Corn Silk Clipping Insects and Economic Thresholds

Jul 24, 2020

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Just a quick reminder to scout corn for silk clipping by either, or both, Japanese beetles and corn rootworm adults.  Japanese Beetles are also attracted to green silk and typically are found along field edges.  Rootworm adults, on the other hand, are more random in their field distribution.
 
Silk clipping is only an economic problem during the pollination stage.  Once kernels are fertilized there is no longer a concern.  Fields that are most likely to suffer economic damage are the earliest and latest pollinating fields in an area.  Beetles are mobile and can concentrate in these fields from all neighboring fields.  Not that other fields are not susceptible, just these are most likely.
 
Threshold guidelines indicate it takes about 3 Japanese beetles/plant to cause economic damage.  However, Japanese beetle damage is usually located along field edges so entire fields may not have to be treated.
 
Northern and Western rootworm beetles are more likely to evenly distributed throughout the field if corn development is consistent.  On average, we anticipate it will take about 5-6 rootworm beetles per plant to cause economic loss. However, do check to make sure that silks are being clipped to with ½ of the tip of the husk.  Corn rootworm are not yet laying eggs so these populations will not predict the potential for root feeding if corn is planted the following year.
 
Japanese beetle on corn
 
Silk clipping by adult corn rootworm beetles
Source : wisc.edu