Walt Sparks was a potato research scientist at the University of Idaho from 1947 to 1981. His famous expression: “A Potato Storage Is Not A Hospital” meaning that diseased potatoes will not get better in storage is still as valid today as it was more than 50 years ago.
Tubers bruised at harvest are easily invaded by soft rot and/or Fusarium dry rot, which can cause serious economic losses in storage. Harvest management is, in large part, bruise management. Bruising affects tuber quality significantly. To harvest potatoes with minimum tuber damage, growers need to implement digging, handling and storage management practices that maintain crop quality for as long as possible following harvest.
Assuming all harvest and handling equipment are mechanically ready to harvest the crop with minimum bruising, there are several tips in this checklist to preserve the quality of potatoes during harvest:
- Timely Vine Killing — Killing the vines when tubers are mature reduces the total vine mass moving through the harvester. This allows for an easier separation of tubers from vines.
- Timely Harvest — Potatoes 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.
- Do test digs on your fields to check the conditions of the crop. If you find problem areas, you can make timely decisions that will help you to keep the potatoes safely stored for several months.
- Do not harvest potatoes from low, poorly drained areas of a field. It is highly probable that tubers from areas where water accumulated will develop soft rot, Pythium leak, pink rot or pink eye. In addition, enlarged lenticels, a common problem of tubers from wet areas, predispose tubers to soft rot.
- Use a roller to minimize soil cracking to reduce both greening and the risk of tuber blight. Monitor soil moisture. Optimal harvest conditions are at 60 to 65 per cent available soil moisture. Excessively wet soil remains caked on tubers and decreases the efficacy of CIPC applied in storage.
- Monitor tuber pulp temperature. The optimal pulp temperature for harvest is from 11 C to 160 C. Proper pulp temperature is critical — tubers are very sensitive to bruising when the pulp temperature is below 7 C. Tubers become very susceptible to soft rot and Pythium leak if pulp temperatures are above 18 C. Pulp temperatures of 21 C increase the risk of pink rot if inoculum is present.
- Harvest when day temperatures are not too warm. Tuber infections develop very rapidly at high temperatures and spread easily in storage. If potatoes are harvested during hot and humid weather (above 27 C) and cooled slowly, the likelihood of storage rot is increased. Dig early in the morning if warm weather is in the forecast
- Monitor tuber hydration — This influences the amount and type of bruising.
- Over-hydrated tubers dug from wet soil are highly sensitive to shatter bruise especially when the pulp is below 7 C. In addition, tubers harvested from cold, wet soils are more difficult to cure and more prone to breakdown in storage.
- Slightly dehydrated tubers dug from dry soil are highly sensitive to blackspot bruise. An intermediate level of hydration results in the least amount of tuber bruising. Where irrigation is available, dry soil should be watered to prevent tuber dehydration and high incidence of blackspot bruise.
- If soil clods are a problem, irrigate at least one week before digging to soften clods and rehydrate tubers
- Adjust harvester chain conveyor speed in relation to ground speed to maintain a full, uniform flow of potatoes on each conveyor.
- Instal padding on the harvester at points where potatoes may be bruised.
- Use Bruise Detection Devices — The volume of soil and tubers moving through the harvester should be held at capacity at all points of the machine. Bruise detection devices can indicate where the tubers are being bruised.
- Make sure all employees are properly trained and aware of bruise reduction strategies. Harvester operators must be on the lookout for equipment problems that may be damaging tubers.
- Ideally, growers should implement a bruise management program which includes all aspects of potato production from planting through to harvest.