By Emily Unglesbee
DTN Staff Reporter
ROCKVILLE, Md. (DTN) -- With so much of the planting season left ahead of farmers this spring, it can be hard to focus on the few corn acres that are in -- but they need your attention.
One grower told AgriGold agronomist Brandon Nystrom his cornfield looked great from the road -- he could see uniform green rows streaking past his windshield at 55 mph. But when Nystrom walked deep into the field, another picture emerged. "I went out and looked and told him he had to replant every acre," he recalled.
Poor planting conditions, disease and even insects are taking their toll on many of the cornfields that were seeded during narrow planting windows in late April and mid-May, agronomists told DTN. Scout fields carefully and calculate whether replanting will be necessary in the coming weeks.
The top problems to watch for are oxygen-starved corn plants, plants or roots restricted by crusting or compaction, fertilizer and herbicide injury, early season disease and insect injury and nutrient deficiencies.
The top culprit of poor stands this year is saturated soils, where corn plants cannot access the oxygen they need to grow, Nystrom said.
Look for stunted and yellowing seedlings or plants and pull them up. Swollen, mushy seeds and limited root systems are signs of a doomed plant, Nystrom said. "We usually want a plant with a firm, creamy white mesocotyl and a radicle root with the appearance of a furry foxtail," he said. "What we're seeing instead are short radicles and seminal roots that are without any root hairs -- the root system is just barely developed because it's been sitting in water."
Nystrom has also spotted sidewall smearing and compaction limiting root systems, as well as some seedlings that ran into crusted soil surfaces. "We have seen some seedlings unfurrowing underground," he warned.
Anhydrous ammonia injury is showing up in some corn plants in Iowa, said Iowa State University field agronomist Meaghan Anderson. When corn roots and tissue come into contact with this source of nitrogen, they are rapidly dehydrated, which produces burn-like symptoms.
"It looks like someone took a lighter to the tips of the corn roots and, depending on how severe it is, you may end up with missing plants," Anderson said. "Typically you'll see variation in the field -- the plants will have uneven height or emergence, which often follows the pattern of the anhydrous ammonia application," she said. "A lot of times, they start to wilt or look blue-grey in color aboveground and when you dig them up, you'll see the burned roots."
Herbicide injury is also common in years when cool, wet conditions slow plant emergence and increase the time they are exposed to pre-emergence herbicides still lingering on the soil. Potential injuries to watch for are plants leafing out underground or "buggy-whipping" in response to Group 15 seedling growth inhibitor herbicides, Anderson said.
Injury from Group 2 ALS-inhibitor herbicides would also be common under these conditions, and can produce yellowing or purpling of leaves, as well as a "bottle-brush" appearance of the root system -- constricted roots with short, stiff root hairs, she added.
See more details on herbicide injury in cold, wet soils from the University of Missouri here: https://ipm.missouri.edu/….
THE PEST FACTOR
Seedling diseases are starting to surface, particularly in cornfields where seeds sat in cold, wet soils for a long time before emerging. Soil-borne diseases like Pythium and Fusarium are almost always present in fields, ready to infect under favorable conditions.
"Some guys planted into cool, wet conditions, and some of those plants are in second- to third-leaf stage where the nodal root system is starting to develop -- that's perfect timing for Pythium to show up," Nystrom noted. "I'm expecting to see a lot more of it." Infected corn plants will display damping off, soft, mushy, brown tissue in the mesocotyl and rotted or discolored seeds. See more details from Iowa State University here: https://crops.extension.iastate.edu/….
Insects are starting to become a presence in cornfields, as well. Black cutworm should be active in Iowa fields this week, said Anderson. "Seed corn maggots (adults) are flying in Iowa right now, so if we have crops sitting in cold, wet soils and taking a while to emerge, that could be a concern," she added.
Wireworms and white grubs have also been spotted, Anderson and Nystrom said. See more on these pests and their damage to corn from Penn State University here: https://ento.psu.edu/….
Ohio State University entomologists are also warning growers to be alert for slugs, which thrive in cool, wet springs and can do serious damage to corn seed and seedlings: https://agcrops.osu.edu/….
Nutrient deficiencies are starting to become visible, as chilly soils limit a plant's ability to take up nutrients like sulfur and potassium, Nystrom said. "I've seen some sulfur deficiency in corn and that will start showing up more now," he predicted.
Given the heavy and persistent rainfall much of the Corn Belt has seen this spring, leaching and nitrogen loss will also be a common threat to cornfields this year. See this guide from Iowa State University for help identifying nutrient deficiencies in corn: https://crops.extension.iastate.edu/….
THE REPLANT CALCULATION
The standard advice for evaluating corn stands is to measure out 1/1000th of your field, based on row width, and multiply the number of healthy plants you find by 1,000 to determine plants per acre -- use this chart here: https://crops.extension.iastate.edu/….
Nystrom recommends dividing a field into sections and doing multiple stand counts, to see if replant can be limited to particular parts of the field. He also urges growers to huddle with their agronomists and seed dealers to figure out how genetics of their particular hybrid might react to lower plant population. Remember that cornfields can retain much of their yield potential even with populations as low as 22,000 plants per acre, depending on planting date, Nystrom said. See more details from his AgriGold article here: http://agrigold.com/….
Emily Unglesbee can be reached at Emily.firstname.lastname@example.org
Follow her on Twitter @Emily_Unglesbee
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