AffiliationUniversity of Arizona, Maricopa, AZ
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AbstractTiming sprays for maximum return on investment requires sampling and counting both Lygus adults and nymphs in a minimum of 100 sweeps. Once at least 15 total Lygus and 4 nymphs per 100 sweeps are detected, sprays for Lygus should be made. This '15/4' regime should protect yields, moderate spray frequency and costs, and maximize profit. Economic thresholds are impacted by the prevailing economic conditions such as lint value and costs of control; however in this case, the relationship that maximizes returns was not changed when varying these parameters well beyond market standards. A key finding of these studies is that aside from profits, yields plateau prior to the more aggressive treatment regimes. This phenomenon, where more protective approaches result in yield reductions, occurred in all three years of study (1997, 1999, 2000). This signals the importance of optimizing inputs so that sprays are made only when indicated by sampling and once the 15/4 level is reached, but no sooner. More aggressive approaches by definition cost more money to maintain, but also have some probability of lowering yields while risking secondary pest outbreaks. The specific mechanism for this yield decline is unknown at this time. At the other end of the spectrum, delaying action beyond the 15/8 action threshold risks economic yield loss and reductions in quality, especially color grade and micronaire. While this work definitively establishes the relative importance of Lygus nymphs to yield loss and to the need for action, the conditions under which these tests were carried out are limited to in-season infestations of Lygus. Further work is necessary to better quantify change in the action levels according to plant phenology and other plant-based factors (e.g., plant population, fruit retention, plantwater status, etc.). Early season infestations may respond differently to the action levels proposed, and it is expected that later season populations of Lygus pose far less damage potential when square populations and retention are very low.