- Agronomic: grass (misc. perennial), hay
- Fruits: apples, general tree fruits
- Animal Production: manure management, feed/forage
- Crop Production: biological inoculants, cover crops
- Education and Training: display, mentoring, on-farm/ranch research, participatory research
- Natural Resources/Environment: habitat enhancement
- Pest Management: biological control, compost extracts, cultural control, integrated pest management
- Production Systems: holistic management
- Soil Management: composting, earthworms, green manures, organic matter
Our main objective is to develop a biologically based program to control the major fungal diseases of apple fruit and foliage in the northern United States. If successful, this would break the continuing reliance on toxic fungicides used by conventional growers and provide a reliable, non-pesticide, low input, and low cost framework for organic growers.
The specific objectives of our current research are to:
1. Assess the ability of an orchard floor cover crop, kura clover, to break the life cycle of the apple scab pathogen.
2. Test the efficacy of environmentally benign compounds used as sprays during the growing season to control scab and other important foliar and fruit diseases, such as cedar apple rust and the sooty blotch/flyspeck complex.
Inoculum (ascospores) of the apple scab pathogen is released in the spring from previously infected apple leaves that have overwintered on the orchard floor. Kura clover is proposed to reduce ascospore dispersal by both providing a barrier to prevent the escape of ascospores from the clover canopy as well as promoting decomposition of the apple leaf litter. For Objective 1, apple plots at two locations were seeded with kura clover in spring 1997. In spring 1998 and 1999, ascospore release was measured using spore samplers positioned above the kura clover plots and control plots (existing ground cover). Apple scab disease was also monitored on the leaves of the orchard trees and leaves of small potted trees placed in the orchard as bioassay plants. Earthworm activity was assessed by counting castings in the kura and control plots. For Objective 2, three environmentally benign experimental sprays, benzothiadiazole ([BTH], an inducer of disease resistance), a methionine (amino acid)-riboflavin (vitamin) mixture (M-R), and potassium bicarbonate (KHCO3), were applied to apple tree branches. Apple scab, cedar-apple rust and the flyspeck/sooty blotch disease complex on apple leaves and fruit were assessed throughout the season.
In 1998, kura clover significantly reduced aerial ascospore concentration compared to the existing ground cover control at one location but not at the other. It did not reduce apple scab disease at either location. In 1999, kura clover did not significantly reduce the aerial ascospore concentration compared to the existing ground cover at either location, nor did it significantly reduce apple scab symptoms on the leaves of the mature or potted bioassay trees at either location. There were significantly more earthworm castings and holes at one location but not at the other.
In 1998 all of the experimental sprays reduced apple scab infection on leaves and fruit, under mild to moderate disease pressure. In 1999, under moderate to severe disease pressure, M-R and BTH reduced apple scab on both leaves and fruit. M-R and KHCO3 significantly reduced sooty blotch and flyspeck infection on fruit in both years. Cedar apple rust infection on leaves or fruit was not evaluated in 1999, because results from 1998 showed little impact of the compounds on this disease.
Impacts and Potential Contributions
Kura clover takes at least three years to become well developed. At the site where the clover is better established, earthworm activity is greater and there is a trend toward lower scab incidence on potted trees. A decrease in aerial ascospores and scab is expected when a better stand of the clover is established. Identifying environmentally benign alternatives to synthetic fungicides will especially benefit organic growers but will also relieve traditional orchardists from dependence on more toxic compounds. Combining the clover as a ground cover with the use of the most effective of the experimental sprays should result in effective, non-toxic, and sustainable disease control.
Kura clover was seeded as a ground cover at two apple orchards in spring 1997 to test its ability to decrease aerial ascospore concentrations of Venturia inaequalis and thus inhibit primary apple scab infection. In 1999, at the Peninsular Research Station in Sturgeon Bay, WI, ascospore counts in kura plots were not different from counts in a control plot with a grass ground cover. The ascospore counts were too low at a second site, the West Madison Research Station in Madison, WI, for a meaningful analysis. At neither location did the kura clover result in a decrease in primary scab infection on the leaves of the orchard trees or potted bioassay trees placed in the orchard. However, kura clover requires approximately three years to develop a dense stand, and we anticipate that the clover will prove to be more effective at preventing primary scab infection in future years.
Three experimental sprays, benzothiadiazole ([BTH], an inducer of systemic acquired resistance), a methionine-riboflavin mixture (M-R), and a potassium bicarbonate-Ultrafine Sunspray Oil™ mixture (KHCO3), as well as a water control, were applied to apple trees at Sturgeon Bay and at Turkey Ridge organic orchard near Gays Mills, WI. Two treatments (BTH and M-R) reduced apple scab on leaves and fruit; two treatments (M-R and KHCO3) reduced sooty blotch and flyspeck symptoms on fruit. Cedar apple rust infection on leaves or fruit was not evaluated in 1999, because results from 1998 showed little impact of the compounds on this disease.
1. Test the ability of the orchard floor cover crop kura clover (Trifolium ambiguum) to break the life cycle of the apple scab pathogen (Venturia inaequalis).
2. Test the efficacy of environmentally benign compounds as sprays during the growing season to control scab and other important foliar and fruit diseases such as cedar apple rust and the sooty blotch/flyspeck complex.