Potato early dying What it is and what you can do to help manage it
POTATO EARLY DYING Potato early dying is an annual production concern for some potato growers. Endemic in many growing areas, it is an economically important issue many growers face particularly in fields with a long and continuous history of potato production. It s also one of the most difficult to recognize and effectively manage. This guide is designed to help you identify potato early dying in your fields. Armed with agronomic information and integrated management strategies, you ll be better able to help combat the issue and maximize plant health and marketable yield for years to come. This guide is for reference only. Please consult your retailer, your Syngenta Territory Representative or the Aprovia fungicide product label for further information.
WHAT IT IS AND WHAT YOU CAN DO TO HELP MANAGE IT What is potato early dying? Potato early dying refers to the premature senescence and ultimate death of a potato plant. When a field experiences early dying, diseased and stressed plants represent reduced yield, with typically smaller tuber size and visible effects on tuber quality. The disease complex first develops throughout a field midway through the growing season. Symptoms don t become evident until crop maturity. What s at stake? Due to decreased photosynthesis and premature death: Tubers do not size optimally Reduced tuber quality Yield reductions between 10 50% 1 The complexities of a complex Potato early dying is not the result of a single disease or cause. It s a complex, with several agents contributing to its devastating effects. Some of these important contributing pathogens and conditions include Verticillium spp., nematodes, black dot, bacterial soft rot and nutrient deficiencies. Early dying pressure tends to build up slowly over time. What s more, symptoms often appear as normal maturing until it s too late. It comes as no surprise, then, that many cases of potato early dying are overlooked or misdiagnosed as other diseases or the product of environmental conditions. Potato early dying is not the result of a single disease or cause. When a field is infected, diseased plants represent reduced yield, with typically smaller tuber size and visible effects on tuber quality. Contributing factors to the early dying complex Verticillium dahliae Verticillium albo-atrum Pathogenic nematodes Black dot (Colletotrichum coccodes) Soft rot bacteria (Pectobacterium sp.) Nutrient deficiencies Yield reductions between 1 10 50% 1 Johnson & Dung, 2010.
POTATO EARLY DYING Verticillium wilt and potato early dying Verticillium wilt is a major component of the potato early dying complex. Two soil-borne fungal pathogens contribute to the complex: Verticillium dahliae and Verticillium albo-atrum. Verticillium pathogens cause damage by invading the xylem elements, disrupting water transport and causing vascular wilt. Once a field is infested, the pathogens move with the soil, including on equipment, wind, water and even seed. Verticillium wilt propagules occur in highest concentration in the top 30 cm (12 inches) of the soil profile. Inoculum densities and disease severity tend to increase from year to year when susceptible crops are planted. Verticillium dahliae Verticillium dahliae is very persistent in soil, but can also be spread through infected seed. It occurs naturally at low levels, has a large host range of over 300 species, and has widespread distribution in temperate climates that reach 25 28ºC. Verticillium dahliae can survive for up to 13 years in soil in the form of tiny, black, seed-like structures called microsclerotia, which are released into the soil with the decomposition of plant material. As such, crop rotation alone will not solve the problem, although it is recommended as a preventative measure and best practice as part of an integrated disease management program. Source: American Phytopathological Society Life cycle of Verticillium dahliae Verticillium dahliae disease cycle V. dahliae overwinters in infested plant debris and soil. Come spring, root secretions stimulate microsclerotia germination and the fungus penetrates the root of a susceptible plant. Once the fungus enters the root, it colonizes its cortex, allowing mycelium to invade xylem vessels. From there, the fungus moves through the vascular system as conidia, causing chlorosis, necrosis and foliar wilting. Tissue senesces, producing new microsclerotia, and come fall, the plant completely dies. Microsclerotia are released into the soil or remain in the plant debris and overwinter, beginning the cycle once again the following spring. Verticillium albo-atrum Verticillium albo-atrum remains a concern. Like V. dahliae, it can be spread through soil and to a lesser extent, infected seed and tends to move through a field with the soil. It has a more limited host range of approximately 100 species, and adapts well in cooler areas where temperatures reach between 20 25ºC. Unlike V dahliae. V. albo-atrum does not form microsclerotia. It survives in soil as dark-coloured mycelium, and is viable for up to three years.
WHAT IT IS AND WHAT YOU CAN DO TO HELP MANAGE IT What to look for In potatoes, symptoms of Verticillium wilt include premature chlorosis (yellowing of the leaves) and necrosis (death of the plant tissue) along with a tan-coloured discolouration or streaking of the vascular system. Individual vines may die but remain erect in contrast to healthy plants, and all vines arising from a single seed-piece do not necessarily become affected. If split lengthwise, the stems of severely wilted stalks reveal a brown ring. Signs and symptoms 1. Yellowing 2. Wilting 3. Flagging 4. Discolouration Initially, lower leaves are affected, become yellow and wilted. A steady development of symptoms follows until the whole vine is completely wilted. As the disease progresses, plants stems stand upright in the field. Lower portion of the stem appear black on the outside with a woody brown colour on the interior. Tuber discolouration can appear on the stem end.
POTATO EARLY DYING Managing the potato early dying complex As with many diseases, no single strategy will completely resolve the issue of potato early dying. Rather, an integrated management approach that includes a combination of methods is needed for lasting and economic management of the complex. Avoid early irrigation Irrigating during tuber initiation may increase pathogen spread Keep soil healthy Nutrient deficiencies are a contributing factor to the complex Avoid compaction Compaction stresses plants, healthier plants can withstand diseases better Clean machinery, bins and containers This helps prevent the spread of the pathogen Practice long rotations Cereals and other grass crops offer good choices Use weed control measures Suppression of broadleaf weeds will lessen the pressure Reduce the impact of Verticillium with Aprovia fungicide Aprovia fungicide is the only fungicide in Canada registered for suppression of Verticillium (V. Dahliae) and can play a key role in an integrated management program. Applying Aprovia in-furrow at planting can reduce the symptoms of Verticillium wilt late in the season and help protect your quality and yield. Suppresses Verticillium wilt* Suppresses Rhizoctonia, the cause of stem and stolon canker, and black scurf Provides silver scurf suppression Helps keep plants healthier longer to enhance yield potential * When applied at the 303 ml/ac rate. Application rates: Apply Aprovia in-furrow on potatoes at 202 to 303 ml/ac (500 to 750 ml/ha). Aprovia in-furrow Reduction of Symptoms Verticillium dahliae 100 90 80 70 60 50 40 30 20 10 0 50% % Reduction in Foliar Symptoms % Reduction in Tuber Discolouration Incidence in Untreated Foliar: 20 27.5% : Tuber 2% Severity in Untreated Foliar: 19 27.5% : Tuber 15% Summary of data from trials conducted in 2012 2013 n = 8 90% At this time, Maximum Residue Limits (MRLs) for Aprovia fungicide have been established for markets in Canada and the United States.
WHAT IT IS AND WHAT YOU CAN DO TO HELP MANAGE IT
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