Farm Progress

Crop Adviser: Stay on top of these stressors to protect your soybean yields this year.

May 1, 2017

3 Min Read
CHECKING BEANS: Scouting soybeans frequently will help you protect yields this year.

By Adam Spelhaug

What are the biggest soybean yield robbers? Keep an eye on these during the growing season:

Disease is one of the biggest yield robbers in soybeans and can hinder yield by nearly 25%. The main points for concern in the Northern Plains are phytophthora, rhizoctonia, fusarium, white mold and brown stem rot. Preventive management can be done with fungicides, either seed-applied or foliar.

For some diseases, such as phytophthora and BSR, variety selection plays a vital role in mitigating the likelihood of encountering the diseases in your field.

For others, such as white mold, environment is the key factor in the development of the disease. I have not seen enough repeatable varietal tolerance to suggest that variety selection significantly lessens the chance for white mold development. Knowing your field’s layout and typical environment behavior is most important when trying to prevent white mold development.

Sudden death syndrome is an issue that growers in southern South Dakota and Minnesota have to contend with, but the problem has not yet made it to the northern section of that region or North Dakota.

Weather is always a factor for soybeans, both good and bad. The two main weather concerns during the summer are flooding rains and hail.

Soybeans can take more water than grass crops, and it is not uncommon for plants to survive being submerged for 48 to 96 hours. Warm, sunny weather during this period will shorten the time frame that soybeans can handle flooding, and there are some varietal differences in beans that can handle saturated soils. Water-logged soils can hurt yields 17% to 44%, depending on severity and duration.

Hail is the other major player. Leaf damage during vegetative growth does not always negatively affect yields. If stems or nodes are injured, yield losses can go up. Hail also opens the plant up for infection by many foliar diseases. If injury is widespread but not severe enough for major yield loss, a fungicide should be considered to prevent disease.

It has been a few years since we have experienced a large aphid infestation, and hopefully this year follows in that trend. If the right conditions are present, such as warmer winters and consistent summer temperatures of 75 to 84 degrees F, aphids can reproduce quickly. It is vitally important that you scout your fields often when such conditions exist.

The economic threshold for spraying aphids is 250 aphids per plant on 80% of the plants. When the aphid population is below the economic threshold, soybeans can tolerate stress. This recommendation is fully backed by more than 10 universities in the major soybean-producing states. Spraying when the aphid count is below 250 can result in spending money unnecessarily or spraying too early, which can lead to a second application later in the year.

Scouting soybean fields is essential. Many times, red-colored areas representing low yields appear on a yield map and you have no idea what happened. By scouting fields many times through the season, you may be able prevent yield losses. By writing down what you find when you are scouting, you will be more able to attribute those red areas to what happened during a specific part of the growth season.

Spelhaug is an agronomist with Peterson Farms Seed, Harwood, N.D. Follow him on Twitter at @PFSAgronomyGuy, and read his contributions to The Peterson Blog at petersonfarmsseed.com/blog. For more information, contact him at 866-481-7333 or [email protected].

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