Evaluating effectiveness of reduced-risk fungicides and a wetness-based warning system for control of sooty blotch and flyspeck of apple, 2007

摘要

A trial was conducted on Golden Delicious apple trees at the University of Illinois Pomology Research Farm at Urbana, IL, to evaluate efficacy of a reduced-risk fungicide (Sovran), an organic fungicide (Kaligreen), and a wetness-basedwarning system for control of sooty blotch and flyspeck. Trees were approximately 3 m tall, and canopies were well pruned. The experimental design was a randomized complete block with four, two-tree replications of six treatments. Trees in allplots were sprayed through the first-cover spray on 25 May. The conventional spray schedule received the second-cover spray on 11 Jun, and subsequent cover sprays every two wk until 22 Aug (a total of 7 sprays). The treatments directed by awetness-based warning system received the second-cover spray after accumulation of 175 leaf wetness hours (LWH) on 28 Jul. LWH were recorded with the Watchdog Leaf Wetness and Temperature Logger (Spectrum Technologies, Inc., Plainfield, IL). One sensor was placed on the northern side of the canopy of a tree in the orchard 5 ft above the ground facingnorth at an angle of 45deg to horizon. Data were downloaded to a computer at least once per wk, and accumulated LWH for all wetting periods greater than 4 hrs were calculated beginning on 25 May, the date of the first cover spray (14 days after petalfall). Following application of the second cover-spray on 28 Jul, the trees were sprayed on a two-week schedule until 22 Aug. Sprays were applied to both sides of the tree rows with a hydraulic hand-gun tractor sprayer. Insect pests in all plots werecontrolled according to the recommended conventional practices for commercial apple orchards in Illinois. On 2 Oct, approximately 10 days before harvest, 60 apples from each tree were examined for incidence (percentage of fruit infected)and severity (percentage of surface area of fruit affected) of sooty blotch and flyspeck. In each tree, five apples from each of upper, middle, and lower canopies of all four sides (northern, eastern, southern, western) were examined. Average monthlyhigh/low temperatures (deg F) were 82/55, 86/61, 85/61, 89/68, 84/58, and 71/49 in May, Jun, Jul, Aug, Sep, and Oct, respectively. Precipitation occurred on 5 days (1.54 in.) in May, 11 days (5.66 in.) in Jun, 6 days (3.82 in.) in Jul, 9 days(0.87 in.) in Aug, 7 day (2.27 in.) in Sep, and 11 days (2.56 in.) in Oct.