• Bioassay Results in Field Persistence of Two Pink Bollworm Parasitic Nematodes

      Lindegren, J. E.; Henneberry, T. J.; Forlow Jech, L. J.; Burke, R. A.; Silvertooth, Jeff; USDA-ARS, HCRL, Fresno, CA; USDA-ARS, WCRL, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Steinernema carpocapsae (Weiser) and S. riobravis Cabanillas, Poinar and Raulston applied in the field at the rate of 1 billion nematodes /acre equivalent persisted in the soil for 63 and 6 days, respectively. Persistence of S. riobravis in the field may offer the potential for introduction and permanent establishment of this nematode for pink bollworm (PBW), Pectinophora gossvpiella (Saunders), control in southwestern cotton growing areas.
    • Chemical Control of the Sweetpotato Whitefly in Cotton

      Watson, T. F.; Tellez, M. A.; Peña, M.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Various registered and experimental insecticides were evaluated for sweetpotato whitefly (Bemisia tabaci Gennadius) control in several field experiments at Yuma, Arizona in 1994. Best controls were obtained with insecticide mixtures, particularly a pyrethroid and an organophosphate, rather than with individual materials. Results of these experiments indicate that severe population densities can be controlled using insecticide combinations, even though sustained use of these insecticides would probably lead quickly to the development of resistance.
    • Community-wide Implementation of Samplin and Action Thresholds for Whiteflies in Cotton

      Diehl, J. W.; Ellsworth, P. C.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Sampling and decision-making plans for managing sweetpotato whiteflies were implemented within 8,000 acres of cotton within the Laveen-Tolleson area of central Arizona. On the average, thresholds utilized for the first whitefly treatment were lower than those recommended, but subsequent treatments were made at about recommended thresholds.
    • Comparative Analysis of Two Sampling Methods for Estimating Abundance of Adult Bemisia tabaci in Cotton

      Naranjo, S. E.; Flint, H. M.; Henneberry, T. J.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      The leaf turn method and the black pan method, two sampling methods for estimating the abundance of Bemisia tabaci (Strain B) on cotton, were compared over a two year period in Maricopa and Phoenix, AZ Both methods were highly correlated with the density of immature stages prior to the use of insecticides, but more poorly correlated after insecticide use began. The two methods were highly correlated with one another, however, leaf turn counts were better predictors of immature infestation. The leaf turn method was also much less variable between individual samplers than the black pan method. Finally, in terms of cost-efficiency it takes, on average, 71% less time to estimate population density with an acceptable precision using the leaf turn method. Based on these criteria, the leaf turn method is a more reliable and efficient technique for estimating adult abundance.
    • Establishment of a Whitefly Resistance Documentation and Management Program in Arizona

      Dennehy, T. J.; Simmons, A.; Russell, J.; Akey, D.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Adult whiteflies were collected from six regions of Arizona and evaluated for susceptibility to fenpropathrin (Danitol®), acephate (Orthene®) and endosulfan (Thiodan®), and mixtures of fenpropathrin+acephate curl fenpropathrin+endosulfan. Strong indications of resistance to fenpropathrin, acephate and the fenpropathrin +acephate mixture were documented in some areas of the state. With all populations evaluated endosulfan was consistently the most toxic of the insecticides evaluated (singly) and was highly toxic in mixtures with fenpropathrin. Whitefly resistance to pyrethroid insecticides and especially mixtures of pyrethroid+organophosphate insecticides could have serious ramifications for the prevention of sticky cotton in Arizona. To combat further development of pyrethroid resistance cotton growers will need to reduce the number of pyrethroid treatments made per season.
    • Evaluation of a Leaf-turn Method for Sampling Whiteflies in Cotton

      Diehl, J. W.; Ellsworth, P. C.; Naranjo, S. E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Plans for sampling sweetpotato whiteflies in cotton were evaluated within 8,000 acres of cotton within central Arizona. These plans were found to be a practical and efficient way to track whitefly populations. In general they should add about 8 minutes to a pest sampling regime. Neither time of day nor sampler experience were found to have a significant effect on the number of whiteflies counted. Therefore, this method provides a common currency for growers, PCAs and others to compare whitefly numbers among fields and through time.
    • Host Preference of Silverleaf Whitefly and Factors Associated with Feeding Site Preference

      Chu, C. C.; Hennberry, T. J.; Cohen, A. C.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Silverleaf whitefly (SLW), Bemisia argentifolii, Bellows and Perring, preferred cantaloupe to cotton, broccoli and lettuce in field and greenhouse studies. In the absence of cantaloupe, SLW preferred cotton to broccoli and lettuce. In the field, more eggs and fewer nymphs were found on broccoli than on cotton. Differences in the relative abundance of vascular bundles per unit of leaf area between the four plant species may partly account for differences in oviposition site selection. Vascular bundle volume/unit of leaf tissue volume was 50% greater in cantaloupe than in cotton and broccoli, which in turn were significantly greater than in lettuce. Most SLW on cotton leaves are found on underside leaf surfaces. Distances from top and underside leaf surfaces to the nearest vascular bundles in cotton leaves were 131 and 60 tun, respectively, in the present studies.
    • Silverleaf Whitefly: Honeydew Sugars and Relationship to Sticky Cotton

      Henneberry, T. J.; Hendrix, D. L.; Perkins, H. H.; Forlow Jech, L.; Burke, R. A.; Silvertooth, Jeff; USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; USDA-ARS, SAA, Clemson, SC (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      In cotton plots heavily infested with silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring, amounts (mg /g of lint) of sugar (fructose, glucose and sucrose combination) on lint from tagged bolls, varied but showed a general trend to increasing amounts with increasing time of exposure (days) for 52 days. Minicard lint stickiness ratings responded in a similar manner and all values were above acceptable thresholds. Lint from harvested mature open bolls that were exposed on trays suspended in the interior of SLW infested cotton plots showed increasing amounts of sugar and higher minicard ratings after 6 days. Amounts of sugar and minicard ratings were drastically reduced following rains of 1.5 inches.
    • Susceptibility of Arizona Populations of Lygus Bugs to Acephate (Orthene®) and Bifenthrin (Capture®)

      Dennehy, T. J.; Cramer, G. C.; DeBolt, J.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      Adult lygus bugs were collected from alfalfa fields in 6 different cotton producing areas of Arizona. The standardized, glass vial method was used to estimate susceptibility of the collected populations to the organophosphate insecticide, acephate (Orthene®), and the pyrethroid, bifenthrin (Capture®). Overall, lygus from throughout the state were very susceptible to bifenthrin. However, some populations were significantly less susceptible to bifenthrin than were others. Lygus populations with greater than 20% survivorship of 100 μg/ml vial bioassays with bifenthrin should be monitored to provide early warning of future problems with pyrethroid resistance. Resistance of lygus to acephate appeared to be widespread but not uniform in Arizona. While some populations had individuals surviving exposure to vial treatments of as high as 10,000 pg/ml acephate, other populations had no survivors of 1,000 pg/ml treatments. Lygus populations with survivors of 10,000 pg/ml vial bioassays should be considered highly resistant to acephate. Our findings illustrate that resistance levels are often unique from farm to farm, even within the same region. To preserve the long-term usefulness of acephate, where possible, cotton growers should consider using it no more than once or twice per season, on any given field.