III.-EXPERIMENTS IN CONTROLLING THE TOMATO

FRUITWORM WITH ARSENICALS.

By THOS. H. JONES,

Entomological Assistant, Truck-Crop Insect Investigations.

Spraying and dusting experiments for the control of the tomato fruitworm (Chloridea obsoleta Fabricius) were conducted during 1916 and 1917 at the Louisiana Experiment Station, Baton Rouge, La. This work was carried on in cooperation with Dr. C. W. Edgerton, plant pathologist of the station, who was especially interested in the fungicidal value of some of the materials used.

In 1916 a spring and a fall crop of tomatoes were used in the experiments. In the case of the fall crop a heavy frost occurred before much fruit had matured. The next day all fruit was gathered and weighings and counts made. In 1917 only a spring crop was used in the experiments.

The sprays were applied by means of small compressed-air sprayers of about 2 gallons capacity. The materials were carefully applied. On the spring crop of 1916 about 10 gallons of spray were used on an average in spraying eight times a row of 54 plants, set 2 feet apart in the row. On the fall crop of 1916 approximately 43 gallons were used in spraying the same number of plants seven times. For spraying the same number of plants five times in the spring of 1917 about 7 gallons were used.

The dusting was done with a dust gun. In dusting the spring crop of 1916 approximately 17 ounces of undiluted powdered arsenate of lead were used in making eight applications to an average row of 54 plants, set 2 feet apart in the rows. In dusting the same number of plants of the spring crop of 1917 five times, approximately 12 ounces were used. For the dusting a specially prepared, light, finely powdered arsenate of lead was used, as was also used in spraying the spring crop of 1916.

In Tables I-III "wormy" refers to fruit that was apparently injured by the larva of Chloridea obsoleta. Without doubt the injury to a small percentage of this fruit was due to other causes, principally the hornworms, Phlegethontius spp. and larvæ of the granulated cutworm Feltia annexa Treitschke.

TABLE I.-Tomatoes set out in field Apr. 11, 1916. Applications of sprays and dusts made Apr. 25, May 5, May 15, May 24, June 2, June 12, June 22, July 3, and July 13. No. 3 not sprayed after May 24. No. 4 not sprayed after June 12. Nos. 5, 6, and 7 not sprayed, and No. 9 not dusted, after July 3. Harvesting began June 14, ended Aug. 3.

TABLE II.-Tomatoes set out in field Aug. 14 and 15, 1916. Applications of sprays made Sept. 2, Sept. 12, Sept. 22, Oct. 2, Oct. 12, Oct. 23, and Nov. 2. Harvesting began Oct. 24, ended Nov. 15.

TABLE II.-Tomatoes set out in field Aug. 14 and 15, 1916-Continued.

1 Hybrid selected by Dr. Edgerton, the parents being the Earliana and a wilt-resistant hybrid.

TABLE III.-Tomatoes set out in field Apr. 4 and 6, 1917. Applications of sprays and dust made May 3, May 12, May 22, June 1, and June 12. Harvesting began June 11, ended Aug. 11.

The results of the two years' work show considerable variation. None of the treatments can be considered to have reduced the injury profitably. Arsenate of lead, applied undiluted as a dust, gave the

best results. It was to be expected that the sprays and dusts used on the spring crop of 1916 would show better results than those used on the spring crop of 1917, as in 1916 their application was continued longer after harvesting began. On the fall crop of 1916, however, where harvesting was completed 13 days after the last spraying, the spraying apparently had little or no effect in some instances in reducing injury. In this connection it should be stated, however, that the plants used as checks produced but a small amount of fruit, partly because they were badly injured by Phlegethontius larvæ when small. Comparisons of results from sprayed and check plants may, therefore, not be indicative of the true value of the sprays.

It is to be noted that the Earliana variety of tomato showed a higher percentage of injured fruit than did either the Globe or the hybrid.

The diagrams (figs. 2-5) show the number of tomatoes produced each week by Earliana and Globe plants set out in the springs of 1916 and 1917, part of these being sprayed with arsenate of lead and the others serving as a check. The percentage of the number of fruit showing injury is also given. The diagrams show that the Earliana produced the greater portion of its crop sooner than did the Globe and that in 1916 both varieties produced their crops within a shorter period of time than in 1917, there being a pronounced "second crop" during 1917.

FIG. 2.-Diagram, prepared from weekly totals during harvesting season, showing number of tomatoes of the Earliana variety and percentage apparently injured by the tomato fruitworm in 1916. Spaces between horizontal lines represent 100 in case of total number of tomatoes, and 20 in case of percentage wormy. Vertical lines represent weeks. The solid line represents the total number of tomatoes from the unsprayed check; the dotted line, the percentage of check wormy; the line of dashes, the total number of tomatoes from plants sprayed with arsenate of lead; the line of dots and dashes, the percentage of sprayed tomatoes wormy.

400

er 80%

300 or 60%

200 or

40%

100 or 20%

0

FIG. 3.-Diagram, prepared from weekly totals during harvesting season, showing number of tomatoes of the Earliana variety and percentage apparently injured by the tomato fruitworm in 1917. Spaces between horizontal lines represent 100 in case of total number of tomatoes, and 20 in case of percentage wormy. Vertical lines represent weeks. The solid line represents the total number of tomatoes from the unsprayed check; the dotted line, the percentage of check wormy; the line of dashes, the total number of tomatoes from plants sprayed with arsenate of lead; the line of dots and dashes, the percentage of sprayed tomatoes wormy.

FIG. 4.-Diagram, prepared from weekly totals during harvesting season, showing number of tomatoes of the Globe variety and percentage apparently injured by the tomato fruitworm in 1916. Spaces between horizontal lines represent 100 in case of total number of tomatoes, and 20 in case of percentage wormy. Vertical lines represent weeks. The solid line represents the total number of tomatoes from the unsprayed check; the dotted line, the percentage of check wormy; the line of dashes, the total number of tomatoes from plants sprayed with arsenate of lead; the line of dots and dashes, the percentage of sprayed tomatoes wormy.

5

200 OF

FIG. 5.-Diagram, prepared from weekly totals during harvesting season, showing number of tomatoes of the Globe variety and percentage apparently injured by the tomato fruitworm in 1917. Spaces between horizontal lines represent 100 in case of total number of tomatoes, and 20 in case of percentage wormy. Vertical lines represent weeks. The solid line represents the total number of tomatoes from the unsprayed check; the dotted line, the percentage of check wormy; the line of dashes, the total number of tomatoes from plants sprayed with arsenate of lead; the line of dots and dashes, the percentage of sprayed tomatoes wormy.