316 
Journal of Agricultural Research 
Vol. XXVIII, No. 4 
A third possible way in which the virus may be carried over winter is in old 
diseased plants growing in or near beet fields. In almost every old beet field 
such plants can be noted as making renewed growth in the spring. Frequently 
such plants are affected with curly-top. They would therefore serve as sources 
of the virus for any nonviruliferous insects that happened to feed on them. 
CONTROL MEASURES 
LEAFHOPPER CONTROL 
The control of the beet leafhopper is naturally the first idea suggested for the 
prevention of curlv-top damage, because this insect is the only known agency 
by which the disease is spread. The only feasible time of attack on the insects 
is in the early spring, when they first enter the beet fields and before they have 
deposited many eggs. They must then be killed or caught. The writers have 
tried the use of a hopperdozer. Large numbers of the insects were caught, but 
such a considerable proportion escaped that little or no benefit resulted. Liquid 
and dust sprays as insecticides and repellapts have been tried to a limited extent 
by the writers. Kerosene emulsion in 6, 12, and 18 per cent strengths were 
tried. No significant decrease in the amount of curly-top resulted, even 
though some of the insects were killed. Nicotine sulphate in three different 
strengths gave only similar results. As repellants the following were tested: 
Bordeaux mixture, oil of citronella, naphthalene diluted with equal parts of lime, 
and mixtures of sulphur and tobacco dust with lime. In none of these tests 
was the benefit worthy of consideration. As has been mentioned before, the use 
of dusts, particularly mixtures containing nicotine sulphate, has been tried 
by others (12). The results thus far reported are not encouraging from the 
standpoint of commercial practice. 
Control of the leafhopper by means of its natural enemies has been considered. 
There are three species of egg parasites and at least four parasites of the nymphs 
and adults. These parasites no doubt hold the leafhoppers in check to a large 
extent, but they can not be relied upon to prevent the production of curly-top 
in disastrous amounts. 
TIME OF PLANTING 
The control of Eutettix tenella by artificial means or by natural enemies seems 
at best a remote possibility, but by planting the beets early the damage due to % 
this leafhopper can be avoided to a large extent. Emphasis should be placed 
in this connection on the fact that by early planting is not meant planting as 
early as possible in the fall, e. g., in October, but rather in the latter part of 
November and December, or as soon thereafter as practicable, and, for most of 
the affected regions, not later than February, if possible. Striking evidence in 
regard to the time-of-planting question was afforded by field observations in 
California in the season of 1918 at Corcoran and Bakersfield in the San Joaquin 
Valley and at Lancaster in the Mojave Desert. At Lancaster and Corcoran 
small plats of beets planted very early in the winter (October and November) 
were much more seriously diseased than were adjacent plats planted a month or 
two later. At Bakersfield, where the curly-top injury has usually been great, 
practically all of the planting of the season of 1917-18 was done in November, 
December, and January, and a good crop was produced, the beets being well 
advanced in size before the leafhoppers became abundant. At Corcoran, on 
the other Jiand, in the near vicinity of Lake Tulare, where the slow drying out of 
the soil retarded operations so that planting was delayed, as late as the latter 
part of March in some cases, great injury from curly-top resulted. In the vicinity 
