Effect of Lime on Criconemella xenoplax and Bacterial Canker in Two California Orchards

Abstract

In a peach orchard with an initial soil pH of 4.9, preplant application of 0, 13.2, 18.2, 27.3, or 54.2 kg lime/tree site altered soil pH (range after 1 year = 4.8-7.3) but did not affect numbers of Criconemella xenoplax or tree circumference. Liming also failed to reduce the incidence of bacterial canker, which affected 17% of the trees by the sixth year after planting. Four years after planting, numbers of C. xenoplax exceeded 400/100 cm³ soil, regardless of treatment. Trees with higher densities of C. xenoplax had a higher incidence of canker. The nematophagous fungus Hirsutella rhossiliensis was not detected until the fourth year. Thereafter, the incidence of H. rhossiliensis and percentage C. xenoplax parasitized by H. rhossiliensis increased, but the increases lagged behind increases in numbers of nematodes. In an almond orchard with an initial soil pH of 4.6, preplant application of 0, 6.4, 12.8, or 25.0 kg lime/tree site altered soil pH (range after 1 year = 4.7-7.1). Numbers of C. xenoplax remained low ( 20/100 cm³ soil), whereas numbers of Paratylenchus sp. increased to high levels ( 500/100 cm³ soil), regardless of treatment. Low levels ( 20/100 cm³ soil) of H. rhossiliensis-parasitized Paratylenchus sp. were detected. No bacterial canker occurred, but tree circumference was greater after 6 years if soil pH was intermediate (6.0-7.0). Key work: almond, biocontrol, biological control, Criconemella xenoplax, Hirsutella rhossiliensis, lime, nematode, Paratylenchus sp., peach, Prunus dulcis, Prunus persica, soil pH.