Five Signs of Disease to Look for From the Combine

October 24, 2022

Many signs of disease can be observed from the cab of a combine during harvest.
Many signs of disease can be observed from the cab of a combine during harvest.

From planting to harvest, signs of disease may be present, but not seen without extensive scouting. Disease management and observation should not stop even after a fungicide application, as disease pressures can develop or intensify through the end of the growing season. In fact, from the cab of the combine, you can spot signs of disease that you did not realize were present during the growing season and make plans to protect against them in the next growing season by using a fungicide such as Delaro® Complete.

Signs of disease that can be seen from the combine

The consequences of disease are often felt the most during harvest, when disease-stricken corn plants reduce harvest efficiency in both time and labor and lead to yield losses. Harvest is a critical time for observing various signs of disease in your corn fields and making plans to adjust your program accordingly in the following year.

“Signs of disease from the combine can provide an explanation as to why growers may be experiencing yield losses or decreased harvest efficiency,” said Randy Myers, fungicides product development manager at Bayer.

To accurately identify diseases that are present in your fields, look for these five signs when you are in the combine:

1. Stalk lodging

When out in the combine, pay careful attention to whether stalks lodge as you harvest. If stalk lodging occurs, it is likely due to stalk rot. The more rotted a stalk is, the more likely it is to lodge during harvest, causing decreased harvest efficiency and yield losses.i Stalk rot and lodging can be caused by anthracnose, among other diseases.

2. Discolored ears

Another sign to look for during harvest is discolored ears, which is often an indicator that ear rot has occurred. Certain fungi that cause ear rots can continue growing throughout the fall, causing damage to the ear and increasing the number of mycotoxins present in the grain. Discolored, rotten ears are often a symptom of Fusarium or Gibberella ear rot diseases.ii

3. Leaf lesions

During harvest, keep your eyes open for leaf lesions, which can signal several different diseases. If you observe lesions that are oval- or spindle-shaped and tan or brown in color, it is likely a sign of anthracnose. Lesions that are rectangular-shaped, gray to brown in color, one-eighth inches wide and three inches long could be a sign of gray leaf spot. Alternatively, if there are oblong lesions that are grayish or tan in color and are one to seven inches long, it is likely to be northern corn leaf blight.

4. Dead, gray leaves

At harvest, almost all the leaves on the corn plants are dead. However, you should be able to tell the difference between leaves that died because of disease and leaves that died down naturally at the end of the season. Dead leaves that appear gray in color are a sure sign of disease. This is commonly caused by gray leaf spot, which is known to reduce yields up to 40 bushels per acre.

5. Pustules

Another sign of disease to look for during harvest is pustules or raised fruiting-bodies on the surfaces of leaves and husks. These are often caused by rusts or tar spot. Densely clustered, light brown to orange pustules on almost exclusively the top of leaves can be a sign of southern corn rust infection. Common rust, on the other hand, produces pustules that are dark reddish-brown and scattered across upper and lower surfaces of the leaves and the leaf sheaths. If the pustules are firm black dots that cannot be rubbed off, the likely culprit is tar spot. Even though the leaves are brown from drying down before harvest, you will still be able to distinguish the presence of pustules due to the texture and coloration.

If you observe any of these signs, make note of them and try to identify the disease using a reference guide. If you are unable to identify the disease on your own, consult your agronomist or extension agent.

“Seeing the signs of and accurately identifying diseases at harvest can also predict what disease pressures a field may face in the next growing season,” said Myers. “This knowledge can also be useful for planning and making decisions for next year.”

Bayer solutions for corn disease management

Myers recommends using Delaro® Complete fungicide for prevention of yield-robbing diseases and improved plant health at harvest. With three modes of action, Delaro Complete provides preventive and curative effects for broad-spectrum control of tough diseases in corn, including gray leaf spot, northern corn leaf blight, anthracnose, common rust, southern rust and tar spot, minimizing the consequences of disease at harvest. Delaro Complete also helps improve harvest efficiency through improved plant health. Delaro Complete promotes healthy, dark green leaves for improved photosynthesis for increased plant stress resistance and stronger stalks for improved standability and harvestability. Through disease prevention and improved plant health, Delaro Complete helps you achieve maximum yields and optimum harvest efficiency.

Download the Check List

We’ve made it easy for you this harvest season and provided a check list to use as you are looking for disease signs in your fields this harvest season.

5 Signs of Diseases to Look for From the Combine Check List

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i Smith, D. “Disease Considerations for Soybean and Corn Harvest.” University of Wisconsin-Extension, Wisconsin Field Crops Pathology, 2014.

ii Jackson-Ziems, T., and Rees, J. “Ear and Stalk Rot Diseases Becoming More Common in Corn Fields.” University of Nebraska-Lincoln CropWatch, 2016.