An experiment was conducted to learn the importance of early-, mid-, late- and full-season infestations of tobacco budworms, Heliothis virescens (F.), on the yield of an early, 'Tamcot CAMD-E' (CAMD-E), and a full season, 'Stoneville 213' (STV-213) cotton, Gossypium hirsutum L., cultivar. The cultivars were planted in 42-foot, single row plots in a two and one skip row pattern. Treatments consisted of applying 12 first instar larvae in the terminal area of each plant weekly for various combinations of weeks. When larvae were not applied in a given week, plots were protected with an insecticide. Treatments consisted of applying larvae, beginning at squaring, for the following times: none (control), weeks 1 through 2, 1 through 4, 1 through 6, 1 through 8, 3 through 8, 3 through 6, 3 through 4, 5 through 8, 5 through 6, and 7 through 8.

The plots were machine harvested three times (Sept. 9, Oct. 19 and Nov. 4). At first harvest CAMD-E yielded significantly more than STV-213. Treatments which received larvae the first week and subsequent weeks of squaring resulted in significantly lower yields by both cultivars when compared to the control. Mid-and late-season applications of larvae also reduced yields. At both the second and third harvest STV-213 yielded significantly more than CAMD-E. Treatments 1-4, 1-6, 1-8, 3-8, 3-6, 3-4, and 5-8 reduced STV-213 yields significantly. The yield of CAMD-E was not reduced significantly; however, lower yields were recorded from all treatments except 1-2 and 1-4. At the third harvest only treatments 1-8 and 5-8 significantly reduced yields of STV- 213. CAMD-E produced significantly more seed cotton with early and Mid-season larval treatments than the control. When yields were accumulated for the season all treatments except 5-6 and 7-8 resulted in significantly lower yields by STV-213 when compared to the control. Only treatments 1-6, 1-8 and 3-8 resulted in significantly lower yields by CAMD-E.

Early season application of larvae had a greater effect in reducing yield of the full season cultivar, STV-213, than of the early maturing cultivar, CAMD-E. The total yield of STV-213 was reduced significantly by early-, mid-, late- and full-season applications of larvae, while only those treatments that lasted for six weeks reduced total yield of CAMD-E.