Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Rainfall over the past week have complicated weed control for fields planted before the rain. The rains have moved most of the herbicide out of the weed emergence zone and will there is probably not much left to provide residual control. With that said, we do not know if the herbicide is all gone, and thus replanting with something other than the original crop, may lead to crop injury.
So, be sure to visit your fields soon, and often, to look for new emergence and time your postemergence sprays before weeds get too large. Fields may need to be treated sooner than you normally would spray since herbicides providing residual control are probably gone.
Areas with drowned out crops may need to be replanted. Weed control in areas being replanted will be challenging. Be sure to start clean and kill any weeds that might be present. Consider if you will be able to get into these replanted areas later. If you are only replanting areas that were drowned out, it may mean that you will need to drive through taller corn to get to these spots. If that is the case, will you be able to get in there when the replanted sections need to be sprayed with postemergence herbicides. The earlier planted corn may be too tall to allow a sprayer to get in when the replanted corn is 10 to 14 inches tall. Therefore, you may need to think about relying more on residual herbicides with these replanted areas.
Drowned out areas that are not replanted should be sprayed to prevent weeds from getting established and ultimately producing seeds. Weeds growing in these areas can produce a tremendous amount of seeds that could cause problems for the next few years.