Slugs and snails, destructors of crops and gardens,

could be

controlled by bread dough

CORVALLIS, Ore. – New research from Oregon State University Extension Service found slugs and snails are strongly attracted to bread dough, a discovery that could lead to better ways of controlling these serious pests of agriculture, nurseries and home gardens.

Since the beginning of recorded history, slugs have ravaged crops and today are responsible for billions of dollars in damage – including between $60-$100 million to Oregon's valuable grass seed industry alone, according to Rory Mc Donnell, associate professor and Extension gastropod specialist.

“Damage to grass seed is a major issue,” said Mc Donnell, who collaborated with scientists from other states on a study that was published in a special issue of Insects that focuses on slugs and snails. “But that's just one crop. It's mind boggling when you think about it. A huge array of crops is affected. They even take out specialty crops like mint. Many times, I've seen farmers lose an entire crop.”

Currently, nurseries, farmers and home gardeners use commercial baits like metaldehyde, iron phosphate or sodium ferric EDTA to control slugs and snails. These molluscicides are relatively expensive, can be toxic to non-targets and work with varying degrees of success, Mc Donnell said. Given its simplicity, low cost and the ready availability of its ingredients, bread dough has potential not only for crop protection in the United States but also for developing countries where access to pesticides is limited by cost. A dry formulation would likely have an indefinite shelf life and be easy to ship. It can be used to attract the slugs to a trap, where they will die, or to attract them to a molluscicides.

“Bread dough is a nontoxic, generic and effective tool that could be used in the detection and management of gastropods worldwide,” Mc Donnell said. “It represents a tool to aid in managing pest gastropod infestations, either using baited traps or in attract-and-kill approaches. It could also be incorporated into existing baits to improve their attractiveness.”

Of the 28 exotic or non-native slug and snail species in Oregon two are particularly troublesome – European brown garden snails (Cornu aspersum) and gray field slugs (Deroceras reticulatum), which plague nurseries and feed on hundreds of important crops with significant financial cost. If European brown garden snails are found in shipments of Oregon nursery plants at ports of entry in other states, the items are either shipped back or treated in place, Mc Donnell said. Either way it's expensive.

“With worldwide trade and travel, we are getting a homogenization of slugs and snails on planet Earth because of the widespread introduction of species,” Mc Donnell said. “This is not just a modern phenomenon. Slugs and snails have been traveling with humans for thousands of years. But it's getting more severe because of purposeful introductions, global trade, intensification of agriculture and development of new crops.”

Mc Donnell and his collaborators haven't determined yet why bread dough – a simple mixture of flour, water and yeast – attracts slugs and snails, but theorize that it is the fermentation process that draws them. They used a range of food in addition to bread dough to determine which would be the most attractive bait, including beer, cucumber, lettuce, strawberries, citrus, tomatoes, hostas and Marmite (a yeast-based food product popular in Great Britain).

“We gave them a choice of food and they consistently went for the bread dough,” Mc Donnell said. “They really, really like it. They went bonkers for it. Bread dough outperformed everything.”

In one instance, over 18,000 snails were trapped in 48 hours, according to Mc Donnell. The research revealed the bread dough can be effective in the field in Oregon for at least eight days.

“It has something we call ‘good field life,'” Mc Donnell said. “That's really, really important. If it worked for 12 hours, that would be good, but eight days gives a much bigger window for use.”

The project was a collaboration between Mc Donnell and his team; Robin Veasey and Jocelyn Millar, University of California at Riverside; Arnold Hara, University of Hawaii at Hilo; Amy Roda, U.S. Department of Agriculture, Miami; Gary Adams, U.S. Department of Agriculture, Billings, Mont.; and Ian Foley, Montana Department of Agriculture. This work was supported by funding from the U.S. Department of Agriculture under the Plant Protection Act Section 7721.

By Cindy Watter, UC Master Gardener of Napa County

 

Snails and slugs never gave me trouble when I lived in the country because my hippie neighbors had a dozen ravenous geese that used to waddle over and gobble up the slimy little morsels. However, after I left that house and moved into town, I spent my tenth wedding anniversary date night plucking hundreds of the creatures off twelve dozen King Alfred daffodils and dropping them into a bucket of beer. Everyone told me that was the non-toxic way to do it. No one told me not to dump them in the compost pile, however. Lesson learned.)

 

Early spring is the time of year when snails and slugs appear. They love to chew on tender young foliage. If your garden suddenly displays leaves with holes and ragged edges, chances are you have slugs and/or snails. They hide in the cool damp areas of your yard and come out at night to do their work.

 

A patch of ivy or weeds or a collection of overturned flowerpots is a perfect habitat for them. You should leave a few leaf piles in your yard to promote biodiversity, but some tidying up can fix your problem. You can also capture them by propping a board on cleats to create a nesting place for them to hide in. Then you drop them in a jar of soapy water.

 

Or you could sprinkle finely ground diatomaceous earth around the roots of your plant or encircle plants or raised beds with copper strips. The diatomaceous-earth granules are uncomfortable to snails and they just don't like crossing copper at all.

 

You may also put out jar lids at night filled with beer to drown them. Don't use salt; it will hurt your plants. Make sure you have a space between the trunk of the plant and mulch, to make it harder for the snails to hide. If you must use commercial bait, find one made with iron phosphate. Baits containing metaldehyde are dangerous to pets and children.

 

Slugs and snails are gastropods, invertebrates that are part of the mollusk family. They have a round mouth, called a radula, with hundreds of tiny teeth that rasp and tear soft young leaves.  

 

These creatures also act as nature's scavengers, removing all sorts of debris from forest and field. They have a purpose, but you don't want them destroying your plants.

 

The only real difference between a slug and a snail is the shell. Management is the same for both.

 

The brown garden snail (Cornu aspersa) is not native to North America. It comes from Europe and was brought here by well-meaning people who thought that escargots would become a popular food item. Alas, the snails escaped and became garden nuisances. Gourmets consider them a delicacy, and snails do appear on menus in the Napa Valley. However, most people think of these creatures as pests.

 

They look festive when they come out after a rain, and I should harden my heart and squash them then and there, but I don't. I keep hoping the birds will eat them.

 

Years ago, when there was a chemical solution for every problem, I stormed down to my garden store with murder in my heart. Snails had eaten my strawberries. I saw a box with an arresting brand name, promising “SLUG AND SNAIL DEATH.”

 

The package had a terrifying illustration that looked like a stone lithograph, printed on yellow cardboard. It featured three creatures—two slugs in the background and a snail in the foreground—with horns rampant, and the snail had an aggressive-looking frill on its front. These horrific invaders were so large they held their own against the background, a post-apocalyptic vermilion sun. I grabbed the box. Salvation was at hand.

 

And then I read the label in the lower left corner. (You should always do this, by the way.) It said: "Keep out of reach of children. CAUTION: This pesticide may be fatal to dogs or other pets if eaten. Keep pets out of treated area." So I went back to hand picking, because I had small children then.

 

The poison was metaldehyde. I have used iron phosphate bait but, unfortunately, my dog finds it attractive. (It smells like dried blood.) It doesn't hurt her, but it unnerves me. I will try diatomaceous earth.

 

I also have plenty of plants snails won't eat. Geranium, rosemary, lavender, California poppy and fuchsia don't attract them. Basil does, however.

 

I was discussing my pest-control quandary with an old friend, who told me I would no longer want to kill snails after I read The Sound of a Wild Snail Eating by Elizabeth Tova Bailey. I am sure that is true. Reading this book will make me feel better about the holes in my brugmansia leaves.

 

Find UC IPM Pest Note for Snails and Slugs here:

http://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html

 

Find UC IPM Quick Tips for Snails and Slugs here:

http://ipm.ucanr.edu/QT/snailsslugscard.html

 

 

Food Growing Forum: Second Sunday of the month through November. Sunday, March 14, 3 pm to 4 pm: “Fertilizers and Soil Health.” Register to get Zoom link: https://bit.ly/3r5bgwi

 

Workshop: UC Master Gardeners will lead a workshop on “Growing Tasty Tomatoes” on Saturday, March 27, from 10 a.m. to noon.” Register to get Zoom link:

https://bit.ly/3qo05gY

 

Napa Library Talks: First Thursday of each month. Thursday, April 1: “Gardening on a Shoestring.” Register to get Zoom link: https://bit.ly/3rn3MF3

 

Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.

 

For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.

 

 

Damage and Signs

The white garden snail feeds on an unusually broad range of plants, including orchard trees, vegetables, and ornamentals. Feeding damage is typical  snail and slug damage. It makes irregular holes with smooth edges primarily on leaves or on the margins of leaves and on flowers (Figure 2). It also feeds on seedlings, ripening fruits, and young plant bark. Because this snail has an exceedingly high reproductive rate and thousands can gather on one tree, severe defoliation and eventual death are possible, making it a major pest. Pests such as earwigs, caterpillars, and other chewing insects can cause similar damage but will not produce the telltale silvery mucous trails of the white garden snail.

Identification and Biology

The shell of this snail is unusually variable in appearance, especially in the dark bands and other markings. The adult has a medium-sized shell about the size of a nickel or dime. The non-glossy shell is typically ivory white (rarely pink), but can be light beige with narrow, dark brown bands. A similar looking but much less damaging snail, the milk snail (Otala lactea), sometimes occurs with the white garden snail and can be confused with it. The milk snail tends to be larger, up to 1.2 inches in diameter, and the inside of the thick opening is dark.

Unlike most snails and slugs, the white garden snail climbs and rests in a dormant state (estivates) on the cooler and least wind-exposed sides of vertical surfaces like trees, shrubs, fences, posts, and walls during the hot, dry season (Figure 3). They can survive for long periods by forming a wall of dry mucus to seal the shell opening and reduce water loss. They typically congregate in great numbers in an exposed, conspicuous manner to “ride out” the hot, dry season until the return of more suitable conditions in the fall.

After the first rains of the season, usually in November in California, the white garden snail, which are cross-fertilizing hermaphrodites, become more active, mate, and descend to the ground from their estivation sites to lay eggs and forage. They deposit eggs just under the soil surface or in humus. Hatching usually occurs after 20 days. This snail has a relatively short life span of  1 to 2 years, breeds only over a single season, and produces a large number of eggs (over 4,500 eggs per pair).

Management

Control of the white garden snail can be time-consuming, difficult, and costly because they have a high reproductive rate, they climb high on objects, and they estivate for long periods. Effective management of this snail must rely on a combination of methods, including exclusion, early detection, and a variety of treatments.

Like most land snails, they move slowly so in order to reach new areas, they must be aided by people. To exclude the white garden snail from your area carefully check crates, boxes, and plants shipped from infested areas. To detect this snail, search plants, fences, posts, walls, and other vertical surfaces.

Measures used to manage other snails, such as sprays, baits, traps, and barriers, are only effective when the white garden snail is active and foraging on or near the ground. However, unlike other snails, this snail estivates in the open where they are visible and conspicuous, perhaps offering the best opportunity for their control; thus, hand-picking, knocking down, and then sweeping or vacuuming might be the best option, especially with limited infestations or in small landscapes. Because it can estivate in vacant fields or untended areas adjacent to landscape sites, these untended areas should be carefully checked and mowed.

For extensive details on the various management methods for the white garden snail, including habitat modification, biological control, hand-picking, and chemical control, see the full article at https://ucanr.edu/sites/HodelPalmsTrees/files/294710.pdf.

 

Word of Caution

Use rubber or latex gloves when picking or handling snails and vegetation with their slime trails, and wash hands thoroughly afterwards. Snails and slugs are intermediate hosts of rat lungworm disease, which is likely present but not yet officially detected in California. Rat lungworm disease is caused by a parasitic nematode that can attack the human brain and spinal cord if ingested.

 

[Original article published in the Summer 2020 issue of the Retail Newsletter]

 

By Iris Craig, U. C. Master Gardener of Napa County           

When I asked a friend how her garden was doing, she told me that the day after she planted lettuce and basil, she found nothing but stumps. I told her that the likely culprits were snails, birds or rodents. Her response: “Okay, but what can I do about it?”

Some say that a French chef introduced brown snails to California during the Gold Rush. They may be tasty with garlic butter, but they are destructive garden pests. What's more, they're prolific. These hermaphrodites lay, on average, 80 eggs every six months. They move on their foot, munching on plants during the night and foggy days. When the sun is out they hide in debris or tight leaves. They leave irregular holes with smooth edges and silvery mucous trails on seedlings, leaves and flowers.

The least toxic way to vanquish snails is to hunt them at night with a flashlight. If you pluck them off plants every other night for six weeks, you can win the battle. I collect them in a lidded jar or can and bring them to friends with chickens. Snail favorites include basil, beans, cabbage, dahlias, delphinium, hosta, lettuce, marigolds and strawberries, so monitor those plants closely.

You can trap snails by burying a shallow tin can or jar lid at ground level and filling it with beer. The snails are attracted to the beer and drown. You can also trap them by laying down boards with a stone at one end as a riser. The snails will crawl underneath. Copper barriers can help as snails don't like to crawl over them, but the copper deteriorates and needs replacing often. I have also had some success with string that emits a small charge. Egg shells and coffee grounds placed around plants can deter snails, especially in conjunction with other pest-management practices.

Before buying snail bait, do some research. Some formulations kill good creatures as well as snails and are potentially dangerous to small animals and plants. Iron phosphate baits such as Sluggo and Slug Magic are safer around children and small animals and can reduce snail populations.

Pesky birds in the Napa Valley include crowned sparrows, house finches, robins, scrub jay, crows, European starlings and yellow-billed magpies. They love ripe blueberries, tomatoes, grapes, strawberries, cherries and many other fruits. They also shred the edges of tender green leaves such as lettuce. Netting is the best deterrent. Drape the top of the tree or plant and secure the edges at ground level to prevent entry. Other methods include noisemakers, visual repellents, shooting, trapping and chemical repellents. All of these options help, but some may harm other animals.

Common rodents in the Napa Valley include roof rats, Norway rats, tree squirrels, ground squirrels, mice and bats. Roof rats and Norway rats are among the most troublesome garden pests in the United States. To control them, you need to know which species you are dealing with.

Sometimes called brown rats or sewer rats, Norway rats are stocky and larger than roof rats. They leave droppings and paper nests and they burrow under buildings and wood piles and in moist areas. Roof rats are climbers and nest in trees, tall shrubs and dense vegetation like ivy. You may also find them in attics and walls. Roof rats have a long tail, longer than their head and body combined. Unlike the Norway rat, they prefer an ocean climate and have a narrower range of habitat.

When you hear scurrying noises at night, grab a flashlight. Young roof rats can be mistaken for mice; however, their heads are larger in proportion to their bodies. Once you see evidence of rats outdoors, prepare to do battle or they will soon invade your home.

The easiest way to foil rats is to call an exterminator. Seal any openings in your home that are larger than one-quarter inch. Remove debris and place wire-mesh barricades around your garden if you have a large infestation. As a last resort, set spring traps. If necessary, use a poison that won't harm pets or children. Place it near pathways or wherever you see droppings.

My friend who asked me what was eating her plants saw a squirrel chomping on one. She now has a cage around her garden.

Workshop: Master Food Preservers will hold a workshop on “Food Preservation by Freezing & Drying” on Friday, July 27, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Canning, freezing and drying are among the most basic food preserving methods. It is important to practice safe methods and to stay up-to-date with the most reliable information about food safety. Master Food Preservers will discuss each process, the equipment required and hazards to avoid, and give demonstrations and recipes. Online registration (credit card only); Mail-in/Walk-in registration (check only or drop off cash payment).

Workshop: Master Food Preservers will hold a workshop on “Pickling and Fermenting” on Saturday, July 28, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Pickles are anything preserved by acidity. Vegetables that are fermented in the home kitchen create their own self-preserving, acidic liquid that is a by-product of the fermentation process. Led by Master Food Preservers, we will learn the basics of pickling and fermenting, understand the cautions involved in home food preservation, watch a demonstration of each process, and discuss recipes easily managed by the home cook.Online registration (credit card only); Mail-in/Walk-in registration (check only or drop off cash payment).

Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.