You've probably been hearing more about Northern Leaf Blight (NLB) lately. It's a corn disease that seems to be increasing in Northern Plains. It's a fungal infection that thrives when relatively cool summer temperatures coincide with high humidity and available moisture.
"There is always the potential for NLB to infest corn fields when the conditions are right. However, the summer of 2014 brought higher-than-normal NLB pressure in parts of South Dakota, North Dakota and western Minnesota," says Larry Osborne, a DuPont Pioneer agronomist.
The fungus generally overwinters in residue and is favored in minimum-till or no-till situations. However, in 2014 NLB may have arrived from southern winds and rain events as its cigar-shaped lesions first appeared on the upper half of plant, rather than infesting the plant from the bottom up, Osborne says.
With favorable weather conditions, new NLB lesions can produce spores in as little as one week. This is much faster than some other common corn leaf diseases such as gray leaf spot, and allows NLB to spread much faster than those diseases.
The earlier in the season that the lesions develop, the more leaf area is reduced leading to more damage. In 2014, highly sensitive hybrids that were infected before tassel and had regular rainfall, likely saw yield losses due to decreased photosynthesis. Harvest losses were possible in areas where secondary stalk rot infection and stalk lodging accompanied loss of leaf area, Osborne says.
NLB is generally a sporadic problem, but growers can expect some residual NLB in hard hit fields due to carryover inoculum, according to Osborne.
"Growers can best manage NLB by selecting resistant hybrids, reducing previous corn residue in affected areas, timely planting and application of fungicides in high-risk fields with recent NLB outbreaks," he says.
One of the most effective means of managing NLB is selecting resistant corn hybrids. This is especially important in areas that have experienced NLB outbreaks in recent years. In such cases, only hybrids with at least above-average resistance to NLB should be considered.
"If NLB does occur early in 2015, timely fungicides may also help (VT-R1 stage). Profitably of using fungicidal control is dependent on several factors, including hybrid susceptibility, cropping history, tillage practices, corn prices, location, yield potential, and weather. Because of this complexity, there is currently no way to predict accurately the economic benefits of a fungicide application on field corn. Typically, only one application can be considered economically feasible. The best time to make the decision is when the disease is at very low levels or near tasseling. Susceptible hybrids are more likely to profit from a fungicide application. Hybrids that have an average or above average score for NLB will have a much lower chance of showing economic benefit from a fungicide application. Ultimately, weather conditions during ear fill will determine the profitability of most fungicide applications," he says.