• Impact and Management of Western Flower Thrips on Romaine Lettuce

      Palumbo, John; Mullis, Clayton Jr.; Reyes, Francisco; Amaya, Andreas; Ledesma, Luis; Cary, Lisa; Byrne, David N.; Baciewicz, Patti (College of Agriculture, University of Arizona (Tucson, AZ), 2000-08)
      A season-long study was conducted to evaluate the efficacy of several conventional, experimental and bio-based insecticide combinations used in rotation against western flower thrips (WFT) in romaine lettuce. Results from this study showed that several insecticide rotational programs provided good control of WFT populations throughout the season. Adult abundance peaked just prior to the fourth spray on 28 March, whereas larvae numbers peaked about 2 weeks earlier on March 13. Fluctuations of larval and adult populations observed from weekly samples suggests that greater than 3 WFT generations developed during the experimental period. Averaged across all sample dates, the Success, Lannate and Warrior based rotations maintained adult and larval populations at significantly lower levels than all other treatments. The Bio-based, organic rotations (Neem/Garlic/COC/Sulfur/Diatect) did not differ from the untreated check. Percentage reduction of WFT larvae and adults compared with the untreated control was significantly greater following sprays which contained Success combinations. Consistent with reduction in WFT numbers, the Success/Lannate/Warrior, and Dimethoate based rotations resulted in significantly greater yields and less damage. Regression analysis suggests that larvae and total thrips abundance more consistently describes the variation measured in plant weights. Overall, this preliminary data further indicates that maintaining WFT abundance at low levels is important for maintaining romaine yield and quality.
    • Management of Western Flower Thrips in Head Lettuce with Conventional and Botanical Insecticides

      Palumbo, John; Mullis, Clayton Jr.; Reyes, Francisco; Amaya, Andreas; Ledesma, Luis; Cary, Lisa; Byrne, David N.; Baciewicz, Patti (College of Agriculture, University of Arizona (Tucson, AZ), 2000-08)
      Studies were conducted in three independent field trials to evaluate the efficacy of conventional and botanical insecticides against western flower thrips in head lettuce. Trials were conducted in spring lettuce under moderate and heavy populations pressures. Actara and Avaunt, two new experiential insecticides did not significantly control adults and provided only marginal activity against the larvae when applied alone. Combination of these products with either Lannate or Warrior significantly enhanced control, but usually not greater than that shown from the Lannate or Warrior applied alone. Several botanical products were evaluated (azadirachtin, pyrethrins, crop oils and garlic). Unfortunately, none of the botanical products significantly reduced thrips numbers to economically acceptable levels of control. Similar to previous studies, our results suggest that even the most efficacious products appeared to maintain thrips populations at constant levels and not necessarily reducing their numbers. More research needs to be conducted to determine the proper timing of applications to achieve optimal thrips using both conventional and botanical insecticides.
    • Population Dynamics and Distribution of Aphid Species on Head Lettuce in the Yuma Valley

      Palumbo, John; Mullis, Clayton Jr.; Reyes, Francisco; Amaya, Andreas; Ledesma, Luis; Cary, Lisa; Byrne, David N.; Baciewicz, Patti (College of Agriculture, University of Arizona (Tucson, AZ), 2000-08)
      Studies were conducted in the 1999/2000 growing season to examine the population dynamics and field distribution of aphid species on winter and spring head lettuce crops. Seven, 0.25 acre planting of head lettuce were established beginning in October with final harvest occurring in April. Plant samples were conducted weekly to estimate the numbers of both alate (winged) and apterous (wingless) green peach aphids, potato aphids, cowpea aphids and lettuce aphids. Lettuce aphids were more abundant this spring than anticipated, which may indicate that lettuce aphid may be a new pest for Yuma growers. However, based on a single years data, it is difficult to measure the threat that this aphid poses to the lettuce industry. Planting date and temperature likely has a strong influence on seasonal abundance of lettuce aphids. Similarly, the consistent appearance of cowpea aphids during the season was surprising , considering that it has seldom been observed on desert lettuce. Perhaps most surprising though was the low population abundance of green peach and potato aphids in out plots. Part of this unusual event may be due to the unseasonably warm, dry growing season that was experienced this year.