Cause Phytophthora spp., fungus-like microorganisms that survive in soil and can be carried in irrigation water from surface sources. Prolonged soil saturation is optimal for the pathogen to infect roots. The OSU Plant Clinic has found the disease. Studies in China have found that lower soil pH (from a range of 4.2 to 8.8) was associated with more pathogen. Warmer soil temperatures (from a range of 12.7 to 24.3°C) were also associated with more pathogen.
Symptoms Reduced terminal shoot growth, undersized leaves, and an open canopy occur in spring. Vines may collapse suddenly as temperatures increase in summer or may decline slowly over several seasons. Roots and root crowns of infected vines exhibit a red brown rot that is easily observed by cutting into the cortical tissue. Generally there is a line between healthy, white tissue and diseased, discolored tissue. Feeder roots are lacking, and active lesions often progress aboveground on one or more sides of the lower trunk, resulting in sunken areas.
Cultural control
- Plant on raised berms in well-drained soil to allow for rapid water drainage.
- Practice good irrigation management since overwatering can lead to root rot problems.
Chemical control Alternate products from different groups with different modes of action to prevent the buildup of resistant fungi.
- Fosphite at 1 to 3 quarts/100 gal water. Do not use copper products within 20 days of treatment and do not use spray adjuvants. Group P7 fungicide. 4-hr reentry.
- OxiPhos at 2.5 to 5 quarts/A as a foliar spray. Group P7 fungicide. 4-hr reentry.
- Rampart at 1 to 3 quarts/100 gal water/A. Group P7 fungicide. 4-hr reentry.
- Ridomil Gold SL at 5.6 to 11.2 oz/40 gal water. Apply 1 quart of mixture around the base of each vine. Apply in fall after harvest and again in the early spring when root growth resumes. Do not apply within 7 days of harvest. Group 4 fungicide. 48-hr reentry.
Reference Li, M., Guo, Q., Liang, M., Zhao, Q. Lin, T., Gao, H., Hieno, A., Kageyama, K., Zhang, X., Cui, L., Yan, Y., and Qiang, Y. 2021. Population dynamics, effective soil factors, and LAMP detection systems for Phytophthora species associated with kiwifruit diseases in China. Plant Disease, 105, https://doi.org/10.1094/PDIS-04-21-0852-RE