Should I spray Canada thistle this Fall?

According to Tim Seipel, MSU Cropland Weed Extension Specialist, producers need to wait until it warms up before they spray. Hopefully, producers will get another window of good fall weather to get out and clean up fields. Glyphosate will not be absorbed if temperatures are below 40 degrees.

In addition, spraying depends on what is going to be sprayed. Canada thistle stalks from this year were recently hammered by the cold. Stalks have most likely finished moving sugars around especially if the temperature gets down to 15 degrees. However, Canada thistle rosettes (next years stalks) are on the surface and will be okay to spray. Spraying will be most effective when daytime temperature is in the 60 degree range. Cold nights will not affect herbicide efficacy if the weed is sprayed on a warm 60 degree day. The idea is to spray the plant when it is photosynthesizing so stoma are open and chemistry is happening.

I’m concerned about stored grain insects. What temperature does it take to kill a stored grain insect pest?

According to David Weaver (MSU Entomologist), To freeze an insect to death you need to reach between -15 and -25 degrees throughout the grain mass. Grain that is between 80-100 degrees Fahrenheit supports rapid population growth. Grain below 70 degrees will dramatically slow population growth. Grain below 50 degrees results in minimal feeding by stored grain pests. In addition, insects will start to die off around 50 degrees.

At what development stage does a winter wheat plant have to be to minimize winter kill?

A good rule of thumb for producers is “three leaves equals nine lives”. At the 3-leaf stage, the plant will have adequate development to survive many cold weather events.

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