An afternoon webinar, organized by Peter Waldock of Hutchinsons and supported by Matt McMillen of PDM, was held on Tuesday, September 2nd. It was delivered by the British Leaf Salad Association in response to the growing challenge of managing slug populations in salad crops. The afternoon began with Matt introducing the session and outlining the challenges salad growers face regarding slugs during the wet 2024 season, albeit with a respite in the much drier 2025 season.

Following Matt, Professor Keith Walters of Harper Adams University began with a lecture on slug biology, their life cycle, and typical IPM control measures. Although there are over 40 slug species in the UK, only four are thought to cause significant damage to crops, of which the grey field slug is considered the primary culprit. It is estimated that, without effective control, grey field slugs could cause between £40 and £100 million in damage to UK crops.

Slugs dehydrate easily, so soil type, structure, crops, irrigation volume, and timing all affect resident populations. Notably, farmers at Harper Adams and BOFIN (British Farming Innovation Network) conducted trials that demonstrated that slug populations are patchy within fields and that the location of these concentrations is relatively fixed over time. Based on easily acquired soil data (such as Omnia Terramap), Harper Adams researchers created a model with good accuracy that identifies potential locations of high-density slug areas in fields. This increases the potential for accurately identifying and addressing high slug densities in fields, a topic explored in more detail by subsequent speakers. The first to discuss slug treatment options was Rob Storer of BASF, who briefed us on the mollusc pathogenic nematode Nemaslug 2.0. BASF has been producing Nemaslug since 1994, with the new and improved Phasmarhabditis californica species in the new and improved 2.0 version, launched in 2022. The principle of using nematodes for pest control is fairly well understood, based on a flooding approach to deposit large numbers (typically billions/ha) of nematodes into the soil, where they seek out and attack their prey. In the case of slugs, infected mollusks quickly stop feeding and die within 4 to 21 days.

Nemaslug 2.0 works better on young, small slugs than on larger, older ones, as it takes a larger number of nematodes to fatally infect a larger pest. Application is done using conventional sprayers (usually without filters) and, for best results, as part of a slug control program, relies on moist soil conditions or a high volume of water. When used correctly, trial data shows similar efficacy to standard ferric phosphate pellets.

To elaborate on ferric phosphate, Jeremy Booth of Certis Belchim was next. Jeremy highlighted the importance of the high palatability, durability, and spreadability of his slug pellet range. In particular, the patented chelating agent, which ensures optimal penetration of the active ingredient into the slug's digestive system, and the high-quality wheat flour used in the recipe ensure the pellets are both palatable and highly effective. The high-quality flour, combined with advanced extrusion and baking processes, produces smooth, uniformly shaped pellets that spread easily with minimal dust and are long-lasting in the field. Their uniform shape reduces the total exposed surface area, limiting the points where water can penetrate, making them more resistant to mold growth and longer-lasting. Jeremy reminded attendees that slugs are random feeders and need to be within 2 cm of a food source to detect and feed. Therefore, growers should increase the likelihood that slugs will encounter a pellet rather than their crops by maximizing bait points through product choice. Certis Belchim offers a slug pellet calibration tool on its website, which growers can use to ensure optimal distribution of their ferric phosphate pellets and maximize slug control.

Next, Mike Stoker of Orion FT explained the importance of silicon in plant health, particularly in creating plants that are more resistant to pest attacks, including slug deterrence. Mike reminded attendees of silicon's role in reducing leaching into the soil, reducing vascular stress in plants, and as a structural component of cell walls and leaf surfaces. He then explained the difference between monomeric silicon, which has these effects, and silicon polymers, which have the well-known adjuvant properties. Orion is a leader in the field with its iNHiB bioactive silicon technology in Rigel and Sirius products, which have been shown to increase silicon phytolith deposits on leaf surfaces and leaf hairs. Both trials and grower experience in the UK and abroad suggest that this combination appears to be effective.