Farmers need to be alert to late-season corn diseases this year, such as stalk rots, ear rots and foliar diseases such as Goss's wilt. That was the advice seed company agronomists were giving to farmers visiting the seed exhibits at the 2010 Farm Progress Show this week at Boone in central Iowa. Detecting late-season corn diseases as soon as possible, assessing their potential impact and harvesting early in some situations can help preserve grain quality.
"The warm, humid weather has primed the pump for fungal diseases in the later part of this growing season," says Scott Heuchelin, a Pioneer plant pathologist. "When the crop reaches physical maturity, it stops actively growing and uses its energy reserves to fill the ear. During this time, root and crown infections, established earlier in the year during saturated soil conditions, can take off and aggressively infect the plant's crown and stalk tissues."
If growers see tops dieback during ear fill, nutrients to the top part of the plant are possibly being cut off by crown or stalk rots, says Heuchelin. If top dieback is evident, test the stalk integrity by pinching the base of the stalk or pushing the plant to the side to assess lodging potential. Fields with significant lodging potential should be harvested first to preserve yield potential.
Give cornstalks the "pinch test" to get an idea of lodging potential
In addition to stalk rot problems, you also want to watch out for potential ear rots this year in cornfields. "If the ear leaf or husk leaves begin to bleach out, this could be a sign of ear rots," he says. "Fusarium, Diplodia and Gibberella are the main ear rots in the northern Corn Belt. Frequent precipitation events from tasseling through ear fill create ideal environments for Diplodia and Gibberella ear rots. Warmer temperatures during this wet period favor Diplodia and cooler temps favor Gibberella. Fusarium ear rots occur most frequently when corn experiences prolonged heat and drought-stress environments."
Agronomists and researchers often see ear rots show up in Indiana, Ohio, Illinois and Ontario. This season, additional regions of the Corn Belt that experienced significant precipitation and humidity may fall victim, too. There are hybrids with resistance ratings to these ear rots.
If you see ear rots in a field, you may want to harvest the field early
"This year is setting the stage for Diplodia to be prominent in parts of the Corn Belt where fields received a lot of precipitation just before tassel emergence and through pollination," he says. "We offer several hybrids that have good resistance to Diplodia, and our company continues to improve resistance to corn stalk rots and ear rots across the product line. You have to look at grain quality not just with high test weights but also preserving grain quality with resistance to ear rots like Diplodia, Gibberella and Fusarium."
Growers who see ear rots in their fields may want to harvest early and dry corn to 15% moisture or below to prevent further molding during storage. In the future, you should try to select ear rot resistant hybrids, practice crop rotation and increase tillage to reduce incidence of these diseases, says Heuchlin.
Goss's wilt, historically more localized in the Great Plains, has been moving eastward into the Midwest and may cause problems late in the season in fields that encountered severe weather.
Fungicide won't control Goss's wilt; hybrid selection is best bet
"It's recently been reported in eastern Nebraska, the Dakotas, Manitoba, Minnesota, Iowa, Wisconsin, Illinois and Indiana," he says. "It typically occurs as the result of hail events and storms. When plants sustain injuries from hail or wind, the Goss's wilt bacterium can infect the leaves where they have been abraded. If growers have had hail damage, they should be on alert."
Agronomists say Goss's wilt can cause significant yield loss on some hybrids, and there are hybrids that typically show good resistance to the disease. Goss's wilt tends to be more of a problem for cornfields that incurred plant damage, especially in corn on corn and minimum or no-till fields.
"This is a bacterial disease," emphasizes Heuchlin. "Fungicides will not help. Sometimes I hear about people recommending fungicides, but they are ill-informed. Instead, manage the debris, which is the source of the inoculum, and work in rotation and tillage along with resistant genetics."