2019 Corn Disease Awareness

Last season Tar Spot, Grey Leaf Spot and Northern Corn Leaf Blight infected corn fields earlier than normal, which impacted yields in the hardest hit areas. In addition, dead fields were susceptible to stalk rots, especially anthracnose. Ear rot, specifically giberella, could also be found last fall. The areas most impacted by giberella have vomitoxin in the grain and there are even reports of problems with silage. No one in the affected areas is eager to repeat these problems, so implementing some management strategies will help alleviate issues if they occur again.

2018 experienced record late season rainfall that created conditions where tropical diseases such as Tar Spot had the opportunity to thrive. The best management strategy here might be “watchful waiting”. If the weather pattern is more normal, I predict that Tar Spot will be difficult to find this fall. Unfortunately, here at the home office, March rainfall is currently more than 3 times its normal amount so this weather pattern has not yet changed.

There were differences in hybrid susceptibility with late season hybrids being healthier than early season varieties. Because there are no completely resistant products, I believe the better strategy is for growers to focus on yield and treat with fungicide if Tar Spot is a concern. A peek at the long-term weather early in the fungicide application window would help growers in the decision process. If the long-term forecast is wetter than average and you’re growing in an area affected the previous season, you should strongly consider fungicide.

There are now multiple fungicides available with a 2(ee) label for Tar Spot on corn. I’ll focus on Delaro® from Bayer since they were the first with the supplemental labelling. In addition, we are currently offering a promotion through Bayer to use their product in conjunction with our hybrids in the affected areas (northern Illinois and southern Wisconsin). Contact your dealer or DM if you’re not aware of this promotion. Delaro®, as well as the others with supplemental labelling, has two active ingredients and is considered a “premium” product in the fungicide chemistry product family.

Northern Corn Leaf Blight (NCLB) and Anthracnose Stalk Rot rarely affect final yield, but standability was highly impacted last season. Anthracnose is favored by saturated soils, cool nights and warm days. Newer hybrids with the ASR gene, which resists Anthracnose Stalk Rot, were much healthier last fall and much easier to harvest as the season dragged into November. Please refer to the Renk Seed catalog and locate the “Anthracnose Stalk Rot” column heading in the chart near the bottom of the page (see example below). Hybrids with this gene have the ASR designation along with a numerical rating.

If your preferred hybrid is not available with the ASR gene, fungicide could also be used to treat Anthracnose. The benefit of course is that you would be controlling all fungal diseases with an application, including NCLB. Carefully analyze local and unbiased data on the use of fungicides in your area to see if they are justified. For those of you in northern locations that are on rotated ground with disease resistant hybrids, you may not break even on the application. Assess your risk by observing the long-term forecasts for wetter and warmer weather patterns which would favor disease development. Last season the crop was mature ahead of schedule and in position for an early October harvest. Unfortunately, weather conspired against us which delayed soybean harvest and pushed corn harvest into November.

White Mold Fungicide

Over the years we have tested a lot of chemicals that claim to do a lot of wonderful things. Sadly we have been disappointed many times with these ‘wonder’ treatments and sprays. This year we tried Endura, a fungicide for control of White Mold in soybeans. By chance we sprayed it in the one field that we actually had White Mold. Half the field was treated with Endura and the other half left untreated. The results were very stunning – a very clear line between the treated and non-treated ground.

While I have not been a big advocate of using fungicide for White Mold control, it is nice to find one that works. There are two reasons I have not supported using fungicide. The first is that White Mold can be a very intermittent issue. Having White Mold every few years makes putting on fungicide economically questionable. The other is that the application of the chemical is very time specific. You need to spray when the spores are flying and the soybeans are flowering, and you may also have to do a second application 7 days after the first application.

I would consider using a foliar fungicide only in fields with a consistent history of White Mold and when conditions are conducive to infection (cool and wet in late June through mid-July).

BY ALEX RENK

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