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How Humidity Can Do Corn In

TAGS: USDA Soybeans
How Humidity Can Do Corn In
Those high dew points can be a key culprit in spreading corn diseases.

No one is talking about a disaster, or anything near that. However, experts are saying that high heat and humidity may have taken the top end off corn yields, compared to what farmers might have expected otherwise. Heat can interfere with photosynthesis, even though most corn pollinated before extremely high heat rolled into Indiana. Humidity has been a mainstay for most of the summer.

"Leaf diseases are more likely to spread in high humidity situations," says Tony Vyn, an Extension specialist who works with tillage systems at Purdue University. "On susceptible hybrids and fields not sprayed with effective fungicides, the leaf area available for photosynthesis during critical grain fill can decline too rapidly. Corn plants are also more susceptible to stalk rot infection with high humidity and wet surface soils."

Planes and even helicopters have been busy most of the season spraying fungicides. However, one person associated with one of the major aerial application outfits in Indiana says some corn sprayed twice still shows some signs of gray leaf spot. Perhaps the lesions won't be as severe, but fungicides aren't always 100% effective in eliminating disease pressure. The other problem is that sometimes it's difficult to get an extremely effective application coverage, even with an airplane, due to trees, houses and other barriers that could interfere with the application.

Ear rots are also being reported, and are the direct result of taking advantage of prime growth opportunities for these fungi, primarily high humidity. Vyn says diplodia ear rot has been detected in some corn ears only halfway through the grain fill process. Ear rots will be most severe on susceptible hybrids that are already under stress from high heat or other conditions.

Excessive rain in north-central Indiana, especially, compounded the problem by adding stress. Even though a large majority of the crop was planted early, some of the soils were compacted from last fall's combine operations. Not every field was tilled. Many times the ruts were simply worked in. Soil compaction was apparent in some fields earlier in the season. Normally, it's less of a problem if it continues to rain. And it's even less likely to be a problem in soybeans, no matter what the weather pattern.

"I am more concerned about the negative consequences of excessive heat and humidity this season than I would normally be because of the other stress factors corn has experienced in 2010," Vyn says. "Overall, corn hybrids are much more stress-tolerant than those of 30 years ago. But compounding stresses, especially during the grain fill period, can impose significant restrictions to final grain yield."

How much of those projections, if any, will be built into the first USDA crop report out this week remains unclear. Normally, the first report is based heavily on observations made by crop reporters at the end of July. Usually, it's more of a population counting exercise. However, with some ear development under way this year when those counts were made, it will be interesting to see what type of numbers USDA comes out with for Indiana and the nation.

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