Our rainy spring weather has been great for our gardens – but may also have encouraged some unwelcome garden visitors, including snails and slugs.

Snails and slugs are similar in structure and biology, but snails have a characteristic spiral shell while slugs lack a shell.  They both chew irregular holes on a variety of plants, preferring to feed on succulent plant parts such as leaves and flowers as well as seedlings.  These pests will also feed on fruits that are close to the ground.  Snails and slugs require a moist habitat, so they are most active at night or on cloudy or foggy days.  They are also hermaphroditic, meaning every individual has the potential to mate and lay eggs.  Thus, slugs and snails have the potential for rapid population growth when conditions are right.

To control snails, slugs and other pests, the University of California recommends that homeowners follow the Integrated Pest Management (IPM) process.  IPM is a strategy that focuses on long-term prevention of pests by utilizing cultural, biological, mechanical and physical controls.  With IPM, pesticides (chemical control) are used only as a last resort, and when pesticides are used, they are applied in ways that minimize harm to nontarget organisms, humans, pets, and the environment.

Cultural controls involve manipulating the environment to make an area less hospitable for a pest.  In the case of snails and slugs, a good first step is to eliminate places they can hide during the day.  Such hiding places include boards, stones, debris, weedy areas around tree trunks, leafy branches close to the ground and dense ground covers.  If hiding places can't be eliminated, vegetable gardens and susceptible plants should be located as far from them as possible.  Switching from sprinklers or flood irrigation to drip irrigation will also make the habitat less desirable for snails and slugs by reducing the humidity and moist surfaces they prefer.

Plant selection can also be a form of cultural control.  The seedlings of most plants and several plant species are particularly susceptible to snail or slug damage.  These include basil, beans, cabbage, dahlia, delphinium, hosta, lettuce, marigolds, strawberries and many other vegetables.  By selecting plants that are more resistant to snails and slugs, a less attractive habitat can be created.  Plants that are resistant to these pests include begonia, California poppy, fuchsia, geranium, impatiens, lantana and nasturtium.  Many plants with stiff leaves or highly scented foliage such as lavender, rosemary, and sage also seem to be unattractive to snails and slugs.  In addition, most ornamental grasses and woody plants are unlikely to suffer serious damage from these pests. 

Mechanical or physical controls kill a pest directly or block a pest from an area experiencing damage. In the case of snails and slugs, handpicking is an effective mechanical control if it is done on a regular basis.  They can be searched out after dark with a flashlight and then either crushed in place or picked up with rubber gloves.  Once they have been picked up, they can be placed in a bag and thrown away in the trash, or placed in a bucket of soapy water and disposed of in a compost pile after they are dead. Alternatively, if you are lucky enough to know someone with pet turtles, you can give your snails and slugs to them (as long as they are healthy) -- most turtle owners are happy to receive these pests, which add protein to the turtle diet.  Those with backyard chickens may be similarly appreciative, as chickens, too, eat snails.

Another method of mechanical control is trapping.  Traps don't have to be elaborate.  Boards, flower pots and even melon rinds scattered throughout the garden will attract snails and slugs and then it is just a matter of scraping off the accumulated pests and destroying them every day or so, using the methods described above. Do not use salt to kill slugs and snails because is harmful to the soil.  Another type of trap consists of a can or jar buried in the ground and baited with beer or a sugar-water yeast mixture. Because the liquid in these traps must be replenished every few days, and will only attract slugs and snails from an area within a few feet, they are not considered to be particularly effective.

Copper flashing or copper foil can be used as a physical barrier for slugs and snails.  It is believed that copper is an effective barrier because it reacts with the slime of these pests, causing a disruption in their nervous system that is similar to an electric shock.  These barriers should be at least four inches wide with the bottom buried in the soil to prevent slugs from crawling under them.  Dry ashes or other abrasives such as diatomaceous earth can also be used as barriers for slugs and snails.  Such abrasives should be piled about one inch high and 3 inches wide to be effective.  However, these materials lose their deterrent value if they become damp, making them not very useful in most garden situations.  Another drawback of wood ashes is that they are quite alkaline and can have a detrimental effect on soil pH.

Biological control involves using natural enemies to control pest populations.  Snails and slugs have many natural enemies, but these beneficials are rarely effective enough to provide satisfactory control in the garden.  Domestic fowl such as chickens, ducks, or geese can be effective snail predators, but will also eat seedlings and should be employed with this in mind. 

Slug and snail baits can be applied as a last resort, but are most effective if used in conjunction with the IPM methods described above.  There are other effective baits, but baits containing iron phosphate are the only ones that are safe for children, domestic animals, birds, fish and other wildlife.  Iron phosphate baits are sold under many trade names including Sluggo and Escar-Go.  The bait should be placed in moist areas that snails or slugs are likely to frequent.  Timing is also important.  If the weather is very hot, dry, or cold, baiting will have a limited effectiveness because slugs and snails are least active during these times.  Take advantage of snail and slug habits by irrigating before baiting and scattering the bait in the late afternoon or evening. 

For more information on dealing with the various pests that plague your garden and home, attend the workshop on Integrated Pest Management (IPM) May 17, at the Demonstration Garden at Patrick Ranch.  This workshop is part of the Master Gardeners' 2024 Spring Workshop Series. For information about all the workshops, and to register, visit our website.  All workshops are free, but registration is required.

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system.  To learn more about us and our upcoming events, and for help with gardening in our area visit our website.  If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at 530-552-5812. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.

Flowers and veggies lingered in my garden this year, encouraged by the mild autumn weather. Then came the holidays, followed by rain. So much for Fall garden tasks and cleanup chores. Between rainstorms in January, I walked around the garden amazed at how quickly the ground turned from golden fall leaves to a green carpet. As the summer garden died back, weeds took advantage of less competition and filled in the open spaces. They grew from seeds that blew in, were dropped by birds, or were stored in the soil “seed bank' from previous plants that went to seed – just waiting for the right conditions to germinate. Constantly moist soil and cool weather allow seedlings to get their roots established before the soil dries out.

Those beds of weeds are often ignored until Spring weather urges us to get our summer garden started. By then, the weeds are lush and well-rooted. “Weeding” becomes an unpleasant, daunting task if we wait.

Since weeds rob plants of nutrients and provide habitat for unwanted pests, it is important to control them early while they are still small. Although pulling weeds seems like a no-brainer, there is a definite way to do it efficiently. Grab a knee pad, hand hoe, Hori-Hori or trowel, and a big bucket. Kneel at the open edge of a bed and work on the weeds closest to you. Gently pull the largest weeds, lifting the root with a Hori-Hori or trowel. Next, with your fingers, pinch the base of an individual plant and “pluck” the weed out. This loosens the soil around it. making the next plant easier to pull. Gently shake the soil off the roots back into the bed before putting the weed in your bucket. Now, give the cleared area a shallow scuffle with the hand hoe to dislodge small seedlings. Don't dig weeds with a spade or disturb the soil deeper than an inch. This is hard on the soil structure and brings more weed seeds to the surface. Don't get anxious. If you try to grab and pull large handfuls, it only breaks off the leafy tops, which soon regrow from the leftover roots. It's better to do a smaller area thoroughly. Finally, add a 1” layer of weed free compost to the cleared area. This prevents light from germinating new seedlings.

Pulling weeds will give you a chance to appreciate the abundance of slugs and snails as well! It always catches me off guard to see how early the eggs begin to hatch. These voracious tiny babies are everywhere I look. Weeds, as it turns out, are a perfect hiding place to avoid predators. Tucked under the flat rosette of Shepherd's Purse or in the axis of an Asparagus leaf, slugs can eat and grow and not be found. Removing the weeds will greatly reduce their hiding places, as will removing last season's straw mulch and keeping the grass short around the garden beds… But slimy things are persistent in coastal gardens.

The undersides of wilted summer foliage keep snails happy and dry until tastier foliage emerges. They do serve a function, of course. Slowly, they help the decomposition of plant material. Summer plants that have been left to rot give slugs and snails an easy dinner. As I clean the debris and cut back the plants, I have found tiny little snails by the hundreds this year. Cleaning the beds reduces snails, but it also redirects them to the fresh new growth of healthy plants. Although I would love to just leave them for natural predators, there aren't enough birds, snakes, opossums, or other critters to make a dent in this year's bumper crop of mollusks.

There are no sure-fire exterminators for slugs and snails in the home garden. Environmentally concerned gardeners use Iron Phosphate baits like Sluggo with some success. But even the heavy-duty snail baits- the ones that contain Metaldehyde or Carbaryl (that also harms worms, reptiles, birds and some mammals) - only work on the snails that come in contact with the chemical. Many of the small hatchlings emerge and head for a sheltered place above the ground. You'll find them hiding in the tender tops of plants, under the lips of flowerpots, or behind shrub foliage where their ‘foot' never touches the ground. In the cool, damp air of night, they glide from their perch to devour prized plants – which seem to be their favorites. Controlling them becomes a bit more problematic and requires a combination of approaches.

I hesitate to share that hunting slimy slugs and snails has become a bit of a questionably sane, definitely weird obsession for me. You won't find me excited by a dish of beer with a few drunken snails in it. Instead, I clean, prune, plot, bait, consider the possibility of becoming an Escargot farmer, and then become the Human Predator. (That's right -  it's my Super- Power. ) To tackle the problem, I put on the garb of a crazed gardener - a bright LED headlamp, rubber gloves, a container of soapy water - and head into the night garden to make my rounds. As I examine each plant, turning over leaves to check bothsides, I pluck my slow-moving prey and pop it into the container, where it sinks to its demise. It's not a pretty sight. But there are just SO many snails!

As the nights go by and the population dwindles, I marvel at the impact I can have on a single population of slugs and snails. Yes, that's right, “a single population” because there will be more eggs hatching. A single snail can lay 6 batches of eggs in a year with up to 80 eggs each. That's 480 eggs for every snail! It's never-ending. But I'm doing my part.

So, I encourage you to get a head start on the weeding and garden cleanup this year. Keep that cool fashion-statement headlamp handy, and just ignore the neighbors' comments about your new nighttime gardening chore. For what it's worth, I can vouch for your sanity.

 

For additional information about Integrated Pest Management (IPM), including weeds and mollusks, Check out the University of California website  https://ipm.ucanr.edu/PMG/menu.homegarden.html?src=302-www&fr=3723

For help identifying and controlling weeds, https://ipm.ucanr.edu/PMG/weeds_intro.html

For more on slugs and snails, https://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html

 

All photos are courtesy of the author, Annie Sicotte, and are used with permission.

 

This odd pattern that has shown up on polyethylene irrigation tubing was sent in by an observant Santa Paula grower.  The fruit trees were covered with aphids and there was sooty mold growing on the honey dew dripping onto the tubing. Such a beautiful pattern, but what causes it? 

Turns out Mark Hoddle, Biocontrol Specialist at UC Riverside had an answer - snails.  Brown garden snails are active with this warm, wet weather and they are enjoying feeding on the sweet taste of honey dew. 

The bottom side of the snail has a mouth composed of raduli which are sharp teeth which scrape along the surface of the tubing, leaving marks.

All images from Los Angeles Natural History Museum - https://nhm.org/stories/microscopic-look-snail-jaws

 

 [From the UC IPM blog Pests in the Urban Landscape] 

Citrus trees need care throughout the year, including cultural practices to keep trees healthy and pest management. During the fall season, several pests can attack citrus trees in many California regions. 

Brown Rot

Monitor for this disease by checking for damaged fruit on your tree, as well as fruit in storage. Sometimes affected fruit develops a pungent odor and can ruin fruit held in storage. See the UC IPM web page on Brown Rot to learn more.

Citrus Leafminer

If you see what look like small “tunnels” on your citrus tree leaves, your tree might have citrus leafminer. The adult stage of this pest is a small, light colored moth; the larval stage feeds and develops inside the leaves of young citrus and other closely related plants.

Citrus leafminer rarely causes problems for mature trees, however, it can seriously damage very young trees. Read the UC IPM Pest Notes: Citrus Leafminer for recommendations for prevention or management.

Snails and Slugs

Snails and slugs are attracted to citrus trees and can feed on foliage and fruit. A good sign that these pests are the perpetrators of tree damage are the silvery trails of slime along the ground or on tree leaves, or even see the snails or slugs themselves. For management tips, read the UC IPM Pest Notes: Snails and Slugs.

Asian Citrus Psyllid and Huanglongbing

You may have heard of the Asian citrus psyllid (ACP) and the deadly disease huanglongbing (also called citrus greening) that has been featured in the news. This disease doesn't pose a threat to humans or animals, but is deadly to citrus trees. Once a tree develops huanglongbing, there is no cure, so for this disease prevention is key.

Stopping this serious citrus pest will require everyone's help. To learn more about the psyllid and the disease, as well as what you can do, visit the UC IPM Pest Notes: Asian Citrus Psyllid and Huanglongbing Disease.

UC IPM Web Site

For information on managing other citrus pests in the garden, see the UC IPM webpage on Pests in Gardens and Landscapes: Citrus.