Harvest and Handling
Harvest potatoes for storage when tuber temperatures are between 45-60°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 60-70°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” 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 post-harvest) to extend storage life. Use maleic hydrazide (MH-30) preharvest (one application; 1-1.33 gal/A (REI 12h)), four to six 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 post-harvest sprout inhibitor registered. CIPC requires licensed commercial applicators to apply the aerosol formulation while the 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 two to three weeks. Timing is critical with all the sprout suppressors. They are most effective when applied before sprouts are one-eighth (1/8”) inch long. Organic growers should check with their certification agency and the National Organic Standards for current regulations regarding alternative sprout control products.