Apr. 26, 1924 
Studies on Curly-Top Disease of the Sugar Beet 
317 
of Riverside and San Bernardino, in southern California, good crops have been 
produced by early planting (November and December), while the crops from 
late planting (March) in the same season were practically complete failures. 
In regard to the time-of-planting question, from the standpoint of minimizing 
the injury from curly-top, two points must be given especial consideration. The 
plantings must not be made early enough in the fall to expose the young plants 
before the movement of the leafhoppers from the cultivated fields or late enough 
in the spring so that the beets will not have made a vigorous growth before the 
leafhoppers move into the cultivated areas. Mention should be made of the fact 
that usually some of the leafhoppers remain in the cultivated areas through the 
winter and that these stragglers may cause a considerable amount of damage. 
In general, however, the damage from those that remain in the cultivated areas, 
as compared with the damage when the main body of the insects is in cultivated 
districts, is relatively slight. With varying seasons the optimum time of planting 
will no doubt vary, but in general the safest plan is to plant as soon as possible 
after the middle of November and at least before the end of February. This 
recommendation is based primarily on conditions in California. 
RESISTANT STRAINS 
The fact that in almost every severely affected beet field a few individual 
plants will stand out conspicuously less affected than the rest has been noted 
by previous workers. The writers have repeatedly made this same observation. 
A project has been started by selecting the seemingly resistant plants from com¬ 
mercial fields, believing that by selection and possibly breeding a resistant strain 
satisfactory for commercial purposes may be developed. 
Difficulties have been encountered in keeping over winter the^beet roots which 
had to be removed frpm the field before harvest time. Siloing the beets in the 
ground, as is done in colder climates, has been found impracticable. Different 
methods of cold storage have been tried and a way of packing the roots for this 
purpose has been tested which seems, from the experience of one year, fairly 
satisfactory. Direct transplanting of the roots when harvested has been tried 
to a limited extent and found satisfactory. 
Seed was produced from a few'of the selected beets in the summer of 1921. 
Plantings of these strains together with control plats of commercial seed were 
tested for resistance in the autumn of that year. This test was made at River¬ 
side, Calif., where leafhoppers were naturally abundant. In addition to the 
natural exposure, each plant of the selected strains was inoculated by caging 
on it a viruliferous leafhopper. The results of the test gave support to the 
belief that a strain of beets resistant to curly-top may be developed. Seeming 
differences in degree of resistance were noted between several of the selected 
strains and the commercial beets, and in one case this difference was marked (PI. 
5, C). Tests of these strains were made in the same manner but on a larger scale 
in the summer of 1922. The situation was complicated in this season by the fact 
that a large proportion of some of the apparently resistant strains developed 
seed stalks. On this account no satisfactory conclusions could be drawn as to 
resistance. Work is now in progress to determine the factors causing the pre¬ 
mature seeding so that these factors may be eliminated. 
More selections were made from commercial fields in California and Utah and 
also from the progeny test plats in the summer of 1922. The selection of more 
individuals from commercial fields and from the progeny plats will be continued 
and the progeny of these selections tested by inoculation for resistance to curly- 
top. The practice being followed in the growing of seed from the selected 
strains is to plant the mother beets singly or in small groups in private gardens, 
so that they will be isolated from each other. 
