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Sclerotinia Infection and Inoculum Production as Influenced by Crop Species and Management Techniques
April 15, 2002

By Bob Henson, Greg Endres, and Blaine Schatz, NDSU Carrington Research Extension Center and Art Lamey, Department of Plant Pathology North Dakota State University

The objective of this project is to develop management strategies to minimize losses due to Sclerotinia (white mold). Canola, field pea, flax, dry bean, soybean, and sunflower are being compared for disease susceptibility, production of sclerotia (the black overwintering bodies), effectiveness of a chemical control agent, variation among varieties, and, in the case of dry bean, soybean, and sunflower, the influence of row spacing (30" vs. 7") on disease and yield.

In 2001, adequate disease pressure was again achieved in dry bean, resulting in an overall average of 65% incidence (% of plants showing symptoms). See Table 1.

One application of Ronilan at beginning bloom slightly reduced the incidence of sclerotinia and the mass of sclerotia produced, but the differences were not statistically significant.

Yield was increased with the fungicide application, but, due to high variability among replications, this difference was also not statistically significant.

In 1999, four applications reduced incidence from 74% to 13%, with a corresponding yield increase of 38%. These results indicate the need for more than one application under high disease pressure. Market prices will dictate how many are economically viable.

Row spacing again had a minimal effect on disease incidence, with a slight reduction in wide rows compared to solid-seeding. However, the plot area was irrigated frequently during flowering to promote disease development and wide rows may be more beneficial under dryland conditions.

Compared to solid-seeding, wide rows reduced sclerotia production from 24.4 to 13.1 lbs. /acre. Differences in disease incidence and the production of sclerotia were also not statistically significant. Yields at the two row spacings were similar.

The major factor affecting Sclerotinia incidence in both years was variety. Norstar (navy) was significantly less susceptible than Maverick (pinto) and also produced a lower mass of sclerotia /acre.

This may be due to the more upright growth habit of Norstar, a higher level of genetic resistance, or a combination of both factors. Norstar tended to respond better than Maverick to chemical control, which may be a result of better fungicide coverage in a more open canopy.

Although these results do not allow a generalization among market classes, the generally more upright architecture of navies favors a more open canopy, more air movement, and a drier, less favorable environment for disease. Combining this characteristic with wide rows may be the preferred option in dry bean fields with relatively high potential for Sclerotinia infection.

Sclerotia production is an issue that should be considered in managing sclerotinia. These bodies either are harvested with the grain, resulting in dockage or rejection of seed lots, or remain in the field to serve as disease inoculum for subsequent crops in the rotation. The results of this project show that dry beans produce much less sclerotia per acre than sunflowers infected with head rot. The implications of this are important in determining not only which crops to include in a dry bean rotation, but also how soon dry beans can be rotated back onto a field.


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