Wednesday, June 17, 2009

Corn, Late Planting and Management

Photo: Possible Mn defiency in corn, which is most likely due to weather and not lack of Mn in the soil.

Believe it or not, corn has emerged on 96% of the acres in Kentucky which is right in line with the five-year average, according to the Kentucky Crop and Weather Report. While emergence is on track, planting was not, and management decisions need to be adjusted.

Preplant nitrogen fertilizer and preplant herbicides may have been lost to the heavy rainfalls. Farmers may need to sidedress additional N and apply postemegernce herbicides. Because of the late planting, farmers will have a smaller window to make these postemergence applications.

Corn planted April 1 will likely reach V6 growth stage in 35 days, while the same hybrid planted May 15 will reach V6 in about 22 days. Corn planted even later will reach V6 earlier.

Many postemergence herbicide labels have restrictions for V6 corn. Corn will need about 20 to 40 lbs of N/acre through about V6. If additional N has not been applied by V6, then yield losses can be expected.

Determining how much N fertilizer or herbicide was lost from the heavy rains is not easy. A calculation for N fertilizer lost is available in the Corn and Soybean Newsletter from April. Assessment of herbicide losses are more of a case-by-case assessment.

In addition, the rapid growth and wet weather can result in some transient nutrient deficiency symptoms...symptoms where weather has more to do with nutrient deficiency that availability of the nutrient. Normally in these cases, the best cure is sunshine and warm weather. Often farmers will spray a foliar fertilizer over the top and a couple days later the crop turns greener, but it may not yield any more. We always suggest to leave a test strip, and take both the treated and non-treated areas to yield.

As always, consult your county agents for more information.

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