It is common in all regions where potatoes are grown. Its importance in Poland is growing due to the growing interest in washed and packaged potatoes and potatoes intended for French fries and crisps. Losses caused by its development may reach even 70% of the yield in extreme cases.

Symptoms of potato anthracnose appear on leaves, stems, stolons, roots and tubers. The disease appears on plants during the flowering period. The first symptoms are yellowing, curling, wilting and gradual death of the leaves. The lesions include the apical leaves and then those located on the lower floors of the plant. The dried leaves hang on the stems, which remain green for a long time (photo 1) or turn brown, then wither. (photos 2A, 2B, 2C, 2D). The bark at the base of the stems rots, cracks, peels and is easily separated from the wood, so that diseased stems can be easily lifted out of the ground (Photo 3). On the infested layer of wood, often of a light purple color, there are numerous black microsclerotia (spore form that allows it to survive unfavorable conditions, e.g. drought, winter) – a symptom characteristic of anthracnose (Photographs 4A, 4B, 4C). Initial damage to the underground parts of stems and stolons can sometimes be confused with other diseases, such as rhizoctoniosis (photos 5A, 5B) – in the photo the middle stem shows symptoms of rhizoctoniosis.

On tubers, irregularly shaped brown to gray discoloration (spots) appear on the skin as a result of infection. A silvery color resembling silver scab symptoms may appear during storage. Anthracnose spots are poorly separated from the healthy part of the rind, unlike silver scab, where the border is clearly marked.As in the case of stems and stolons, tubers have numerous regularly spaced sclerotia (Fig. 6), in contrast to silver sclerosis , where the brown-black coating is abundant and irregularly distributed (photo 7). Tubers of infected plants lose turgor, become rubbery and wrinkled. Such tubers lose weight during storage (with infection covering about 60% of the surface of the tuber skin, 10% of the weight is lost after 18 weeks of storage). Such tubers used for planting give a large percentage of threadlike sprouts. Another characteristic symptom of anthracnose is the difficulty in separating the infected tubers from the stolons, the sections of which 40-50 mm long remain at the tubers (Photo 8).

A number of factors contribute to the development of the disease, including:

• progressive global warming,
• cultivation on soils with unregulated moisture conditions,
• high temperatures during the growing season (optimal temperatures for the development of the disease are 25 to 31 ° C,
• the state of soil saturation with moisture when the plants close in rows and higher temperatures later in the growing season.

Prevention

Combating anthracnose, like other potato diseases, is based primarily on the use of agrotechnical methods and the use of chemical plant protection products.

The most important agrotechnical procedures include:

• healthy, certified seed material,
• properly selected crop rotation, the potato should come to the same field after a break of at least 3-4 years,
• the use of the so-called biofumigants – cultivation as forecrops of green fertilizers, e.g. mustard seed,
• choosing the right place for cultivation, soil with regulated water-air relations, not too heavy and not prone to crusting,
• maintaining proper agrotechnics of the soil, winter plowing to a depth of at least 30 cm,
• thorough performance of care treatments, especially ridding of ridges.

Chemical protection in Poland is difficult due to the lack of plant protection products registered for direct control of potato anthracnose. Therefore, the application of chemical protection includes the control of weeds and the desiccation of the leaves. The perpetrator of potato anthracnosis has many intermediate hosts among the weeds found in potato plantations, which include black nightshade, white quinoa, arctic grass, knotweed and datura.

The last, but also an important element of the control of anthracnose is the proper preparation of tubers for storage. The evaporation of excess moisture in the tubers, and especially the drying of the skin, is of great importance here. The drying period of the tubers becomes particularly effective in reducing disease during storage, when the tubers harvested in humid conditions are muddy.