potato 5-9-12 CLEAN - Vegetableipmasia.org

ORGANIC POTATO PRODUCTION 12.16 Silver Scurf, Helminthosporium solaniTime for concern: At planting, through growing season, post harvest and storage. Warm, wet soil favors sporulation anddisease spread in the field. Post harvest handling and first weeks of storage are the primary times of infection and spread ofsilver scurf. Warm pulp temperatures and high relative humidity greatly favor spread of silver scurf in storageKey characteristics: This seed and soil borne fungus infects only the skin of the potato. Symptoms appear at the stolon endas small, pale, brown spots. Severe browning of the surface layers of tubers may occur, followed by sloughing-off of the outerlayers of the periderm. Lesions are circular. The silvery appearance of older lesions is most obvious when the tubers are wet.See Idaho HUfact sheetUH (Reference 81), Cornell HUfact sheetUH (Reference 82) and HUinteractive silver scurf potato photoUH (Reference 66).Relative risk: This disease occurs annually and is especially noticeable on red, blue and purple-skinned varieties.Management Option Scouting/thresholds Resistant varieties Seed selection/treatment Harvest Postharvest Crop rotation Sanitation Recommendation for Silver Scurf Lesions may be difficult to detect at harvest, but applying moisture to the tuber surface reveals a silvery sheen. Tubers often develop symptoms in storage along with extensive sporulation. No resistant varieties are available, but thin-­‐skinned varieties are more susceptible and blemishes on red and purple-­‐skinned varieties are very noticeable. Infected seed pieces are the primary source of inoculum. Plant phytosanitary certified seed (see Section 7.1: Seed sources). Seed can be tested for presence of silver scurf. Harvest tubers as soon as they are mature. Vine killing 2-­‐3 weeks before harvest showed less silver scurf than when tubers were harvested green. Disinfect storages to kill spores that remain from the previous years' crop. High relative humidity (90-­‐95%) and warm temperatures (47-­‐56˚F) favor the development and spread of silver scurf in storage. Lowering the temperature to 39-­‐45˚F and the relative humidity to 85-­‐90% as quickly as possible in the first month of storage can delay sporulation. Monitor storage conditions to eliminate free moisture on tuber surfaces. For more information on storage conditions, see University of Idaho’s HUfact sheetUH (Reference 81) Soil-­‐borne inoculum has been implicated in the seasonal occurrence of silver scurf. Maintain minimum of 2 year rotation of potatoes. Clean and disinfect storage facilities (see 10.3.1: Equipment and Storage Facility Disinfectants). At the time this guide was produced, the following materials were labeled in New York State for managing this pest and were allowable for organic production. Listing a pest on a pesticide label does not assure the pesticide’s effectiveness. The registration status of pesticides can and does change. Pesticides must be currently registered with the New York State Department of Environmental Conservation (DEC) to be used legally in NY. Those pesticides meeting requirements in EPA Ruling 40 CFR Part 152.25(b) (also known as 25(b) pesticides) do not require registration. Current NY pesticide registrations can be checked on the Pesticide Product, Ingredient, and Manufacturer System (PIMS website) http://pims.psur.cornell.edu/ (Reference 3). ALWAYS CHECK WITH YOUR CERTIFIER before using a new product. Table 12.16 Pesticides Labeled for Postharvest Treatment of Silver Scurf Class of Compounds Product Name (active ingredient) Product Rate PHI (days) BIOLOGICALS Bio-­‐Save 10LP (Pseudomonas syringae) BOTANICAL Certified organic clove oil 1250 g/40 gal water 67 ppm initial, then 23 ppm/ 1 ton potatoes REI (hours) Efficacy Comments 0 0 1 Agitate mixture to ensure proper suspension. Apply on a conveyor belt or on rollers by dip or spray to tubers prior to storage. Uniform coverage is necessary. Best application is applied with a rate of one gallon of suspension to 2,000-­‐4,000 lbs of potatoes. -­‐ -­‐ 1 Effective in 1/1 trial. 25(b) pesticide. Postharvest application. Thermal aerosol applications; lower concentration was repeated 7 times. 502012