Expect to spend more time babysitting the crop, say agronomists and seasoned continuous corn farmers. Devote extra time to in-season N, disease and insect management advises John Kretzmeier, Fowler, IN. He was all continuous corn until the last two years, when drainage on his flat land became too problematic for all but about 20% of his ground.
His checklist of continuous corn in-season management needs resembles agronomists’, with a twist here and there.
• N replenishment. Be ready to apply an extra 30-50 lbs. of N at about knee-high stage. Kretzmeier virtually guarantees its need. “Take tissue samples when knee high to check fertility,” he says. “It’s your last chance to address N deficiency.”
Bob Nielsen, Purdue University Extension agronomist, says Purdue N trials consistently show that over 35 lbs./acre more N is needed than for corn following soybean, he says. “If it’s wet and cold, 40-50 lbs. may be needed.”
Emerson Nafziger, University of Illinois Extension corn and soybean specialist, says cool, wet weather slows the plant’s ability to absorb N. “Starter fertilizer has an inconsistent effect on yield, but when we do see a response, it’s usually where soils are cooler and wetter,” he says. “As long as we apply the right amount of N, we’re usually OK.”
No-till specialist Paul Jasa, University of Nebraska agricultural engineer, says timing of supplemental N is critical in continuous corn. “It should be applied before the V5 growth period,” he says. “This will help avoid stress when the plant is determining potential ear size. For no-till, apply N below the corn residue.”
• Disease determination. Walk the fields, then walk them again. Jasa says scouting is essential, since foliar diseases overwinter in corn stover, and warm humid nights make continuous corn more susceptible to disease. Gray leaf spot, northern corn leaf blight, diplodia, anthracnose and Goss’s wilt may be lurking.
“The risk of some corn diseases is greater when corn follows corn,” adds Nielsen, “especially when reduced tillage leaves greater amounts of non-decomposed, inoculum-bearing residue on the soil surface.”
Nielsen says conventional tillage helps manage the stover challenge. “In Indiana, many successful continuous corn growers have fairly aggressive tillage practices,” he says. “Conventional tillage is an effective tool for managing the risks of continuous corn that are mainly caused by the stover challenge.”
Nielsen doesn’t encourage growers to apply fungicides unless disease is present, adding there’s no scientific proof that fungicide treatments enhance corn growth even if no disease is found.
“Besides the reality that foliar fungicides do not pay dividends every time they are used in corn, the risk is that excessive use of these products may result in the development of resistance by important corn diseases like gray leaf spot,” Nielsen says. “By selecting hybrids with good disease resistance traits, the need for foliar fungicides decreases dramatically.”
• Scout for bugs early: Nielsen says more surface corn residue can delay corn emergence and growth. Consequently, slowly developing seedlings can be more susceptible to secondary pests like wireworms, seed corn maggots, white grubs and slugs, which can hurt stand numbers. Insecticide-treated seed is a must, he says.
Live winter annual weeds or winter cover crops can attract cutworm and armyworm moths for egg laying, he adds. That can lead to corn seedling damage and death from subsequent larval feeding on corn seedlings once the weeds or cover crops are dead. “Given all of these factors, pressure levels from these pests could potentially increase in continuous corn,” Nielsen says.
Adds Kretzmeier, “With the abnormally warm winter we’ve had, if there’s anything lying in those stalks, they could still be there at planting. Stacked seed traits provide good insect resistance, but we still need to keep an eye on it.”
Nafziger says rootworm management is necessary in both continuous and rotated corn where the Western corn rootworm variant lays eggs in soybean fields.
• Watch for more weeds: Nielsen says additional corn residue can decrease the efficacy of many soil-applied herbicides and favors certain weeds that thrive in that environment. “Certain annual grasses like johnsongrass and certain small-seeded broadleaf weeds can be more problematic,” he says.
It may require more herbicide selection because continuous corn limits growers to fewer herbicide options, he says.
“Use full rates to compensate for the effects of greater residue.”
Watch for herbicide-resistant volunteer corn. “Harvesting the previous year without much loss is one defense, and tillage to bury seeds or to kill emerging volunteer plants is another,” Nafziger says. “But there’s little besides cultivation that will take out glyphosate- and glufosinate-resistant volunteer corn once it’s growing with planted corn.”
• Earlier harvest. Jasa says that with continuous corn, there is an “N penalty,” meaning that toward the end of the season, “corn may cannibalize itself,” pulling strength from the stalk and leaves to the ears. Stalks may be weaker, so growers should consider harvesting those fields first to prevent added pressure for downed corn, he says.
Nafziger stresses that continuous corn will perform better if there’s less compaction. “Low parts of the field this past year were the most damaged from compaction in continuous corn,” he says, encouraging auto-steer use to help prevent compaction through more precise field routes. “Compaction can restrict the ability of the corn root to tap soil water from deeper in the profile.”
For 2013 continuous corn, “a minimum amount of leveling could help relieve compaction problems,” he says.
No matter what in-season practices you use, weather may decide the fate of continuous corn.
In Illinois, too much water in 2010 hurt June root development and cut continuous corn yields, notes Nafziger. But in 2011, dry weather in some areas slashed yields by 100 bu. for continuous corn compared to corn after beans.
“We won’t always see yield penalties that large, and sometimes they’ll be larger,” he says. “That doesn’t mean we shouldn’t consider corn following corn, it just means that we should pencil in that yield difference when we’re making the decision.”
Brad Hinrichs farms some land blessed with some of the richest black soil in Nebraska. It’s a perfect match for irrigated continuous corn grown in a ridge-till system. An extra in-season shot of urea boosts growth, as do one or two cultivations that help conserve precious moisture.(?)
Hinrichs, Fairfield, NE, grows corn and soybeans. Most is in a corn-bean rotation, with about a quarter of his corn following corn.
“I have some really good river ground that works well in my ridge-till continuous corn,” Hinrichs says. “I rotate the corn-on-corn acres back into beans after two or three years. The ridge-till system holds the moisture and works a lot better than no-till for me. Ridge-till picks up trash and puts it down in the bottom of the furrow and makes a blanket.”
Tissue samples tell Hinrichs he usually needs to come back with 40-50 lbs. of 28% N when plants are 6-8 in. high. He then cultivates at about knee high. If weeds are particularly bad, he applies glyphosate or another herbicide. “But usually, by the time I cultivate, two weeks later the canopy is shut,” he says.
Disease is rare but he still scouts for gray leaf spot and other problems. Like other growers, he is sold on applying a fungicide on continuous corn, whether he has a disease situation or not. “My yields are within 5-10 bu./acre of my corn in a soybean rotation,” Hinrichs says.