Background: Starting in the year 2000, growers in the Temecula Valley of Riverside County experienced severe damage to wine grapes due to Pierce's Disease. The disease was being vectored by a non-native insect called the glassy-winged sharpshooter (GWSS). Surveys have shown GWSS widely distributed in Southern California including Kern County and southern Santa Barbara County. At this time, GWSS is not established in the north and central coastal or northern California grape growing counties, including Yolo County. This presents an opportunity to develop strategies on a regional or local basis to deal with GWSS once it is found outside of the generally infested area.
Detection of GWSS for Growers: In the event that GWSS does spread to Yolo County, it is essential that GWSS be detected at the earliest possible time, to best develop a control strategy. Early detection can be achieved with a consistent trapping program using sticky traps and by doing a visual survey. Keep in mind that lack of detection on sticky cards does not necessarily mean that sharpshooters are not present, although if you find trapped adults you have solid evidence of their presence. Sticky cards will not detect sharpshooters in the juvenile or egg stages. Using both sticky traps and visual checks is the best way to find new infestations.
County Detection for GWSS: Yolo County currently traps residential areas with 115 traps throughout the summer. Commercial crops are not monitored by county trappers.
The California Department of Food and Agriculture (Plant Health and Pest Prevention Services)
suggests the following survey guidelines:
Visual survey: County agricultural personnel conducted the initial visual survey. We surveyed all commercial plantings of citrus, vitis and prunus spp. which fell entirely or partially within a 1/2 mile radius of residential areas or other known GWSS reservoirs (i.e., riparian habitats and/or oak woodlands) and all new citrus plantings.
Trap deployment: Traps should be deployed at a minimum density of one per 120 acres. Trap from April through October, relocating the trap into a new 20-acre sub-quadrant every six weeks. Service trap (inspect) every two to three weeks. Use a new trap at the time of each relocation; replace traps as needed.
Traps deployed in citrus and prunus should be placed in the upper canopy near flush foliage in exposed positions (not inside the foliage). Hang the traps perpendicular to the trunk of the tree so that both sides of the trap are visible. Hang them so they will not get stuck to the foliage. Deployment of traps in or near stressed trees may enhance the probability of detection.
In vineyards, poles/stakes should be used to suspend yellow panel traps just above the grape canopy. Deployment in perimeter rows or along heavily traveled routes within the planting should be avoided. Hang the trap perpendicular to the vine so that both sides of the trap are visible. Hang them so they will not get stuck to the foliage. Additionally, if a winery is present at the vineyard location, place traps at the edge adjacent to the winery or landscape plantings. Vineyard managers should train their field worker personnel to recognize what the egg masses, nymphs, and adults of the glassy-winged sharpshooter look like. Field workers have close contact with the foliage and vines (tying, etc.) on a daily basis, therefore they will be more likely to encounter a suspect sharpshooter.
Specimen Collection and Submission of Samples: Growers should contact county personnel to assist with the packaging of suspect finds. Leaves with suspect egg masses and/or egg scars should be placed in sealed plastic bags. Free-living adults and nymphs should be killed by placing them in vials containing 70% alcohol. These containers should have tight fitting corks or screw top lids to prevent/minimize the loss of specimens or preservative during transit to the laboratory. Suspect adults on sticky traps can be submitted by either sending the entire trap or by cutting out and sending the portion of the trap containing the suspect sharpshooter. Prior to packaging, yellow panel traps should be reversed so that the sticky surfaces are on the inside (fold the card board tab to the inside-sticky side of the trap. Use this as a barrier to prevent the trap from sticking to itself. If the sticky sides stick together it will be virtually impossible to identify the suspect sharpshooter). Place a rubber band around the outside to hold the two halves in position. Care should be taken to insure that the sticky surfaces are not in contact. Do not submit traps covered with clear plastic. Sticky traps should be placed in sealed plastic bag(s) before shipment. "Cut-outs" should be placed in dry plastic vials and sized to fit tightly inside so that neither the specimen nor the "stickem" comes in contact with the inner surface of the container. Mark the trap, plastic bag or vial with the field ID or block number and date of the find. County personnel will assist with packaging of suspect finds. Deliver any suspect insects to or call for pickup from:
Yolo County Agricultural Commissioner's Office
(530) 666-8140 E-mail: email@example.com
UC Cooperative Extension Yolo County
Sources of additional information and pictures:
Xylella fastidiosa Web Site