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June 16, 2010

Small grains:

Army cutworms, Phyllophaga beetle grubs, and wireworm adults (click beetles) were found in a barley field in the Upham area that was declared a total stand loss by the crop adjuster.   Many of the cutworms were in the pupal stage but beetle grubs were found at various stages (early and late instar larvae). 

When deciding whether or not to make an insecticide application for cutworms and other soil dwelling insects it is important to determine the stage of the insect and the pest density.  Although early instar larvae can cause significant damage, a disproportionate amount of damage is caused by late instar, one inch cutworms and one to two inch beetle grubs.  When a majority of the cutworms in a field are in the orange-brown pupa stage, most of the damage is done and insecticide treatments are generally not economical.  Spring hatching cutworms (e.g., pale western cutworms) may still be at early larval instars when control is warranted.  Thresholds for cutworms range from 0.3 larvae/ft2 in canola, field peas, and lentils to 2-5 larvae/ft2 in small grains depending on plant population and species of cutworm.  Although insecticide seed treatments are effective at controlling wireworms, they generally are less effective against cutworms. 

For more information and photos:

Peas and Lentils:

Some bacterial blight has been found in the area.  It is important to differentiate bacterial blight from the fungal disease, Mycosphaerella/Ascochyta, because fungicides are not effective against bacterial blight.  Please refer to the article on bacterial blight in this edition of the Crop and Pest Report for more information.    

 With the wet cool weather we’ve had, root rots are also common, especially in fields that did not use fungicide treated seed.  Fungal root rots have a darkening and softening of the stem near the soil level. Root loss and damage can be seen on plants that are carefully removed from the soil.  

Pea aphids have been found in pea and lentil fields in the area.  At this point the aphids were well below the threshold.  Bloom time is the best time to scout for these insects.  Treatment is recommended post-bloom when aphids are greater than four per plant.  


Diamond-backed moth and bertha army worm moths have been caught in traps at the North Central Research Extension Center and in a canola field in McLean County.  Flea beetle damage is common but fields above the 25% damage threshold have not been observed.  Flea beetle damage is still a risk up to the 6 leaf stage.

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