Date of Total Small Large Wormy
Bagging Nuts Chestnut Chestnut Nuts
Nuts Bagged Weevil Weevil
Year and Orchard
Number Number Number Percent
1945 July 9 52 2 5 13
Glenn Dale, Md. Aug. 1 46 4 2 13
Aug. 15 107 18 11 27
Fairfax, Va. Aug. 21 110 22 13 32
Sept. 12 123 63 11 60
1946 July 12 65 0 0
Glenn Dale, Md. July 18 40 0 0
July 26 67 0 0
Aug. 1 71 0 0
Aug. 9 29 1 0 3
Aug. 14 88 3 2 6
Aug. 23 53 18 2 38
Aug. 29 53 23 11 64
Fairfax, Va. July 26 98 0 0 0
Aug. 15 168 0 0 0
Sept. 4 164 139 16 95
1947 Aug. 15 54 5 1 11
Glenn Dale, Md. Aug. 25 38 8 0 21
Sept. 2 24 7 1 33
Sept. 9 42 18 4 52
Sept. 15 56 29 7 64
Sept. 22 90 27 11 64
Sept. 29 143 83 22 73
Fairfax, Va. Aug. 26 35 9 1 29
Sept. 10 58 25 4 50
Sept. 28 50 35 7 84
Oct. 7 217 177 22 92
Elkton, Md. Aug. 21 139 11 13 17
Sept. 4 83 22 25 57
Sept. 18 116 21 35 48
Oct. 1 108 31 44 69
+Spray Experiments in 1944+
Shortly after adults of the large chestnut weevil first appeared in the orchards in 1944, six trees isolated from other chestnuts were selected for treatment. Five trees were sprayed with from 1 to 5 pounds of technical DDT plus 1/2 pound of sodium lauryl sulfate to 100 gallons of water, and the sixth tree was left untreated as a check. A thorough application of a coarse, drenching spray at a pressure of 400 pounds per square inch was used in an attempt to force the DDT between the many spines of the burs. The DDT used was very coarse, and difficulty was experienced in getting a proper suspension. This formula was used, however, in preference to one which contained other ingredients that might have formed a protective coating over the particles of DDT. Heavy rains prevented later spray applications.
Adult weevils obtained by jarring untreated trees were then confined in screen cages placed over the lower branches of the trees. At the end of each cage was a cloth sleeve which was tied to the limb to hold the cage in place. The treatments used and the results are given in Table 2.
Table 2. Percentage mortality of chestnut weevils placed in field cages on trees at different intervals after they had been sprayed with with DDT, 1944.
Strength of
DDT (lb. per Small Chestnut Weevil Large Chestnut Weevil
100 gal.) 48 Hrs. 96 Hrs. 144 Hrs. 48 Hrs. 96 Hrs. 144 Hrs.
1 0 61 100 25 50 100
2 19 69 100 0 34 100
3 4 50 100 0 40 100
4 27 87 100 0 50 100
5 18 50 100 30 46 100
Check 0 0 0 0 7 7
Although the results obtained the first few days in the cages containing treated foliage were somewhat irregular, because of the small numbers of tests made, all weevils were killed within 6 days. The results indicate definitely that DDT is toxic to the adults of both species of weevils. No consistent differences between species were noted.
As the matured nuts dropped from the treated trees, daily collections were made, and one-third of each collection was used as a sample in determining the percentage of wormy nuts. At the time the nuts drop, the holes in the shell through which the eggs were inserted are very difficult to detect. The nuts were therefore held in wire baskets to permit most of the larvae to emerge before the final examination. All nuts not showing exit holes were cut open to find out whether they were wormy. The marked increase in clean nuts after all treatments indicates that DDT is a promising insecticide for use against the weevils. The treatment and infestation records for the sprayed trees and the check tree are given in Table 3, which also includes the results obtained in later years.
+Spray Experiments 1945 to 1947+