Management of lesion nematode (Pratylenchus jordanensis) on replanted apple trees

Abstract

Chemical and non-chemical strategies for managing lesion nematode (Pratylenchus jordanensis) on apple replants were investigated in field experiments at Applethorpe, Queensland. In the first experiment, old trees from a nematode-infested orchard were removed in June 1987 or April 1988. Plots then received one of the following treatments: solarisation; fallow; animal manures (¦ 900 kg urea/ha); green manure crops of forage sorghum or lablab bean ploughed in (¦ 1800 kg urea/ha); ethylene dibromide or methyl bromide. Lesion nematode populations before replanting apple trees in July 1988 were generally lower if trees had been removed 12 months rather than 3 months previously. Nematodes increased on forage sorghum, but populations were reduced substantially when the crop was ploughed in with urea. Methyl bromide was the only treatment to reduce nematode populations at planting to very low levels. Two years after planting, nematode populations on apples were reduced by some of the chemical and non-chemical treatments. Most non-chemical treatments increased the growth of replanted apple trees, but methyl bromide produced the largest trees. In a second experiment, methyl bromide again enhanced early growth, but after 5 years, trees mulched with sawdust or sawdust and manure had the lowest nematode populations and produced yields as good as, or better than, methyl bromide. The results of both experiments suggested that lesion nematodes on apple replants could be managed without fumigant nematicides through a combination of early removal of the previous orchard, incorporation of animal manure or a green manure crop with urea, choice of an appropriate rootstock, and maintenance of a layer of organic mulch around trees.