Based on our moth catches, this appears to be a good time for CONSIDERING an insecticide application to non-Bt corn for southwestern corn borer (SWCB). The reality is I cannot even hazard a guess on the question above unless I know a few things.
1) Do you have non-Bt corn on your farm? You should to have a non-Bt corn refuge. The likelihood of having SWCB is higher in areas where there is a fair share of non-Bt corn (duh). Our hottest areas tend to be where white corn is traditionally grown because it is more likely to be non-Bt. In West Tennessee, this often includes Carroll, Gibson, Henry, Weakley, Obion and Dyer counties, but infestations can occur anywhere there is enough non-Bt corn to support a local population.
2) How many SWCB moths have you been catching? Running traps is critical to predicting potential infestations levels, and I discussed this last week. You are missing a big piece of the puzzle if you are not running 3-4 traps on you farm on a weekly basis. Everyone gets hung up on spraying a fungicide. The recommended timing for fungicide application will often not be the best for insect control. Trap catches can indicate whether you should be more worried about corn borers or timing your foliar fungicide application. I’ve seen lots of non-Bt corn lose 10-40 bushels per acre due to corn borer infestations. I’ve had several tests showing 5-30 bushel yield increases from spraying May planted non-Bt corn in the presence of SWCB. Traps catching > 100 moths per week during the second generation is cause for concern; >200 moths suggest a potential for serious infestations.
3) What is the planting date/maturity of your corn? Very early corn is at less risk to second generation infestations of corn borers. It is not as attractive or susceptible. If your corn started tassling several weeks ago, it should mostly escape the effects of a moth flight that has just begun. Unfortunately, much of our corn is May planted and will be more susceptible. Ultra late fields planted in late May or June may be infested by the third (August) generation of SWCB. Very late corn will be a magnet of SWCB in August as the earlier corn become less attractive, and moth trap catches well below 100 moths per week may result in heavy infestations.
Link to last week’s blog with more tips and choosing insecticide
- Corn earworm larva
Should you be spraying field corn for corn earworms? The answer to this is NO! This question has come up several times. At least in some areas, corn earworm infestations in the ear are unusually high. It is not possible to kill corn earworms once they are in the ear, so preventing corn earworm infestations requires multiple insecticide applications targeting hatching eggs that are laid on the silks. There has been a lot of previous research on this topic indicating that this will cost more than it saves. Indeed, when pressure is high, it may take five or more application to reduce (not eliminate) larval numbers in the ear. In non-Bt corn, you are more likely to see a yield increase because the insecticides may control corn borers. FYI – commercial sweet corn often requires 5-15 insecticide applications, sometime more, during a three week period to keep it free of corn earworm.
