the world, vineyards cover around 8 million ha. Depending on location, grapes
are grown for winemaking, table grapes and drying.
Historically, Europe has accounted for the
largest share of vineyard area, with Spain, France, Italy and Portugal
accounting for the majority of European production. Asia accounts for an
increasing amount, with Turkey second only to China in vineyard acreage. South
Africa has around 100,000ha under vine, one-tenth of the Spanish area, while New Zealand vineyards continue to increase their area, reaching 36,000ha in
Susceptibility to Slug Damage
are significant vineyard pests. Typically, damage arises either through
contamination (the snails being present on the fruit at picking) or, more likely,
the snail having damaged the skin of the fruit, allowing fungal infection to
summer, snails enter a period of hibernation known as aestivation, which last
until the early autumn rains. Vines provide the snails with an ideal habitat
for this process, the consequence being that they’re either in the vines at
harvest, or beginning to feed on the grapes as they make their way back to the
For control, growth stage of the vine is less
important than the time at which bait is applied.
Species of Concern
species of greatest concern to the vineyard owner are Helix aspersa, Theba pisana
and Cochicella barbara.
Theba pisana can
reach very high numbers; infestations of up to 200-250 snails per vine have
been recorded (Sanderson, G. (1995) Snails in viticulture. Australian Grapegrower
and Winemaker 378a, 115-118) and in one case, 87kg of snails were collected
from vines yielding 30 tonnes of fruit.
Symptoms of Attack
contamination and fungal infection are the most common symptoms of snail
damage, occasionally Helix aspersa will feed on growing buds and new foliage.
snail infestations can also result in clogged sprinkler heads and water lines,
reducing irrigation efficiency and adding to labour costs.
snails once they have started to move up into the vine canopy is almost
impossible, as they will not return to the ground to feed on pellets.
it’s important to control snails while they’re most active. If control measures
are put in place before they start mating, greater reductions in population
will be observed.
labour-intensive, manual removal of snails from vines and supporting posts can
significantly help control the population.
using pellets, the greatest effect will come from application during early
autumn, after the initial rains, particularly if the soil beneath vines is kept
clear of vegetation to remove alternative food sources. On-going applications
during autumn and winter will continue to reduce populations further.