Sorghum head worms

Sorghum head worms

  Getting a number of calls about what is probably the corn ear worm, aka the sorghum head worm, aka the soybean pod worm. In the double cropped grain sorghum this worm is in the whorl of the leaves and causing the "shot holing" the producers see as the leaves extend from the whorl.  Usually it is not cost effective to spray for these worms at that time as it takes up to 30% of the leaf area of the plant to be damaged before it starts affecting the yield and it is almost impossible to contact the worm inside that whorl. Imagine hitting an insect wrapped inside a cigar.  The exceptions to this would be in smaller sorghum and the worm is destroying the entire leaf before or as it comes out or the worm is chewing on the head of the plant right before it emerges.  In these instances it might be worth an insecticide application but the expectancy of the producer needs to be reduced.  It is hard to kill that wrapped up worm.
However, when and if that same worm gets up into the emerged head where he is exposed then my personal tolerance for them is very limited.  The economic threshold is dependent on the yield potential and the price of grain but 1 worm per head is about a 5% reduction in yield.  2 would be a 10% etc.  At this time as far as we know pyrethroids still have efficacy on these worms so it probably would pay to spray that cheaper chemical on 1 worm per head.
Kim

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