Evil Weevils Crushing Collars

While Annual Bluegrass (or Poa annua) can provide a great putting surface, it does have several disadvantages when compared to Creeping Bentgrass.  Among these is Poa's susceptibility to damage from the Annual Bluegrass Weevil.  (Yes, it really isn't a good sign when there's an insect named for the grass you're growing...)  We are currently seeing thinning in several collars caused by the weevils.

Over the past decade, this has become far and away the most troublesome insect we have to deal with.  There are several different control products in the arsenal for use on weevils, with some geared towards adults and others targeting larvae.  However, inconsistent warming this past spring appears to have contributed to our finding all life stages sooner than we have in prior years.  Currently we are finding larvae, pupae, and adults in the same location at the same time, making control a challenge.

The weevils are tiny, often smaller than a grain of rice.  So, how much damage could something 1/8" cause?

Well, there is definitely strength in numbers, and we have been finding 100-200 weevils per square foot in isolated sections of the collars this past week.

Weevil damage to  the Poa in the collar on the back of #13 green can easily be seen, while the surrounding Bentgrass is unharmed.

This onslaught of weevils is a bit discouraging given the time and efforts we put into preventing such an occurrence. A few things that are positive about the situation:  While weevils can cause damage to Bentgrass, it is seldom a crushing blow.  Given the tiny percentage of Poa in the tees and fairways, the weevils can actually go from "evil" to beneficial, as they provide a biological control of Poa for us in these areas.

We will also rarely see weevil damage to the actual putting surfaces, even though they are primarily Poa.  It seems that the low mowing height often leads to the mowers picking up adult weevils, and is not conducive to egg-laying for them.

This past week, we applied an aggressive control product on the collars, but with weevils having multiple generations in a single season, this game of cat and mouse is likely to continue into the fall.