Corn and sorghum withstood our severe weather quite well this spring, and most fields got a good start. The first cloud is now on the horizon because fall armyworm pheromone trap captures are unusually high; 7.7x the 10 year average. The graphic below shows this year's captures and the 10-year average for my traps at the Lubbock Research and Extension Center.
Whorl stage sorghum and corn take take a lot of leaf damage, perhaps 30% tissue loss before yields are affected. (This number is shaky and has little research behind it.) These big flights in late spring were uncommon prior to about four years ago, and I do not know why they are now becoming less rare.
The next question would be how our high numbers now will affect numbers in the next generation. The graphic below shows the seasonal captures in 2019, the last year we had a really high spring flight.
The first peak in 2019 was about two weeks earlier than it is this year, and it resulted in heavy flights four and a half to six weeks later as the progeny of these early moths completed development and became adults.
It does not always happen that a big late July flight follows a big early June flight, as illustrated by the 2018 trap data below.
The bottom line is that our susceptible crops should be scouted very soon for larvae from this generation, and increased scouting five to six weeks down the road would be a good idea. Insect development is based on temperature to a large extent, so we need to watch for another large flight to begin in late July. The timing will likely elevate our headworms in sorghum. Unlike corn earworm that prefers to lay eggs in sinking corn, fall armyworm will lay eggs long past the brown silk stage, and the resulting larvae can still do a lot of damage to corn ears even in the dent stage and later.
In recent years my traps have been the northern limit of where we monitor fall armyworm. However, IPM Agents John Thobe (Parmer, Bailey and Castro counties) and Dagan Teague (Crosby and Floyd counties) set up traps last week. These will give us a look at how far north fall armyworm might be a problem.
You can sign up for our weekly IPM Audio Update for the Southern High Plains, a short 7-8 minute summary that we record and deliver on Wednesday afternoon. It covers everything we are finding in the field, and once you sign up you will get a short text message with a link to the audio file online.
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