Annual Bluegrass Weevil...

Annual Bluegrass Weevil

A growing insect problem on golf courses in northeast Pennsylvania is the annual bluegrass weevil (ABW).  Long a problem on golf courses to our north in states like Connecticut and Massachusetts, this tiny insect is now making it's way south and can now be found as far south as Maryland.




Annual Bluegrass Weevil

 The annual bluegrass weevil is unique in that it feeds almost exclusively on poa annua.  When we first saw this pest on our course, our first thought was to allow this insect to feed on the poa.  After all we were trying to get rid of the poa annua why not let this insect help us out.  As we found out however although the ABW prefers poa when the poa runs out it will feed on the bentgrass.  By the time we realized this several of our collars had been completely wiped out.





ABW damage

Since that time we have learned it is wise to treat for this pest.  To control this insect it is first important to understand its life cycle.  The annual bluegrass weevil overwinters as an adult in long grass or leaf litter along the margins of the golf course.  In the spring the adults migrate from their overwintering locations to low cut grass areas such as greens, tees and fairways.  Once there the adults lay their eggs on the leaf blades.  Then the eggs hatch, the larva burrow into the grass stems and feed from the inside out.  Damage first appears as wilt stress. When you water the grass and it does not recover, you know to look for this insect.  Because it is difficult to treat for this insect while it is feeding inside the grass stems, the best control strategy is to target the adults before they lay their eggs.  The success of this strategy is to time the insecticide application during the peak migration of the adults.  One way to do this is to use a growing degree model.  Growing degree models take the average of day time high and low and then subtract it from a base temperature of 50.  You keep a running total and when the number of growing degree days reach a certain number you treat for the adults.  This method has been very successful. 


Forsythia

Another method is to watch for when certain plants flower in the spring. This is called phenological indicators.  For annual bluegrass weevils the phenological indicator is when the forsythia is half yellow from the flowers and half green from the leaves.  We have also had good results with this method.


ABW can be a very destructive insect and requires careful monitoring to avoid turf loss.