White Mold Refresher

In 2014, the thumb of Michigan was devastated by White Mold and this year it was a problem in Wisconsin, Iowa, and Minnesota. While White Mold tends to be a sporadic problem when it rears its head, it tends to be very damaging.

Here is a quick guide to White Mold.

White Mold is a soil borne pathogen with numerous host weed species in addition to soybeans and dry beans. The likelihood of it being in your soil is very high even if you don’t see it for years at a time. What keeps White Mold from being a perennial problem is that it needs special conditions to infect soybeans. Cool and wet conditions during flowering, late June through early July, are required for the spores to infest the plants. Once the disease is inside the plant there are no control options, the disease will cause damage and kill the plant prematurely.

Some people spray fungicides to control White Mold but I’m a little leery of this control. Fungicide has to be sprayed during the early flowering phase to have any chance of working, and timing can be critical.

Another practice has been to burn back the soybean plants using Cobra. The theory being this opens up the canopy and allows moisture to evaporate, reducing the positive environment that White Mold is looking for. The risk here is that burning back your soybeans can impact final yield. This may be a case where the cure is worse than the disease.

The worst thing about White Mold is that it is a ‘high yield’ disease. Everything that should increase yield also increases the chance for White Mold. Narrow rows, early planting, lots of water, and quick canopy contributes to increased yield, but also sets up a good environment for White Mold infestation.

There is limited help genetically for White Mold. There is no resistance gene. Soybeans are rated based on historical and genetic family rates of infestation. While some beans are definitely better than others when it comes to White Mold, all varieties still can get infested.

Unless you are getting White Mold every other year you probably do not need to alter your practices. If you do have a high incidence of White Mold, pick varieties with good White Mold tolerance and widen your rows to 22 or 30 inches. These two simple steps can help a lot. You may also consider delaying your planting and spraying fungicide if the season is cool and wet.

White Mold is a disease we have to live with, but most of the time we can make changes to reduce its damage.

December 2015 Earfull Newsletter
Written by Alex Renk

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