Potato Review

www.potatoreview.com POTATO REVIEW MARCH/APRIL 2023 43 NEMATODE CONTROL 4. Plant only certi ed seed 5. Consider biological measures 6. Use good chemical control Good machinery hygiene is considered a valuable means of control and may help limit the spread of other undesirable weeds, pests and diseases such as black-grass seeds and the brassica club root bacterium. e company’s potato team goes on to say that all waste, soil and by-products from potato harvesting, grading and processing operations should be disposed of in line with the Plant Health Code of Practice on Management of Agricultural and Horticultural Waste. ose with access to commercial composting facilities may nd it interesting to note that the German Biowaste Ordinance prescribes sanitation of organic waste before it can be used on arable land, the team points out. Cysts of G. rostochiensis have been shown to be killed by composting for seven days at 50-55°C and by pasteurisation for 30 minutes at 70°C. In the case of free living nematodes (FLN), good weed control is considered vital as common species such as eld pansy, knotgrass, groundsel, shepherd’s purse and chickweed can act as hosts for tobacco rattle virus (TRV) which causes the disorder known as ‘spraing’ and is transmitted by stubby root nematodes. Positive results have been observed with trap crops such as Sticky Nightshade (Solanum sisymbriifolium), a non-tuber bearing solanaceous plant, that appears to e ectively stimulate PCN hatch while preventing it from reproducing, the company points out in an advisory article. “ e downside is it needs to be sown into warm soils (above 8°C to emerge) and requires a full growing season to reach the 700g/m2 of dry matter needed to be e ective. You also need to consider the e ects on soil-borne diseases they may be hosts for. Furthermore, it is reasonably expensive with a 2015 estimate suggesting it costs about £550/ha.” It goes on to acknowledge that bio- fumigants such as mustard sown in the autumn and incorporated ahead of planting have shown similar promise. Good chemical control Nematicides are most e ective when PCN is at its most vulnerable: e juvenile stage when they migrate from their protective cyst to the potato root. e peak of egg hatch of G. pallida has been estimated as six to seven weeks after planting, with an extended hatch of up to 12 weeks, compared with a peak of about three to four weeks for G. rostochiensis over a period of about six weeks. “Consequently, against G. pallida, some products may not be e ective for the entire hatch period. In addition, if there were second generations as a result of favourable weather, there would be no chemical remaining to exert control,” the Bayer team states, going on to add that Velum Prime ( uopyram) is the rst nematicide to act by inhibiting the target’s mitochondrial respiratory chain. “In short, it inhibits the production of adenosine triphosphate (ATP), a compound found in all living tissue. With its source of metabolic energy blocked, treated nematodes are quickly immobilised. Once paralysed the nematodes take on a needle-like appearance. Unable to enter the roots to feed, death occurs within hours.” In addition to yield protection Velum Prime has been shown to make a valid contribution to population management. In trials spanning many seasons and across a range of situations, it delivered an average 34% reduction in post- crop populations relative to the untreated control with a Pf:Pi ratio of 6.1, close to that achieved with fosthiazate of 5.7. In low pressure situations, the Bayer team states it will provide an e ective level of yield protection when applied on its own. In trials, where Pi is below 5, average yield increases from Velum Prime is 2.1t/ha and there is a reduction in PCN multiplication. In higher pressure instances, the best protection is achieved when Velum Prime is applied in conjunction with a granular nematicide. Research has found that PCN mortality is increased after exposure to hydrolysed glucocinolates which release volatile isothiocyanates (ITC), a form of mustard gas. Indian mustard (Brassica juncea) has been found to be higher in the derivatives 2-propenyl-ITC and 2 –phenylethyl-ITC and studies suggest egg viability can be reduced by up to 40% depending on the accumulation of biomass prior to maceration and incorporation. e exacting nature of the maceration and incorporation process needed to achieve the desired control, however, means that as with trap crops these are still a work in progress for most growers. “Using bioindicators including both plant-parasitic and in-soil nematode groups applied to practical on-farm management practices in the UK, provides a holistic approach to quantify what is currently in the soil, how current farm management is a ecting the soil biology, and how you can influence and manage this going forward to maximise yields.” Rebecca Lawson, Senior Nematologist, Fera Longer rotations have helped reduce use of nematicides.