Is this a year for White Mold — Ohio soybean update
The following article was written by OSU Plant Pathologist Anne Dorrance, and appears in the OSU Corn newsletter at http://corn.osu.edu/newsletters/2010/2010-18/is-this-a-year-for-white-mold
There are no tried and true solid prediction systems, currently for white mold development on soybeans. However, conditions exist in the state similar to last year – with one key difference, it is hotter this year and moisture levels have been exceedingly higher in some parts of the state. White mold infections are favored by consistently damp conditions (not flooded) from the time of canopy closure through flowering. These conditions favor the development of the fruiting structures, called apothecia, which form from those overwintering or survival structures called sclerotia. Sclerotia are the hard, black, irregular shaped fruiting bodies that form on and in the soybean plant. IN many cases they look just like rat and mouse droppings but the difference is they are pink or white on the inside. Once these very small sclerotia germinate, the spores are deposited on the dying blossoms and from there they can infect the plants.
Not all fields in Ohio have inoculum for white mold. IN general, there are some fields that have a consistent history of the disease and it tends to be in pockets – fields that have poor air drainage, high yielding, and high plant populations.
For those high yielding, high value soybeans, in areas of the state where this is a constant issue, this is the time to consider a fungicide. Applications should be made at the R1-R2 phase. At this time, only Topsin M is labeled for control of this disease. We have seen this work, when conditions are favorable at the early flowering stages. If the following conditions occur through flowering a second application is necessary at the R3 stage: weather pattern of cool nights, light rains, and heavy dews. However, if temperatures hit the high 80’s and dews do not form, these conditions are not favorable for disease to develop and the fungus will just sit there.
There are several other management measures that have been touted for Sclerotinia stem rot and white mold of soybean. Some have secondary effects that contribute to yield loss due to the late application time (Cobra) while others only reduce disease levels slightly based on some data from other states. The best disease management strategies for this disease are resistant varieties, reduced plant populations (<160,000 plants/acre) and 15” row widths. Putting some numbers on paper and calculating out the cost of application based on how the field looks, reduced yield due to application will help you make these types of decisions. Late planted fields that have been hit repeatedly with rains and have poor root development are probably best left alone. Putting more money into these fields is like keeping that old truck going – with all of the repair costs you could have bought a newer better truck!
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