Apple, Dilute Insecticide Experiment, 1991

Abstract

Abstract Experimental sprays were applied to run-off to single-tree plots in a randomized block design consisting of 2 replicates of'Golden Delicious' and 2 replicates of'Yorking'. Treated single trees were separated by others not sprayed with insecticides. The trees were planted to a spacing of 20 × 35 ft and were 35-yrs-old. Sprays were applied with a John Bean sprayer, 35 gpm pump, equipped with a spray mast carrying 7 spray guns arranged to wet to run-off the uniformly trimmed trees. Approximately 6.0 gallons of spray were applied per replicate tree (ca 400 GPA). Refer to the first table for application dates. Applications for Exp. Comp. 1 and 2 were timed for CM control based on pheromone trap catches and a degree day based computer predictive model. The first two treatments of Exp. Comp. 1 and 2 received Guthion applications at petal-fall (15 May) and 4th cover (9 Jul) to lessen OFM damage that might mask CM damage. The last two treatments of Exp. Comp. 1 and 2 were optimally timed single applications for peak egg deposition of each CM generation. Effectiveness on the aphid complex was evaluated by counting aphid-infested leaves/10 top terminals, and aphis/most infested leaf. Effect of sprays on WALH was evaluated by counting nymphs/25 injured leaves/tree. Effectiveness of test chemicals on ERM was evaluated by counting mites several times during the season on samples of 25 random leaves/tree, 100 leaves/treatment. Effect of sprays on the predator S. punctum was evaluated by 3-min counts of adults and larvae around the periphery of test trees. STLM was evaluated by a 5-min count of mines around the periphery of trees at the end of each of the three generations before peak emergence of the next generation adults. TABM were also evaluated with a similar 5-min count of rolled leaf shelters on 11 Jul during the first generation when most larvae were late fourth and fifth instars. Effectiveness of chemicals on fruit feeders was assessed by scoring for injury all dropped apples from 1 Jul to 28 Aug and picked samples of 25 fruit/tree on 9 Aug and 35 fruit/tree on 20 Aug. A final harvest pick evaluation of 120 fruit/tree was made on 18 Sep. All internal lepidopteran larvae from one replicate of each treatment at each drop and pick evaluation date were placed singly on an artificial lima diet normally used for rearing TABM. These larvae were then reared to adults in sealed 22 ml plastic cups at 25°C and 16:8 LD. Adult lepidoptera were identified to species and parasites were noted to give an indication of the proportion of species attacking apples at various times of the season. Lepidoptera pest pressure was extremely high throughout the season. Fruits were rated as 0 (no russet), 1 (raised lenticels), 2 (1-10% russeted surface), 3 (11-25% russeted surface), 4 (26-50% russeted surface), or 5 (>51% russeted surface). Possible ranges are 0-30 (none to raised lenticels), 31-60 (raised lenticels to 1-10% russeted surface), 61-90 (1-10% to 11-25% russeted surface), 91-120 (11-25% to 26-50% russeted surface), and 121-150 (26-50% to >51% russeted surface).