Development of Sustainable Practices for Integrated Management of Apple Diseases
The specific objectives of this proposal are to test the efficacy of:
1) A novel orchard floor cover crop to break the life cycle of the apple scab pathogen, which over winters in apple leaf litter; and
2) Environmentally benign compounds applied to apple trees to control scab and the sooty blotch/fly speck disease complex. These diseases are so serious that apples cannot currently be produced in quantity anywhere in the world without synthetic fungicides.
We will develop key components of a biologically based, coordinated program to control the major fruit and foliar diseases of apple in the northern U.S. Our long-term goal is to integrate the best of these methods to achieve an additive or synergistic effect. This strategy would break continuing reliance on fungicides by conventional orchardists and provide a reliable, non-pesticide, low-input and low-cost framework for organic growers.
Researchers from the University of Wisconsin departments of pathology, agronomy and pomology, as well as orchardists and a mushroom farmer, will collaborate on the project.
To accomplish objective 1, apple plots were seeded in spring 1997 with kura clover (Trifolium ambiguum). The expected results are that this clover will foster soil fauna which eat apple leaf litter, trap leaves as they fall in the autumn, retain moisture optimal for leaf decomposition and reduce escape of primary spore inoculum in spring from remaining litter. The beneficial side effects of kura clover are that it will provide a source of nitrogen used in part by the trees (minimizing purchased N inputs and nitrate leaching), a favored nectar source for bees, a highly effective crop for soil conservation and a non-chemical means of weed control.
In 2000 at both the Peninsular Research Station in Sturgeon Bay, WI, and the West Madison Research Station in Madison, WI, the airborne ascospore counts in Kura plots were not different from counts in a control plot with a grass ground cover. At neither location did the Kura clover result in a significant decrease in primary scab infection on the leaves of the orchard trees nor on potted bioassay trees placed in the orchard at Sturgeon Bay; at West Madison bioassay trees placed in the Kura plot had fewer lesions than those placed in existing ground cover.
In 2000, two experimental sprays, a methionine-riboflavin mixture (M-R), and potassium bicarbonate-Ultrafine Sunspray OilTM mixture (KHCO3), as well as a water negative control and sulfur positive control, were applied to apple trees at an organic orchard in Gays Mills, WI and a conventional orchard in Cottage Grove, WI. They were also tested on fruit in a growth chamber. In general, M-R and KHCO3 reduced sooty blotch and flyspeck as well or better than sulfur.