Friday, August 2, 2013

Crop Alert: June 21, 2013

This Crop Alert was originally written for and distributed to farmers and other members of the agricultural industry in western New York.

By Bill Verbeten & Mike Stanyard, Cornell Cooperative Extension

Purple & Yellow Corn
Reports have come in from across the region of purple corn, Figure 1, and concerns have been raised about phosphorous deficiency and taking corrective action. There is nothing that can be done except to wait until the soil warms up and dries out. The purpling is caused by an accumulation of anthocyanins and is very common at the 3-4 leaf stage because the corn plant is changing how it grows. Up until about three weeks after planting the corn plant relies solely on the energy in the kernel to grow before transitioning fully to photosynthesis. Any stress that reduces root growth at that time (i.e. the flooded conditions across western New York) can cause a build-up of sugars in the leaves and increase the purpling in the corn. Some corn varieties naturally “purple” more than others. Bright, sunny days followed by cool nights can also increase leaf purpling. True phosphorous deficiency should be evaluated at the 6-8 leaf stage when soils are warm and root growth not restricted by cool, wet conditions. For more info on corn purpling see the following from Midwest Labs, Iowa State, and Purdue.

Heavy rainfall and flooded conditions have resulted in large nitrogen losses across the region in corn fields, especially where the fertilizer was applied at planting. Yellow corn has been the result. Side dressing nitrogen will be a requirement on most, if not all corn fields this year. The million dollar question right now is how much nitrogen needs to be applied. At minimum we are recommending to sidedress 50 lbs N/acre, though some situations may need more and will vary by soil type, manure history, and previous crop. If you want to test your soil for nitrate content (PSNT) your corn needs to be 6-12 inch high, the soil should be sampled at 8-12 inches deep, and samples need to be dried immediately to stop mineralization. See Agro-One’s website for the full description of the sampling procedure.

Figure 1: Yellow & Purple Corn

Rolling Soybeans & Aphids
Mike Stanyard and I have gotten numerous questions about rolling soybeans this past week. This has been done before or immediately after planting in the Midwest to improve field conditions for harvest (pushing down rocks & residue, creating a smooth surface). The University of Minnesota has put together a bulletin discussing their research along with findings from Iowa State and North Dakota State. The have found that rolling soybeans does not increase yield, and can greatly damage soybeans especially after the V3 stage and under wet field conditions. Soybeans should not be rolled under current wet field conditions in western New York. For reduce tillage farmers seeking to smooth out their fields, rolling immediately before or after planting is a good practice when done under proper field conditions in order to increase the ease of harvest. Delayed soybean planting continues across the region, with timely rains in August these later plantings will probably still yield well. The flooded conditions have also resulted in stand failures on the heavier clay soils in western New York due to soybeans rotting underground.

Mike has found soybean aphids over threshold (250+ aphids per plant) on soybean fields that did not have an insecticide seed treatment, Figure 2. If you did not use an insecticide seed treatment, you need to scout your fields for aphids. Most insecticides containing pyrethroids will control aphids.

Figure 2: Soybean Aphids

Wheat Head Scab
The weather conditions have favored the development of fusarium head blight across the region, Figure 3. It will be important to get out into your wheat and other winter small grain fields this next week to start evaluating how severe this disease is in your fields. Fungicide applications have reduced, but not eliminated the oc-currence of fusarium head blight. This is expected, and while disease will still be present if you sprayed, the severity will be greatly reduced (usually at least 50% reduction com-pared to not spraying). Spring small grains are starting to reach Feekes 10.5 (pollination) and will continue to do so next week(see picture). This growth stage generally occurs within 2-3 days after the heads completely emerge. Apply Caramba (10-17 oz/A), Prosaro (6.5-8.2 oz/A), or Proline (5-5.7 oz/A) within 5 days of seeing pollen on small grain heads to reduce the incidence of fusarium head blight.

Figure 3: Fusarium Head Blight in Wheat

Colorful Alfalfa
The wet conditions have also affected alfalfa and other hay crops. If your hay/silage field is molding (white, brown, or black color) after laying in the field during multiple rainstorms it will probably be better to just chop it back into the field instead trying to deal with the anti-quality compounds in the feed. Despite short feed inventories and high current hay prices it is better to buy clean feed than to compromise cow health by feeding garbage.

We have also seen potentially K deficient alfalfa in wet field conditions, but are waiting on a tissue sample analysis to confirm, Figure 4. Reports of ‘wrinkled’ alfalfa with general yellowing has also been found and are most likely due to feeding by plant bugs. There are not economic thresholds for plant bugs as leafhoppers and weevils are more damaging pests in alfalfa.

Figure 4: Potentially K Deficient Alfalfa in Flooded Field

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