White mould and leaf disease strategies in soybeans

Category: Grow Grain

Short soybean rotations increase the chance of white mould and leaf diseases. Follow these strategies to protect your crops.

As part of our Growing Series 2016-17 season, we’re bringing you timely agronomic advice to help you achieve your yield goals. Soybeans are susceptible to a range of plant diseases, from white mould to various leaf issues. The tighter your rotations, the greater the disease risk. Here’s how to deal with the pressure.

Soybean field showing white mould damage.

1. Short rotations, high risk

The biggest yield robber in soybeans is white mould. Fields that have short soybean rotations and include tillage are most vulnerable. 

With white mould, the spore-producing sclerotia can survive in the soil up to seven years. If conditions are right, they can produce spores to infect current year plants. Heavy dews, high humidity, a lush environment and cooler temperatures (between 15 and 20 C°) are perfect for white mould to develop. 

If your pants get wet from walking in your field at 3 p.m., the environment is conducive to white mould development. 

For soybeans, evaluate the growing conditions and then determine whether to protect the plant with a fungicide. If you’ve got good, lush growing conditions, there’s a higher risk that fungal diseases will get established.

2. White mould and leaf disease strategies

When targeting white mould, spray preventatively. Once you see the disease in the field, it’s too late to spray. Consider the risk factors for that field, and then decide if it makes sense to use a white mould strategy or just focus on leaf diseases. 

An effective white mould fungicide strategy protects the soybean flowers from getting infected by spores. Because the plants flower for up to five weeks, and most fungicides are active for about two 

weeks, it usually takes two applications to provide adequate protection. 

Adding KP Plus to the fungicide application can also help yields. KP Plus improves drought resistance and stress tolerance, and it also increases the plant’s resistance to disease.

Photo of white mould on the stem of a soybean plant.

3. Growth stage and rates

Targeting white mould: spray at the R1 growth stage – when there’s a flower anywhere on the stem in 75% of the field. Apply a half-rate of Allegro® 500F, and then spray again 10 days later. 

Targeting leaf diseases: For frog-eye leaf spot or septoria brown spot, wait to spray at the R2 or R3 growth stage – when there’s flowers at the top of the soybean plant. 

Allegro® has activity on white mould but doesn’t have any activity on foliar disease. A follow-up application could be a half-rate of Allegro again. Other options could be Stratego® Pro or Acapela®, which will suppress white mould and also control leaf disease.

4. Significant loss if not controlled

Research suggests that if 25% of a field is infected with white mould, yield loss can be 12 bu/acre or more. Under the right conditions, white mould can cause a near total crop loss.

Other leaf diseases could reduce yields by 4 or 5 bu/acre. If beans are trading at $13 to $14/bu, the cost-effectiveness of an application is obvious. 

5. Benefits of fungicides in a dry year

Strobiluron fungicides have shown to reduce stress on the crop in a dry year by reducing the amount of ethylene (a stress hormone) that is produced by the plant. Reducing ethylene production allows the plant to use nitrogen more efficiently and improve photosynthesis under stress conditions, thereby protecting the crop from some yield loss as a result of stress. 

Looking at 12 years of Headline® and Priaxor® data, the years that showed the biggest response to fungicide in soybeans (in the absence of white mould) were 2007 and 2011, which were the two driest years of the 12. 

If you’re concerned about disease pressure on your farm, tank to your Cargill agronomist. We’re happy to check your field and find the best fungicide strategy that will get you the biggest return at harvest. 

 

Allegro® 500F is a registered trademark of Syngenta. Stragego® Pro is a registered trademark Bayer CropScience. Acapela® is a registered trademark of E. I. du Pont de Nemours and Company. Headline® and Priaxor® are registered trademarks of BASF.

Tags: Soybeans, Fungicide, Disease Management, Crop Staging, Crop Protection

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