Monitoring and timing key to effective snail control
Snails and slugs are problematic pests in vineyards that impact productivity and yield of grapevines. They feed on foliage, buds, shoots, roots and berries of vines, and other organic matter within vineyards. During harvest, snails and slugs may infest the fruit resulting in lowered quality or rejection of crop (MOG issues with machine harvesting).
As snails and slugs require cool, moist conditions to grow and reproduce, they are known to block irrigation drip lines, reducing the distribution and efficacy of irrigation. Although slugs are less often an issue in vineyards compared to snails, they should be controlled appropriately if found in significant numbers.
As autumn approaches, snails and slugs will become increasingly active following seasonal rainfall. Monitoring snail and slug populations plays an important role in any vineyard management plan. A combination of cultural, biological or chemical controls can be highly effective in preventing snail or slug infestations from becoming severe.
The small pointed snail and conical snail are less common in WA vineyards. Both species are similar in shell colour and pattern, however there are differences in shell length between the two.
If you see a snail or slug that you do not recognise, please collect the specimen(s) and submit them to be identified by the DPIRD.
Habitat and Lifecycle
Snails and slugs thrive in cool, moist conditions that are shady, such as under plants and organic matter. Snails prefer broadleaf plants with soft, palatable leaves. Snails and slugs become most active following rainfall that brings mild, damp conditions; but do not like heavy rain and strong wind. Snails occur in a range of soil types. The White Italian snail prefers areas with sandy, alkaline soils with high calcium content in coastal regions. Slugs prefer heavier clay soils where they can hide in cracks under clods, and generally do not survive in fine, light or highly compacted soils. In hot and dry weather, snails will climb upward onto plants, posts, fences and other vertical surfaces to avoid unfavourable conditions on the ground.
Snails and slugs undergo dormancy (aestivation) in order to survive prolonged periods of hot, dry weather. They are all hermaphrodites, possessing male and female organs, meaning all have the potential to lay eggs after mating. Snails lay eggs in about seven days after mating and hatch after two to four weeks. Young snails develop through winter and into spring before entering dormancy for the hottest periods of the year.
Management of snails and slugs in vineyards
There are three main methods of controlling snails and slugs in vineyards: cultural, biological and chemical. The most effective way to control pest snail and slug populations is a combination of two or more methods. It is important to remember that small or juvenile snails and slugs may hide underground and stay unnoticed unless controlled effectively through multiple approaches.
It is important to monitor snail and slug activity as this helps make better-informed management decisions. Early autumn, particularly after rain events such as what the southern regions have experienced this season has been conducive to breeding and presents an opportune time to begin baiting.
Check for snail and slug presence early in the morning or just after rainfall, snails will be most active searching for food and mates. Inspect grapevine trunks, canes, leaves, irrigation equipment, fence posts, tree trunks, and areas where grass or other vegetation is dense. Counting the number of pests per square metre is an effective way to estimate how many snails and slugs are present.
Start by estimating a 10 x 10 cm square and counting the number of snails in the square. Repeat this in 50 spots in the vineyard, and then multiply the total number of pests by 2 to give the number per square metre. Counting many squares will give an accurate indication of how many pests there are and where they are located.
Patch baiting small sections of a vineyard by hand may help to make informed decisions about timing and extent of baiting. Look for dead snails the day after bait was applied in the area. Use this as a guide to help decide whether to bait the entire vineyard. See more on patch baiting in ‘Chemical control’ below.
If an infestation is severe, consider one of the following control methods. Importantly, treatments should be applied before snails have an opportunity to lay eggs as this prevents the next generation coming through.
For controlling pest snails and slugs, the less plant matter in the vineyard the better. Management of cover and inter-row crops is recommended during periods when snails and slugs are expected to be most prevalent. Reducing the amount of organic matter available for snails will increase the chance of baited being encountered by snails.
Cultivation of vegetation in the inter-row may result in some mortality of snails. Mowing or brush cutting grass and weeds approximately 2 metres on each side of the vineyard fence line or boundary will help prevent invasions of pest snails and slugs.
Avoid liming during periods where snails may be most active. Snails can feed on lime - strengthening the shell of young snails and increasing survival. Even lime that has been incorporated into the soil may be encountered by snails and encourage a healthy pest population.
Poultry such as ducks, chickens and Guinea fowl are effective at controlling snails and slugs in vineyards. Chickens and Guinea fowl need to be managed carefully as they may damage fruit as it matures. Ducks are considered the best of all bird species for control, with ‘Khaki Campbell’ or ‘Indian Runner’ to be the most efficient. Flocks of birds, ranging from 5 – 8 individuals per hectare are recommended to control snails and slugs.
There are two major considerations when using birds as biological controls: housing and use of chemical controls. Housing birds appropriately during the night is essential to protect them from predators such as foxes and wild dogs. Birds should be released 1 or more hours after sunrise, and re-housed at least 1 hour before sunset to reduce the likelihood of predation.
If chemicals such as sprays or baits are to be used, birds should be removed from the area while chemical treatments are active. This is critical if eggs from birds are intended to be consumed.
Sprays are most effective when applied while snails and slugs are active in the vine canopy. Products registered for snail and slug control contain copper mixed with silicate salts or methiocarb.
If the mode of action is dehydration, application of spray should be done early in the morning on a day when the weather is predicted to be fine and dry to prevent pests from rehydrating. Sprays containing copper and silicate salts must only be applied to grapevines that are in dormancy. Apply copper and silicate salt sprays to trunks and canes only, these sprays may burn leaves and cause fruit to drop.
Methiocarb based sprays have withholding periods (WHP) when used on fruiting vines. Sprays used to control pathogens may also be useful for controlling certain snail species. Copper based sprays are effective at controlling Brown Garden Snails, which are more likely to climb onto vines.
Always check the label to ensure the spray intended to be used is registered for use in grapevines.
Baits registered to control snails and slugs in WA vineyards contain either an iron EDTA complex, methiocarb or metaldehyde. If rainfall greater than 10 mm is expected, do not apply iron EDTA or metaldehyde baits as they will degrade rapidly. High temperatures will also degrade metaldehyde based baits. Do not combine copper-based sprays and chemical baits, copper may contaminate baits and repel pests from consuming baits.
For the most effective results, baiting should occur from early autumn before egg-lay. Baits must not compete with available organic matter, which snails may preferentially feed on instead of baits. Monitor the vineyards to assess the extent of infestation of snails or slugs. Patch baiting where snails and slugs vary in numbers within the vineyard may be a cost effective option.
In areas of the vineyard where there are higher densities of pests, bait heavily; and where numbers are lower, bait less. Specifically, the positioning of baits per m2 is crucial as it increases the chance of snails encountering bait. Reapply baits after 10 – 14 days if necessary, especially after rainfall or until pests are appropriately controlled.
Jesse Bowman, Viticulture Development Officer