BIBLIOTECA HORTICULTURA

BIBLIOTECA HORTICULTURA

Potato storage disease control in both theory and practicePotato storage disease control in both theory and practice

Potato storage disease control in both theory and practice

Storage diseases cannot be seen apart from the growing period prior to storage

During the summer period, we often remember well how the previous storage season went. Meanwhile, the new harvest is growing in the field and we can still make small adjustments for the coming storage period that will start again in a few months. In addition to the right storage technique, the right use is at least as important for this reason TOLSMA GRISNICH is answering: When and how long to dry in which situation. How quickly can the temperature be brought down? And if diseased tubers are present, how should we handle drying and cooling? In this article, information is given on the most common storage diseases and how to deal with them if they are spotted in storage.

As potatoes are planted in different soil types in different climates, often under irrigation, many organisms are trying to profit from the tubers as a food source. This can be done by wild animals who really dig up the tubers to eat them, but most of the time the organisms attacking the planted seed potatoes are not even visible and their number is overwhelming: bacteria, fungi, viruses, insects and nematodes. When optimal climate conditions are there, bacteria and fungi can cause serious harm to potato tubers which can result in rot or extra moisture loss during the storage period.

Most of the time it will not really cause big problems during storage when there is just a small percentage of affected tubers. But during specific phases of storage,  climate conditions may be very supportive for a specific bacteria or fungus to expand. In this article we’ll focus on a number of potato diseases which can cause serious problems in the storage period. Some problems will occur more often in seed potatoes and others in processing potatoes. This distinction has to be made and has two reasons. The quality requirements for seed or processing are different and the storage conditions are different. So, although we do talk about potatoes in both situations different storage diseases need to be discussed.


Late blight - Potato disease
The world’s best known potato disease late blight caused by the fungus phytophthora infestans causes tuber infections both in the field and during harvest/storage. There is a higher risk of tuber infection in wet and heavy soils. Tuber infection is first being recognized by change of color on some spots on the potato skin to blue. After some time, the spots dry out and the surface becomes rough and knobbly. The color of the affected tissue changes to rust-colored. Late blight tuber affection is often succeeded by other types of rot (fungi and bacteria) which cause the leakage of moisture. Due to the weight/pressure of above laying tubers in storage moisture may start leaking from deteriorating tubers. This free moisture is risky because bacteria and fungi can easily spread and  effect other healthy tubers. The fungi will start sporulating on the affected and wet spots and by ventilation this is easily spread over the storage.

The different stages are not always easy to see, so when there has been an infection during the field period a thorough inspection of the tubers before (during) harvest is necessary to know exactly what percentage of the tubers is affected. If this is too high maybe the best decision is not storing such a crop or at least only for a very short period. Depending on how many affected tubers come into storage late blight can be kept under control by regularly drying away the leaking moisture from the tubers. Tuber deteriorating is a slow process with late blight and can last up to 20 weeks. This means continuous drying is not necessary and undesirable because it will also dehydrate the healthy tubers. Regular drying e.g., two times per day for one hour can easily keep the surrounding tubers dry and will avoid new sporulation.

But this must be done for 20 weeks, which means that potato temperature should be kept at such level that outside air can always be used for this. So, don’t cool down to quick. Cold potatoes are  always difficult to dry. When there is no possibility to dry with outside air and the storage is just equipped with a refrigeration system one should at least consider decreasing the humidity by stopping the humidification system. Together with ventilation/circulation this will at least support the evaporation of free moisture. Potato temperature should be kept below 15 °C because optimal fungus growth is between 15 – 20 °C.