Annual bluegrass weevil and plant indicators

There are many different pests that attack turf grass and insects can be some of the most damaging pests we face. Because of the predominance of annual bluegrass on our course, the annual bluegrass weevil can be the most damaging of all. This insect attacks annual bluegrass from early April to the end of September and can cause irreparable damage in a short period of time.

Larva and pupa in the soil

The annual bluegrass weevil is a small insect that can be very difficult to find. The adult is only 1/8” of an inch long and moves mostly at night. The female lays eggs inside the stem of the annual bluegrass plant in the spring; the eggs hatch and spend several days inside the stem, and then eat their way out. Once outside the plant, the larvae, about the size of a small grain of rice, begin to feed on the crown and roots of the plant. This is the most damaging time in the life cycle. Any insect eating the roots and crown of a plant will very quickly kill that plant. Within about 14 days the larvae mature through adolescent stages and become adults. The females lay eggs and the whole cycle starts again.

Larva in the soil

The battle against this pest has become more and more difficult each year. The volume of annual bluegrass weevils has increased, their appetite has adjusted to include bent grass instead of solely annual bluegrass, and the amount of generations per year has slowly changed as well. The generational increase has become the most difficult aspect of managing the weevil. Early on in the management of the annual bluegrass weevil, there were only 2-3 generations per year. The adults that appeared first in spring would lay their eggs and the cycle would repeat 2 more times. We could time our control with these generations and attain good control. However, lately, the first eggs laid in spring mature at different rates. The next wave of adults lay eggs at different times and quickly the generations are no longer in sync. We may see 5-7 generations per year and at any point there may be adults, eggs, larvae and pupae. This is especially troublesome because the insecticides that we use to target this pest specifically, only work against larvae. So at any point, if only ¼ of the total population is in this stage, we are never achieving more than 25% control. Once the population is in this state of imbalance, control is difficult and we are simply trying to manage as best as possible.

The yellow-orange areas are damaged plants

More damage

Half green half gold forsythia

We do have one very important weapon that we use to help us against the weevil. We observe forsythia bushes as plant phenological indicators. This process relies on monitoring forsythia and timing our chemical applications based on where the plant is in its flowering cycle. Since the annual bluegrass weevil and the forsythia rely on warming spring weather to start emerging and blooming, we watch the forsythia because it is much easier to see. When the forsythias are half green and half gold, we make our application. Research has repeatedly shown this is when the most adults are concentrated on the turf grass we want to protect. By striking this initial blow to the population of weevils, we set ourselves up for a much more manageable season. The beauty of using forsythia blooms to our advantage is that it is reliable and site specific. Forsythias are a very hardy plant and we can count on them to perform year after year no matter how strong the winter was. It is also useful to know what is happening here at Bretton Woods. As you travel around the area you may see forsythias in several stages of blooming all at the same time. By watching the forsythias on the property we are in tune with what our temperatures have been doing and how our site is reacting to the spring, which relates very well to how the weevils are reacting to the weather as well.

We have several other tools we use against the annual bluegrass weevil, including soap flushes, pit-traps, and vacuums, but nothing has proven as reliable or as easy as monitoring our plant indicators. Nature has a way of keeping everything in order, we just have to learn the cycle and us it to our advantage.

Etiquette Reminder of the Month

Carts are to remain on cart paths only until the Bermuda grass resumes normal growth.

See you on the course!

Joe

jvillegas@bwrc.org