Weed Management in Organic Orchards and Vineyards in the San Joaquin Valley of California.

Weed management in organic cropping systems continue to be a challenge due to the lack of economically sustainable alternatives.  The perennial cropping systems, such as orchards and vineyards, in the San Joaquin Valley (SJV) of California are no exception to this challenge. Further, there are additional issues associated with air quality (dust and smoke) regulations with some of the non-herbicide alternate treatments in the SJV.  On-farm studies have been initiated in a transition-organic almond orchard, an organic raisin grape vineyard, and an organic winegrape vineyard to compare several organic weed management options.  Treatments include steam, flame (orchard only), French plow (raisin vineyard only), Bezzerides cultivator (vineyards only), and an organic herbicide (Greenmatch®).  A non-treated control at each site has also been included.  Results in the almond orchard study indicate that steam, flaming, and organic herbicide provide up to 4 weeks of weed suppression and monthly applications of these treatments will be necessary.  It may not be safe to use a flamer in the orchards after early spring because of fire hazards in an arid environment such as that in the SJV.  Preliminary results from the vineyard study show that steam was less effective in raisin vineyards with raised berms but more effective in winegrape vineyards with no raised berms.  The organic herbicide provided a selective bundown effect on certain broad-leaved weed species.  The mechanical weed control treatments (French plow and Bezzerides cultivator) provided the greatest amount of weed control.  However, there may be disadvantages associated with mechanical weed control because of the soil disturbance process.  The study is ongoing and more parameters will be evaluated to compare the sustainability of each treatment at each site.