Snails, Slugs Love Autumn

 This time of year, many spring-flowering plants are a bit confused. The temperatures and day length of mid-autumn are similar to mid-spring. It's not a surprise that azaleas, alstroemeria, banana shrubs and magnolias might put on a bit of a flower show right now, here in Northern California. 

Slugs

And showing up beneath those plants now? Snails and slugs....again.









The UC Integrated Pest Management Program has some great information on snail and slug control for your garden. Here's a link to the complete report. 

The report reinforces much of what you already know about snails and slugs, as well as how to control them. But there are some interesting twists, including:

There are snail and slug-resistant plants!

"On the other hand, many plants resist snail and slug damage including begonias, California poppy, fuchias, geraniums, impatiens, lantana, nasturtiums, and purple robe cup flower as well as many plants with stiff leaves and highly scented foliage such as lavender, rosemary, and sage. Most ornamental, woody plants, and ornamental grasses also aren’t seriously affected. If you design your landscape using snail and slug resistant plants, you are likely to have very limited damage."

And these are the plants they enjoy the most: 

"Because they prefer succulent foliage or flowers, they primarily are pests of seedlings and herbaceous plants, but they also are serious pests of ripening fruits that are close to the ground such as strawberries, artichokes, and tomatoes. They also will feed on foliage and fruit of some trees; citrus are especially susceptible to damage. Look for the silvery mucous trails to confirm slugs or snails caused the damage and not earwigs, caterpillars, or other chewing insects."

"Some plants these pests will seriously damage include basil, beans, cabbage, dahlia, delphinium, hosta, lettuce, marigolds, strawberries, and many other vegetable plants."

Another reason to turn off the sprinklers and turn on to drip: 

"Switching from sprinkler irrigation to drip irrigation will reduce humidity and moist surfaces, making the habitat less favorable for these pests"

Shopping for snail bait? The advice remains the same: Choose iron phosphate over metaldehyde.

"Baits containing the active ingredient metaldehyde are most common; however, metaldehyde baits are particularly poisonous to dogs and cats, and the pelleted form is especially attractive to dogs. Don’t use metaldehyde snail baits where children and pets could encounter them. Avoid getting metaldehyde bait on plants, especially vegetables. Some metaldehyde products are formulated with carbaryl, partly to increase the spectrum of pests controlled such as soil- and debris-dwelling insects, spiders, and sowbugs. However, carbaryl is toxic to earthworms and soil-inhabiting beneficial insects such as ground beetles, so it is better to avoid using snail baits containing carbaryl."

"Iron phosphate baits—available under many trade names including Sluggo and Escar-Go—have the advantage of being safe for use around children, domestic animals, birds, fish, and other wildlife, making them a good choice for an integrated pest management program in your garden. Ingesting even small amounts of the bait will cause snails and slugs to stop feeding, although it can take several days for the snails to die. You can scatter the bait on lawns or on the soil around any vegetable, ornamental, or fruit tree that needs protection. Iron phosphate baits can be more effective against snails than slugs overall and more effective than metaldehyde during periods of higher humidity. Snails and slugs tend to hide before they die, so you won’t see scattered empty shells or dead snails and slugs as you would if treating them with metaldehyde.

"Some formulations of iron phosphate include the insecticide spinosad to increase the spectrum of pests controlled (e.g. Sluggo Plus). Spinosad is an insecticide that will control earwigs and cutworms. These products can also be used in organic systems.

"Products that contain ferric sodium EDTA (e.g. Eliminator Snail and Slug Killer or newer boxes of Corry’s Snail and Slug Killer), work in a similar manner to iron phosphate but are somewhat faster, killing snails in three days instead of seven. EDTA is used to make the ferric (which is also iron) more available and, therefore, kills the mollusks faster. Products containing ferric sodium EDTA are not labeled for organic use.

"Molluscicides that have sulfur as the active ingredient (e.g. Bug-Geta Snail & Slug Killer 2) also reduce feeding damage caused by snails and slugs, but to a lesser extent than the iron-based products.

"The timing of any baiting is critical; baiting is less effective during very hot, very dry, or cold times of the year, because snails and slugs are less active during these periods. Irrigate before applying a bait to promote snail activity, and apply the bait in the late afternoon or evening. Sprinkle bait around sprinklers, close to walls and fences, or in other moist and protected locations, or scatter it along areas that snails and slugs cross to get from sheltered areas to the garden."

A nifty new addition to the UC IPM information: links to pages where you can compare the toxicity of all the recommended pesticides listed for that particular pest, entitled "Active Ingredients, Compare Risks". For instance, the page link to the controls for snails and slugs analyzes Bordeaux mixture, carbaryl, iron phosphate, Metaldehyde and tribasic copper sulfate in four categories: harm to water quality, harm to beneficials, harm to honeybees and harm to people and other mammals. With that chart, gardeners can now choose the least toxic chemical alternative first.

But as always, pest control in the garden begins with cultural, physical and mechanical controls. In the case of snails and slugs, that might include limiting the number and density of snail-attractive plants (cultural); handpicking (mechanical); or installing a copper barrier around vegetable seedlings (physical). By employing cultural, physical and mechanical controls first in your battle against bad bugs (and weeds), you're helping the population of the garden good guys - beneficial insects - help you do the dirty work.