Grain corn ear molds can lead to yield loss at harvest. If mycotoxins are present, grain may be toxic to animals and ultimately unusable. It’s important to understand environmental conditions that lead to diseases and how those diseases affect grain.

Factors that stress corn throughout the growing season can lead to stalk rots, which can lead to yield loss due to premature plant death or lodging. Understanding stalk rots risk factors and management practices are critical.

Traditionally a problem disease in the western Corn Belt, Goss’s wilt is now prevalent across the Corn Belt and spreading into Canada. Once corn plants are infected, yield potential can be reduced by up to 50 percent. There are no effective chemical control measures for Goss’s wilt. The best way to limit spread of the disease is by selecting hybrids with strong Goss’s wilt tolerance.

This bulletin provides information about Goss’s wilt and tolerance ratings for Mycogen® brand corn hybrid families. The ratings are the result of 2011-14 field trials conducted in Illinois, Iowa, Minnesota, Nebraska, South Dakota and Wyoming.


DISEASE INFORMATION
Goss’s wilt is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis. It overwinters in infected corn residue, primarily found on or near the soil surface. Inoculum in the infected residue primarily spreads by wind and splashing rain. To a minor degree, Goss’s wilt also can survive in seed.

To infect a corn plant, the bacterium needs an entry point or wound, which is generally caused by heavy rain storms, hail, wind, blowing sand or mechanical damage. Humid, wet weather is another risk factor because moist or wet leaves are conducive to the spread of disease.


IDENTIFYING GOSS’S WILT
Scouting is important because infection can occur at any point during the growing season. Infested seedlings show systemic wilting, stunting and a variety of leaf symptoms.

More-mature plants demonstrate the foliar leaf blight version of the disease. The first signs of infection are dark green to black, oblong spots that are water-soaked with a greasy look that appear parallel to leaf veins. Streaks of freckles within the lesions are a distinctive feature of Goss’s wilt. Droplets of bacterial exudate ooze from the freckles, leaving a crystalline substance that glistens in direct sunlight. The spots coalesce as they enlarge, forming long lesions with wavy edges. As the lesions age, they turn tan and can blight much of the leaf. Systematically infected plants have discolored (orange) vascular tissue and likely slimy stalk rot.

Key Symptoms:
• Freckles in lesions
• Crystalline deposits
• Droplets of exudate

Commonly confused with:
• Drought damage
• Heat stress or sun scalding
• Other leaf blights


CONTROLLING GOSS'S WILT
Because Goss’s wilt is a bacterial disease, it cannot be treated with fungicides. The best method of control is planting hybrids with strong Goss’s wilt tolerance. Tables 1 through 4 demonstrate the wide range of tolerance in hybrids.

Growers can limit the spread of Goss’s wilt to uninfected fields by selecting tolerant hybrids, harvesting infected fields last and thoroughly cleaning harvest equipment. Destroying infected crop residue will lower the amount of bacteria present. This is most effective when done immediately after harvest. In most situations, rotating to a nonhost crop, such as soybeans, dry beans, sugarbeets or alfalfa, is a more viable option. Last, manage irrigation to reduce humidity in the field during the growing season.

Talk to your Mycogen Seeds sales representative or customer agronomist to learn more about managing Goss’s wilt on your corn acres.

Zipper ears, or ears with missing kernel rows, are a result of stress during pollination or grain fill. Ears affected by zippering have kernels that developed poorly or more slowly than other kernels or have ovules that aborted shortly after pollination. It’s important to understand how and why zipper ears occur and how to minimize their occurrence in the future.

If your central Corn Belt fields have been damaged by heavy rain, hail, pests or poor emergence, you may consider replanting.

Northern corn rootworm (NCRW) is one of the most damaging corn pests in North America. Because the NCRW typically has a one-year life cycle, rotating corn with another crop has been a successful management strategy. Unfortunately, some populations of NCRW have successfully adapted to a corn soybean rotation and now have a two-year life cycle. This is called extended diapause because the eggs remain dormant in the soil for almost two years before hatching.

Flooding affects fields differently based on a variety of factors. Manage flooded corn to minimize damage and ensure optimum plant health and yields.

Heavy wind and rain late in the growing season can dramatically affect corn. Flooding, downed plants and disease are just a few of the potential management challenges related to extreme weather. Consider your options for recovering as much value as possible and take precautions when storing and feeding damaged corn.

A high rate of black cutworm (BCW) moth catches, green fields and late planting dates are the perfect recipe for significant damage from black cutworm. Damage can range from very little to almost 100 percent stand loss. To give late-planted corn the best yield potential, make controlling this pest a high priority.

Greensnap occurs when wind causes corn stalk breakage. This yield-robbing phenomenon is most prevalent in the central and western Corn Belt, where high winds are common. Corn is most susceptible to greensnap during the five- to eight-leaf stages and again from the 12th-leaf stage to one week after silking. During these rapid growth stages, lignin is not deposited into the new cells, leaving them brittle and vulnerable.

A bacterial disease that has been prevalent in areas of the western Corn Belt for decades, Goss’s wilt has expanded to additional areas of the central and eastern Corn Belt in recent years. If infections occur early in the season, during key crop development times, yield potential can be reduced by up to 50 percent.

Warm, moist conditions from July to September can cause increased disease incidence in corn. Recent studies have show potential economic benefits from foliar fungicide applications. Fungicide treatments can give protective or curative benefits for corn diseases such as: gray leaf spot, common rust, eyespot and antracnose. These diseases can limit photosynthesis due to tissue death. Loss of leaf tissue also may result in grain production loss or harvest loss due to weakened stalk strength and harvestability issues.

The brown marmorated stink bug (BMSB) is an invasive species that is causing economic damage to fruit, vegetable and agronomic crops in the Mid-Atlantic states. The insect now is expanding its range westward across the Corn Belt.

Southern rust is a common threat to corn crops across the southern United States. The disease damages crops in the Corn Belt only about once every five years, but when it does yields may be cut by more than 40 percent.

Hailstorms regularly strike growing corn fields. But not all damage is created equal. Know how to accurately assess yield loss.

Nutrient deficiency symptoms are not always caused by a lack of nutrients in the soil. Other factors can be to blame, such as poor root development, unfavorable soil conditions or weather. Plant tissue sampling helps identify the problem and determine corrective action.

Grasshopper population levels are highest during hot, dry summers. Active scouting and applying appropriate crop management practices can help guard your crop from damage.