Rhizoctonia, a yield and quality problem for the potato industry

Rhizoctonia is a fungus with two main effects on potatoes; from fungal hyphae positioned mainly around the sprouting parts of the potato, what are known as the eyes, it attacks the fresh sprouts directly, inhibiting their growth. And Rhizoctonia also strikes for a second time during the potato season. The hyphae remain on the surface of the newly grown tubers and cover them with black crusts. This is not only a cosmetic problem, but also harbor the risk of transmitting the disease to the next potato generation and to other fields. In summary, Rhizoctonia infestation means a reduced yield and also fewer tubers which meet the requirements of the food industry in terms of size and skin quality. Harvest early, store in a cool placeEric Anderson is a Senior Agronomist at Scottish Agronomy, an agricultural cooperative. He has first-hand experience of the everyday challenges facing potato growers;? he answers to the following questions. Why does a fungus like Rhizoctonia pose such a threat to potato growers?Rhizoctonia solani is seed- and soil-borne. It is commonly found to persist in many soils ? although inoculums is usually higher in lighter textured soils and where potatoes are grown in short rotation. It causes a range of symptoms on the potato plant including delayed emergence, reduced yields due to rot and quality losses when the black scurf develops on tubers. What other diseases can affect potato harvests in storage?Amongst others, silver scurf and black dot (*). Both fungi cause lesions that look very similar, especially in the early stages of disease development: gray to silvery blotches and dark brown-gray blemishes on the tuber surface. The challenge is that symptom expression usually lags several weeks behind infection. As the infection progresses, the lesions usually become more prominent. Black dot has become a major problem in pre-pack potatoes ? they look unappealing to consumers. An early harvest will minimize tuber infection. Holding tubers in cold storage delays symptom expression as well. What factors does a farmer have to bear in mind when he decides to grow potatoes?A continued challenge for potato growers is the supply of contracted potatoes to packers and processors at prices and production costs that provide reasonable profits. To minimize risk you should really clearly define what kind of potatoes you want to grow ?table, processing or seed potatoes. To get a better understanding of your potato-growing costs, you should consider changing your growing systems and take customer expectations into account. Penflufen, a new active ingredientThe source of the information is an article published by the Bayer magazine Research, with information based mainly on Anne Suty-Heinze, a crop protection researcher in the company, working with potatoes and the new active substance penflufen, which started to be studied by Japan research colleagues. The article includes the above interview to Eric Anderson. Seed potatoes treated with penflufen, in a process known in technical terms as seed dressing, get the newly developed active substance evenly distributed all over the tubers, providing optimum protection for the young sprouts. Penflufen is distributed locally beneath the ground in the tuber and on the sprouts. This is different to other active substances which are quickly distributed systematically via the xylem, and therefore also reach the parts above the ground. As a result, only very tiny amount of active substance are needed, as they remain precisely where they are needed. The new fungicide also has additional effects; it also is useful against silver scurf, caused by Helminthosporium solani. Another noted effect is that plants treated with it grow more quickly and also have larger, stronger sprouts. ? (*) Black dot, Colletotrichum coccodes; Cornell University indicates that it is generally considered to be a weak root pathogen of potato. Studies in New York and elsewhere have revealed, however, that this disease must be considered as part of the total disease complex affecting potato Source and more information Magazine Research, published by Bayer, edition 24, 16-19, ?Head start for young potatoes?. Original article or the pdf below The picture indicates that after harvest time, only a few potatoes are sold straight away. Most of them are first stored for several months. During this time, they may become infected by fungi. ? ? ? ? ? ?