Vine Removal and Desiccation

In preparation for harvest, it may be necessary to remove potato vines prior to harvesting the tubers. Remove vines mechanically (flail beaters, rotary choppers) or by applying chemical vine-killers. Mechanical beaters effectively remove potato tops but should be adjusted to remove the tops without injuring any tubers near the soil surface. Organic growers prefer this method of top-killing.

When potatoes have excessive top growth, use a chemical vine-killer first, followed by mechanical removal to shred tops. This combination provides effective vine kill. Potato vines should be chemically killed approximately 21 days prior to harvest. This provides time to ensure good skin set. Note that rapid vine desiccation (either chemical or mechanical) can cause stem-end discoloration in tubers.

With chemical vine-killers, use the lower application rates if plants are stressed (see the label). Good spray coverage is important for these chemicals to work effectively, and the speed of vine desiccation varies greatly between the different chemicals.

CAUTIONS: When using chemical vine-killers, always follow the label instructions. The information provided below is very general and does not provide full label instructions regarding the application or full use of the materials.

• carfentrazone (Aim):  3.2 to 5.8 ounces/acre (7 dh; REI 12h) and spray adjuvant (NIS, MSO, or COC) is required (1%-2% v/v).  Suitable for seed and storage potatoes. Thorough coverage is essential. May be tank mixed or used sequentially with other desiccants (see labels for restrictions).
• diquat (Reglone): 1 to 2 pints/acre (7 dh; REI 12h) and always use a spray adjuvant (0.1-0.5% v/v NIS). Suitable for seed and storage potatoes.
• glufosinate-ammonium (Rely):  3 pints/acre (9 dh; REI 12h). Do NOT use on seed potatoes.
• paraquat (Firestorm or Parazone 3SL):  0.7 to 1.3 pints/acre (9 dh; REI 24h) and always use either NIS (0.125% v/v) or COC (1.0% v/v). NOTE: paraquat is NOT registered as a vine desiccant for storage or seed potatoes. May ONLY be used for Fresh Market Potatoes. Potatoes must be harvested promptly and processed or consumed immediately.  
• pyraflufen-ethyl (Vida): 2.75 to 5.5 ounces/acre (7 dh; REI 12h). Apply when vines are starting to senesce for best results. May be tank-mixed in sequence with other desiccant products.

Harvest and Handling

Harvest potatoes for storage when tuber temperatures are between 45 ° to 60 °F. At warmer soil temperatures (above 60 °F), field heat contributes to tuber quality deterioration before cooling can occur in storage. When tubers are cold (below 45 °F), potatoes bruise easily during harvest. If days are warm, harvest early in the day; conversely, if it’s cold, start harvest later in the day and continue into the evening. The ideal temperature during harvest is 60 °F to 70 °F.

Bruising can be further reduced by controlling fertilizer and irrigations late in the season. Initiate better skin set through vine killing, controlling late season nutrient/water management, ensuring harvesters (chain and forward speed ratios) are adjusted properly, and keeping harvester chains filled. Potatoes should not drop more than 4-6 inches and equipment surfaces should be properly padded. Premature harvesting results in reduced yields and low specific gravity. When harvesting is delayed, frost and diseases can cause serious storage losses.

Potatoes intended for long-term storage are often treated with sprout inhibitors (pre or postharvest) to extend storage life. Use maleic hydrazide (MH-30) preharvest (one application; 1-1.33 gal/A [REI 12h]), 4-6 weeks before potatoes are mature and ready for harvest. Potatoes treated with MH-30 cannot be used for seed. Chlorpropham (CIPC) is the most effective postharvest sprout inhibitor registered. CIPC requires licensed commercial applicators to apply the aerosol formulation while, the emulsifiable concentrate (EC) formulation can be applied as a direct spray during the fresh packing operation. CIPC can be applied any time after wound healing but before tubers break dormancy or sprouts start to grow. 

For organic growers, some essential oils (peppermint, spearmint, and clove oils) have been shown to reduce sprouting in potatoes. These alternative compounds are not true “sprout inhibitors” like CIPC but are “sprout suppressors” since they physically damage developing sprouts. Because of their high volatility, these oils leave behind little or no residue. However, new sprouts continue to develop, so repeat applications are required every 2-3 weeks. Timing is critical with all the sprout suppressors. They are most effective when applied before sprouts are 1/8 inch long. Organic growers should check with their certification agency and the National Organic Standards Board for current regulations regarding alternative sprout control products.

Postharvest Handling and Storage

An important aspect of potato quality control is to provide a pathogen-free storage environment. Clean and disinfect all storage and potato handling equipment surfaces before placing the crop into storage. Surfaces should be well moistened by the disinfectant spray. Spray bin walls until there is a slight runoff.  Several disinfectant materials are available including quaternary ammonium compounds (Prosan and Ster-Bac), sodium hypochlorite products (Agclor), and hydrogen dioxide products (Storox). Consult the labels for specific directions. Once the storage environment is clean and sterilized, it is ready for potatoes.

Healing of cuts and bruises that occur during harvest is most rapid in storage when:

• The environment has a high relative humidity (95%).
• Tubers are at an appropriate temperature (50 °F to 60 °F).
• When adequate ventilation is provided throughout the pile. 

These conditions should be provided for 2 to 3 weeks at the beginning of storage and helps the tubers suberize. Effective suberization reduces tuber water loss and prevents rot organisms from entering damaged tubers. After suberization the temperature should be gradually lowered to 40 °F (table stock or seed potatoes) or maintained at 50 °F (chipping potatoes). When rot potential is high (field frost, late blight, or ring rot is present), eliminate the curing period, drop the temperature immediately, and increase ventilation.  Crops with these issues should be used as soon as possible.

Storage temperature control is best achieved with forced air ventilation. Storage relative humidity should be kept as high as possible without causing condensation on the storage walls and ceilings. Good insulation properly protected with a vapor barrier reduces the danger of condensation.

Once potatoes reach the long-term storage temperature, ventilate several hours per day or just enough to maintain pile temperature. Continuous ventilation is not necessary unless condensation or rot development occurs within the storage area or pile. Constant ventilation increases tuber weight loss and influences quality. A relative humidity of 95% is desirable for long term storage to maintain quality and minimize shrinkage.

For more detail on storage, handling, and maintaining postharvest potato quality, reference the resources and fact sheets from the Postharvest Research and Extension Center, University of California, Davis.

Potatoes are susceptible to various noninfectious disorders that affect the shape, function, and appearance of the plants or tubers. These are called physiological disorders since they are often caused by abiotic, nonpathogenic, nonparasitic, or noninfectious maladies that have nothing to do with diseases or pests. Physiological disorders growth or appearance changes, which contribute to economic losses since the tubers may not make grade standards. Table 9.4 names some of the more important disorders and plant part affected and describes ways to minimize or control the problem. Most physiological disorders develop slowly, may only be observed very late in the crop’s growth cycle, are difficult to correctly identify, and thus make it hard to determine when the problem started. Most occur erratically in time (not evident each year) and location (field to field).

More Information