Farm Horizons, Aug. 2016

August is prime time for field scouting

August and September are my favorite months for scouting corn fields. By this time, we have an idea of what to expect for corn yield. When I scout, I look for insect and disease pressure, nutrient deficiencies, and differences between corn hybrids.


The major corn insect I scout for is corn rootworm.

The northern corn rootworm (green beetle) is normally what we find in our area, unless the field has been continuous corn.

Western corn rootworm (beetle with black stripes on back) is pretty much limited to fields in continuous corn. These rootworms do not overwinter in our area, as well as northern corn rootworm.

Corn fields most at risk of corn rootworm are those that are in a continuous corn rotation and those planted very late in the season. Beetles will migrate into late planted fields, feed on silks and pollen, and then lay their eggs. If high numbers of corn rootworm beetles are found, fields will either need to be rotated out of corn the following year or managed with a hybrid with a corn rootworm trait.


From a disease standpoint, there are several diseases to scout. Stalk rot may be the most common disease that seems to show up somewhere, nearly every year.

Identifying stalk rot early in the fall is important so growers know what fields to harvest first. This is done by simply walking down the field and pushing stalks to the side. Healthy stalks will spring back to an upright position. Plants infected with stalk rot will stay bent over.

Irrigated fields normally have more disease pressure, because more corn is typically grown on this land and the environment is wetter than dryland corn.

Goss’s Wilt is a disease that was identified a few years ago in western Minnesota. It can now be found all the way up into the Red River Valley. Goss’s Wilt needs a continuous corn rotation because it’s a bacterial disease and doesn’t overwinter well. It can be found in many continuous corn fields that are irrigated.

The other disease to watch for is northern corn leaf blight. Its cigar-shaped lesions are quite easy to identify.

When diseases build up in a field, it’s a good idea to rotate out of that crop for a few years.

The main nutrient deficiency I see in August is nitrogen. I’m afraid this will be an issue in too many fields this year, because of the saturated soil growers had to deal with back in May and June. Lower leaves on the plant turn yellow beginning at the leaf tip and then down the midrib. Nutrient deficiency appearing in August can take away 20 to 40 bushels per acre.

Corn hybrids

The third item I scout is the corn hybrid itself. How well does the hybrid withstand moisture stress? Does the husk hold tight to the ear and stay in an upright position, or does the husk open up and ear hang down, allowing grain to dry down? What is the general health of the plant in September? Are hybrids maturing on schedule?

I have discovered that there is no perfect hybrid. This is why it’s important to scout fields now, and then select hybrids that best match the needs of individual fields.

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