Why are my soybeans dropping their leaves?

Written by Lisa Eastley on Aug 29 2014

Category: Grow Grain

Leaf drop is a normal part of soybean development. Here's what to expect.

Soybean leaves browning and falling off

Maybe it’s a lack of experience with this relative newcomer to Manitoba, or maybe it’s the fact that foliage loss is typically a bad sign in field crops. Whatever the case may be, soybean leaf drop always freaks out farmers growing the crop for the first time. 

Over the next few weeks, I’ll get plenty of calls from concerned farmers asking, “What’s wrong with my soybeans? They’re shutting down.”

I’m happy to assure them that their crop is just fine. Leaf drop is a normal part of soybean development. When plants reach the R7 stage, their leaves begin yellowing and wilting. In the R8 stage, the leaves start to fall off. By the time the plant reaches full maturity, it will look like a bundle of sticks with pods attached.

Maturity and temperature tell the soybean plant to begin dropping its leaves. In Manitoba, we’re on par or a little ahead of a typical maturity schedule, so you can expect to see leaves to start dropping anytime now and continue through to September or October.

  Pods with only two beans Leaves can drop prematurely during periods of drought. There were a few fields in Manitoba that hadn’t received rain since July, and soybean plants in these areas were looking a little crispy. However, a literal deluge hit the province during the last week of August, and these plants should return to health very soon.

To be perfectly honest, we’re in the sit-and-wait stage of soybean management. Take this time to scout your fields for insect pressure and focus on other crops. 

Aphids and spider mites

There has been a late arrival of soybean aphids. Once you reach the economic threshold, spraying insecticide is no longer a cost-effective option. If there are more than 250 aphids per plant, the value of the crop destroyed exceeds the cost of controlling the pest. However, Mother Nature may come to your aid. Ladybugs are a natural predator of aphids, so check their populations too. They might take care of the pest problem for you.

There was also a growing concern about spider mites in some parts of Manitoba, but the rain we’ve had will minimize their numbers. 

Swath timing for canola

I encourage you to focus on your canola right now. It’s important to time your swathing correctly to minimize pod shatter – particularly if you’re planting soybeans in your canola field next year. Start controlling volunteers this season and wait for 60% seed colour change before swathing. If you’re straight cutting, wait for all seeds to turn dark brown or black. Aim for 9% moisture to reduce pod shatter. There’s plenty of great information on harvest management on the Canola Council website

If you’d like more advice on soybean maturation, insect pressure or swath timing, we’re here to help. Contact your nearest Cargill location or get in touch with your Cargill agronomist. 

Remember to follow me on Twitter @StalkOption to see how soybean crops are performing in Manitoba and Ontario.

Tags: Agronomy, Soybeans, Insecticide, Canola, @StalkOption, Cargill Experts, Cargill Experts, @StalkOption

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