Nematode Control

Nematode problems in established orchards are difficult to control, and, therefore, good management should focus on preventive measures. As with many other pest problems, nematode control begins with sanitation and good cultural practices. Transplanting of infected stock and movement of infested soil by humans are primary means of dissemination. Interregional and intercontinental movement of infested soil and plant material has almost certainly extended the geographic range of many nematodes. Cultural practices such as optimization of soil pH, proper fertilization, improvement of soil tilth and organic matter, and weed control promote healthy trees and thus minimize the effects of nematode damage.

Some nematode and nepovirus problems can be controlled with genetically resistant rootstocks. When available, this is one of the most economical and environmentally sound methods for managing these problems. However, for most nematode and nepovirus diseases, genetic resistance is not available.

The best time to begin a nematode control program is before a new orchard is planted (Figure N1.3). Soil fumigants are the most efficient and effective chemicals for nematode control, and these can be applied only prior to planting. In general, fumigants are broad-spectrum biocides and also provide some level of disease and weed control; however, efficacy will vary depending upon the particular fumi-gant used and soil conditions at the time of incorporation. The most volatile soil fumigants require tarping.

Contact nematicides can be used as preplant or postplant treatments. When used as preplant treatments, they can be thoroughly incorporated before the orchard is planted, making broadcast application more effective. These products can be incorporated into the soil with a rototiller or other mechanical means or by irrigation. Nema-ticides are highly effective, but the level of control is usually not as good as fumigation due to limited movement of the chemicals through the soil. For control of nepovirus diseases, it is also important to effectively manage broadleaf weeds that serve as reservoirs of the virus.

FIGURE N1.3. Nectarine orchard with dead and declining trees due to prunus stem pitting disease, caused by tomato ringspot virus. Replant sites require extensive renovation for successful tree establishment.

The use of a crop rotation for nematode control can provide several benefits. Aside from suppressing nematode populations, rotation crops can also reduce weed problems, increase soil organic matter, improve nutrient availability, and help control erosion. In addition, decomposition of rotation crops improves soil drainage and aeration. This improves tree growth and promotes nutrient recycling. Some crops, such as rapeseed and marigold, also release nematicidal compounds upon decomposition.

Plant-parasitic nematodes are economically important pathogens of fruit trees. Heavily infested orchards may never reach their full production potential and, in the most severe cases, may fail completely due to poor yield, reduced quality, and/or tree death. A preplant soil assay can determine the potential for nematode problems and whether control measures are needed. Preplant detection and treatment of orchard nematode problems is the most economical, efficient, and effective control strategy.

Related Topics: DISEASES; ORCHARD PLANNING AND SITE PREPARATION; PLANT-PEST RELATIONSHIPS AND THE ORCHARD ECOSYSTEM; ROOTSTOCK SELECTION

SELECTED BIBLIOGRAPHY

Nyzcepir, A. P. and J. M. Halbrendt (1993). Nematode parasites of fruit trees. In Evans, K., D. Trudgill, and J. Webster (eds.), Plant parasitic nematodes in temperate agriculture (pp. 381-425). Wallingford, UK: CAB International.

Whitehead, A. G. (1998). Plant nematode control. Wallingford, UK: CAB International.

Yadava, U. L. andS. L. Doud(1980). The short life and replant problems of deciduous fruit trees. Hort. Rev. 2:1-116.

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