Browsing Cotton Report 1994 by Authors
Action Thresholds for Whiteflies in ArizonaEllsworth, Peter C.; Meade, Donna L.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)Three field tests were set -up for evaluation of action threshold levels for sweetpotato whitefly control with two different chemical combinations. The thresholds used to initiate treatments were ca. 1, 10, and 25 adult whiteflies per leaf designated as "early ", "moderate ", or "late ". Immatures were present during these treatment initiation points at the rate of ca. 5 nymphs and ca. 10 eggs per sq.in. in the 'early' plots, 15.3 nymphs and 39.1 eggs per sq.in. in the 'moderate' plots, and 52.1 nymphs and 299.3 eggs per sq.in. in the 'late' plots. The insecticides used included a pyrethroid combination [Danitol® (.1 lb a.i/A) + Orthene® (.5)] and a non-pyrethroid combination [endosulfan(.75) + Ovasyn® (.25)1 Applications were by ground, broadcast, over-the-top, at 20 GPA. Populations were monitored as whitefly adults (leaf turns & net sweeps) and nymphs and eggs (leaf counts). Once applications were triggered, they continued ca. weekly. The early threshold required seven applications, starting 10 July, and produced yields (4038.8 lbs seed cotton/A) which were 2 or 3 times larger than the untreated check (1589.3 lbs seed cotton/A). Lint or leaf stickiness was not apparent; however, 2 or 3 sprays were required before any significant differences in whitefly populations could be found. Whitefly numbers were lowered significantly in both insecticide regimens, with somewhat lower numbers present in the pyrethroid treated plots. The late threshold was sprayed only twice, starting 12 August, and yielded no more cotton (1719.2 lbs seed cotton/A) than the untreated check (1395.0 lbs seed cotton/A). Lint and leaf surfaces were covered in stickiness and sooty mold. Whitefly populations were excessive and led to premature cut -out and poor fruit retention. The moderate threshold (10 adults per leaf) received five applications, starting 22 July, and produced high yielding and high quality cotton (3462.2 lbs seed cotton/A). Some stickiness and sooty mold growth was observable only on the lowest leaves. This was a result of limited honeydew production prior to the threshold and well before any boll opening. Lygus populations were extremely high and caused large differences in yields which favored the pyrethroid combination slightly and the earliest threshold significantly. Given commercial farm control realities (e.g., delays in sampling or application, differences in coverage or application, variable efficacy), the ideal threshold for initiation of treatments is likely between 1 and 10 adults per leaf.
Validity of the Pinhead Square Treatment Program for Pink Bollworm Suppression and Impact of Several Insecticides on Arthropod Fauna in CottonEllsworth, Peter C.; Meade, Donna L.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1994-03)A limited chemical control tactic known as pinhead square treatment has gained recent Favor as a component of pink bollworm population management. The strategy has economic and ecologic goals of using reduced insecticides early in the season (to include lower rates, half the acreage, and less potent chemistry) in order to reduce later season risk of pink bollworm infestations. This strategy also depends in part on the cultural tactic which results in "suicidal emergence" of overwintering pink bollworms through optimal planting date management. The combination of these tactics has been used in the past to overcome boll weevil populations area-wide. This study is focused on the evaluation of this system as a basis for pink bollworm suppression. Though only preliminary is presented here, it is clear that there are numerous insects impacted by this practice which interact in complex ways to influence pest populations of all kinds. Furthermore, the fate of such a practice in any production system is also influenced by the specific chemical agent used. This experiment details the use of four different classes of insecticide chemistry as well as one bioinsecticide. The experiment has been duplicated in 1993; however, only 1992 data are shown here.