Andersen, Astrid H.

Beers, Elizabeth H.

Undetermined

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n. Pome Fruitsd. Chemical control1. Twospotted spider mite (Tetranychus urticae) and apple.Astrid H. Andersen and Elizabeth H. BeersTree Fruit Research and Extension CenterWashington State University1100 N. Western Ave.Wenatchee,WA 98801The Effect of Leaf Age on the Length of Residual Activity of Agri-Mek in PearFoliage as determined by Twospotted Spider Mite Mortality.Site and method description.This study was conducted in a mature 'd'Anjou' orchard at the Tree Fruit Research andExtension Center in Wenatchee, Washington. A cohort of leaves (the leaf closest to mid-shoot on current season's growth) was tagged on 16 May. The experimental design wasrandomized complete block with three treatments (leaf age at time of application) and 10replications. Leaf ages were 2, 6 and 12 weeks old, applied on 17 May, 16 June and 26July respectively. Treatments were applied with a handgun sprayer at 350 psi to the pointof drip, and untreated trees were left as checks. To avoid pear psylla damage the plotwas treated with fenoxycarb pre-bloom and detergent several times during theexperimental period. The pear psylla sprays were never applied closer than 3 days beforea bioassay was initiated.The Agri-Mek residues were bioassayed weekly or biweekly starting 1 week post-treatment continuing through 13 Sept. Ten tagged leaves were collected from eachtreatment on each bioassay date. A 2-cm leaf disk was cut from each leaf and floated in ajelly cup with distilled water and cotton, and with the bottom surface facing up. Tenadult female TSM were transferred to each leaf disk and evaluated for mortality after 72h at 24°C. Dead and moribund mites were classed as dead, and mites that were not foundon the leaf disk were not included in the analyses. Replicates with less than five mitesfound on the disk at time of evaluation were also excluded from the analyses. Treatmentmortality data were corrected for check mortality with Abbott's formula.Leaf age-dependent residual activity.This experiment on pear is a follow-up to our 1992 bioassay study of the effect ofleaf age on the length of residual activity of Agri-Mek in apple foliage. In both apple andpear there is clearly stronger residual effect of Agri-Mek the earlier in the season it isapplied. Although these studies were performed in different growing seasons underdifferent weather conditions, the period of residual control appear to be much longer inpear than in apple foliage, especially when applications were made to older leaves.Residual activity is most easily explained by initial absorption into the leaf. Thisstudy indicates that changes in leaf surface characteristics as the leaf ages and areexposed to environmental factors are the reason for the decrease in rate of initialabsorption of Agri-Mek as the foliage ages. The results of the study emphasizes theimportance of using Agri-Mek early in the season for obtaining the best results in fieldperformance.4748o 75k_o2&ST3Q)^^U ^n<D JUV-W-OoCO.w«*•»o25<o-fc-'oT3"oCDk-i_ooJ»•*-»o-D<42 56 70 84Residue age (days)Figure 1. Effect of leaf age (2, 6, and 12 weeks) at time of Agri-Mek application on residualcontrol of twospotted spider mite as determined by leaf-disk bioassay.

The effect of leaf age on the length of residual activity of Agri-Mek in pear foliage as determined by twospotted spider mite mortality

https://ir.library.oregonstate.edu/downloads/j9602684d

The effect of leaf age on the length of residual activity of Agri-Mek in pear foliage as determined by twospotted spider mite mortality

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