Annual Bluegrass Weevil Control Solutions

Timing is of the utmost importance to avoid multi-generational infestations of annual bluegrass weevil (ABW). Identifying and suppressing overwintered adults is key, as is controlling the first and second generations of the season. Overlapping life stages in the summer and fall also need to be closely monitored. If you miss your window for early control, you’ll likely be treating ABW all season. You can help ensure success by properly timing early-season treatments.

Managing infestations is difficult due to their varied development and activity. Activity will depend on weather conditions and location, as spring temperatures vary widely. They also converge from multiple overwintering sites. There are multiple peak times of activity if cooler temperatures interrupt migration. ABW reproduce quickly and can have one to three generations in one season. 

Syngenta has a WeevilTrakSM program with monitoring tools, researched insights, and timing recommendations. However you track activity, be diligent and vigilant.

Scouting

Scouting is necessary to determine when the first adult insecticide treatment should begin. There are multiple techniques to try, such as soap flushes, soil core sampling, visual examination, pitfall traps, checking mower baskets, and vacuuming. Visual examination and a past history of controlling ABW will warrant preventative control measures.

Pitfall traps monitor adult movement, but not adult density. Mower baskets pick up adults; if you use the mowing technique, discard clippings carefully as most adults survive mowing unharmed. Using an inverted leaf blower sucks the adult ABWs into a sieve basket and if there are adults, this indicates that there are larvae within the turf.  

To conduct a soap flush, use 1 fluid ounce of lemon scented liquid detergent per gallon of water. Test multiple areas and collect adults after four, 5-minute increments. This extracts over 75% of adults. Once completed, water to avoid scald. 

Collect soil samples with a turf plugger or knife. Break up the soil on a tray, then count the ABW. For a more detailed examination, submerge the samples in lukewarm water. After five to ten minutes, the ABW will float to the surface, no matter the life stage.

Lifecycle and Damage

ABW start as an egg, turning into larva, prepupa, pupas, then finally adults. Eggs are laid underneath the leaf’s sheath. ABW larva is legless, with a slightly curved, cream-colored body and a brown head. The larva feeds inside the stem, then as it matures, eats the crown of the turf. 

Feeding damage looks like small, yellow-brown spots, scattered dead spots, and tunneled stems that break off at the crown. Initial feeding damage occurs in late May, then the worst damage occurs mid-June from the first generation, mostly on the edges of fairways. Second generation damage occurs in late July and early August and is usually less severe. Once the larva pupates in the soil, they hatch as immature adults. 

Mature adults overwinter in the top half inch of the soil, and can be found in leaf litter, under taller grass, around trees, and in roughs. They have short snouts with mouthparts and antennae, look dark gray, and are covered with fine yellow hair and scales. The scales wear off as they age. The adults move to the mowed turf areas over a few weeks once the spring weather arrives. Adult damage can be seen as leaf notching in grass stems to deposit eggs. 

The first, second, and third larvae instars are stem borers. These cause limited damage. The fourth and fifth larvae instars are older and feed on turfgrass crowns, causing severe damage.

Mitigating Damage

There are a few considerations to mitigate ABW damage on your turf. 

One option is to find a host plant resistance for ABW management. This is low cost, long lasting, and compatible with other means of control. This method is doubly helpful, as resistance is detrimental for pest development, and the turf better tolerates feeding. 

Bentgrass species are ABW resistant or tolerant, with creeping bentgrass the most resistant. P. annua allows for more larval development than creeping bentgrass, but it is less tolerant of ABW adults. Creeping bentgrass can be damaged, but ABW damage is less likely and to a lesser degree, so it has a better recovery time. Keep P. annua percentage low when possible. Herbicides can help keep percentages low. 

If you have annual bluegrass turf, consider overseeding with creeping bentgrass cultivars to elevate ABW resistance. Try to overseed in mid-June to July, when ABW damage is the worst and the annual bluegrass is weak, as the bentgrass should establish better. 

Another option is to put down control products as both a preventative measure and to diminish current infestations. Bayer’s Tetrino is effective at managing the first generation ABW populations. In areas with a high-density population, a second application can be put down to target the larvae in July. Other options include Provaunt and Acelepryn, which are both available in liquid and granular forms.

Prepare with SiteOne

SiteOne has all the products you need to get the ABW treatment job done. If you have any questions, our associates are always available to help. If you’re working on the go, consider shopping on SiteOne.com/PestManagement or our mobile app.