Potato Review

54 POTATO REVIEW NOVEMBER/DECEMBER 2019 FOCUS: Rhizoctonia Solani advised, and seed samples should be washed and inspected for signs of visible black scurf. Microscopic fungal growth that isn’t visible to the naked eye can also be present, so laboratory testing can help detect seed infection and help guide seed treatment requirements. 2. Know eld history Rhizoctonia is a sporadic disease and risk is di cult to assess, but eld history can help. Consider the frequency of potato growing on a particular eld and whether potato cyst nematode (PCN) is present. Where soils have been subject to intense potato production, risk from both R. solani and PCNwill be high. Soil testing can help quantify this risk. PCN damage on potato roots leads to a greater loss of the carbohydrates that stimulate and guide R. solani hyphae to the surface of plant tissue, increasing infection risk. Try to minimise the impact of PCN on any potato crop with integrated control, including longer rotations, PCN-resistant varieties and nematicides. is will help reduce the impact of R. solani. 3. Manage volunteers Allowing potato volunteers to ourish through an arable rotation helps many soil- borne pests and pathogens to survive until the next crop is planted, including R. solani. Ensure potato harvesters are set up to minimise tuber losses at harvest. An application of growth regulator/sprout suppressant maleic hydrazide can help minimise volunteer establishment. Any growing volunteers should be controlled with herbicides in all crops or stubbles through the year to reduce disease inoculum in the soil. 4. Variety choice Varietal susceptibility to black scurf caused by R. solani varies and is linked to how long potatoes are in the ground, which is determined by speed of skin set. In high- risk situations and where growing for fresh markets, choose a less susceptible variety with rapid skin set. Where this is not possible due to market requirements, carefully manage nitrogen applications and ensure rapid haulm destruction to speed up skin set. Also consider an early harvest to minimise build-up of black scurf on tubers. 5. Plant into warm, moist seed-beds As slow crop emergence can increase the risk of R. solani infection, consider delaying planting where it could be a problem. If forced to plant in cold and wet conditions, place seed at a shallower planting depth to reduce the risk of compaction under ridges, prevent rooting issues and speed up emergence. 6. Consider chemical treatment Where R. solani risk has been identi ed, chemical treatments may be required to minimise problems such as black scurf, particularly when growing for the packing market where skin blemish tolerance is low. Whilst black scurf is not as important in processing crops, R. solani can cause deep necrosis on tubers in the form of netted scab and may a ect tuber size distribution due to stolon cankers, so fungicide treatment may still be justi ed. In addition, some processors now require a good skin nish for skin-on convenience products, which are becoming more popular with consumers. e available fungicides negate stem and stolon canker and treatments are applied to seed tubers as a liquid at grading or a powder at planting. Accurate and even application of these seed treatments is essential for suppressing seed-borne sclerotia and mycelium of R. solani. Liquid in-furrow fungicides at planting can also help reduce disease severity. e availability of liquid and powder formulations of fungicide RhiNo ( utolanil) gives growers the exibility of two di erent applicationmethods at di erent timings for e ective control of R. solani, according tomanufacturer Certis. Liquid formulation RhiNo allows for the treatment of seed tubers using application equipment above a roller table or conveyor as seed is being graded, while powder product RhiNo DS is applied at planting via a specialist applicator tted to the potato planter. Both formulations are systemic and provide protection of stems and stolons during growth and guard against soil-borne infection, protecting total and marketable yield. Flutolanil also has some curative e ect on seed-borne R. solani and is active against all anastomosis groups. ere is an added bene t of a reduction in silver scurf. www.certistubercare.co.uk Sponsor’s comment RhiNo: Two application approaches Elephant hide - copyright Blackthorn Arable Stolon pruning - copyright Blackthorn Arable