SW MN IPM Stuff 2020 Issue 9

Volume 23 number 9

6/18/2020

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This newsletter and the advice herein are free. You usually get what you pay for.

Greetings,

What started off as an easy spring for many 2020 crops has turned difficult for some. Some areas are in need of rain. Hopefully they can receive a moderate amount over the next few days. A lot of weed control still needs to happen.

Weed control has been less than stellar in many fields, particularly in areas that have seen limited rainfall. In some cases, pre-emergence herbicides have struggled. More recently, as folks check their weed control, post-emergence corn and soybean herbicide performance is causing concerns in some fields. If you have not evaluated the performance of your herbicide applications, it might be worth the effort. From the calls and texts I have been receiving, common lambsquarters and the ever problematic waterhemp and giant ragweed appear to be the most common escapees.  

Part of the issue is a lack of suitable days for spraying and likely a bigger factor is environmental conditions. One of my crop consulting friends, frustrated with uncooperative weeds explained, "After the last few years people have forgotten what hot, dry weather does to weed control".  It usually isn't good.  Weed size and crop stage restrictions are going to make weeds hard to deal with in some of these fields.

Corn

Western corn rootworm egg hatch is on. Most larvae are still small so it's still a bit early to evaluate infestation levels. If you are interested in collecting and sharing data for adults contact me or see What's your risk from corn rootworm?

Scouting for 1st generation European corn borers should be underway. Focus on the tallest non-Bt fields first. The recent weather has not been the most favorable for ECB adults, eggs, or small larvae. I created a spreadsheet to help calculate economic thresholds that's available to download at IPM Tips & Resources. It's still a work in progress but you may be able to make use of it.  There is also an old video on ECB Scouting for whorl stage corn: Sampling for First Generation of European Corn Borer. Use the threshold calculator to determine what level of larval infestation/plant you can tolerate. Based on my hat placement, it must have been a rough day filming.  

Soybeans

Early planted soybeans are beginning to bloom.

Soybean cyst nematode (SCN) females are emerging from soybean roots in southern Minnesota now. Yellow beans have started to become visible also.

This year, you might want to start looking at some of those fields that tend to see problems with soybean aphids first a bit earlier than usual. Particularly in early-planted, smaller and sheltered fields, aphids have been able hang on through the windy days and have done OK in spite of the recent hot, dry weather. 

I've received reports of soybean aphids on soybeans as far north as Lac Qui Parle (Dorian Gatchall), Grant (Mike Flint) and Benton Counties (Nathan Drewitz). I suspect they are present much further north but portions of central Minnesota and the upper Minnesota River Valley often see aphid populations climb early. Yesterday, I checked a couple fields in Brown and Nicollet Counties where the percentage of plants infested was reported to be increasing (Steve Commerford). They were.

I have not yet observed soybean gall midge larvae in Minnesota soybeans but expect to see them very soon. Adult emergence has stopped, at least temporarily, at the Rock County research site. 

Happy trails,

Bruce Potter