ESTABLISHMENT OF APRICOT AND ALMOND TREES USING SOIL MULCHING WITH TRANSPARENT (SOLARIZATION) AND BLACK POLYETHYLENE FILM - EFFECTS ON VERTICILLIUM WILT AND TREE HEALTH

Apricot (Prunus armeniaca) and almond (P. dulcis) trees at the first l eaf stage were planted in soil infested with Verticillium dahliae and mulched with transparent or black polyethylene film, or not mulched, i n the San Joaquin Valley of California, March-August 1990. During the 19-week mulching treatment, summer soil temperatures reached as high a s 46, 41, and 33-degrees-C at 18 cm depth; and 41, 37, and 32-degrees- C at 30 cm depth under clear film, black film, and no film, respective ly. Trees mulched from the time of planting with transparent polyethyl ene (solarization) did not survive or grow as well as those mulched wi th black film or not mulched. Incidence of foliar symptoms due to Vert icillium wilt was reduced by 86-100% in both apricot and almond trees by black, as well as transparent film mulch the following season. Inci dence of vascular discoloration symptoms of trunks and primary scaffol ds due to Verticillium wilt was similarly reduced by both mulches. Mul ching with black polyethylene film gave better overall results than so larization with transparent film. The intermediate soil temperatures p roduced did not chronically harm trees, as judged by tree survival and annual growth of trunk diameter, yet the prolonged period of soil hea ting provided control of Verticillium wilt equivalent to that of solar ization with transparent polyethylene. These studies provided further evidence that in-season mulching can be used to conserve water during establishment of new orchards or replant trees in warm, arid climates.