Spring frosts in 1945 destroyed 95 per cent of the crop of chestnuts in the Eastern States. Only six trees of different species and ages in the Government orchard at Glenn Dale, had sufficient nuts for experimental purposes. Applications of a 50 per cent DDT wettable powder in the proportions of 4 and 6 pounds plus 1/2 gallon of summer oil as a sticker to 100 gallons of water were made on August 20 and September 9.
Spring frosts again damaged the orchards in 1946, destroying about 80 per cent of the possible chestnut crop, and leaving only eight trees in the Government orchard that were suitable for experimental purposes. The remaining trees having a small scattered crop were disregarded. A mixture consisting of equal parts by weight of DDT and kaolin 41 was used in the strength of 2 pounds of DDT to 100 gallons of water. The time and number of applications were varied.
Table 3. Results of spray tests with DDT against chestnut weevils, 1944-1947.
Larvae Emerging from Sample
Reduction
Nuts Small Large Wormy of
DDT (per Application in Chestnut Chestnut Nuts Injured
100 gal.) Sample Weevil Weevil Nuts
Year
Pounds Number Number Number Percent Percent
Government Orchard, Glenn Dale, Md.
1944 1 Aug. 14 533 1896 21 44 42
2 646 402 45 25 67
3 712 421 5 18 76
4 951 814 5 22 71
5 1844 850 10 16 79
0 976 3238 100 76
1945 2 Aug. 20 & Sept. 9 660 434 38 30 57
3 305 285 58 22 69
0 297 1164 61 70
1946 2 Aug. 15 & 30, Sept. 11 621 131 12 9 90
2 Aug. 15 & 30 371 171 23 19 79
2 Aug. 30 & Sept. 11 292 87 21 26 71
2 Aug. 15 & Sept. 11 949 553 190 43 53
2 Aug. 30 1267 1407 98 43 53
2 Aug. 15 1212 3207 66 43 53
2 Sept. 11 368 1832 53 58 36
0 870 5364 134 91
1947 2 Aug. 13 & 29, Sept. 12 4084 3817 234 30 66
2 Aug. 13 & 29 2618 4255 151 52 40
2 Sept. 12 3029 9498 402 79 9
2 Aug. 13 2639 5049 198 51 41
0 974 4714 121 87
Van Reynolds Orchard, Elkton, Md.
1947 2 Aug. 21, Sept. 4 & 18 1153 264 64 14 84 2 Sept. 4 & 18 338 5 118 67 23 2 Aug. 21 & Sept. 18 149 18 59 34 61 2 Aug. 21 & Sept. 4 669 102 12 51 41 2 Sept. 18 324 63 129 77 11 2 Sept. 4 270 303 67 56 36 2 Aug. 21 500 192 127 57 34 0 338 152 118 87
Sprays containing DDT were applied in two orchards in 1947, the Government orchard at Glenn Dale, and the Van Reynolds orchard at Elkton, Md. Spring frosts injured 50 per cent of the chestnut crop at Glenn Dale and 70 per cent at Elkton, and as a result only a few trees suitable for tests were available. The remaining trees were not sprayed. Four pounds of the standard mixture of equal parts of DDT and kaolin were used to 100 gallons of water in all applications.
In Table 3 will be found information on the quantities of DDT used, the schedules followed, and the results obtained during the period 1944 through 1947.