9. Gl. til. El│71.| 11.|01| 60.| 80.|40. |90. | SO. | +0. | € 0. |20.|10.00.|66.|86. Lb. 9b. £b. tib. Ɛb. 76. 16.

Figs. 4 and 5.

Showing the periodic occurrence of outbreaks of curly.

leaf in the different regions.

(Note The curve shows the com

parative amount and severity of the blight in the worst section of each area only.) The total damage in the worst years would be

191 192 193 194 195 196 197 98 99 00 01 02 103 104 105 106 107 108 109 10 11 12 13 14 15 16 Boise

Valley

ON

Beets

the curves, nor to the occurrence of the disease. year in which they were built. These names have no reference to The names of the older factories in each area are inserted in the proportionally much greater than that represented by the curve.

at the end of the 1910 run. The Glendale curve was interrupted by the absence of beets, but probably belongs in a similar class. The fragmentary curve from Corcoran, together with the known record of the factories there, suggest that in these four regions blight is the rule and that a year when it would be absent, the exception. As has been suggested, these regions are probably within the breeding range and do not depend upon flights for their infections.

The record for the region east of the Rocky Mountains is not as complete as could be wished, but there have been only two serious outbreaks, and these have not coincided with any curves from west of the mountains. This suggests that the source of the flights of leafhoppers to this area is from a different region under different influences from the source of the western flights.

We have then, apparently, two different types of areasone in which the blight is the rule and in which sugar-beet growing has not succeeded, and another in which outbreaks of blight are the exception and appear only periodically. To this class belong the very best producing beet regions of America and in these areas the industry will continue to develop.

Any information by which the probable occurrence of these periodic outbreaks could be foretold would, therefore, be worth millions of dollars to this industry. This information can only be obtained by long and careful study of the habits and reproductive power of the insect on its native food plants and in its natural breeding range. As both the extent of its food plants and the limit of its breeding range are still in doubt, the problem is a complex one.

PECULIAR NATURE OF THE CURLY-LEAF DISEASE

A puncture of the beet leafhopper is absolutely necessary to cause the disease to develop in the beet. Under favorable conditions Titus found that à very short application of a single insect. would produce the disease on a young beet. Smith and Bonequet (1915) found that a single hopper applied for five minutes on an eight-leafed beet produced the disease.

The disease never appears on any but growing leaves and usually on the younger ones first. Thus it is rare that the leaf which is punctured is the one to show curly-leaf first. As long

as conditions are favorable blighted leaves continue to appear unless the disease becomes so severe as to entirely stop the growth of the beet. If all the leaves are cut off the new ones will appear with the characteristic symptoms. If the beet is planted the following year to raise seed the disease will again

appear.

On the other hand, if conditions are not favorable the curlyleaf may not appear at all, almost regardless of the number of leafhoppers and length of time they feed upon it (Pl. IV, fig. 2) When conditions change widely during a season, the development of curly-leaf will often change accordingly. A beet starting to blight early in the season may, under cold and wet conditions, develop a number of healthy looking leaves and still later, when hot weather has returned, put out others badly curly (Pl. 2, figs. 4 and 4a). Often a beet that showed no curly-leaf symptoms the first year will blight as a mother beet planted for seed raising. In one case a strain of beets whose vitality had been lowered blighted much worse than normal beets along side of them. The disease never spreads from beet to beet except as it is transmitted by the leafhopper. All attempts to transfer the disease by innoculation have failed. Smith and Bonequet (1915) were able to transfer the disease by grafting in a section of the shoulder of a beet containing a bud.

DOES THE PUNCTURE OF THE BEET LEAFHOPPER CAUSE CURLY-LEAF?

The writer had at hand in 1906 so much evidence pointing unquestionably to the conclusion that the curly-leaf condition was due to the puncture of Eutettix tenella that this was announced as a fact without extended discussion in the brief space allowed in an annual report (Ball, 1906). The two succeeding papers (Ball, 1908 and 1909) were both prepared in 1907 before any controversy had arisen, and so while most of the facts. were brought out in the discussion that feature was not emphasized.

This conclusion was accepted by most of those then engaged in the work, with the exception of Townsend (1908), who expressed doubt. The writer immediately took the matter up with Dr. Townsend's assistant. Mr. Shaw, in charge of sugar-beet in