Written by Tianna DuPont, WSU Extension. October 31, 2023
Apple replant disease is a soil-borne disease syndrome which occurs when new orchards are planted on sites previously planted to the same or closely related tree fruit species. It can also occur on sites previously planted to other non-grass crops which harbor nematodes and replant fungi. Replant disease causes tree stunting and reduced yields (Mai and Abawi 1981). In Washington State fungi including Ilyonectria robusta, Rhizoctonia solani, multiple species of oomycetes in the genera Phytophthora and Pythium, as well as the lesion nematode Pratylenchus penetrans are known components of the replant complex (Mazzola 1998; Mazzola and Mullinix 2005).
If replanting in previously planted soil, whether apples, pears or cherries, and regardless of the root’s ability to withstand replant disease, the ground should be deeply ripped and fumigated prior to planting. In Washington the general practice is to fumigate with 1-3 Dichloroprene plus chloropicrin. 1,3-dicloropropene is nematicidal while the chloropicrin is fungicidal. Remember when fumigating it is important to remove crowns and roots that can harbor nematodes. Rip to break up compaction layers that can also limit root growth of young trees. Adequate soil moisture and temperature is critical for the fumigant to move properly through the soil. Make sure you allot enough time for fumigation chemicals to fully dissipate from the soil before planting. Check this by digging test holes throughout the orchard and checking for the scent of fumigation. Follow fumigation labels.
- Remove crowns and roots.
- Rip to reduce compaction.
- Apply fumigation at adequate soil moisture and temperature.
- Allow fumigation to dissipate before planting.
Reducing replant pressure before planting is critical. For example, in recent studies WA38 on M.9 rootstock tree growth was significantly lower in non-fumigated soil compared to soil that had been fumigated (1-3 Dichloroprene plus chloropicrin) or treated with a brassica seedmeal biorenovation at a site in Rock Island (DuPont et al. 2021). In the first three harvest years trees in non-fumigated soils averaged 4 to 6 bins fewer per acre on G.41 and 4 to 8 bins fewer per acre on M.9 rootstock than soil treated with fumigation, brassica seedmeal biorenovation or anaerobic soil disinfestation (p<0.05; DuPont, Mazzola et al 2023 unpublished).
Funding and acknowledgements
Alternatives to fumigation project supported by grants from the Washington State Tree Fruit Research Commission grant # 10211000 and the USDA Crop Protection grant # 2017-70006-27267. Thank you to in kind support from Progen Seed, Trident Ag Products, Farm Fuel Inc and generous support of labor, materials and equipment from orchardists Mike Robinson, Jim Baird and Sam Godwin. Thank you to valuable contributions from orchardists hosting project sites Mike Robinson, Jim Baird and Sam Godwin; work and efforts of technicians Abby Kowalski, Ashley Thompson, Allie Druffel, Chris Strohm; and orchard management Cameron Burt.
DuPont, S. T., Hewavitharana, S. S., and Mazzola, M. 2021. Field scale application of Brassica seed meal and anaerobic soil disinfestation for the control of apple replant disease. Appl. Soil Ecol. 166.
Mai, W. F., and Abawi, G. S. 1981. Controling replant disease of Pome and Stone fruit in Northeastern United States by preplant fumigation. Plant Dis. 65:859.
Mazzola, M. 1998. Elucidation of the microbial complex having a causal role in the development of apple replant disease in Washington. Phytopathology 88:930-938.
Mazzola, M., and Mullinix, K. 2005. Comparative field efficacy of management strategies containing Brassica napus seed meal or green manure for the control of apple replant disease. Plant Dis. 89:1207-1213.
Fruit Matters articles may only be republished with prior author permission © Washington State University. Reprint articles with permission must include: Originally published by Washington State Tree Fruit Extension Fruit Matters at treefruit.wsu.edu and a link to the original article.
Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.
YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.