Planting Date and Susceptibility to Pink Bollworm

The susceptibility of cotton to spring emergence of pink bollworm (PBW) was evaluated for a variety of planting dates in Pinal, Maricopa, LaPaz and Yuma counties using historical climate records and heat unit -based models that predict PBW emergence and cotton development. Early planted cotton proved most susceptible to the PBW emergence, however, springtime weather conditions also played an important role in determining overall susceptibility. Growers wishing to incorporate planting date as one aspect of PBW management should keep abreast of early season weather conditions. Introduction Control of pink bollworm (PBW) (Pectinophora gossypiella (Saunders)) is most successfully accomplished using a combination of cultural and chemical control. One aspect of cultural control involves making adjustments in planting date to minimize the survival of early season PBW larvae. Low survival in this initial larval population reduces the size of subsequent generations, making control of PBW less difficult and costly. The PBW overwinters in a dormant, larval form. As weather conditions warm in the late winter and early spring, overwintering PBWs complete their life cycle and emerge as adults. Upon emergence, the female moths lay eggs which produce the next generation of PBW larvae. The survival of this new generation is heavily dependent on whether the young larvae find cotton (Gossypium spp.) that has developed squares 1/3 of full size or larger (defined as the susceptible square stage). Younger cotton provides inadequate food and shelter, resulting in poor survival of larvae. Planting date affects when cotton reaches susceptible square and therefore can have a major impact on the survival of early season PBW larvae. To conduct a quantitative assessment of how planting date impacts the susceptibility of cotton to early season PBW larvae, one must carefully examine early season weather conditions, since both PBW emergence and early season cotton development are dependent on temperature. One such assessment conducted by Brown et al. (3) revealed that planting date, springtime weather conditions and cotton type (short vs. long staple) all played a role in determining overall susceptibility of cotton to early season PBW larvae. Early planted cotton proved more susceptible than late planted cotton as expected. However, springtime weather conditions also impacted overall susceptibility. For a given planting date, cotton proved far less susceptible to spring PBW emergence when springtime weather conditions were hot. Susceptibility was highest in cool springs. Another conclusion of the work by Brown et al. was that for a given planting date long staple cotton was less susceptible to spring PBW emergence than short staple cotton. This conclusion was reached based on preliminary information from Huber that indicated long staple cotton required more time (heat units) to reach susceptible square than short staple cotton. Recent work by Silvertooth et al. (4) revealed that Pima S -6, Deltapine 90, 50 and 51 all reach susceptible square after approximately 900 heat units have accumulated after planting. This is due primarily to the similarity of these varieties to initiate fruiting at similar node positions. Because no significant difference in heat unit requirement to susceptible square was observed for Pima and common short staple varieties, both types