With Brian Cal­laghan

Aim to con­trol num­bers, not elim­i­nate them

Country Smallholding - - Front Page -

Pre­ven­ta­tive Slug Treat­ment

Al­though most snails be­come dor­mant dur­ing the win­ter months many slugs will re­main ac­tive down to 5C – a tem­per­a­ture fre­quently en­coun­tered out­doors in win­ter and al­most a con­stant min­i­mum where crops such as broad beans, sweet peas etc. are over­win­tered in poly­tun­nels and glasshouses. For this rea­son, and to min­imise prob­lems next year, it is worth be­gin­ning your slug con­trol strat­egy now rather than wait­ing to be­come over­whelmed in spring.

Un­der­stand­ing the prob­lem

Slugs are gas­tropods, quite lit­er­ally a stom­ach and a foot. As this sug­gests they move about and they eat, mostly at night, but any­time wet and mild con­di­tions pre­vail. Most dam­age is caused by a rel­a­tively small num­ber of species with the ma­jor­ity qui­etly per­form­ing their role as pri­mary de­com­posers help­ing con­vert or­ganic mat­ter into the hu­mus and nu­tri­ents es­sen­tial to plant growth. Th­ese few species, how­ever, cause mil­lions of pounds of dam­age to com­mer­cial crops ev­ery year, not to men­tion the mass out­breaks of rage and frus­tra­tion amongst the many oth­ers who suf­fer the ef­fects of a sin­gle night’s at­tack from a few slugs.


Be­gin by ac­cept­ing that slugs play a valu­able role in the nat­u­ral en­vi­ron­ment and that even the sever­est con­trol regime is un­likely to erad­i­cate them en­tirely. The aim is al­ways to con­trol their num­bers to ac­cept­able lev­els rather than elim­i­na­tion.

Slugs are ran­dom feed­ers – they bump into food sources rather than hunt them down and tend not to travel more than a few me­tres in a night be­fore re­tir­ing some­where dark, damp and undis­turbed where they will lose mois­ture less rapidly. Re­duce the num­ber of po­ten­tial day­time refuges by car­ry­ing out a thor­ough win­ter clean of poly­tun­nels and glasshouses. Clear out any de­bris plus the junk which th­ese struc­tures in­evitably get filled with over win­ter. Next, re­move the pots, trays, sacks and other grow­ing equip­ment to an­other lo­ca­tion and place a one or two roof tiles around to where any re­main­ing slugs will gather dur­ing day­light hours. Col­lect them up each morn­ing and feed them to the chick­ens.

Next, tar­get your ef­forts. Many crops, such as cab­bages and sprouts, can with­stand a few nib­bles whilst oth­ers can be dev­as­tated over the course of a night. Soft, suc­cu­lent leaves such as seedlings, let­tuce and other sal­ads are prime tar­gets and thus need the high­est level of pro­tec­tion.

Al­though beer traps etc. do work, hand­pick­ing, with the aid of a torch, for a few evenings quickly re­duces num­bers to tol­er­a­ble lev­els. Sup­ple­ment this by stand­ing trays of seedlings on gravel which drains quickly and slugs find dif­fi­cult to tra­verse. Fi­nally use grit, crushed eggshells and cof­fee grounds as bar­ri­ers around each plant.

Out­doors, use win­ter soil cul­ti­va­tions to re­duce pop­u­la­tion num­bers. Rough dig all un­cropped ground in early au­tumn, ex­pos­ing as much of the sur­face area to the win­ter cold as pos­si­ble. In ad­di­tion to im­prov­ing the work­a­bil­ity and drainage of heav­ier soils this will also ex­pose pock­ets of slug eggs to preda­tors, frost and ul­tra vi­o­let ra­di­a­tion. Thor­oughly cul­ti­vat­ing the soil again in spring will dis­rupt the peak breed­ing time of many dam­ag­ing slug species such as the field slug. When con­di­tions al­low, reg­u­larly hoe the sur­face of soil to aid rapid dry­ing of the sur­face and con­trol weed growth and any ex­ces­sive veg­e­ta­tion sur­round­ing ar­eas of sus­cep­ti­ble crops.

Slug Pel­lets

With methio­carb now ef­fec­tively banned across most of Europe, grow­ers are left with a choice of those based upon met­alde­hyde (the com­mon­est type) or fer­rous-phos­phate. Al­though both types can be equally ef­fec­tive the former is not al­lowed un­der or­ganic grow­ing sys­tems due to the toxic na­ture of its ac­tive in­gre­di­ent which has been im­pli­cated in dam­age to wildlife, do­mes­tic pets and wa­ter con­tam­i­na­tion.

The use of slug pel­lets based upon fer­rous sul­phate is par­tially per­mit­ted within or­ganic sys­tems as the ac­tive ma­te­ri­als are con­sid­ered to have low tox­i­c­ity and are usu­ally present in most soils in lower con­cen­tra­tions as the plant nu­tri­ents iron and phosphorous. There are con­cerns in some quar­ters that al­though the iron and phos­pho­rus may be rel­a­tively harm­less, other in­gre­di­ents, such as EDTA, which are added to im­prove the ef­fec­tive­ness of the prod­uct, may lead to poi­son­ing in other an­i­mals and hu­mans. Which­ever ma­te­rial you choose, both or­ganic and con­ven­tional ad­vice is that an in­te­grated ap­proach to slug con­trol, util­is­ing a broad range of tech­niques, pro­vides a higher de­gree of con­trol than sole re­liance on slug pel­lets of one sort or an­other.

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