MN Fruit & Vegetable IPM News - Vol. 4, No. 5

Provided by Dr. Vince Fritz, Dept. of Horticultural Science, Southern Research and Outreach Center, Waseca, Minn. (Reprinted from Vegetable Grower News).

Soil health is certainly one of the producer’s largest assets in growing quality fruits and vegetables. Tilth, drainage, and fertility are some of its key characteristics that together create an environment for excellent root growth and crop uniformity. However, if pathogen loads increase over time, crops that are susceptible to the disease will fall victim. If the pathogen is persistent in the soil for many years, producers are faced with the challenge of effectively managing the disease when basic crop rotation principles are not successful. Fungicide seed treatments are often a strategy, however indiscriminate use of them can lead to pathogen acquired resistance and ineffective results. Choosing a variety with genetic resistance to the disease is often a useful approach however this does not apply to several pathogens.

Three stages of A. euteiches life cycle.

A sustainable approach to effective disease management often integrates many of the strategies mentioned above. Another strategy that has shown promise in the management of persistent soil diseases is the use of green manure cover crops. Professor and Extension Vegetable Specialist, Dr. Vince Fritz, at the University of Minnesota Southern Research and Outreach Center, has conducted research over a number of years to develop a strategy to manage root rot in processing peas, caused by Aphanomyces euteiches.

The disease has been a big challenge for vegetable processors located in Minnesota, Wisconsin, and Illinois who routinely struggle with the disease that robs yield potential and leaves fields undesirable for future pea production. The reasons for the struggle are many: 1) the pathogen is randomly distributed in fields, 2) different strains of the pathogen vary in their pathogenicity, 3) all 3 stages of its life cycle are infective, 4) it forms oospores that are very persistent survival structures, 4) wet, cool, weather, like for most diseases, can promote early infection and 5) budget cuts across public universities have eliminated pea breeding programs.

Early work of Dr. Fritz and his colleagues discovered a significant suppressive effect from a previous crop of oats when grown as a green manure crop in late summer and fall and chisel plowed down before pea planting the following spring (picture above). Two theories on how the oats reduced the disease were 1) leachates from the oat residue come in direct contact with oospores causing them to rupture, and 2) leachates released from the oat residue served as an oospore germination triggering mechanism and effectively “tricked” the pathogen into thinking peas, the host, was present in the field. Once germinated, it can’t sustain itself in the absence of the host plant.

A former graduate student of Dr. Fritz gathered evidence that suggested that theory #2 was likely to occur. The use of this kind of management strategy (2 bushels oats planted /A) may serve the producer well when used as a preventive tool in fields with low disease pressure. The effects of the oat residue were also best realized when it was chisel plowed compared to moldboard plowing which places the residue deeper in the soil, and often beyond the “zone of influence”, the rooting zone of the pea plant.

In an effort to further improve the ability to manage root rot consistently, Dr. Fritz recently tested the ability of rape as a green manure crop because of its known phytotoxicity on weeds and reported fungal-toxic effects on some pathogens. Early results suggested that in fields that are heavily infested, rape offers greater benefit from that realized in oats. Although the use of green manure crops works as an effective strategy against a pathogen like A. euteiches, it became difficult to implement it into a typical corn – soybean production system that is so prevalent in the Midwest.

Impact of using genetic resistance and oat green manure crop
on severity of root rot in peas. Short peas are susceptible and tall peas are resistant. Short peas in second tier of plots were
planted after incorporating an oat green manure crop. Short peas in foreground were planted without using the green manure crop.

In-furrow, ground rape seed at planting significantly reduced
symptoms in heavily infested soil. Left, peas receiving the
in-furrow treatment; right, peas planted without treatment.

Dr. Fritz’s team began to investigate the potential of using ground rape seed as a treatment at planting, since the chemicals thought to be responsible for disease control, glucosinolates, were highly concentrated in the seeds. Initial studies included coating the pea seed with ground rape seed directly and placing it in the furrow along with pea seed at planting. The results revealed that when ground rape seed is applied directly to the pea seed, pea emergence was reduced due to its toxicity to the young pea seedling. However, when it was placed in the furrow emergence was good and infection by the pathogen was greatly reduced.

“This observation may provide us with an approach to developing a strategy that will realize the benefits from green manure crops in preventing soil borne diseases but in a way that doesn’t require growing the crop itself”, Fritz said. Work continues to calibrate the timing and amount of rape seed that will provide the best results. “If we are able to get consistent results from our tests in a soil with extremely high disease pressure, we will feel more confident in the potential performance on commercial crop acreage”, Fritz said. Recent work conducted by Fritz and his team has been financially supported by the Minnesota Department of Agriculture.

For More Information:
Dr. Vince Fritz
Professor of Horticultural Science
Extension Vegetable Specialist
Southern Research and Outreach Center
Waseca, MN 56093
vafritz@umn.edu

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jeanne Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us , MDA, 625 Robert St. North, St. Paul, MN 55155. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: www.mda.state.mn.us/plants/pestmanagement/ipm/ipmnews.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.

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Last Revised June, 2007 by woldx018@umn.edu
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Research Update: Use of Green Manure Cover Crops Improves Disease Management

Research Update:
Use of Green Manure Cover Crops Improves Disease Management