Nematode Pests of Deciduous Fruit

Abstract

The deciduous fruit industry produces 3.26 million metric tons (MT) of fruit annually, of which 0.48 million MT is exported. It is a significant contributor to the agricultural economy of the country, especially the Western Cape province. A variety of pome fruit is planted locally, with apple dominating, followed by pear. Stone fruit such as peach, plum, and apricot are produced throughout South Africa, with almost 90 % being grown in the Western Cape. Initially, research focused mainly on insect and disease management, with underground pest problems receiving little attention. Nematodes cause substantial damage to deciduous fruit crops, especially Criconematinae, Pratylenchus, Xiphinema, and Trichodoridae. Parasitism by these pests results in poor root growth, low water and nutrient uptake, and thus smaller fruits. Control of nematode pests in deciduous fruit orchards is a challenge, since many factors play a role. These include rootstock, presence of apple replant disease, and soil type. Management options currently available include chemical control and some root-knot nematode resistance in certain rootstocks, calling for more research to be done on alternative control methods. The major nematode pest problems of pome fruit are dagger, lesion, and stubby-root nematodes, whereas lesion, ring, dagger, and stubby-root nematodes are abundant on stone-fruit rootstocks. On apples, mixed populations of various lesion nematode species are present in 98 % of orchards, and stubby-root and dagger nematodes in 58 and 40 %, respectively. Likewise on pears, mixed populations of stubby-root nematodes are present in 50 %, while dagger and lesion nematodes occur in 48 and 40 %, respectively. Experiments with aldicarb, oxamyl, and fenamiphos to control lesion and dagger nematodes resulted in increased yields of up to 89 % over 2 years. On apricot, the ring nematode, Criconemoides xenoplax, causes branch-die-back and tree death, while on peaches and nectarines, it is associated with peach-tree-short-life-syndrome. On plum, C. xenoplax infections are implicated with bacterial canker and environmental stress factors in causing “plum tree death.” On stone fruit, the rootstock used dictates the nature of yield loss. Marianna, a root-knot nematode-resistant plum variety is used as a rootstock on plums and apricots, but is extremely susceptible to ring nematodes.