Ten tips for a tip-top harvest
By Eugenia Banks
The potato person who said many years ago "A potato storage is not a hospital" was absolutely right. Diseased or bruised tubers do not get better in storage. Tubers bruised at harvest are easily invaded by soft rot or Fusarium dry rot, which can cause serious economic losses in storage.
Harvest management, in large part, is bruise management. Bruising also affects tuber quality significantly. In order to harvest potatoes with minimum tuber damage, growers need to implement digging, handling and storage management practices that maintain the crop quality for as long as possible after harvest.
Assuming all harvest and handling equipment are mechanically ready to harvest the crop with minimum bruising, there are several tips to preserve the quality of potatoes crop during harvest:
- Timely Vine Killing. Killing the vines when tubers are mature makes harvesting easier by reducing the total vine mass moving through the harvester. This allows an easier separation of tubers from vines.
- Timely Harvest. Potatoes intended for long term storage should not be harvested until the vines have been dead for at least 14 days to allow for full skin set to occur.
- Soil Moisture. Optimal harvest conditions are at 60-65% available soil moisture.
- Tuber Pulp Temperature. Optimal pulp temperatures for harvest are from 500F to 600F. Proper pulp temperature is critical; tubers are very sensitive to bruising when the pulp temperature is below 450F. If pulp temperatures are above 650F, tubers become very susceptible to soft rot and Pythium leak. Pulp temperatures above 70°F increase the risk of pink rot tremendously no matter how gently you handle the tubers if there is inoculum in the soil.
- Tuber Hydration. An intermediate level of tuber hydration results in the least bruising. Overhydrated tubers dug from wet soil are highly sensitive to shatter bruising especially when the pulp temperature is below 450F. In addition, tubers harvested from cold, wet soil are more difficult to cure and more prone to breakdown in storage. Slightly dehydrated tubers dug from dry soil are highly sensitive to blackspot bruising.
- Reducing Blackspot Bruising. Irrigate soil that is excessively dry before digging to prevent tuber dehydration and blackspot bruising.
- Bruise Detection Devices. Try to keep the volume of soil and tubers moving through the digger at capacity at all points of the machine. If bruising is noticeable, use a bruise detection device to determine where in the machinery the tubers are being bruised.
- Do not harvest potatoes from low, poorly drained areas of a field where water may have accumulated and/or dig tests have indicated the presence of tubers infected with late blight.
- Train all employees on how to reduce bruising. Harvester operators must be continually on the lookout for equipment problems that may be damaging tubers. Ideally, growers should implement a bruise management program that includes all aspects of potato production from planting through harvest.
- Harvest when day temperatures are not too warm to avoid tuber infections. Storage rots develop very rapidly at high temperatures and spread easily in storage. If potatoes are harvested at temperatures above 27o C and cool off slowly in storage, the likelihood of storage rots is increased. If warm weather is forecast, dig the crop early in the morning when it is not so warm.