Article for V-C Peanut News Peanut Notes No. 17 2018

— Written By

Over the past few weeks I have been asked a number of questions about weed control in peanuts. A paraphrase from the first line of one question is, “Got a grower in SC that is desperate to control Palmer in peanuts.”  My answer was, “Prowl PPI, Valor at 3 oz plus a full rate of Dual PRE, paraquat plus Basagran plus more Dual or Warrant or Zidua EPOST, then Cadre plus Cobra if something comes through.”  That is a lot of herbicide and a lot of money but in a bad Palmer amaranth field that may be what it takes. Before I go further, there are several formulations of flumioxazin that work well, there are several formulations of metolachlor/S-metolachlor that are available, and the same can be said for paraquat and imazapic. And somehow I left off Outlook as a possible component in the mixture with paraquat plus Basagran. The recommendation I made is “heavy” on the front end but in many ways that is what is needed. Timely application of herbicides to small weeds along with several residual treatments within the first month of the season is needed for Palmer amaranth control. For these applications, catching a rain sometime within that period is critical for adequate early season control. Playing catch up on Palmer amaranth is just as expensive but less effective than being heavy on the front end.

So, what I thought I would do with this article is add a little bit of nuance to my recommendation above with the following section out of our 2018 Peanut Information guide. I hope this helps as you deal with problem weeds in peanuts this coming season. We also have a chapter in that guide that includes comments on mixing pesticides.

Prowl or Sonalan (PPI)

These herbicides are relatively inexpensive and provide early season control of grasses and small-seeded broadleaf weeds. Although Prowl can be applied preemergence, it is generally more effective incorporated. Sonalan always needs to be incorporated. These herbicides are an important part of a comprehensive weed management strategy and should always be applied.

Dual Magnum (various formulations), Outlook, or Warrant (PPI or PRE)

These herbicides are important in suppressing yellow nutsedge, especially Dual Magnum, and provide control of small-seeded broadleaf weeds including pigweeds. While these herbicides do not control weeds for the entire season, they provide good early season control and are an important foundation of a comprehensive weed management strategy for peanuts.

Valor SX (various formulations) or Strongarm (PRE)

Under current situations with increased prevalence of Palmer amaranth and traditional broadleaf weeds such as eclipta, common ragweed, and common lambsquarters, one of these two herbicides is needed in a comprehensive weed management strategy for peanuts. Valor SX provides excellent rotation options for crops grown the following season, while Strongarm will carry over to corn and grain sorghum, and there is some concern about carryover to cotton on some soils. Weeds present, especially Palmer amaranth, that express resistance to Strongarm keep this herbicide from being a complete answer in some fields. Although Valor SX is effective early in the season, the rate used in peanut (2 oz/acre) generally does not control morningglories and will not control other weeds season-long every year.

Paraquat plus Basagran plus Dual Magnum (various formulations), Outlook, Warrant, or Zidua

Given that Palmer amaranth is present in many fields and that preplant incorporated and preemergence herbicides often are incomplete in control due to weather conditions or poor incorporation, this treatment (paraquat, with Gramoxone SL being the most prevalent commercial product) can often clean up fields when applied on time, taking pressure off of other postemergence options. Basagaran reduces injury from paraquat. In fields with known histories of Palmer amaranth and other problematic weeds, applying Dual Magnum, Outlook, Warrant or Zidua with paraquat plus Basagran will improve early season weed control. Apply paraquat early in the season, no later than 28 days after peanuts emerge, but preferably within the first three weeks.

Cobra, Ultra Blazer, Storm, Basagran (Postemergence)

These herbicides should be applied as needed. In fact, many if not most peanut fields will need at least one application of these herbicides. Weed size has a major impact on the degree of control obtained with these herbicides. If weeds exceed 3 inches, control is often incomplete. When preplant incorporated or preemergence herbicides are not applied or are marginally effective, growers often have to repeat applications of these herbicides (Cobra, Storm, and Ultra Blazer). Multiple applications in some cases can negatively affect peanut yield. For this reason growers are encouraged to have a comprehensive program of preplant incorporated and preemergence herbicides to take the pressure off of Cobra, Storm, and Ultra Blazer. Note that Storm does not contain sufficient Ultra Blazer to control Palmer amaranth and other weeds, so adding additional Ultra Blazer to Storm is recommended in some circumstances. Residual herbicides can be added to improve control.

Postemergence grass herbicides (clethodim and sethoxydim are active ingredients in these herbicides)

Preplant incorporated and preemergence herbicides often control annual grasses through midseason and sometimes late into the season. However, many fields need a postemergence application of sethoxydim (several formulations) and clethodim (several formulations). These herbicides should be applied as needed because grasses often cause peanut pod loss during the digging process.

Cadre or Pursuit Postemergence

Pursuit is used much less often now than in previous years. Cadre (also formulated as Impose) is a very good herbicide that controls yellow and purple nutsedge, annual grasses in many cases, and a range of broadleaf weeds. The challenge with Cadre is presence of resistant Palmer amaranth and carryover potential to cotton and grain sorghum. Cadre continues to be a good option for peanut growers as long as they realize carryover potential and whether or not resistance to this herbicide is present in certain fields. Residual herbicides can be added to improve control.

2,4-DB Postemergence

The broadleaf herbicides mentioned above, with the exception of paraquat, benefit from the addition of 2,4-DB. For example, when Palmer amaranth is slightly larger than the size recommended for complete control by Cobra, Ultra Blazer, or Storm, the inclusion of 2,4-DB can help obtain complete control. 2,4-DB is often effective when applied alone, but this is very species dependent. For example, common cocklebur can be controlled completely by 2,4-DB. 2,4-DB is also a viable option for suppression of escapes of sicklepod and Palmer amaranth when applied sequentially.