Hi I'm Damon Smith.
Extension field crops technologist for University of Wisconsin Madison.
Today we're out in a soybean field at the Hancock Agricultural Research Station located
in Hancock Wisconsin.
And these are a series of white mold trials that we're looking at here and so I want us
to spend a little bit of time talking about white mold in the white mold life cycling
and specifically how soybeans are affected by the fungus. The fungus that causes white
mold is called sclerotinia sclerotiorum. It survive in the field as small survival structures
which we call sclerotia they're hardened round or irregular round black structures. And those
structures are very important because what happens is in the late spring and early summer,
as the rows begin to close and a canopy begins to fill in in soybeans, a small mushroom like
structure called apothecia, forms. That apothecia then has microscopic spores which are born
on the surface of the cup, on on the top of that cup. And those spores are then forcibly
ejected up into the canopy of the soybean. Those spores will land on flowers or senescing
flower parts in soybeans. So the window of opportunity for infection of soybeans
by the white mold fungus, is in the R1 to early R4 grow stages. That's also the
prime time if you're going to do an in-season pesticide application, such as a Cobra application,
Endura or Approach or one of these fungicide programs, that's the window of opportunity to
apply those fungicides. Once the fungus infects through the flowers, it then grows down
into the stem and causes a damaged on the stem. And the scientific name of this
disease is actually sclerotinia stem rot. And you can see it gets his name because of the
rotting that we have on the stem. You can also see that the fungus has ruptured through the stem
and we have the white cottony growth which is where we get the name white mold from. If
we split the stems open, we will also see internal damage inside the stem. And eventually more
sclerotia will form on the inside the stem material. And you can see there's actually
sclerotia inside already forming. At the end of the season when we come through with our
combines to actually harvest this material, our combines then spread those sclerotia back
out on the field. So it's very important at harvest time that you either save fields
that are heavily affected by white mold, you save those fields to the end of the harvest.
Or your are diligent about cleaning your combines between fields, because those sclerotia can
get caught in the combine and be spread out on the field that may not have a history of
white mold. In terms of management of this fungus, we like to see cultural practices and fungicide
or a pesticide program layered on top of those cultural practices; This is a multi-pronged
approach in terms of managing white mold in soybeans. We know that using wider row spacing,
going from a 15 inch row spacing to a 30 inch row spacing, like what you're looking at here,
can help reduce the amount of white mold in the field. And also dropping planting population.
Here's some work with planting population where we actually imitated low and high fertility
situations and planted it 160,000 seeds/a, and 100,000 seeds/a. And further layered
fungicides, or the herbicide Cobra, and compared that against an untreated control. And you can see
if we look at the low fertility situation here, we will get a nice reduction where we have
a hundred thousand seeds per acre, and then a further reduction where we get Endura put
on at the are the R3 growth stage- which seemed to be optimum timing in this particular situation.
We look at yield, we can see actually higher yields where we had 100,000 seeds per
acre planting compared to the 160,000 seeds per acre, and we apply Endura
at R3. Thus we're recommending that folks consider dropping seeding rates in these environments
where they have high white mold pressure. Spend some time also studying variety trials and
variety ratings. While we don't have varieties that are immune to white mold, we do you have
varieties with decent resistance out there. So you can also layer that on top. And then looking
at those fungicide applications, and again your window is somewhere between that R1
to R3 in terms of putting a fungicide on. In order to help you make that decision,
we do have an app for that. It's called Sporscaster. We've done a lot of research with the app. And
that app was partially funded by the Wisconsin Soybean Marketing Board. What we're doing with
that app, we're using the weather information during that bloom time in soybean. The app is
pulling down weather from the internet, pulling it into the phone. And we're using some statistical
models to make a daily risk prediction at that bloom time, of whether you'll actually
have white mold later in the season. And that risk tool can then be used to make that decision-
should you be spraying or not, and when you might be spraying within that window
of opportunity for the fungus, again somewhere between that R1 and R3 growth stage. So feel
free to go out to the Apple Store or Google Play Store and download that app to your phone.
And it uses the GPS on your phone to actually find the weather information for a particular
field. If you'd like to learn more about white mold, or management of white mold, or other
field crop diseases, feel free to visit Badgercropdoc.com or see your local Extension agent.