Signs of Disease, Insects Showing on Young Corn

This might be year where scouting and possible treatment pays.

One year ago part of the Corn Illustrated plots were sprayed with fungicide as a scheduled treatment. There was very little disease present when the fungicide was applied at tasseling and results were inconclusive. This year the story could be different, says Dave Nanda, president of Bird Hybrids, Tiffin, Ohio and consultant for Corn Illustrated.

After inspecting knee-high plots planted May 29, Nanda reports finding early signs of several diseases and even some insects. He's not surprised since the start of this season was completely different from a year ago. In '07 the plot site received a total of just over 5 inches of rain from May 1 through Sept. 15. This June the total was roughly 20 inches in a single month, nearly four times what fell all last year!

What that means for disease is more moisture available, more humidity on some days, and slower growing corn, at least at first. Corn is beginning to recover nicely and enter its rapid growth phase. Nothing is nearly widespread enough or at the right stage to warrant treatment yet. Nanda is simply raising the flag to note that this summer would be a good one to scout fields. Most fungicides are labeled to be applied around tasseling. Keeping your eyes open as that window approaches would be a good idea, he notes. Fungicide applications are not scheduled on the Corn Illustrated plots this year, but they will be considered if conditions warrant it.

Diseases Nanda noticed on the young corn include rust, northern corn leaf blight, and anthracnose stalk rot. He also noticed signs of nitrogen deficiency on a few plants, even though urea was applied pre-plant just before that particular plot was planted. While it suffered through heavy rains, Jim Camberato, a Purdue University soil fertility specialist, has noted that since only a fourth of the nitrogen in urea was in a leachable, vulnerable form when rains came, losses may have happened, but shouldn't have been major. Whether he's right may not be known until later in the season, when plants try to fill out ears and nitrogen demands are higher.

Nanda also discovered aphids feeding on corn. Aphids are killed by ladybugs, and he did find a few of the natural predators in the field as well. However, he says aphids are worth watching. Under unusual conditions, they can become thick enough to interfere with proper silking. They can be easily controlled with insecticide.

Nanda isn't ready to suggest that you order fungicide or insecticide yet nor line up someone to apply it. He is saying that this is a year these pests will deserve watching. Know what your plan of action will be should conditions favor development of the diseases and insects as the season progresses, and treatment for one or both become necessary. Be sure to factor in current corn prices when determining if treatment will pay. Higher price for corn means that the treatment threshold will be reached sooner than if corn was cheap.

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