3 strikes and you’re out (of corn)
Summer is a great time of year to sit back and relax with a tall glass of sweet tea, enjoy a baseball game and watch the corn grow. Just like the growing season for corn, baseball season runs from April to October, and in most locations, this will be true with a few exceptions. If you’ve ever watched a baseball game, several things must go right to hit a home run, and Mother Nature is just like a pitcher trying to strike you out.
Three key pitches Mother Nature likes to use late in the season are:
• anthracnose leaf blight (Colleto-trichum graminicola)
• common rust (Puccinia sorghi)
• northern corn leaf blight (Exsero-hilum turcicum)
As corn farmers, we all strive to give our best swings each season. Often we change things up during the growing season, and 2015 is a bit more challenging than recent seasons in most parts of Iowa.
Common corn diseases
Anthracnose leaf blight is one of the most common leaf diseases found in corn. The fungus overwinters as sclerotia or mycelium in corn residue. Spores are spread by splashing water. When temperatures are between 70 and 85 degrees F, followed by moist air and rainfall, the fungus can become severe.
Corn-on-corn fields tend to have a higher incidence of the disease than does corn following soybeans, due to the remaining corn crop residue from the previous year.
Research at Iowa State University and University of Wisconsin has shown no relationship between the leaf blight and the stalk rot feature of the disease.
Common rust differs from anthracnose and northern leaf blight in that the fungal spores do not overwinter in Iowa. The urediniospores spend the winters in the southern U.S., similar to spring training camp. Common rust develops when weather conditions provide high humidity, nighttime temperatures of 65 to 70 degrees and normal daytime temperatures.
Oftentimes fungicide applications are not warranted when rust is the only disease present in the field. Cultural practices have little influence on the incidence of rust development. Most hybrids have moderate levels of resistance to common rust.
Northern leaf blight is the most damaging leaf disease of corn in the Midwest. The fungus overwinters in corn residue as mycelium and spores.
Northern leaf blight like other fungus is promoted with leaf moisture caused by rainfall or high humidity. Temperatures between 65 and 70 degrees also play a key role in development of this disease. Northern leaf blight is challenging for corn breeders due to the fact that multiple races of the fungus are present.
When breeding corn for resistance plant breeders rely on two types of resistance, monogenetic and polygenic.
When monogenetic Ht resistance is used for breeding purposes, not all races of the fungus are controlled.
Polygenetic resistance is more complicated due to the fact it has some resistance to all races but plants often show physical presence of the disease, and hybrids vary in response.
Using a fungicide
When looking for disease presence of corn leaf disease, we need to evaluate the incidence level of northern leaf blight.
When northern leaf blight incidence occurs on susceptible hybrids, with over 50% of the plants showing one or more lesions at tasseling time on the ear leaf and above, I recommend you spray a fungicide. Fungicides have proven effective in high-incidence cases in helping to maintain corn yield.
When considering fungicide applications, target the primary disease and look for fungicides rated to provide the best opportunity to slow the development of the disease any further on the plant.
To assist farmers with those decisions corn pathologists from across the Midwest have collaborated to form the Corn Disease Working Group. One important resource is a fungicide rating chart farmers can reference at.
So on your drive for a home run this summer, sip a little sweet tea after scouting for corn disease and swing for the bleachers when the pitch is right.
Saeugling is the ISU Extension field agronomist in southwest Iowa, located at Lewis. You can contact him at firstname.lastname@example.org.
Photo: Alison Robertson, ISU
Photo: Wyatt Saeugling, CPS intern
Photo: Daren Mueller, ISU
This article published in the July, 2015 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2015.