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College of Food, Agricultural, and Environmental Sciences


Myriad of Problems May Await Late-Planted Crops

June 11, 2002

COLUMBUS, Ohio - Everything from reduced yields, to insect and disease problems, to poor growth performance may be in store for corn and soybean growers this summer as a result of late planting.

Ohio State University crop production specialists have little positive news regarding the shape the crops may be in come harvest time. One thing is known, and that is the fate of the crops' condition lies with Mother Nature.

"We basically have two scenarios," said Anne Dorrance, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center in Wooster, Ohio. "We can keep the same weather pattern we have right now through summer and have disease problems, or if it turns dry and we end up with a drought, we'll have the same problems we had last year - stunted plant growth and reduced yields. Either situation doesn't sound very favorable. What we always hope for in farming is that we get the rains when we need them and not in excess." Growers may have had enough rainfall already, as heavy rains throughout the state since April have kept them out of their fields. According to the Ohio Agricultural Statistics Service, as of June 9, 89 percent of the corn crop has been planted, with 65 percent of that crop having emerged. By this time last year, all of the crop was planted and had emerged.

Waiting for drier field conditions may cost corn growers in reduced yields, as a late-planted crop is more conducive to insect and disease stresses and poor growth performance.

"Late-planted corn, since it's developing later in the season, is more exposed to insect problems and can present a tempting target," said Peter Thomison, an Ohio State Extension agricultural agronomist. Insects, such as western corn rootworm and European corn borer, may cause problems for late-developing corn.

Western corn rootworm, which can cause the most damage through larval feeding on the root system, can also cause significant foliar injury and interfere with pollination through excessive feeding on the silks - known commonly as silk clipping.

Adult European corn borer moths prefer to lay their eggs on late-planted corn. The larvae that hatch feed on corn stalks, interfering with the flow of nutrients, enhancing infection by stalk diseases, causing stalk breakage and ear drop, and reducing corn yield.

Pat Lipps, an Ohio State Extension plant pathologist with OARDC, said the development of diseases, specifically gray leaf spot, could create problems for late-planted corn.

"That disease is on our minds at this point in time," he said. "We know there is a lot of gray leaf spot that survived the winter. There was plenty of the disease on the corn last fall, so we know that inoculum levels are high and there's plenty of the fungus in the fields. All we need is the right weather conditions to bring it out." Lipps said gray leaf spot spreads the quickest during the hottest parts of the summer, usually August and the first part of September.

"Usually by that time, if the corn crop was planted in April, the grain-filling is complete and the crop is entering the dent stage," said Lipps. "This year, with the late planting, grain fill might occur during that critical time period and if you get significant leaf damage before dent you can have yield losses. We are hoping for a cool summer, because then you won't see the disease." In addition to contending with potential insects and diseases, corn growers may also be looking at poor crop performance if it turns into a dry, hot summer.

"The late planting this year is very similar to what we had in 1996. That year it turned hot and dry in July and August, the corn was planted too late and was planted in wetter-than-normal soils. The crop ended up with shallow root systems, which stressed the plants and reduced yields significantly," said Thomison. "If we have good moisture from this point on, we'll probably get through harvest with average to above-average yields. If we receive below-average moisture, we could be looking at significantly reduced yields." Thomison added that late-planted corn might also be prone to stalk lodging and will be less responsive to nitrogen.

"Sometimes late planted corn grows taller and doesn't have as much stalk strength late in the season as with corn planted early. As a result, you get more rapid vegetative growth and a reduced root system, which makes the plants more prone to lodging problems," said Thomison. "We also won't see as strong of a response to high nitrogen rates from late-planted corn. That's one of the things we try to alert growers to if they haven't put much nitrogen on their corn late in the season." Corn growers may be seeking to avoid such late-planting problems by switching their acreage to soybeans. However, increased acreage of continuous soybeans may result in increased insect and disease populations.

"That's the big concern," said Dorrance. "If we hit a 10 percent increase in soybean acreage, that'll mean we'll probably hit five million acres of soybeans this year. We would have a million to a million and a half of soybean acres that will be put in continuous bean production and that will just increase pathogen populations." Dorrance said soybean cyst nematode and diseases such as Phytophthora root rot thrive on continuous soybean production.

"The benefit of a rotation for soybean cyst nematode is that you do decrease their populations but for root rotting fungi it is different. For these pathogens it isn't that you decrease the number, but what you do is prevent a rapid build-up of populations," said Dorrance. "When you get a rapid increase in numbers, that's when you start getting into significant yield impacts. You can tolerate a few plants in every field that are infected, but you can't tolerate it when it turns into hundreds." Ohio State specialists agree that the increased soybean acres may contribute to additional problems growers may be facing with late-planted soybeans. According to the Ohio Agricultural Statistics Service, 69 percent of the soybean acreage has been planted, still three weeks behind the normal pace. Only 37 percent of the crop has emerged, compared to 84 percent that emerged this same time last year.

"The biggest impact will be reduced yields," said Ohio State Extension agronomist Jim Beuerlein. "We've already lost a month of the crop year. The plants are getting off to a late start and are emerging late. That means fewer nodes on the plant, which means fewer flowers that will develop, which means fewer pods to harvest." Beuerlein said the later a soybean grower goes without planting his crop, the greater the yield loss. "A three-day delay in planting usually translates into about a one-day delay in harvest," he said. "Additionally, late-planted crops can't fully take advantage of available sunlight. Photosynthesis slows down, the plants don't pollinate well and they just aren't as productive. It's like they are starving." Diseases, like Sclerotinia white mold, can also cause problems for late-planted soybeans.

"Sclerotinia becomes a problem because the plants will flower later. The fields planted now will flower sometime in mid-July through mid-August and if we have cool weather with moist nights, Sclerotinia will become a problem," said Dorrance. "We haven't had to deal with the disease in several years, but that pathogen is still in those fields. What we need to be aware of is to be sure that those fields with a history of Sclerotinia are planted with a variety that has some resistance to the disease." What would be ideal weather conditions the remainder of the season for a productive crop? "Eighty-degree to 85-degree, perfectly clear, sunny days with an inch and a half of rain one night each week. In August and September, 55-degree to 60-degree temperatures at night," said Beuerlein. "The odds of that actually happening? About five percent."

Candace Pollock
Anne Dorrance, Pat Lipps, Jim Beuerlein, Peter Thomison