Some of the 2016 Nebraska corn crop experienced prolonged stress and sometimes wounding earlier this season. While most of the crop looks good, we are beginning to see early evidence of problems developing. In particular, stalk and crown rot diseases, including Anthracnose top dieback symptoms, are beginning to develop. Producers should watch for early symptoms and consider monitoring high risk corn fields for stalk rot diseases as harvest approaches.
Crop stress during the growing season has and will likely contribute to the development of some stalk rot diseases. These can lead to weakened stalks, already evident in some corn, can be vulnerable to lodging under high wind conditions. Pay special attention to fields that have one or more of these risk factors for stalk rot diseases and lodging:
Scouting for Stalk Rot Diseases
The first indication of a problem could be the early, and sometimes rapid, discoloration of the corn plant turning from green to brown or gray (Figure 2). Individual plants or patches of several plants may be affected. Affected plants often have stalks that are hollow and easily crushed by hand or bent using the “push or pinch” test. Stalk rots can occur at any point in the stalk from the crown at/below the soil line (Figure 3) all the way to the tassel. Rotting that occurs at an upper node and kills only the upper plant parts is referred to as “top rot” and does not necessarily cause lodging of the whole plant. However, degradation of the stalk below the ear can lead to plant lodging and losses during harvest.
To scout for stalk rots, walk through a field, randomly selecting a minimum of 100 plants representing a large portion of the field. To test for stalk rot push the plant tops away from you approximately 30° from vertical. If plants don’t snap back to vertical, the stalk has been compromised by stalk rot. An alternative method is to use the pinch test to evaluate plants for stalk rots. Pinch or squeeze the plant at one of the lowest internodes above the brace roots. If the stalk crushes easily by hand, that’s a sign its integrity has been reduced by stalk rot and it’s prone to lodging. If more than 10% of plants exhibit stalk rot symptoms, harvesting that field should be a priority over others at less risk in order to reduce the chance of plant lodging and the potential for yield loss.
Several fungal and bacterial pathogens can cause stalk rot diseases. The more common ones are summarized below.
More details and photos of these and other diseases can be found inCorn Disease Profile II: Stalk Rot Diseases and in greater depth in Common Stalk Rot Diseases of Corn.
There is nothing to be done at this point in the season to stop stalk rot diseases; affected plants will continue to degrade over time further weakening them. But, you can work to minimize your losses by identifying which fields have the worst stalk rot diseases and harvest or chop heavily impacted fields first to minimize losses from lodging. When making hybrid selections for later years, consider choosing hybrids with better resistance to one or more stalk rot diseases to help reduce disease pressure.
Source: University of Nebraska-Lincoln
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