METHYL BROMIDE ALTERNATIVES, FOCUS ON ROOTSTOCKS Michael McKenry ABSTRACT At Rio Oso, CA, Chandler scion was grafted onto two different one-year-old Paradox seedlings in the presence of three different pre-plant soil treatments. As reported earlier, the soil treatments resulted in varying volumes of nematode-free soil available for root exploration. Broadcast treatments of methyl bromide or metam sodium supplied a larger volume of nematode-free soil compared to strip applied Telone II. The vigor imparted by these two rootstocks in methyl bromide treated soil is relatively similar. However, a mechanism for pre- infection nematode resistance in NX compared to DN rootstock has enabled NX to fare better when planted after soil treatments that were restricted in distribution. NX seedlings and UZ229 clones are the only two Paradox rootstocks known to possess a mechanism for pre-infection nematode resistance, the commercial value of which was not previously known. Paradox clone VX211 imparts high vigor plus tolerance to nematode feeding. Its tolerance appears to be associated with reduced nematode presence within the terminus 12 inches of each root. In field settings where nematode populations are already low VX211 rootstock does provide nematode relief. Cloned Serr, an English walnut cultivar, is resistant to Meloidogyne incognita but remains a good host for Pratylenchus vulnus. Seedlings of Juglans cathayensis were grafted with Chandler in spring 2008 and 6 of 15 graft sticks were successful through the end of 2008. There is an abnormal swelling that surrounds each graft union, its practical impact not yet known. Five clones of J. cathanensis #21 were received in fall 2008, enough to hopefully confirm its putative resistance to M. incognita and P. vulnus. The walnut hull tea available as NatureCur does not control P. vulnus but is effective against other nematode species. At 20,000 ppm as a pre-plant treatment NatureCur is detrimental to growth of young walnut trees. Fosthiazate is too short- lived to be used as a pre-plant treatment, however drenched Telone EC can be highly nematicidal through fall of the first year. OBJECTIVES 1) Maintain the Rio Oso trial for yield data, rates of nematode return and tree growth. 2) Remove up to half the trees (6 reps) from the VX211 and AX1 trial at Kearney Ag Center and graft over to Chandler for yield data. 3) Obtain for further nematode and field evaluations the clones of RX032 and UZ229 (Wes Hackett). 4) Continue nematode evaluations of various Juglans species from the USDA Davis Repository. 5) Compare all Juglans selections in adjacent replicated fumigated and non-fumigated sites in two walnut replant orchards, one following NCB the other Paradox. 6) Quantify the number of root tips/tree, their length, and the length of each root tip that will host P. vulnus and Meloidogyne spp. 7) Explore at our KAC trial site the value of Garlon + one year of chemical drenches and/or non-hosts as methods for reducing soil populations of P. vulnus, Mesocriconema xenoplax and Meloidogyne spp. down to various soil depths.