Growers warned to prepare for slug battle this autumn

Growers should prepare for a high slug burden this autumn after the recent run of warm and wet weather led to growers reporting a flurry of slug activity in standing crops.

In a typical season breeding activity usually peaks during April and May when slugs are able to exploit the warm temperatures and regular rain showers to come to the surface and feed before laying up to 500 eggs each over a period lasting several weeks.  

The weather this year has so far proved highly favourable and juvenile slugs are being reported in large numbers. Populations are likely to be boosted by a greater-than-normal carryover of eggs from last autumn due to the mild winter, says independent expert Dr David Glen.

“Autumn-laid eggs will have easily been kept moist by the wet winter while the absence of any ground frosts means many will have remained viable coming into the spring. Unless we experience a run of hot, dry weather it seems certain that this autumn’s crops will be under pressure from the outset,” he adds.

The slug species of greatest threat to combinable crops is the grey field slug (Deroceras reticulatum). It attacks all crops, is active at lower temperatures and is able to move across ground faster than other species. When conditions are favourable, as they were in 2012, it can breed year round.

“It is the slug that inflicts the most damage to crops, but because it is often smaller than other species, such as some Arion species and Keeled slugs, its importance often goes overlooked,” he says.  

With populations active and visible some growers have asked whether it makes sense to apply pellets now in an attempt to reduce numbers, but Dr Glen says this is unlikely to yield the impact growers desire in autumn-sown crops. Instead, they should prepare to apply pellets up to a week before drilling where populations have been found to breach thresholds.

“Any pellets applied before harvest are likely to have limited effect as populations will quickly rebound. Instead, growers should be planning to apply a wet-process pellet about a week before drilling begins, provided soil conditions are suitable for slug activity and the ground can be left undisturbed for three days after treatment,” he says.

“But it’s not worth delaying drilling to allow this treatment to be applied. An application of pellets to the soil surface immediately after drilling and rolling is often the best practical option.”

His advice is largely supported by Scotland’s Rural College (SRUC) pest management researcher Dr Andy Evans.

“Spring sown cereals and oilseeds will largely be past the point of serious damage from slugs by now, but is likely to be a different story with vegetable and potato crops, particularly those under plastic or receiving irrigation.  In these cases, control from slugs this spring and summer may well be required,” he says.

Should the weather continue to get warm and dry it is likely he says that numbers going into the summer and subsequently into the autumn will be reduced to some extent, but probably not to the degree that growers would like.

His advice is to check field vegetable crops for early signs of slug damage and apply a quality wet-process pellet such as TDS if damage is seen.

“The important thing to remember about slug control in potatoes is that pellets need to be applied before the crop canopies meet across the rows so more pellets reach the surface where they can be located by the slugs,” he says.

Whatever the crop though, pellet choice is an important factor in determining effective control.

“The adage that you get what you pay for could have been conceived with slug pellets in mind. The first bit of rain and most mini-pellets turn to mush, so it is better to spend a bit more on a premium pellet, such as TDS which are formulated so as to offer a good level of persistence in the field,” he concludes.