David Owens, Extension Entomologist, firstname.lastname@example.org
The much-anticipated corn earworm flight has begun for 2023, albeit more than 2 weeks later than last year. Traps that were catching 1 – 12 moths last week at this time are now catching dozens per night, as the table below will show. Not to be outdone by our trap catches, traps at Virginia Tech’s Eastern Shore AREC in Painter caught nearly 400 moths per night earlier this week. Crops to be scouting for over the next several weeks include snap bean, lima bean, tomato, and soybean and sorghum (more on that in the agronomic insect scouting report). Female moths are attracted to blooming crops to fuel up so they can lay eggs. They also prefer open canopies so that it is easier to get to the flowers. This is why double crop soybeans get earworm populations that full season beans, which have largely completed flowering, usually do not. These moths are very quickly going to be laying eggs, in our current warm conditions it will take those eggs two days to hatch. When reared under constant 77-degree F temperatures, it takes 3.7 days to complete the first instar and 2.8 days to complete the 2nd, giving us about 8-9 days before we reach the third instar. There is a high level of first and second instar mortality, but once they reach 3rd instar, mortality decreases and feeding picks up. I reckon the earliest we may see third instar worms in other crops will be next Thursday.
Trap counts from Thursday are as follows:
|3 nights total catch|
Begin including worm materials in tomato sprays. Be sure to use a high volume and high pressure to get good canopy penetration. We have a lot of good options: spinosyns, Proclaim, Bt’s, Rimon, Intrepid, Avaunt, and diamides. I found in a trial a couple of seasons ago that under low pressure, all of these products work equally well.
That is not the case for sweet corn. We have diamides (Vantacor), Intrepid Edge (and generics), Radiant and Blackhawk, pyrethroids, and Lannate. None of the modes of action by themselves perform well under high pressure. Our most powerful treatments are Besiege and Elevest. Besiege can be applied up to 31 fl oz and gives us 3-4 applications (no more than 4 per label). We can only apply 2 applications of Elevest. There are active ingredient restrictions on these products, meaning if you apply Elevest, you cannot use much if any other bifenthrin product; if you apply the two applications of Elevest or the 31 fl oz of Besiege, you cannot apply the other or Vantacor – you would have exceeded the label restriction on amount of chlorantraniliprole active ingredient in those products. Elevest in recent spray trials does not significantly differ from Besiege but does tend to perform a couple of percent better, most likely due to the bifenthrin. Over the previous 4 seasons, we have tested many of the labeled pyrethroids alone for earworm management. Hero at its higher rate performs the best, followed by Baythroid XL, which sometimes is better than or is as good as bifenthrin, and those usually perform significantly better than Warrior II.
Some producers have asked about alternatives to Lannate as a pyrethroid tank mix partner. Radiant and Intrepid Edge when tank mixed with Warrior II and applied for all treatments will perform as well as a Besiege/Baythroid XL rotation applied every 3 days.
How often should sprays be made? If you do not have fall armyworm, make the first application at first silk, not prior. During the first 10 days or so of silking, pyrethroid applications should be followed 2 days later with a diamide product (ex-Besiege or Elevest). Those applications can be followed 3 days. If the temperatures go down into the low 80’s, a 3-day spray schedule will suffice. This is conservative. If foul weather or other life or farm event prevents an application after 2 days, that does not mean you will experience higher crop injury. The downside to applying pyrethroids as frequently as this is that we risk flaring aphids, so be sure to scout for aphids about 10 days after silking. If a significant aphid population is growing and depositing honeydew, add Sivanto or Assail into the spray program. Neither product alone will get corn earworm.
What if you are growing a Bt variety? If it is an Attribute II or Attribute Plus variety, you do not need to treat for worms. If you are growing Attribute or Obsession, treat them as you would a non-Bt sweet corn variety.
Continue scouting for fall armyworm. If they are present, you may want to consider starting ear sprays a few days early. Thresholds are 15% infested plants during late whorl stage. We did an unreplicated trial this week for fall armyworm and got surprisingly low amount of mortality. Avaunt performed the best, followed by chlorantraniliprole. Warrior II only gave us about a 40% reduction in armyworm.
Striped cucumber beetles and rindworms are the primary pests present at this time. Aphids seem to be quiet this year. Remember, pyrethroids have not given us control in bioassays this year for striped cucumber beetle. New in the rindworm complex is the potential for beet armyworm. They were spotted in pigweed this week in a melon field. Beet armyworms are resistant to pyrethroids.
Be sure to scout for beet armyworm, their larvae are resistant to pyrethroids. You can tell from other species in that beet armyworm has a narrow black spot behind the head. Sometimes, fall armyworm is gray and at other times almost green. Beet armyworm produces webbing in which to feed in the early stars.