Trials at Cooperating Orchards

Methods

On-farm cooperative trials evaluated the disease-warning system for SB/FS control. The number of cooperating orchards was 5 in 1997, 7 in 1998, 10 in 1999, 14 in 2001, and 14 in 2002. Cooperators followed recommendations for timing of the 2nd-cover fungicide spray (175 hr after the first cover spray) on a small portion of their orchard (minimum 10 trees) and applied their standard disease-control practices to same-variety, same-age trees nearby (control block). Wetness was measured by a Wetness/Temperature Logger (Spectrum Technologies), placed at 1.5-m height under the canopy of an apple tree in the test block of each cooperating orchard. The Logger was downloaded weekly to a laptop computer by a university scout. The scout tracked accumulation of wet hours at cooperating orchards and advised cooperators by phone when the 2nd-cover spray should be applied in the test block. One week before harvest, scouts rated incidence of sooty blotch and flyspeck on 50 apples on each of 5 trees in the test and control blocks, so that 500 apples were evaluated per cooperating orchard.

Results

Overall, growers in Illinois and Iowa were very pleased with the success of the disease prediction system. Two growers have actually purchased their own sensor, and several others are interested in doing future trials of the system with our cooperation. In Wisconsin, however, the system failed in half of the trials. Possible reasons for failure include: poor spray penetration in inadequately pruned trees, careless spraying, use of a fungicide other than a benzimidazole, late first or second cover spray application, or earlier wetness threshold for symptom development for some of the SBFS fungi at the failed sites. The next steps will be to help growers become independent in their use of the sensors and to modify the prediction system for success in Wisconsin.