Weed Control in a Dry Year Peanut Notes No. 72 2021

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Weed control in a dry year can be more challenging and even more expensive than weed control in a wet year. Preplant incorporated herbicides have provided some degree of control but in many fields, herbicides applied preemergence right after planting have not been activated. Some residual control can be achieved from these herbicides after rain occurs even several weeks later, but the challenge is that weeds will have emerged in the interim and herbicides with foliar activity will be needed. And, you simply cannot wait for all of the weeds to come up. I am seeing nutsedge and morningglory in fields. These weeds can emerge from greater depths because of the tubers (nutsedge) and the size of seed (morningglory.)  Texas panicum is likely a grass you will be seeing in fields. This grass has a large seed and can emerge from lower depths. These three weeds may be an issue under our dry conditions in part because they are starting the life cycle lower in soil where some moisture is available. Also, the herbicides we use in many fields as preemergence applications (metolachlor and Valor) do not control these weeds particularly well in general and certainly not when they do not get activated. This year you are likely to spend more money on postemergence sprays to catch up from the poor control by residual herbicides at planting.

Consider paraquat (several formulations) plus Basagran plus any of the residual herbicides available (Anthem Flex, Dual Magnum, Outlook, Warrant, Zidua – these are listed alphabetically and not based on efficacy or cost.)  Just get more residual herbicide out there. Pick one and spray it. The paraquat will kill many small weeds and the residual control will help for several weeks after the application (if we get activating rain.)  Make sure you do not have appreciable amounts of injury from thrips before you spray paraquat. You can add acephate to the herbicide spray, but if you have a lot of thrips injury when the application is made there is a window of time where the paraquat injury and the thrips injury combined can hurt yields. As with Rick’s note, consider acephate sooner rather than later before you really jump on the weeds. But this is a case by case basis. If you have some crinkled leaves from thrips a spray of paraquat, Basagran, residual herbicide and acephate can be effective. If peanut terminals are injured and certainly black from thrips damage, do not spray paraquat mixtures. Correct the thrips issue first and then come back in a week or so with paraquat – or move on to another herbicide like Storm or Cobra or Ultra Blazer a week or so after you correct the thrips issue.

You may need two sprays once peanuts are up (with residual and contact herbicides.)  Paraquat plus Basagran is option 1 and then Ultra Blazer, Storm or Cobra is option 2. Both options (in this sequence) can be applied with the residual herbicides listed above.

In my view you need to get a postemergence spray out there soon in many fields even if you have just a few weeds and you know more will come. You can’t wait for them all to come up. That is risky. And you will likely be busy playing catch up when the rains come. That is one reason why the residual herbicides are extremely important.

I mentioned nutsedge, morningglory and Texas panicum at the beginning of this note. They may be the first ones up but all the others are still there and just waiting for a rain. Your next round of residuals with option 1 or option 2 will be important in controlling the entire weed complex and protecting yield.