Comments on Residual Herbicides Peanut Notes No. 16 2018

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One approach that has become common in peanut and other crops is to make sure herbicides applied at or close to planting get activated. While we can spend a great deal of money cleaning up fields the effectiveness of weed control and the protection of yield is often related to how clean peanuts are during the first 4-6 weeks (the critical weed-free period.)  You can take a look at pages 78-79 in 2018 Peanut Information for a summary of each group of herbicides and whether I think they should be used.

Here is a brief summary:

I think a DNA should be applied on every acre of peanuts. Incorporate if possible but even if in reduced tillage (apply Prowl H2O if surface applied and not incorporated) pendimethalin should be applied. This is relatively inexpensive and provides some control. Incorporation is a buffer against little or no rainfall and ensures at least partial activation.

Dual Magnum, metolachlor products, Warrant, and Outlook should be applied once or twice (perhaps not the same herbicide twice, but one followed by the other, if possible.)  This increases the likelihood that one of the herbicides will receive rain shortly after application and this can increase control. Many people apply Valor SX (or other flumioxazin products) immediately after planting along with a metolachlor product. Then, they will come back with either another metolachlor application or Outlook or Warrant mixed with paraquat (several formulations) plus Basagran. But, I don’t have a huge preference between what is mixed with Valor SX preemergence or what is mixed with paraquat plus Basagran postemergence. I think the key is to have two applications within the first month of the season.

Zidua is a new product labeled for peanut. It cannot be applied until the peanuts have emerged but it fits well when applied with paraquat plus Basagran. None of these products have appreciable postemergence activity on weeds (metolachlor products, Outlook, Warrant, or Zidua) but they can give a lot of good residual control. Check price on these for the decision. We are still working on whether or not we get longer residual out of Zidua compared with the other products. We do feel confident that all 4 of these products can give good control in a program with other herbicides applied at planting and when followed by postemergence herbicides. These residual herbicides (metolachlor, Warrant, Outlook, and Zidua) can be applied with Cobra, Storm, Ultra Blazer and Cadre for contact and residual control later in the season but in my mind the best place to add these is with paraquat and Basagran earlier in the season. We have looked at how compatible these products are when acephate is added to the mix and right now we don’t see any issues in terms of crop safety or thrips control.

I was asked about whether or not Zidua decreases injury potential compared with metolachlor products simply because these products are formulated differently. Metolachlor (also Outlook) contains EC (emulsifiable concentrate) in the formulation while Zidua does not. That is certainly the case but I have seen limited increases in injury when paraquat and Basagran are applied with metolachlor or Outlook versus paraquat and Basagran alone. We may see 10-15% more injury but it is transient and peanut grow out of it quickly. When alachlor (Lasso or Intrro) the amount per acre is higher and these are formulated as ECs (there was higher injury potential with these products simply due to formulation).