Managing large Palmer amaranth in corn near atrazine cut-off
Judging by our research here as well as phone calls from folks walking corn fields, it is very apparent that pretty much any PRE applied herbicide in corn has given out. Even some of the PRE applied herbicides that traditionally have provided consistently long weed control like Lexar or Bicep have clearly given out about 25 days after application. In other instances, I have had folks report that no PRE was applied to the corn and Palmer amaranth is good size.
Everyone is well behind with respect to spraying. Way too many windy days and now a very wet Wednesday will keep sprayers out of the field until next week. With that in mind there will be many fields of corn where both the corn and the Palmer amaranth will be large at time of spraying. What are some good management strategies for this situation?
Popular premixes such as Halex GT or Capreno are effective in controlling Palmer up to 6’’ depending on the rate of application. These herbicides are commonly tank mixed with atrazine to provide control of Palmer that is larger than 6’’ tall. However, atrazine can only be applied to corn that is 12’’ or less in height.
Halex GT or Capreno are good options, but in field of high pressure or with large Palmer, these herbicides as a standalone application aren’t enough. Relying solely on either of these herbicides, particularly on Palmer greater than 6’’ can promote resistance development in weeds to HPPD inhibiting herbicides. An ongoing study has shown that both Halex GT and Capreno in combination with Status provides effective control of Palmer larger than 6’’. The recommended rate is 4 pts./A of Halex GT or 3 ozs./A of Capreno plus 8 ozs./A of Status. Status and Halex GT can be applied up to 30’’ tall corn. Capreno can be applied to corn up to the 6 leaf stage.