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Serving: Central

Pigweed problems grow quickly

Last week I wrote about overpowering pigweed populations, drought stress, application timing, and how those can all be related. A day or so later I was driving along early in the morning (forgot my camera as usual) and there was my article in a field of newly emerging soybeans and Palmer pigweed.

The accompanying photograph was taken by Extension agent Randy Chlapecka.

All of the things are there that I tried to describe last week. The pigweeds are in the “red stage.” If you have the problem, you know what I mean. That was what caught my eye as I was driving along — the entire field had a red hue with the sun coming up back lighting them. That is the perfect application timing stage for any postemergence herbicide.

The soybeans were in the true leaf stage, which is earlier than most would consider applying a herbicide. However, the weeds are around 10 days after emergence — the perfect timing stage.

The pigweed population in this field is not quite at the overpowering stage described last week, but it is getting close. The field has not had a rain on it since planting and the moisture is disappearing in a hurry.

I do not know anything about the practices used in this field. I do not know whether or not a pre-emergence herbicide was applied. However, this is how a field can look without one, or if one was applied and no rainfall has occurred for activation. I do not know if the field is planted to conventional, LibertyLink or Roundup Ready soybeans. I do not even know if the pigweeds are glyphosate-resistant, but I assume they are.

If this field is planted to conventional or Roundup Ready soybeans, a Flexstar application at the stage in the photos can kill all or most of the pigweeds. A repeat application in another 10 to 14 days will be needed for cripples and re-infestation. If the field is not sprayed quickly, factors begin to compound. First they will be too large for Flexstar within a very few days. Second, unless a timely rainfall occurs, they will be drought stressed in a very few days. Either of those factors will likely result in failure. However, when you combine the two, failure is certain.

If the field is planted to LibertyLink soybeans, there might be a few more days of timing flexibility. However, that can also get you in trouble, so why chance it?

The field in the photograph is at a perfect stage for the first Ignite application, even if you may sometimes kill bigger pigweeds. The statement I written more than any other in my career is: “I have never seen a field in trouble because a postemergence herbicide was applied too early!” I am still waiting for someone to call me and tell me they are grown up because they sprayed their first postemergence application too early.

If the first Ignite application is sprayed at the stage in the photograph and repeated in 10 to 14 days you will find out how simple the LibertyLink system can be. If the application is delayed, larger weeds are harder to kill, drought-stressed weeds are harder to kill, so there you go compounding things again.

Regardless of the herbicide system and how successful it may sometimes be on bigger weeds, irreversible yield loss begins at around 14 days after weed emergence. I guessed the weeds in the photograph at around 10 DAE. In another four days you begin the transition from a best management practice to revenge weed control — even if you are successful.


TAGS: Soybean
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