What is in this article?:
- Grape growers urged to remain vigilant against sharpshooter pest
- Northward march of GWSS
- Lulled into complacency
- California's strategy for slowing or stopping the spread of the GWSS and for finding solutions to PD has been so successful that growers sometimes get lulled into complacency.
- Southern California epidemics were almost entirely the result of vine-to-vine transmission.
- Uptick in PD discoveries in southern Kern County, Calif., alarming.
UC Riverside Extension entomologist Nick Toscano, right, watches at Temecula-area wine grape grower and vineyard manager Ben Drake, left, checks one of 450 sticky GWSS traps in Temecula with one of his employees Jim Hakrey.
Northward march of GWSS
And still the seemingly inevitable northward march of the GWSS continued with infestations found as far north as Chico. Wine grape growers lobbied hard for an assessment that would help bolster research and fund a monitoring and control program. In 2001 a $3 per $1,000 value was enacted. For some, the assessment marked the official beginning of this highly cooperative program.
Nick Toscano is the University of California, Riverside, Extension entomologist who developed the original GWSS control proposal adopted by the CDFA. He continues to manage the tracking and reporting program in Temecula.
Tracking is key to the success of the management program, Toscano said. In Temecula, 450 yellow sticky traps monitor GWSS numbers and movements in citrus groves and vineyards. If even one adult GWSS is found in the weekly trap inspection a visual inspection is triggered. A weekly newsletter emailed to stakeholders alerts growers and managers to GWSS buildups at their sites and the need to initiate insecticide treatment to prevent GWSS populations from becoming established.
Research found that the Southern California epidemics were almost entirely the result of vine-to-vine transmission, a pattern rarely seen before the GWSS became established. Infections that occur in June and July have enough time to get established, survive the winter, causing PD during the next growing season. A protocol of applying one carefully timed application of a persistent systemic insecticide such as imidacloprid virtually eliminates the vine-to-vine spread.
Ben Drake is a Temecula-area wine grape grower and vineyard manager who began seeing problems from PD in the Temecula Valley as early as 1997. He and others in the area became key players in galvanizing the multi-pronged approach to the PD/GWSS threat. Drake was an inaugural member of the state task force and the PD/GWSS board, and continues to serve on both today.
“We’ve found that if we apply (imidacloprid) at the middle to the end of May, before the sharpshooter moves out of the citrus and goes into the vineyards, we get levels of the material into the plant high enough that when the sharpshooter flies over from the citrus groves to try it, they just fly back where they came from. Or, if they feed long enough, it will kill them.
“I’m not saying that we won’t find a vine that we will lose to Pierce’s disease, but we don’t have that epidemic level that we had in previous history.”