20 ANNUAL REPORTS OF DEPARTMENT OF AGRIC1 LTURE, 1952 
of expected injury based upon studies of factor.- affecting beet leaf- 
hopper populations during the 10-year period 1941-4>0. Since the 
conditions of this experiment required that all of the heavily infested 
weed areas be treated with the insecticide, it was not possible to leave 
an unt reated area of such weeds to serve as a check. 
Similar results had been obtained in L950. Aa a result of spraying 
approximately 15,000 acres of the spring breeding area- wit ! i DDT 
emulsion, the number of bean plants infected with curly-top dis 
in 1950 was reduced from an expected 17 -J percent to an observed 9.6 
percent. 
It has thus been demonstrated in two consecutive year- that the 
application of a DDT emulsion spray to heavily infested weed host 
plants in breeding areas of the beet leafhopper in southern Idaho 
will reduce the numbers of this pest sufficiently to result in an im- 
portant decline in the percentage of garden bean seed plant- infi 
by curly-top disease in adjacent or nearby areas. Satisfactory equip- 
ment and methods for applying the insecticides were also developed. 
Since the research objectives of this project appear to have been 
accomplished, the work was discontinued in the fall of 1951. 
Control of Beet Leafhopper on Sugar Beets Requires 
Proper Timing 
Two series of experiments were carried on in southern Idaho on 
the direct control of the beet leafhopper on sugar beets. The first 
series, consisting of five experiments, was designed to protect suirar 
beet plants from curly-top infection during the seedling stage, the 
period of greatest susceptibility. DDT was the only insecticide used, 
and it was applied at a dosage of 1.5 pounds of toxicant per acre, per 
application, in 30 gallons of spray. The number of applications 
ranged from 2 to 6. The average gains in yields of sugar beet-, over 
the checks, as a result of the insecticide treatment for experiments 
1 to 5 wci-e 1.1, 2.5, 1.1, 1.6, and 1.3 tons, respectively, per acre. The 
monetary value of this increase at $13 per ton for beets amounted 
to $14.30, $32.50, $14.30, $20.80, and $16.90, respectively, per acre. 
A study of the results disclosed that there seemed to be no correlation 
between the number of application- and increased yields. Evidently 
the timing in relation to the movement of leaf hoppers into the beet 
tields was more important than the number of application-. 
The second series of experiments to control beef leafhoppers on 
sugar beets was designed to reduce spring-generation beef leafhopper 
populations at the peak of their movement from their breeding areas 
to the beets. Ml >T was applied at a dosage of 2.4 pound- of toxicant 
in 5 gallons of spray per acre in two beet fields. The heavy flight 
of beef leafhoppers into the beet fields occurred from June 11 to -J*), 
when sl percent of the leafhoppers moved in. The timing of the 
Insecticide application was uear the peak of the movement. The 
average gain in yield of sugar beets, over the check, as a result of the 
insecticide treatmenf in both fields, was 2.9 ton- per acre. The mon- 
etary value of this increase at $13 per ton for beets amounted to 
$37.70 pel" acre. 
