Farm News
09-15-06
Dry weather, pests stressed plants in June and July
By KRISTIN GREINER- Farm News staff
Many farmers are thinking about the harvest ahead and prepping equipment. But there are a few things they should be keeping an eye out for in their fields until the combines begin to roll soon.
Jason Koln, agronomist with Pioneer, said this year there are a few things producers should especially watch out for. Because the dry weather in June and
July stressed corn plants to the point where stalk rot was able to effectively infect corn plants, producers need to keep tabsî on stalk quality and be ready to harvest fields early to avoid potential stalk lodging.
“While the weather in late July and August was good, the disease was already likely present in the plants,”î Koln said. “Once we received good weather in
August, the diseases in the plants aggressively advanced up the stalk as the plant translocated additional nutrients and water to feed the developing kernels in the ear.î”
Increased infestation levels of western bean cutworm have resulted in higher than normal ear rot occurrences, Koln said, so growers need to be aware of heavy levels of ear rot in their fields prior to harvest, so they can manage accordingly.
Western bean cutworms feed on kernels and chew holes in cornhusks, allowing easy entry points for ear diseases. Damage from western bean cutworm, along with dry weather in June and above average moisture, has created an ideal environment for ear rot. Ear rot can cause storage issues, decrease grain quality for feed and ethanol, and can also produce dangerous mycotoxins that can cause sickness if fed to livestock,î Koln said.
“Not all ear rots result in mycotoxins, so if growers are planning to feed grain with ear rots to livestock, it’s recommended to have the grain tested for mycotoxins,î” he continued. “Growers can help reduce the incidence of ear rots by controlling insects such as the western bean cutworm.î”
Koln said diplodia ear rot may show up in some fields. Penicillium ear rot and
Gibb ear rot also may be found on the exposed tips of ears, around insects tunnels and on ears that have remained upright.
“Some corn plants and ears are showing the black discoloration caused by secondary fungi coming in on the senescing plant tissues. With the hot, dry

conditions during much of the season over much of the state, Aspergillus flavus certainly has the potential to be a problem on corn in Iowa this season,”î Koln said. “Both Diplodia maydis and Diplodia macrospora can cause diplodia ear rot of corn. The ear leaf and husks on the ear may appear prematurely bleached or straw-colored. When the husk is peeled back, dense white to grayish-white mold growth will be matted between the kernels and between the ear and the husks.
“Small, black fungal fruiting bodies may be scattered on husks or embedded in cob tissues and kernels. The entire ear may be grayish-brown, shrunken, very lightweight and completely rotted. Diplodia ear rot is favored by wet weather just after silking and is more severe w hen corn is planted following corn,”î he continued.
Penicillium rot is usually evident as discrete tufts or clumps of a blue-green or gray-green mold erupting through the pericarp of individual kernels or on broken kernels, Koln said. Penicillium appears as small, discrete colonies of mold growth with a dusty or powdery appearance. The fungus may actually invade the kernel giving the embryo a blue discoloration. Blue-eye is the term used for this blue discoloration of the embryo.
Gibb ear rot, caused by Gibberella zeae, usually begins as a reddish mold at the tip of the ear, Koln said. Early infected ears may rot completely with husks adhering tightly to the ear and a pinkish to reddish mold growing between husks and ears. Although mold growth usually has a pinkish to reddish color, it can appear yellow to yellow-orange or yellow-red. Gibb ear rot typically begins at the tip of the ear, but under favorable conditions it can move down the ear causing extensive damage. It may also develop around injuries from hail, birds or insects, he said.
John Holmes, Iowa State University Extension crop specialist in Clarion , said corn fields in north Iowa have lodged due to recent straight-line winds. While the impacted area was small in size, the damage was significant, he said. Most corn in his area has black layered and begun to dry down, while later hybrids are very closeî to maturity.
“The corn has shown signs of anthracnose top die back in the last two to three weeks,”î Holmes said. “The leaves turn yellow and die from the top of the plant down. The disease actually infected the plants early this spring. This disease usually shows up during heavy grain filling times. Farmers can take stalk nitrate tests as soon as the corn reaches black layer. This test indicates if the appropriate amount of nitrogen was used.î”
Holmes said producers should watch for stalk rot and ear rot in corn, and while getting ready to harvest, which could begin yet this week or next week in some spots, to contemplate using less tillage.

“Any fall tillage of soybean stubble makes the soil very susceptible to soil erosion, especially wind erosion in the spring,î” Holmes said.
Joel DeJong, Extension crop specialist in LeMars , said producers should check for stalk rot in corn via field scouting and to check areas that are dying prematurely for a cause.
“Is it a plant disease or something else? Knowing what caused the problem can help plan for the next time the crop is in the rotation, which applies to soybeans and corn,î” he said.