Problems in tree replacement. III.* The effects of cultural practices and soil fumigation on root-lesion nematodes and on the growth of apple replants

Abstract

The growth of replant apple trees cv. Delicious was much less in field plots after a mixture of cover crops, including rye cv. Black Winter and lupin cv. New Zealand Blue, had been grown for 16 months than where the land had been left to volunteer weeds or kept free of plant growth. In a subsequent glasshouse experiment, growing rye or blue lupin in old orchard soil before planting apple seedlings caused severe stunting. In a field trial, soil fumigation with dichloropropene-dichloropropane (DD) before planting increased the first season's shoot growth of apple trees cv. Delicious after rye cv. Black Winter by 79% and after lupin cv. New Zealand Blue by 60%. Trees grew well after prairie grass cv. Priebe or oats cv. Saia, increases due to fumigation being 4.0 and 4.5% respectively. In a glasshouse experiment rye and blue lupin were shown to be much better hosts for the root-lesion nematode Pratylenchus penetrans than prairie grass or oats. A survey of Queensland apple orchards indicated that Pratylenchus penetvans and another species previously identified as Pratylenchus coffeae often occurred together. In a glasshouse experiment the addition of large numbers of P. penetrans to soil severely stunted apple seedlings cv. Granny Smith, whereas the other Pratylenchus species had little effect. ________________ *Part II, J. Aust. Inst. Agric. Sci., 20: 234 (1954).