Project Title: Weed Management in Washington Wine Grapes: Where Do We Currently Stand and Where Can We Go in the Future

Project Duration: 1 year

Principal Investigator(s): Lynn M. Sosnoskie
Organization: Washington State University
Address: WSU TFREC, Wenatchee, WA 98801
Telephone: 229-326-2676

CO-PI: Ian C. Burke
Organization: WSU
Address: Pullman, WA 99164
Telephone: 509-335-2858

Project Summary:

Weed control is a critical component of newly established and bearing vineyard production as weeds compete with the crop water, nutrients, and light, which can affect yield quantity and quality. In addition to direct interference, non-managed weeds can negatively affect orchard production by: blocking sprinklers, thereby resulting in micro-sites that are alternately drought- and flood-stressed; supporting populations of insect, rodent, and pathogenic pests detrimental to crop health; and interfering with harvest activities. Furthermore, the chemical products used for weed control can also have adverse effects on vine health if they are applied improperly or at a time when vines are susceptible to injury. Continuing research is needed to evaluate the most effective and sustainable practices managers to optimize (both environmentally and economically) wine grape management programs while reducing the development of herbicide-resistant, or other difficult to control, weed populations.

The primary goal of the project was to develop a survey that could be submitted to WA wine grape growers to describe current weed management practices and determine future weed control needs. Twenty-nine respondents responsible for managing 10,000 acres of vineyards (representing approximately 20% of the total wine grape acreage in WA) completed a voluntary 18 question survey designed to address these concerns. Results from the survey determined that pre- and post-emergence applied herbicides are widely used tools for managing unwanted vegetation under grape vines. Fifty-nine percent of the respondents indicated that they used pre-emergence herbicides for weed control, whereas 83% reported using post emergence products. In addition to herbicides, WA wine grape growers also utilized mowing, cultivation, hand-weeding, and cover crops to suppress weeds. With respect to problematic species and future weed control needs, summer broadleaf species were primarily considered to be a big problem in vineyards, specifically noting Salsola tragus (Russian thistle), Tribulus terrestris (puncturevine/goatheads/caltrops), Conyza canadensis (marestail), Kochia scoparia (kochia), Amaranthus spp (pigweed), Centaurea spp (knapweed). While the identification of new herbicides for use in wine grape systems is desirable, reducing the industry’s reliance on chemical control strategies also appears to be of interest to the wine to the survey respondents. Cultivation practices can be an effective alternate weed management strategy; however, growers appear to be interested in minimizing soil disturbance.

The second major goal of the project was to increase the extension and outreach presence of WSU weed science in grape production systems. Consequently, three articles designed to address weed management related concerns were published in WSU’s Viticulture and Enology Extension Newsletter (VEEN). The first paper, which was published in the 2017 spring edition of VEEN, entitled ‘Understanding Herbicides and Resistance’, described 1) the sites of action (SOA) available to grape growers in WA, 2) how herbicides in different Weed Science Society of America (WSSA) SOAs worked to control weeds, and 3) the number of species with resistance to each SOA occurring in the PNW. The second paper was published in the fall of 2017 and described pre-emergence herbicides for use in grapes in the PNW. The article also addressed the biological, physical, and environmental factors affecting herbicide efficacy. The third and last VEEN article, published in spring of 2018, described the results obtained from the previously described grower survey. The 2018 Pest Management Guide for Grapes in Washington was updated to include a new section describing the factors affecting herbicide efficacy such as: the kinds of weeds to be controlled, the size and age of weeds to be controlled, soil type and herbicide incorporation strategy, the quantity and quality of spray water, and the age and health of the vine.

Read more by downloading the full report above.

Pest & Disease //