Cull Disposal Regulations
- Vine and tuber waste debris are hosts for late blight and are primary inoculum
for both early and mid-season outbreaks of this disease. Phytophthora spores can
be massively produced on the leaves, vines, sprouts and tubers in a cull pile. All cull
potato material must be routinely discarded to help prevent spore production and
seasonal spread of late blight.
- Idaho State Department of Agriculture regulations require daily disposal of
waste potatoes from all operations, including seed cutting operations, after April 15
in Magic and Treasure Valleys, and after May 15 in the Upper Snake River Valley in
eastern Idaho.
- Daily disposal of cull or waste potatoes must continue through September 20 to
help protect the actively growing potato crop.
Disposal Options
- Field Spreading
- Cull potatoes may be spread in a thin layer on fields during late fall and early winter.
- Exposure to thorough freezing prevents tubers and vines from serving as live hosts for late blight.
- The depth of spreading should be no more than two potato layers (6 inches).
- Do not cultivate areas spread with cull potatoes until t hey are thoroughly and completely frozen.
- Culls should not be spread on fields intended for potato production because of the danger of introducing weeds, nematodes and soilborne diseases.
- Field spreading should not be done in late winter during years when air temperatures are not cold enough to cause freeze damage or after the spring cut-off date requiring daily disposal of culls.
- Burial
- This disposal method can be used any season of the year.
- Trenches filled with cull materials should be covered with a minimum of 18 inches of clean soil to prevent sprouts from emerging.
- The deeper the cull tubers are buried, the less likely sprouts will be able to emerge.
- Potato tare dirt is not an acceptable cover because of the risk that small pieces of tuber may be mixed with the soil.
- Cull materiel in trenches must be covered daily after the spring cut-off dates.
- Livestock Feed
- Cull and waste potatoes can be utilized as a feed for livestock during late fall and winter. Feeding cull potatoes in spring or summer is not recommended unless all exposed culls are completely consumed each day.
- Large cull potatoes should be chopped before feeding to cattle to avoid choking.
- Cull potatoes that are field spread are still good feed after natural freeze-drying occurs. Do not spread onto deep soft snow which may provide insulation against freezing.
- Culls should not be spread on fields intended for potato production because of the danger of introducing weeds, nematodes and soil borne diseases. Manure produced by livestock fed with cull potatoes should also not be spread onto fields intended for potato production.
- Sprouting must not occur in culls spread onto fields or placed within feed bunks.
- Composting
- Potatoes can be placed in large composting piles during late fall and winter. Compost piles started during the summer may have small tubers on the outer surface of the pile that can sprout or serve as a host for late blight.
- The temperatures within a properly managed compost pile not only speed decay of tuber tissue, but may also help to directly kill the late blight fungus.
- Compost piles must be turned and mixed routinely, and may require special equipment for large piles.
- A poorly managed compost pile is nothing more than a cull pile in disguise.
Disposal Options
- Slivers and discarded tubers generated during the cutting operation can sprout quickly under the right conditions. Tare dirt and discarded potatoes are cull potato debris and should be properly managed to prevent this material from hosting the late blight fungus.
Monitoring Cull Disposal Sites
- All cull disposal sites should be closely monitored the next spring to make sure that volunteer plants are not emerging.
- Broad spectrum herbicides typically are slow to kill vines or emerging sprouts on cull potatoes, or only temporarily suppress vine growth. Other disposal methods are available that are more effective than herbicides.
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