Bob Henson, Greg Endres, and Blaine Schatz,
NDSU Research Extension Center, Carrington, ND,
and Art Lamey, Department of Plant Pathology,
NDSU, Fargo, ND
The objective of this 3-year 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 2000, the second year of the trial, high disease pressure was again achieved, resulting in 63% incidence in dry bean (% of plants showing symptoms). One application of Ronilan at beginning bloom had no effect on disease incidence or yield (Ronilan is not labeled for use in dry beans. It was used only for research purposes. Do not use unlabled fungicides in commercial production). 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.
In both years, row spacing had a minimal effect on disease, 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 less humid conditions. Averaged over the two years, wide rows resulted in a reduction in Sclerotia production from 9 to 3 lbs/acre. Yield was higher in 7 than in 30 rows, but this relationship may change if moisture is a limiting factor.
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.
The issue of Sclerotia production is an issue which should be considered in managing Sclerotinia. These bodies either are harvested with the grain, which may result 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 experiment to date show that dry beans are similar to soybeans in that they produce much less Sclerotia per acre than sunflowers infested with head rot. The implications of this are important in determining not only the other crops in a dry bean rotation, but also how soon can dry beans be planted again on a field.