper populations could be observed on both treated a n d u n t r e a t e d structed for the last treatment by m o u n t i n g a spray nozzle directly behind the p l a n t i n g shoe of the planter. The rate of application was set at 13 gallons per acre and the desired quantity of the active ingredient was then diluted with water to 13 gallons.
Each treatment was replicated three times and its effectiveness was determined by caging leafhoppers on plants in the two-leaf and four-leal stages of development, or 10 and 18 days after emergence of seedlings. In the two-leaf stage glass-vial clip cages were attached to the leaves of four plants on each plot and five beet leafhoppers placed in each cage to make a total of 60 leafhoppers per treatment. When the plants reached the four-leaf stage, cylindrical cloth-covered cages 3 1/2 by 7 inches were used, each cage enclosing two or three plants. Three of these cages were placed on each plot and 25 leafhoppers were placed in each cage to make a total of approximately 225 leafhoppers per treatment. After the cages had re- mained on the plants for 18 hours, they were removed and the leafhopper mortality determined.
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Table 2.—Numbers of Beet Leafhoppers per Foot of Row on Five-Acre Plots in Different Stages of Development in Which Seeds Were Treated With American Cyanamid 12008.
p o r t i o n s of the field without the complication of commercial control with D D T . On o n e plot, the seeds were treated with an emulsion of American C y a n a m i d 12008 at the r a t e of 1/4 p o u n d p e r acre (15 p o u n d s of seed) and on the o t h e r plot with 12008 in an i m p r e g n a t e d carbon dust at 1/2 pound p e r acre. 'The n u m b e r s of leafhoppers p e r foot of row as d e t e r m i n e d with a c o u n t i n g cage are given in T a b l e 2. G o o d results were o b t a i n e d w i t h both treatments. In fact, p o p u l a t i o n s t h r o u g h o u t the season on the plots grown from treated seed were well below w h a t m i g h t be considered an economic level, whereas on t h a t p o r t i o n of the field grown from u n t r e a t e d seed they were so high t h a t the field would have been dusted for leafhopper control h a d it n o t been a curly-top resistant variety.
Discussion
A l t h o u g h this p a p e r reports only o n e season's work, the data indicate t h a t it is possible to o b t a i n control of the beet leafhopper on seedling beets by t r e a t i n g the seed before p l a n t i n g . T h e y further indicate t h a t beet p l a n t s grown from treated seed may r e m a i n sufficiently toxic to the leaf- h o p p e r to protect t h e m t h r o u g h the four-leaf stage, which in the Salt River Valley would be a b o u t two weeks after the seedlings emerge. It is probable that in m a n y instances no further control would be n e e d e d .
Observations on b o t h large a n d small plots indicate t h a t seed treat- m e n t with e i t h e r American C y a n a m i d 12008 or 3911 gives some protection against l e p i d o p t e r o u s larvae in p l a n t s in the cotyledon a n d two-leaf stages.
Heavily infested fields would p r o b a b l y have to be dusted once later, but protection to the small p l a n t s shortly after emergence could p r e v e n t the loss of stands.
Summary
G r e e n h o u s e tests with several systemic insecticides showed t h e m to be toxic to the beet leafhopper, b o t h as a soil d r e n c h a n d as a seed treatment.
Field tests in small plots and in five-acre commercial p l a n t i n g s showed that seed t r e a t m e n t with the p h o s p h o r o u s c o m p o u n d s American C y a n a m i d 12008 a n d 3911 would protect the seedling p l a n t s for at least two weeks after their emergence.
References
(1) H I L L S , O R I N A., M A S T , A. A., a n d W O O D , R . C. 1948. F i e l d insecticide tests against the beet l e a f h o p p e r in sugar beets grown for seed.
Amer. Soc. Sugar Beet T e c h . Proc. p p . 298-318.
(2) R O M N E Y , V A N E. 1943. T h e beet l e a f h o p p e r a n d its control on beets grown for seed in Arizona a n d N e w Mexico. U. S. D e p t . Agr. Tech.
Bul. 855, 24 p p .