Scout for Diseases and Protect Yield With a Fungicide This Season
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With a wet start to spring across much of the Midwest, we could be in for a growing season heavy with crop disease. Most yield-limiting corn and soybean diseases thrive in wet weather, so it’s important to scout for symptoms regularly and protect your yield potential with a timely fungicide application this year.
Scouting for Crop Disease
When it comes to scouting for crop diseases, there are some general guidelines to follow for success:
- Create a scouting kit: Having a few important items in a bag in an easy-to-remember place will help save a little bit of time on your scouting trips.
Here are suggestions for items to put in the kit:- A notebook or tablet
- Plastic bags for plant samples
- Markers to mark sample bags
- Magnifying glass/hand lens to get a closer look at disease symptoms
- Camera or mobile phone for taking photos
- Field guide (hard copy or mobile application)
- Small shovel for digging up infected plants
- Scout often and regularly: It’s recommended to get into your fields at least once or twice per week. You may want to scout more often if weather conditions are favorable for disease or if disease pressure is high in your area. Some diseases can spread to large areas within a matter of days, so regular scouting can help you stay on top of symptoms and apply fungicides when necessary.
- Know your fields: Refer back to your previous seasons’ notes about disease occurrence in your fields so that you know where the trouble areas are, and be sure to check those areas. Also, pay attention to spots where diseases may be more likely to flourish, such as wet sections with poor drainage.
- Scout in a pattern: To get a better understanding of the field as a whole, it’s a good idea to walk in a type of pattern. That could be as simple as a diagonal line across the field or something a bit more complex like a diamond or a zigzag pattern (W or Z shape). Your field’s disease history and problem areas may help dictate the pattern you choose. Experts recommend making about five to 10 stops per field in each pattern, checking about 10 plants at each stop.
- Look high and low: Pay attention to both the field level and the plant level. At the field level, observe things like variations in color, height and emergence patterns. At the plant level, you can get a closer look at specific disease symptoms. While a few diseases first appear on upper leaves, many diseases start on lower leaves and stems, so it’s important to make sure to look for symptoms from the tops of plants all the way down to ground level.
- Take notes: And keep notes for future reference. Record any disease symptoms you find, number of infected plants, date, time of day, weather conditions, fungicide application status and any other criteria you think may be important. Remember to use these notes to highlight any problem areas when scouting for diseases during future growing seasons.
- Collect samples: If you’re having trouble diagnosing any possible diseases you find, collect samples and ask for help. You can start by asking your local ag retailer or other trusted advisers if they know what you’re dealing with and how to treat it. If not, you can dig up samples of affected plants (try to get the entire plant — roots and all) and submit them to your state diagnostic lab for diagnosis.
While the guidelines listed above are for disease scouting in general, there are some diseases that experts say could be particularly problematic in the Midwest this season. In this video, Corteva Agriscience market development specialist Jason Gibson walks through two diseases (one corn and one soybean) to watch for this season and how to control them.
Below are more corn and soybean diseases to watch for this summer and their signs and symptoms.
Corn Diseases
Symptoms: Black ovular or circular lesions on corn leaves that spread from the lower leaves to the upper leaves, leaf sheathes and eventually husks of developing corn ears.
Symptoms: Long, thin, rectangular lesions, up to 2 inches in length, that appear on leaves. The lesions start out tan and usually turn gray.
Symptoms: Elliptical, gray to tan lesions that develop on leaves. Lesions can be anywhere from 1 to 6 inches long. Symptoms tend to start on lower leaves. Under high humidity, spores coating the lesions turn olive-green or black, giving leaves a dark or dirty appearance.
Symptoms: Lesions that begin as flecks on leaves and develop into small tan spots. Spots turn into elongated brick-red to cinnamon-brown pustules with a jagged appearance. Symptoms of common rust are found on both upper and lower leaf surfaces (unlike southern rust, where symptoms only appear on upper leaf surfaces).
Symptoms: Round or pinhead-shaped pustules that develop on upper leaf surfaces. The pustules are orange or reddish-orange in color.
Soybean Diseases
Symptoms: Infection signs are not immediately visible. The obvious signs may be apparent within three to four weeks of infection but generally go unnoticed for another week or more. Check stems of potentially infected plants to diagnose white mold. The first signs are gray to white lesions at nodes. Lesions rapidly spread above and below infected nodes and often are covered in fluffy, white growths.
Symptoms: The most common initial signs are small yellow spots on leaves. The spots enlarge to a diameter of about 1/4 inch. Lesion centers become gray to brown and have reddish-purple margins. Check tops and undersides of leaves for tan-brown elliptical lesions with brown to purple borders. Under humid conditions, inspection with a magnifying glass/hand lens may reveal long, silver, spore-bearing hyphae extending from black dots on the undersides of leaves.
Unlike other soybean diseases, frogeye leaf spot produces infection on younger upper foliage rather than older foliage at the base of plants. Diseased plants tend to have a layered appearance because infection is more severe on younger leaves.
Photo from Eric Alinger, Pioneer Field Agronomist
Symptoms: Sun-exposed leaves on the upper part of the plant that develop a bronze to reddish-purple discoloration. Discoloration results from numerous irregular-shaped lesions that range from small specks to 1/2-inch spots and may extend to the upper stems, petioles and pods.
Fungicide Applications
One of the best ways to keep diseases from robbing your yield potential is to keep those diseases from developing in the first place. Applying a timely, preventive fungicide is a great step toward doing just that.
Aproach® and Aproach® Prima fungicides are two powerful choices to combat corn and soybean diseases. Both solutions are labeled for all the diseases listed above, with one exception: Aproach is labeled for control of white mold, while Aproach Prima is not. The following graphics show application guidelines for Aproach and Aproach Prima for corn and soybeans.
To find suggested use rates for Aproach and Aproach Prima, you can download the Disease ID Guide from Corteva Agriscience. The guide also contains more detailed information about the diseases listed in this article and more diseases to watch for as you scout your fields this summer.
Aproach® and Aproach® Prima are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.
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