Stalk Rot Threat Increases with Stress

Major players in disease can vary by area.

All you needed to see huge differences in stalk rots at the end of this season were areas that received stress and areas protected from the worst stresses. At the Corn Illustrated plots, that boiled down to whether the plot had water or not. Even corn in the same row bore very little resemblance to the same corn in the same row at the other end of the field, depending upon which end received water and which didn't, and when and how much water those plants received.

By harvest in mid-October, plants that received no irrigation were showing definite signs of stalk rot. Soils in the entire plot were underlain with sand and gravel at about 3 feet, perhaps less. Corn that received irrigation, even corn not irrigated until a week after pollination, showed little signs of stalk rot and consequently, very little lodging, especially at more typical plant populations around 32,000 plants per acre. Lodging picked up slightly at 40,000 plants per acre.

A trip through the non-irrigated section of the field before harvest confirmed that lack of water, not high population, was the major stressor this year, at least in this situation. Both the 32,000 and 40,000 plants per acre, non-irrigated plots revealed similar lodging. In both plots, about 30% of the plants were lodged. That decreased to near zero in the mid-season irrigated plots at 32,000, and to around 10% in the mid-season irrigated plots with 40,000 plants per acre. Very little lodging was observed at either population in the part of the field that received irrigation all season long.

Dave Nanda, Corn Illustrated consultant and president of Bird Hybrids, LLC, Tiffin, Ohio, quickly identified anthracnose stalk rot in the non-irrigated section of the plot. It's an opportunistic disease that quite typically comes in after something else stresses plants and draws down their defenses. In this case, that 'something else' was a severe shortage of moisture earlier in the season. Anthracnose symptoms include a black spattering on various stalk tissues. It's a disease that can lead to severe stalk lodging, as it did in this case.

In your area, it may have been anthracnose that affected stressed fields late in the season, or it may have been some other disease. Pressures of various diseases can vary by area. Nanda noted high levels of northern corn leaf blight while touring plots in early September in the northern half of Indiana. Those areas received more rain, beginning around the first of August. When Nanda saw the plots, they had not yet begun to dry down, like many fields further south did.

Other areas typically experience more problems with gray leaf spot, or perhaps Stewart's wilt. Some of these diseases are mainly leaf diseases that come in earlier in the season. This year, conditions weren't favorable for some of these leaf diseases, especially where it was dry and humidity levels were unusually low at mid-season. Even many fields that were sprayed with fungicides for disease control in mid-July, right after tasseling, did not show symptoms of leaf diseases at the time. Nanda suspects that if disease wasn't present at time of application, the fungicide likely helped little, if any.

There is good resistance available in certain hybrids to various diseases. Make sure you check out the disease package of any hybrids you consider planting this year, and compare them to known disease problems within your area. Remember that if gray leaf spot is typically a problem on your farm, just because you didn't see it this year certainly doesn't mean that it won't return in the future. The inoculum to start the disease will be there. All it will take are the right weather conditions at the right time in the season.

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