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Tuesday, August 20, 2013

Bollworm, Earworm, or Headworm?



                For the past several weeks, we have been expecting a large moth flight this month, based upon regional trap catches and what we, and other area entomologist, have been seeing in the field.  Now that we have had some moonlit nights, we are starting to pick up fresh bollworm egg-lay in our program fields this week.  There has also been some debate about which area crop the bollworm would choose.   With a large amount of late planted corn and sorghum, it was suspected that the bollworms would prefer to lay eggs in late corn first, late sorghum second, and cotton as a last resort.  Early indications from the field show that this is probably correct. 

                Yesterday, August 19th, a field scout reported finding 15 bollworm eggs per plant in a late corn field with a mix of brown and green silks, a prime bollworm habitat.  This morning, August 20th, I scouted a field just starting green silk stage, a field where we would expect to only see the beginnings of moth attractiveness, and found 2 bollworm eggs per plant.  I feel it is likely that this trend of corn preference will continue as long as green corn remains prevalent in the area this fall.   Typically we are not economically concerned about bollworms that choose to be earworms.  Even heavy egg lay of bollworms in corn should not be a major economic concern for Hale & Swisher Counties.  Eventually, the larval caterpillars will cannibalize each other until there will only one worm per ear remains ensuring that the strongest survive.  While we do not like to see even one worm feeding in our corn, it is not economically feasible to attack those few earworms who are protected inside the corn shucks with multiple, predator damaging sprays, especially with spider mites already in the mix. 

                The bollworms that choose to be headworms in sorghum (and millet) are much more of an economic threat.  Mostly because we can make effective sprays to the exposed head of grain, but also headworms do more damage to our sorghum yields proportionally.  Yesterday, August 19th, I scouted a field in milk stage and found 0.5 small headworms per head.  This is sub-economic but something to watch nonetheless.  Roughly half these headworms were FAW (fall army worms), another important species that make up the sorghum headworm complex.

                Any non-BGII cotton is now at a heightened risk, but doubly so if that field is not near any late corn.  This morning, August 20th, I scouted a late and growthy cotton field not near any grass crops and found 7,199 bollworm eggs per acre.  With no corn or sorghum in the vicinity, I would expect bollworms to settle on cotton, the lusher the better for the worms.  So far, we are not finding bollworm eggs in cotton if late corn is in the area. 

 

                We already know that FAW is an economic concern in cotton and sorghum.  Recent research, much of which is still ongoing by Dr. Pat Porter, indicates that FAW should be a concern in corn, especially late corn.  Gary Cross, CEA – Hale, and David Graf, CEA – Swisher, are assisting Dr. Ed Bynum in some area wide moth trapping studies.  Their FAW trap catches remain low, and we are still finding large FAW larva in whorl stage sorghum.  We are also not finding FAW egg masses at any significant level yet.  All of these indicate that FAW are late but may join the mix in the moth flights soon, at least locally.  

 

Please call with any questions, or leave a comment about what you are seeing.  Thanks,

Blayne

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