Post-plant nematicides: too little, too late for Northern root-knot nematode management

Abstract

Context and Purpose. Management of plant-parasitic nematodes in perennial cropping systems such as wines grapes is challenging. Yet, management of these pests remains important, as some vector pathogens, while others inflict direct damage on a grapevine’s root system. The study presented here evaluated different post-planting nematicide treatments in own-rooted Vitis vinifera vineyards, for their ability to reduce densities of Northern Root-knot nematode (RKN, Meloidogyne hapla). This information can be used by grape growers and crop consultants to better understand whether chemical options can play a role in long-term nematode management, or if cultural practices (use of resistant rootstocks or suppressive cover crops) are more appropriate in nematode-affected vineyards.

Materials and Methods. The products evaluated were: fluazaindolizine, fluensulfone, fluopyram, fosthiazate, and spirotetramat. Nematicides were evaluated under different application regimes (spring, summer, fall, or a combination therein), at 3 different commercial vineyards in eastern Washington State. Evaluations were conducted for 2-3 consecutive years (depending on site), between 2015-2020. Not all sites received the same treatments, but all included untreated controls. Products were applied following manufacturer’s suggested rates using the drip-cup method to simulate chemigation. Treatments were applied to 9 to 20 consecutive in-row vines, replicated 4 times.  Soil densities of RKN 2nd stage juveniles (J2) were determined prior to treatment, and again after treatment each year. Phytotoxicity was rated.

Results. Of the post-plant nematicides evaluated, fluazaindolizine was the only product that had sustained reductions in RKN J2 soil densities after multiple years of treatment. This reduction, however, was only after treatment 3X within a season, and at rates that now exceed label suggestions. Evaluations of fluopyram stopped after 2 years of use, due to phytotoxicity. This phytotoxicity mimicked exposure to auxin herbicides, as seen in other studies on fluopyram. Ultimately, this study showed that routine use of post-plant nematicides for the control of RKN is not the best approach for management. This means the primary focus should be on the adoption of resistant or tolerant rootstocks, and practices that either directly control nematodes (suppressive cover crops) or promote ecological diversity that may reduce RKN densities through direct resource competition or parasitism.