Control of the Potato Tuberworm in Potatoes

In California, the potato tuberworm, Gnorimoschema operculella (Zell.) is especially difficult to control in potato varieties such as Kennebec which produce tubers close to the surface of the soil. Chemical control measures are aimed at preventing population increases in foliage during the growing period so that fewer moths and larvae will be present to infest tubers when the crop matures. Insecticides tested as foliage sprays in field trials conducted during 1958 and 1959 included DDT, endrin, Thiodan® (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9- methano-2,4,3-benzodioxathiepin-3-oxide), Guthion® ( O,O -dimethyl S - (4-oxo-1,2,3-benzotriazin-3-(4H)ylmethyl) phosphorodithioate), Sevin® (1-naphthyl methylcarbamate), and dimethoate. A 50% calcium arsenate dust was also tested and was found to be ineffective. In the 1958 trials, five applications of each insecticide were made at biweekly intervals. In 1959, treatments were repeated at 10-day intervals for u total of six applications. Endrin and Guthion were the most effective materials tested. Guthion applied at the rate of 0.75 pound per acre appeared to be superior to endrin used at the rate of 0.6 pound per acre in killing larvae in their leaf mines and in controlling adults. Thiodan applied at the rate of 1.0 pound per acre gave excellent results 1958 but control of larvae in foliage with this material in 1959 was poor. Sevin applied at 1.5 pounds per acre was about as effective as endrin applied at 0.6 pound. Dimethoate applied at the rate of 1.0 pound per acre gave only fair control of larvae in the foliage. DDT at a dosage of 2 pounds per acre had little effect on larvae in the foliage. Despite excellent control of larvae in the foliage with endrin and Guthion, only 51% control of larvae in the tubers of the Kennebec variety resulted. With Russett, a deeper-setting variety, endrin gave 81% control and Guthion 75%. Undoubtedly these infestations developed as a result of flights of moths from heavily infested nearby areas, indicating that although a producer may keep his field free of infestation during the growing season he may still harvest appreciably infested tubers if nearby sources of moths are disregarded. In 1958, DDT and Guthion caused populations of the potato aphid, Macrosiphum solanifolii (Ashm.), to increase 6-fold and nearly 12-fold, respectively. Guthion and Sevin resulted in 7-fold and 20-fold increases in populations of the green peach aphid, Myzus persicae (Sulz.) in 1959.