GWSS activity has increased sharply over the last two weeks. A total of 525 GWSS were collected among 131 traps in citrus groves and select vineyards throughout the valley. This level of activity is now well above historic averages for Temecula, but noticeably delayed compared to most years. The delay may be due in part to the relatively moderate temperatures we've had most of the Summer

65 traps captured at least one GWSS adult, up to 39 on an individual trap. 20 traps collected 10 or more GWSS, mostly in the south-central and northeast portions of the valley 

This is now two successive seasons with higher than usual levels of GWSS activity. On the one hand this is troubling because multiple years of high vector pressure increases the risk of triggering significant Pierce's disease incidence in the coming years. On the other hand, there is not necessarily much to be done in response at this time of year, for a couple of reasons.

One reason is a logistical constraint on applications at this time of year, having to work around harvest. Due to postharvest intervals (PHI), several options for conventional applications are impractical in that they conflict with harvest. More information about which products are labelled for GWSS use in grapes and their PHI can be found at the following UC IPM webpage  

The other reason that a response to GWSS may not be practical at this time of year is an epidemiological one. Research has shown that vines that get infected later in the season are more likely to recover from the infection over the winter. Nearly all vines infected after mid-Summer showed no evidence of infection or disease the following season. In other words, although there are outstanding questions about carryover benefits of late-season treatments on vector pressure at the beginning of the following year, protecting vines from infection at this time of year may not be that important. Instead, the main concern is vines infected during the Spring and early Summer, which are more likely to develop chronic PD 

Please contact Matt (mattd@ucr.edu) with any questions