The pictures of tubers with shatter bruises and blackspot bruises (below) were taken by Rabecka Hendricks, University of Idaho
Potatoes are easily battered and bruised during harvest operations and storage loading. Here is a review of some common types of bruising, and tips to minimize the damage.
SHATTER BRUISE is when the skin splits upon impact. The tuber surface can have tiny cracks (as in the picture below) or splits that go deeper into the tuber. Pathogens that cause bacterial soft rot, Fusarium dry rot, and early blight can easily invade through splits in the skin.
Shatter bruise is associated with handling tubers that are cold and turgid (crisp from hydration). Potato cultivars with high dry matter are usually more susceptible to shatter bruises.
BLACKSPOT BRUISE results from impacts, but the damage is to cells beneath the skin. The damaged cells leak enzymes that react with phenolic compounds to form melanin, a black pigment. The reaction takes 12-24 hours to develop.
Dehydrated tubers are more susceptible to blackspot bruise (opposite of shatter bruise). Pre-irrigation before harvesting can help to rehydrate tubers in dry soil. Blackspot bruise is also associated with cold tubers, large-sized tubers, and higher dry matter content.
PRESSURE BRUISE develops in storage from pressure at points of contact with other potatoes or the floor. It’s characterized by flattened or depressed areas on the tuber.
Tubers that are dehydrated at harvest are more susceptible to pressure bruise in storage. Pressure bruise can also result from low humidity in storage.
The pictures of tubers with shatter bruises and blackspot bruises (below) were taken by Rabecka Hendricks, University of Idaho.
TIPS TO MINIMIZE BRUISING: Bruise is a costly problem, but you can minimize tuber bruising at harvest by taking precautions. For more information, visit the University of Idaho Bruise and Harvest Management webpage.
- Harvest tubers when mature with good skin set to avoid skinning.
- Harvest tubers when pulp temperatures are 50 to 60 degrees F. Colder tubers are susceptible to both shatter bruises and blackspot bruises. Warmer tubers are more susceptible to storage rots, and they can be difficult to cool down after loading into storage.
- An intermediate level of tuber hydration may be best because dehydrated tubers are more susceptible to blackspot bruises, but overly hydrated tubers are prone to shatter.
- Some cultivars are more susceptible to one form of bruising vs. another, so strategies to avoid bruising should vary depending on their relative susceptibilities.
The University of Idaho and Idaho Potato Commission produced several Training Videos for Bruise Management that explain how to run and operate harvesting and loading equipment and pilers. They are available in both English and Spanish.
