Growers affected by late blight need to be aggressive in managing disease at the end of the season and into storage. The steps below will help with late-season and storage management of late blight. This list was adapted from a list originally published by Dr. Dennis Johnson at Washington State University.
1. Continue late blight fungicide applications until harvest or until all vines are dead. Consider the pre-harvest interval when selecting a fungicide close to vine kill and harvest. Fungicides with good activity against late blight include (in alphabetical order):
a. Chlorothalonil (multiple products)
b. Curzate and Tanos (both contain cymoxanil)
c. Forum (dimethomorph)
d. Gavel (zoxamide + mancozeb)
e. Mancozeb or metiram (multiple products)
f. Omega (fluazinam)
g. Previcur (propamocarb-HCl)
h. Ranman (cyazofamid)
i. Revus Top (mandipropamid + difenoconazole)
j. SuperTin (triphenyltin hydroxide); use with a mancozeb
2. Be sure vines are completely dead prior to harvest. Ideally, it is best to use sulfuric acid in infected fields. If not available, use a fungicide in combination with a chemical desiccant. If rolling or flailing vines, immediately apply a fungicide or fungicide/chemical dessicant.
3. Harvest only during dry weather.
4. Harvest when pulp temperatures are between 45 and 65 degrees Fahrenheit. Minimize wounding.
5. Treat with a phosphite-based fungicide going into storage (e.g. Resist 57 or Phostrol). The recommended rate is 12.8 fluid ounces of product applied in 0.5 gallons of water per ton of tubers. Application volume and rate are critical for the success of this application. Potatoes should not be shiny-wet; this indicates too high a volume of product is being applied.
6. Store nfected lots separate from healthy lots and/or where they can be moved easily.
7. Sort out rot going into storage. Minimize dirt and debris inthe pile.
8. Provide a high ventilation rate through the storage.
9. Remove field heat and cool quickly to curing temperatures of 50 degrees. If process potatoes, check if lower curing temperatures are acceptable.
10. After curing, cool the pile to the final storage temperature as quickly as possible and/or allowable.
11. If available, use evaporative cooling pads for additional cooling time and humidification. Adjust use of supplemental humidifiers to cut back on humidity to further dry out potatoes.
12. Maximize run time and intake of fresh air. Run fans continuously. Re-circulate air even when outside air is not being introduced.
13. Monitor storages closely and watch for hot spots, temperature changes and odor.
14. Tubers of Russet Burbank, Alturas and Umatilla are moderately resistant, and tubers of Defender and Clearwater are considered resistant. Storage problems with these cultivars should be less than with other cultivars. Russet Norkotah tubers are moderately susceptible and Ranger Russet tubers are highly susceptible to tuber blight. Good air movement and temperature and humidity management will be needed when storing infected tubers of all cultivars.