Gardener’s Corner

Monthly Article by Cate White, San Joaquin County Master Gardener

November 2020

Now that cooler and (hopefully) wetter weather has arrived, slugs and snails, some of the most voracious pests in the garden have become active again.  These pests usually estivate, or hibernate, during our hot dry months.  Snails do this by crawling onto walls, fences or the trunks of woody plants in shady areas and and sealing off their shells with a thin mucus membrane in order to stay moist.  Slugs will hide under stones, boards, old flowerpots, leaf litter or even just under the soil until conditions are right for them to emerge.

When active, slugs and snails come out most often at night and on cool, wet, cloudy or foggy days.  They feed on a variety of live plants and decaying matter, usually creating irregularly shaped holes with smooth edges on leaves, sometimes clipping off seedlings or tender plant parts.  It is easy to discern that they are the cause of damage by the slime trails they leave behind.  Preferring tender seedlings and herbaceous plants, they can seriously damage turfgrass seedlings, lettuces, strawberries, cabbages, hostas, marigolds and pansies.  They also eat the young bark and leaves of some fruit trees, particularly citrus, including fruits close to the ground.

Snails mature in about two years and begin laying eggs after mating.  They deposit an average of 80 round pearly eggs at a time into a hole made in the soil, and can lay up to six times per year.  Slugs reach maturity after three to six months, and lay between 3 to 40 eggs at a time, usually in leaf litter, soil cracks, and other sheltered areas.  Their eggs are oval or round and almost translucent.  So, as you can see, populations of slugs and snails can increase quickly!

A cluster of snail eggs

The best way to control these pests is by using a variety of methods.  Begin by eliminating as many hiding spots as possible, removing low growing weeds, trimming low branches off the ground, and picking up any discarded boards or other debris. 

Traps such as overturned flowerpots, cantaloupe or orange shells can be left in strategic areas around the garden. You can also make traps by attaching one-inch runners under short boards, or by sinking shallow, steep sided containers at ground level and filling them with beer or a sugar-water and yeast mixture. Traps are even available for purchase.  Examine these traps regularly in the morning and dispose of any snails or slugs by sealing them in a plastic bag or immersing them in soapy water.  Beer or yeast traps need to be renewed frequently and are only effective within an area of a few feet.

Making areas less appealing to snails and slugs is another a good strategy.  Since they like moist, cool areas, water early in the day, giving soil time to dry out before evening, and use drip irrigation instead of overhead watering.

Another good method is handpicking.  Water an area you suspect is infested late in the day then look for the pests after dark using a flashlight.  Pick them up wearing gloves and dispose of them as described above. 

Foil tape can be an effective barrier to keep snails and slugs out of raised beds by attaching it to the perimeter of the beds.   It can also be taped around tree trunks to keep snails and slugs out.  The tape loses its effectiveness when tarnished, but can be renewed by wiping with vinegar. 

Lastly, although they cannot completely control these pests alone, chemical baits are useful.  Only use baits containing iron phosphate or ferric sodium EDTA instead of those containing metaldehyde, since metaldehyde is extremely poisonous to pets and can also harm small children.  Baits should be broadcast over a wide area, instead of being placed in piles.  Avoid getting the baits directly on your plants, especially vegetables.  Apply late in the day to lightly moist soil for the greatest effectiveness.  You may have to renew them fairly often especially after a rainfall.

Snails and slugs are annoying and destructive pests during the cool months, but with a variety of strategies, it is possible to minimize their damage.

Snail Feasting on an Orange
Slugs Attacking Tender Leaves
Article information and pictures taken from UC ANR publication #8336

November Garden Check List

  • Continue planting trees and shrubs until nighttime temperatures drop below freezing.
  • Plant spring bulbs and winter annuals such as pansies, violas, stock, Iceland poppies and decorative kale
  • There’s still time to plant starts of winter vegetables including lettuce, kale, swiss chard and parsley.
  • Cover frost sensitive plants when temperatures drop below freezing.
  • Manage snails, slugs, earwigs and ants using baits.  Sticky barriers on tree trunks will keep off ants.
  • Adjust your watering schedule, taking into account dry windy weather, cold and rainfall.
  • Strip any “mummies” (dried, shrunken or rotten fruits) from fruit trees.
  • Trim citrus 6 inches above the ground to prevent transfer of fungus spores.
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