Potato Review

18 POTATO REVIEW MARCH/APRIL 2021 NEMATODE CONTROL Where egg counts are low, typically less that 10 eggs per gram of soil, Paul’s standard course of action would be to apply Velum Prime ( uopyram). If the preferred variety has poor resistance, consider applying a granular nematicide for both additional yield protection and population management, he said. Where egg counts are between 10 and 20 eggs per gram of soil and depending on the soil type, time since last potato crop, and the resistance status of the preferred variety, Paul’s suggested course of action would either be to apply Velum Prime in sequence with Nemathorin ( fosthiazate) or Nemathorin alone. In higher pressure situations, and only if after considering the risks the decision is to proceed, perhaps because it is pro table ground that is easy to access, easy to travel, and easy to lift, then a resistant variety should be selected with Velum Prime applied in sequence with Nemathorin, he said. Much has been made of the role of resistant and tolerant varieties in managing PCN populations and while they have a place, they are not suited to all situations, Paul said. He feels they should be grown on contract with a processor and the grower must be able to harvest them before tuber temperatures fall below 8 o C as this increases the risk of bruising. In East Anglia, this typically means nishing lifting before October 23rd but will vary depending on the region and eld aspect. Paul said using Velum Prime in sequence with a granule has been shown to improve yields and reduce post-harvest populations compared with programmes where the granular product is applied alone. For many users, however, it is a case of seeing is believing. “No one product or approach is good enough to manage populations. It is beholden on all of us to use all the available products and the synergies they present if populations are to be brought down to a level that means that land can be used for potato production for the long-term,” he said. Implementing best practice when protecting potatoes from PCN Granular nematicides are a key tool to protect crops from Potato Cyst Nematode (PCN) and are vital to growing high quality and pro table potatoes, according to Sophie and Tony Bambridge, from B & C Farming Ltd in Norfolk. “We have PCN present on the land where we grow ware potatoes, so we test to understand the population we’re dealing with, which informs our control strategy,” said Sophie. “We test in two-hectare blocks, so a ten-hectare eld has ve testing strips. We take 100g of soil from each block, so if PCN is detected, we can be sure there’s more there. “Based on the level of PCN detected, we have to decide whether the eld is suitable for potato production and if so, what variety to plant and what level of pest control is needed. For example, a higher population of four or ve eggs per gram, may mean we select a variety with resistance or higher tolerance to PCN.” However, there is a downside to choosing PCN tolerant varieties, as multiplication with these varieties can be greater, she said. “As farmers, we can’t always choose the varieties we grow, because we have to use the varieties which the customer wants to buy. ese are often the ones which aren’t resistant to PCN and may also be susceptible to Spraing, which is caused by Tobacco Rattle Virus (TRV). is is spread by free living nematodes, which can also be controlled by granular nematicides, so we have to work with our agronomists to overcome challenges in other ways,” said Sophie. Rotations A longer rotation can help prevent the build-up of PCN populations in the soil over time. Sophie said they have extended their rotations for ware potatoes to one in eight years. “ is helps slow population growth of PCN, but the knock-on impact is that we are now selecting the PCN species with the highest resilience and ability to survive, so we know PCN is going to continue to persist and adapt. “With control, hopefully the PCN population will have declined when we come back to the land, but we do have to think about cleanliness in the intervening years, for example by reducing volunteers,” adds Sophie. “If we factor in the pressure to grow the best varieties for processing, rather than the PCN resistant varieties, this highlights how crucial nematicides are for potato production in the UK.” Tony Bambridge, B & C Farming Ltd Eric Anderson of Scottish Agronomy