On January 19, 2015 David Granatstein spoke at the Lake Chelan Hort Day about why weed control is needed in orchards, weed control options, herbicides and other choices, and economics. He also discussed the results of non-chemical weed control research.
Speaker: Mr. David Granatstein, Sustainable Agriculture Specialist. Affiliation: WSU Center for Sustaining Agriculture and Natural Resources, Tree fruit Research and Extension Center, Wenatchee, WA 98801-1230. Synopsis: First, Mr. Granatstein notes several reasons to control weeds including limiting competition for young trees with nutrients and water, minimizing rodent (e.g., voles) habitat, eliminating hosts for pest and disease and to avoid blocking irrigation sprinklers. He describes the standard orchard system with herbicide strip and grass alley and noted that about 20 sq. ft. of weed free space is needed per tree during May-July. He lists six different weed control options (noting pros and cons) including: residual and contact herbicides, mowing, tillage, flaming, inert mulches and living mulches. Mr. Granatstein briefly discusses the issue of sub-lethal effects of glyphosate. He described research supporting the benefits of using wood chip mulch for weed control. He also discussed the concept of growing your own mulch. He notes that the use of living mulches in older trees has several benefits including excluding undesirable weeds while fixing nitrogen, improving soil quality and providing beneficial insect habitat. He presents economic data for several alternative weed control strategies. He described a large-scale, 3-year organic trial looking at mulch, tillage, flaming or herbicides in Gala apple and Anjou pears. Over the three year period for Gala apple, they noted significant positive return on investment using mulch verse herbicide/flaming or tillage. He suggests several options for the future.