Location: Pest Management and Biocontrol Research2013 Annual Report
1a. Objectives (from AD-416):
1)Determine the incidence of Pierce’s disease in Arizona vineyards; 2) Identify vector species present in vineyards and determine their seasonal prevalence; 3) Evaluate various chemical and cultural management approaches that reduces spread of Pierce’s disease; 4) design an effective and sustainable IPM program to combat Pierce’s disease
1b. Approach (from AD-416):
Basic epidemiological data will be collected to identify the strain(s) of Xylella fastidiosa, the causal agent of Pierce’s disease, present in Arizona wine grape vineyards. Potential host plants in native and ornamental vegetation surrounding vineyards will be sampled and tested as potential hosts of X. fastidiosa. Conventional insect trapping and sampling methods will be employed to determine vector pressure in vineyards. Cultural and chemical management approaches will be developed based on the epidemiological data and tried experimentally in vineyards. The most successful management approaches will be incorporated into IPM recommendations and provided to growers in pamphlet form.
3. Progress Report:
This Reimbursable Agreement is in support of Objective 1, "Develop knowledge and control tactics based on the physiology, biochemistry, genetics and vector-pathogen interactions of insect pests", and, Subobjective 1.4, "Pathogen-mediated changes in host plants and their impact on vector populations", of the inhouse parent project. Field studies commenced in April of 2013, with the first leaf samples from grapevines collected in Yavapai and Cochise counties. Samples collected periodically since that time and tested by enzyme-linked immunosorbent assay (ELISA) have shown a steady increase in both the incidence and average titer of Xylella fastidiosa in multiple vineyards. Leaf scorch symptoms, typical of Pierce’s disease, began to show in late June and have progressed in July to a level where multiple branches on individual plants are now showing symptoms along with an increasing proportion of grapevines within vineyards. Equipment has been ordered that will enable higher throughput of samples for ELISA and polymerase chain reaction (PCR) testing and allow additional vineyards to be tested. Along with testing for the presence of the bacterial pathogen in grapevines, isolations of X. fastidiosa have been made from grapevines and cultures established on media that will be used to compare DNA sequences from Arizona strains to X. fastidosa strains collected from other geographical regions. Xylella fastidiosa has also been isolated from native and ornamental vegetation proximal to vineyards and detected by ELISA in these hosts. This information may become useful to vineyard managers in terms of recognizing alternative hosts that can be eliminated to reduce inoculum pressure around vineyards. Identifying potential vector species of X. fastidiosa and monitoring vector pressure in Arizona vineyards is a key objective of this project. Yellow-sticky traps were first deployed in April and have been collected biweekly and exchanged for new traps at three vineyard locations in Yavapai County. Light traps were also set up at two locations and have been regularly monitored for leafhoppers and spittlebugs. Trap catches have been limited from all locations so far this year. In addition to being unfamiliar with the potential vector species in Arizona, their seasonal populations patterns are unknown. Specimens collected thus far have been sent to leafhopper specialists for identification so that relative abundances and seasonal timings can be described. It is widely assumed that all xylem feeding insects are potential vectors of X. fastidiosa, a key point that will be used to differentiate leafhopper vectors from leafhopper non-vectors. These two groups can be distinguished based on pronounced mouthpart musculature of xylem-feeding leafhoppers compared with phloem- or parenchyma-feeding leafhoppers. Reports of spittlebug colonization of grapevines are common in Yavapai and Cochise counties where two of the three Arizona wine regions are located. Collections of live spittlebugs on grapevines in Yavapai County were made in October, 2012, and are now in culture in Arid Land Agricultural Research Center (ALARC) greenhouses. Insects from this colony will be used for vector transmission experiments and/or toxicological bioassays with neonicotinoid insecticides. Reducing the potential of X. fastidiosa spread by eliminating plant inoculum sources and minimizing vector populations and activities in and around vineyards is a central goal of this project and X. fastidiosa management in general. Field trials are underway in three vineyards in Yavapai County to investigate the activity profile of imidacloprid, a neonicotinoid insecticide having antifeedant properties and a record of reducing pathogen transmission by insect vectors. Grapevine leaf samples have been collected biweekly since late April when the first treatment applications were made. A commercially available test kit with a sensitivity limit of 0.2 ppb is being used to quantify imidacloprid titers in leaf samples. These data are being compiled and will be used to develop an activity profile of imidacloprid to characterize its overall persistence and time of peak activity in grapevines. When merged with data on vector phenologies, the goal will be to identify periods of greatest vulnerability in Arizona vineyards to vector pressure so that imidacloprid applications and other control measures can be implemented in the most timely and effective manner.