Peanut weed management trials were conducted at the Oklahoma State University Caddo Research Station near Fort Cobb in 2020. Peanuts were planted in early May. Cool temperatures slowed development in 2020 and may have contributed to some of the early season injury observed in some of the trials. Even with the slow start peanut yields often exceeded 6,000 pounds per acre in 2020. Peanut planting and herbicide application information is presented before each data set. 

 

Trial PFCS20-01 was established to evaluate peanut response to Strongarm in the Spanish peanut (Ole). Strongarm was applied at a 1X (0.45 ounces per acre) and 2X (0.9 ounces per acre) rate. Each rate was applied preemergence (PRE) or At-Crack. The entire trial was maintained weed-free through hand weeding. No stand reduction were observed from any applications. Peanut injury were over 20% with 0.45 ounces per acre (1X rate) and over 30% with 0.9 ounces per acre (2X rate) when Strongarm was applied PRE (Table 1). Peanut injury was 5% or lower when the application was delayed to an At-Crack timing. All injury had dissipated by season’s end. Peanut yield reduced with both rates PRE. This research indicated that Strongarm PRE could injure peanuts, while delaying applications to At-Crack was much safer. 

 

Trial PFCS20-07 was established to evaluate peanut response to Zidua, which was applied to the Virginia peanut (Wynne). Zidua was applied at 2.5 or 3.5 fluid ounces per acre at three different postemergence (POST) timings. The entire trial was maintained weed-free through hand weeding. Peanut stand reduction, stunting and injury was less than 5% from any applications (Table 2). None of the Zidua treatment rates or application timings affected yield when compared to the weed-free check. This research indicated that Zidua applied POST was safe for use in peanuts. 

 

Trial PFCS20-05 was established to evaluate preemergence combinations of Valor, Outlook and Pursuit for weed control in peanuts. All treatments except Treatment #12 included a PRE application of Prowl H₂O (32 fluid ounces per acre). These same treatments were followed by POST applications of Cobra (12.5 fluid ounces per acre) + 2,4-DB (21 fluid ounces per acre) and Select Max (16 fluid ounces per acre). All Gramoxone POST treatments included Zidua (1.75 fluid ounces per acre) + Agridex (1 % v/v).

 

Peanut injury was generally less than 5% except where Pursuit was applied PRE at 4 fluid ounces per acre (Table 3). In some instances, injury was over 15% when Pursuit was applied PRE at 4 fluid ounces per acre. Applying Pursuit as a split application, to 2 fluid ounces per acre PRE and 2 fluid ounces per acre At-Crack, lowered injury to 6% or less. Peanuts had recovered from early season injury by early July.

 

Early season Palmer amaranth (AMAPA) control was at least 99% when Valor was applied PRE (Table 4). An At-Crack application of Gramoxone + Zidua controlled Palmer amaranth at least 94%, except when following a PRE application of Outlook alone. Late season Palmer amaranth control was at least 95% when At-Crack and POST applications followed Prowl H₂O + Valor PRE alone or in combination with Outlook or Pursuit. Early season Texas panicum (PANTE) control was at least 95% with all PRE treatments, except when Valor was applied alone (Table 5). Gramoxone + Zidua applied At-Crack controlled Texas panicum at least 99%, except when following Valor or Outlook applied alone. Late season Texas panicum control was at least 99%, except with the PRE applications of Valor or Outlook alone and when Valor was followed by Cadre + Dual Magnum + 2,4-DB. Yellow nutsedge (CYPES) and ivyleaf morningglory (IPOHE) populations were very low (Table 6 and table 7). Control was at least 99% with all treatments by the end of the season. 

 

All treatments increased yield over the untreated check (Table 7). The only treatment that had yields below 4,000 pound per acre was Prowl H₂O PRE + Pursuit applied as split application (PRE and At-Crack). Treatments that yielded over 5,000 pound per acre included Valor PRE followed by Cadre + Dual Magnum + 2,4-DB POST and Prowl H₂O + Valor PRE + Pursuit Split and Prowl H₂O + Valor + Outlook PRE in combination with Pursuit PRE or Pursuit Split. This trial indicates the need for a comprehensive weed control program to manage a diverse population of weeds while maintaining peanut yields.