A round the table discussion hosted by Bayer CropScience focused on the threat posed by slugs to potato crops this season. Dominic Kilburn reports
A round the table discussion hosted by Bayer CropScience focused on the threat posed by slugs to potato crops this season. Dominic Kilburn reports.Backward winter crops, harsh weather and high populations have all combined to make this season one of the worst in terms of crop damage by slugs. However, the message for growers who have planted potatoes, and other spring crops, is to be aware of the potential threat from the pest for the remainder of the season, get timing of applications right and use high quality pellets where possible.According to Bayer CropScience’s molluscicide manager, Peter Stacey, slug pellet use in 2012 rose by between 450-480 per cent compared with 2011 (which was a low use year), resulting in the highest use of slug control products for many years.He says that last autumn was a near ‘perfect storm’ due to the wet conditions, late planted crops and cold soils – all resulting in slow crop establishment and crops being at risk from attack for much longer. “Last year showed us how vulnerable crops were to high slug numbers and how critical good quality pellets were in giving growers control. A lot of pellets applied in the autumn sat in very wet conditions which limited their efficacy.”
In terms of control of slugs in potato crops, Peter suggests that it is critical to get pellets on the soil surface for at least a 7-10 day period when slugs are likely to be active. “It’s difficult to know exactly when slugs are likely to feed and therefore methiocarb-based pellets, which have activity across a range of slug types and provide greater longevity, are an important consideration.”Bayer suggests that there are two critical control periods for potatoes; the first at 50-75 per cent canopy closure – usually in late June to early July. In this period shade encourages surface activity but the canopy is sufficiently open to allow for pellet penetration.
The second period is during the early stages of tuber bulking and before slugs go underground to find developing tubers. August, says Bayer, is the pivotal month for a follow up application of pellets with slugs still likely to be active below the canopy.”It’s about being aware of the risk they pose and if we get anything like a normal summer then slugs will continue to be a threat. Even other spring crops such as barley – not normally considered at risk – could be threatened if conditions dictate that they establish slowly. “Slug control hasn’t changed but it’s becoming more critical to get it right,” he adds.Yorkshire-based SPUD Agronomy consultant John Sarup (left) agrees that the best time for slug pellet application in potato crops is just prior to canopy closure to ensure the pellets land on the soil. He says that timing is crucial as canopy closure often creates the ideal microclimate for slug activity. “Once the first application has been made a ‘little and often’ approach to applications is best, depending on canopy density, with potentially more applications being targeted on the headland to protect against slugs coming in from the field margins and neighbouring crops.”I advise my growers to simply use the best products available and methiocarb-based pellets did a good job for us last season. The important thing about them is that I know they are going to hang around in wet conditions – rainfall or irrigation – and still remain effective.”
John says that while last season he used 2 per cent (methiocarb) product, he is considering applying stronger, 4 per cent pellets for at least the first application for this season. “It’s interesting to learn that slugs that survive lower dosed product that might have been affected by the conditions, tend not to be attracted to pellets again, and so it could be important to hit them with a stronger product at the first attempt of the season.”Newcastle University slug expert Dr Gordon Port (right) says that there is no doubt that because of the wet conditions throughout most of 2012, growers will currently be facing high numbers of slugs in crops. He reckons the fact that slug numbers bounced back after such a dry 2011/12 winter, and early spring in 2012, shows how resilient they are at adapting to conditions. “Slugs are very susceptible to temperature and water availability and they will go down into the soil profile to find warmth and moisture.”While there was little slug activity in March 2012, for the remainder of that year there was a lot of rainfall and no limitations on slug development.
“My advice is to try and wait for warm days before application of slug pellets. The warmer it gets the more activity and, at above 5C soil and air temperatures, you are likely to get activity.”