Symptoms and Signs
Symptoms of Phytophthora root and crown rot commonly occur in spring and include reduced terminal shoot growth, chlorotic and/or undersized leaves, and an open canopy. As temperatures increase in summer, vines may collapse suddenly, or alternatively, vines may decline slowly over a few seasons. Roots and crowns of infected vines exhibit a red-brown rot that is easily observed by cutting into the cortical tissue. Often a margin where healthy, white tissue meets diseased tissue may be found. Feeder roots are lacking and active lesions often progress above ground on one or more sides of the lower trunk resulting in sunken areas.
Comments on the Disease
The pathogens survive in soil and can be carried in irrigation water obtained from surface sources. Prolonged periods of saturated soil are optimal for the pathogen to infect roots. Disease development is enhanced in poorly drained soils or where vineyards receive long durations of flood irrigation. Several species of Phytophthora are known to attack kiwifruit roots and crowns.
Management
This disease can be managed using strict planting practices, water management, and fungicide treatments. Plant on raised berms in well-drained soil to allow for rapid water drainage following irrigation or rains. Duration of irrigations should not exceed six hours in fields where disease occurs. Intervals between irrigations may be shortened as needed as long as the soil has drained adequately since the last irrigation.
Fungicides with efficacy that are currently registered in California for the control of root and crown rot include mefenoxam and phosphonates. Hydrogen dioxide is also registered, but yields variable results.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide’s properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| PREPLANT | ||||
| A. | MEFENOXAM | |||
| (various) | 5.6–11.2 oz/40 gals of water | 48 | 7 | |
| MODE OF ACTION, GROUP NAME (NUMBER1): nucleic acids synthesis, Phenylamides (4) | ||||
| COMMENTS: REI may be shorter or not required if the product is soil-injected or soil-incorporated and workers will have no contact with anything that has been treated. | ||||
| B. | PHOSPHONATES | |||
| (Fungi-phite) | 32–64 fl oz | 4 | NA | |
| MODE OF ACTION, GROUP NAME (NUMBER1): unknown (33) | ||||
| COMMENTS: Foliar and chemigation applications are labeled. | ||||
| C. | HYDROGEN DIOXIDE | |||
| (TerraClean) | 3–270 ppm | 0 | NA | |
| MODE OF ACTION: Oxidizer | ||||
| COMMENTS: Highly toxic to bees. | ||||
| ‡ | Restricted entry interval(REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1,4,9,11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number. |
| NA | Not applicable. |