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Snail control in vineyards – timing is everything!
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Snails are becoming a major problem in Australian vineyards, particularly with the increased area planted to cover crops, the use of surface mulch, and a decrease in cultivation.
Dr. Angela Lush, Angela Lush Consulting, says snails can cause problems by feeding on grapevine buds and young leaves, reducing yield potential of vines, and contaminating grapes at harvest.
Grape contamination can be significant, and impacts fruit destined for wine, fresh market and dried fruit.
Many growers also find snails interfere with irrigation management by clogging sprinkler heads and irrigation systems, and this costs them significant time and money.
The most common species which can impact on production/contamination are the common garden snail (Cantareus aspersus) and the white Italian snail (Theba pisana), although there are as many as five snail species that can cause problems in vineyards across southern Australia.
Very little research has been done on these snails in irrigated systems, however as a rule most can lay multiple batches of eggs from autumn to spring.
Eggs hatch in approximately two weeks and the snail population can build up quickly during this time. Snails are generally active at night, early in the morning and during cool damp periods, and these are the best times to monitor their numbers in the vineyard.
In late spring and early summer, snails will seek shelter from the heat by moving into the vine canopy, and can remain there essentially inactive until early autumn. This is when they are most noticeable in the vineyard, but unfortunately it is also a sign that it may be too late to bait.
Hence timing is everything, and it is vital snail control measures are implemented months before spring/summer.
For snail baits to be effective, snails must be active on the ground, and ideally application will be in late autumn or early winter. At this time snails are active and feeding in cool, damp conditions, and more likely to feed on baits, although this may vary depending on the climate in the region
Furthermore, baits must remain intact following rainfall, and a weather-resistant formulation such as Metarex is ideal.
Effective baiting will reduce snail numbers, thereby preventing egg lays and hence restricting the snail population prior to spring/summer. Baiting in spring may be less effective, and close monitoring is needed to ensure that snails are active when bait is applied; current recommendations suggest baiting at least four weeks before bud burst.
As well as applying baits earlier rather than later, it is important to be aware of how vineyard management can impact on snail damage.
Cultivation near budburst can take away the food source of snails and drive them into the canopy where they can feed on buds and young leaves, thereby causing stunted shoot growth and loss of bunches.
Hence cultivation should be carried out well before budburst, and dense weed populations removed at the same time. Snails can be quite mobile, and it is of benefit to remove weeds around the edges of vineyards and then bait the area to prevent reinfestation from surrounding sites.
An effective snail control program needs to be in place now. Autumn rains will trigger snail activity. Vineyards should be monitored and baited if necessary using a quality weather resistant bait. Monitoring should be maintained and fresh bait applied as necessary.
A dose of prevention in autumn is better than fighting a losing battle in summer.