Sunday, September 16, 2012

John Deere Beans

Drought stress causes responses in soybeans that are quite striking.  With all due respect to a certain much revered farm equipment manufacturer, the colour green in soybeans at harvest time is not a good thing. 
Soybean harvest is underway and we are hearing about green stems, leaves and what some folks are calling secondary growth or re-growth.  A corn plant tends to die when subjected to drought stress during the growing season, but a soybean plant does the opposite.  There is a genetic component to the symptom because certain varieties will hang onto the green colour more than others, but the condition is always worse in the drought effected pockets in the field.  The heat and drought stress caused the soybean plant to abort flower production and set fewer pods. The reason the plant stays green is because there are not enough beans hanging on the plant to drain the carbohydrate reserves from the stems and leaves.  The draw of the beans on these reserves is part of the maturation process which cause the plant to die.  With fewer beans to feed, the plant's death spiral takes longer than it should.  If there are green leaves still hanging on it indicates the plant could have fed a lot more beans.  It is not a re-growth symptom like we sometimes see in edible beans.  The soybean plant will not take a late season growth spurt and try to make more beans because its day length mechanism is telling it to shut down. 

And remember those potash deficient soybeans that I had shown in a previous post.
This is what they look like now.
A lot of green stems and leaves because the problem is the same.  Poor pod set and few beans.  Any stress that interferes with pod set can create more "John Deere beans".
Green seed can also be a problem in the stressed areas, especially for IP soybean contracts.  The green seed will be very slow to dry, but if you have a bin and can store them for a few months the green beans will dry down.  It just takes time.
And speaking of time, with harvest occurring earlier this year there is a perfect opportunity to spray soybean stubble ahead of or just after wheat planting.  Even my buddy Peter Johnson will agree that the perfect time for weed control in your wheat crop is at planting time.  Spring herbicide application is too often just revenge spraying.  The damage usually has been done before we realize weeds are present or it rains too much, keeping the sprayer out of the field.  A fall spray of your favourite glyphosate product will almost guarantee you don't have to spray in the spring. 

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