This isn't my favorite subject, and the Hosta Mill has had - keep my
fingers crossed - little animal damage so far. That's the reason
why it has taken me so long to start this topic.
Some of the information is first hand, most isn't.
Slugs for one are a universal problem, so I've had to deal with them .
Voles, on the other hand, I've seen around, but haven't had any hosta damage by these rodents yet.
If the Hosta Mill has ever suffered a nematode attack, I've missed it,
and there are very few deer around here, so I have to rely on the information of others on that matter.
Why do slugs and snails prefer hostas ?
There was a time this article started like this: "Most articles treat snails and slugs on the same base, but apparently snails seem to do relatively little damage." Must be my biggest mistake ever. In 2009 and 2010 was invaded by huge numbers of vine grape snails; the damage was massive.'
Hostas mixed with slugs and snails, a very bad combination: slugs make big holes in your lovely hostas, making them unsightly, and when conditions are optimal for slugs, they can devastate a complete plant overnight. The plants are not lost, but it will take at least a couple of weeks before a healthy crown of foliage reappears, and the plants may be reduced in size.
Why then is it that slugs tend to target hostas? I believe the most important reason is just coincidental: hostas and slugs both prefer the same shady, cool, moist conditions. Under these conditions leaves tend to be soft and juicy, just the way slugs and snails like them.
As a hosta collector you will have to fight an ever continuing battle against these pests, relentless, or otherwise face bitter defeat. The larger your collection gets, the more fierce the battle. And don't have the illusion you can win the war. But at least you can win a few battles and keep them under control.
The "slug proof" myth
No hosta is slug proof, nor will there ever be one, I guess. But some are easier to devour than others. Hostas with thin substance are preferred slug food
What you need to know about slugs
- They like damp places;
- They feed at night, sometimes just after a rain shower;
- They prefer tender new growth, seedlings, plants with thin substance;
- They make slime trails they follow to return to their "food supply". Others will follow;
- They spend the winter in the soil;
- They can live for years;
- The eggs are white or yellow and are laid in clusters of about +20;
- You can find the eggs in moist soil, under rocks, plant containers, etc;
- The eggs can hatch years after they'd been laid;
Ways to fight slugs
There are many ways to take on slugs. I've divided them up in five categories. As there isn't a single technique that works a 100%, best practice is to combine several and to keep your eyes open for slugs at all times.
- Fighting slug shelters and attract slug eaters
- Traps and baits
- Chemical warfare
- Biological warfare
- Physical barriers
Fighting slug shelters and attract slug eaters
- Spring cultivation may kill a number of hibernating slugs and their eggs;
- Keep the area your hostas grow in, and your garden in general free from weeds at all times. Working the soil to remove the weeds will not only remove the slugs hideouts, but will bring them to the surface, were slug eating animals will eat them;
- Remove dead leaves in autumn or in spring. Piles of dead leaves are ideal hibernation shelters for slugs ands snails. Removing them in autumn means the snails will have less hibernating places. I usually remove the leaves at the end of winter. I like to believe the slugs and snails hibernating in the leaf piles would have found a shelter elsewhere if the leaves had been removed during autumn. Clearing the leaves at the end of winter means removing a lot of slugs and snails with them.
- Try to eliminate as many daytime shelters as possible: slugs like a cool, moist shelter during daytime: under rocks, in and under wood stacks, etc. Remove all of them near your hostas and as many of them as possible throughout the garden.
- There should be no decaying matter in or near your garden beds. Clear all debris on a regular basis. Keep the compost pile in an area far away from your hostas.
- Do not place you plants to close together. Not only do you create ideal shelters for slugs, but other infections will spread more easily too.
- Avoid watering in the late afternoon or evening. The soil will be dryer and less slug friendly.
- Provide shelter for toads, hedgehogs and birds, as they eat slugs and their eggs.
- Chicken love slugs.
- Catching them yourself: This is a good way to really combat slugs, and will give you a
clear idea about the severity of the infestation: go out in the evening/night/morning or after a rain shower and catch as many of
the little buggers as you can.
- Wear kitchen gloves.
- Chopsticks or barbecue skewers may come handy to attack the slugs.
- To remove slime from your hands, vinegar works well.
- Take a container of bucket with an ammonium solution around with you to dispose of the snails and slugs you caught. I kills instantaneously and prevents dead snails and slugs all over the place.
I've heard of people keeping record of the number of slugs caught; this can reach impressive numbers.
- Beer traps: Sink containers in the soil (the rim should be about 1" above soil level) and fill with beer. Slugs love it and drown. Refresh regularly. For some people this works, for others it doesn't.
- The same works with grape juice. Apparently they really love it.
- A lot of different baits have been tried (beer, grape juice, yeast and honey solutions, ...) . Some will work better for you, others not at all.
- Build a slug shelter yourself with a flat piece of stone, wood or anything you have at hand, and make a slug feeding area and shelter underneath. Dispose of the slugs under it every day.
- Drenching the soil around the hostas with diluted ammonium (16 parts water, 3 parts ammonium) will kill a number of slugs and their eggs; it doesn't harm the plants, it's cheap and will even act as a source of nitrogen.
- Spraying the plants with diluted ammonium. The same dilution as mentioned above. Wait until night and spray directly on the slugs and snails. This is the way I've been fighting the massive attacks since 2010. I try to go out one night every week.
- Replace the ammonium with borax. Personally I don't like this very much, because the borax salt, when applied to often, will poison your soil. If you'd like to try it, only apply it once every year.
- Heroic discussions have been fought out to prove slug baits
are/are not toxic and harmful to wildlife. I don't want to find out
first hand if dogs, birds or hedgehogs are harmed by commercial slug
baits, but they work, so I want to use them, in a safe way.
The best way is to build a shelter the slugs can reach, but other animals can't. I use a roof tile that's placed almost flat on the ground and put some pellets under it. This way other animals are kept away, and the pellets stay dry and active.
Commercial slug baits contain metaldehyde, that dehydrates slugs, or iron sulphate, that simply stops the slugs from feeding, and they die. Metaldehyde is the stuff that is could poison wildlife and should be used only with maximum care.
Iron phosphate is used in slug bait, but it can also be applied to spray an infested area. Dilute 2 tablespoons in a quart of water and spray the area you want to clean.
- Last but not least, caffeine. Don't row away your coffee ground. Sprinkled around hostas, it acts like a slug repellant. Left over coffee can be sprayed around your plants and will kill slugs. You could ever consider sprinkling cheap ground coffee, as it more effective than the stuff you've already used. And it's absolutely safe.
- Applying a systematic pesticide makes the plants toxic to sucking an chewing insects, but also to slugs and snails.
Phasmarhabditas hermaphrodita is a nematode that is effective against slugs. Google the web for a supplier/product name. They are watered onto the soil and will kill slugs in the soil.
This appears to be a very effective method, provided you follow the guidelines.
Wormwood (Artemisia) tea is a rather strong 'biological' insecticide that will kill slugs. Drenching the soil will kill the snails that have found subterranean shelter.
How to make wormwood tea: let one cup of Artemisia cuttings soak in a quart of warm water for at least 24 hours. Strain the liquid until it is clean. Add 1 tablespoon of liquid soap.
Dilute 8 ounces of the liquid in a quart of water.
Plant fragrant plants and herbs in between and around your hostas. Slugs hate them and will avoid them.
- Slugs and snails really hate copper. Attaching a copper strip (1" wide) on the outside of containers or a strip surrounding a bed will surely drive away all but the bravest slugs out.
- Anything dry and/or sharp used as a mulch will keep the slimy invaders away: crushed eggs shells, gravel chips, coarsely ground bark, saw dust, ... It will dehydrate and/or desiccate the slugs.
- Diatomaceous earth is a natural product with tiny sharp edges that injures the pests on contact, causing them to dry out and die. I wouldn't advice it however, as it is very unhealthy stuff if you inhale it, and it kills other, beneficial soil inhabitants as well.
Although there are other rodents, like rabbits and squirrels, that occasionally may cause some damage to hostas, the main thread is voles.
VolesVoles do a lot of damage in gardens, but seldom do they get the blame. Because voles are experts in staying unseen, we blame mice and moles for the damage that they do.
Most voles are brown or gray, slightly larger than mice. With their large eyes, small ears, blunt head, short legs and short tail they are well adapted to a subterranean lifestyle. Especially the last characteristic makes it easy to distinguish from a mouse. They prefer living underground, were they build a large tunnel system with a network of runways just beneath the surface, often making small mounds of soil. Superficially this may look like the work of a mole, but on a smaller scale.
In good rodent style, voles are prolific breeders.
They can have up to four litters a year, with up to
seven babies per litter.
Voles are active day and night year-round. They construct extensive tunnel systems and surface runways. Several adults and young may live in one tunnel system. Populations seem to peak every 2 to 3 years, depending on food availability, climate and other stress factors.
How do you know if you have voles
When winter is over and snow disappears, you can see the system of surface runways easily. These runways often are tunnels build with fragments of weeds and grasses, or through a layer of mulch. Smaller plants that disappear in a hole also are an indication, as are larger plants that return decimated, because during winter time voles often rely on roots as a food source. Because this happens during winter, when there is little human control in the garden, they can carry on their destructive work for weeks, and wreck complete hosta beds.
They relish young shoots and leaves in spring time.
How to fight voles
Getting rid of voles all together is almost impossible. If you
would succeed in destroying the complete population in your garden,
voles from the surrounding area will soon discover the free space and
The objective is to control the population, especially the periodical peaks in the vole numbers.
Creating a vole unfriendly environment.
Like with slugs, it's important to keep your garden free of weeds. Removing grasses and weeds removes the protective cover they like.
Mixing stone gravel trough your top soil will make most of the voles leave the treated part of the garden, because they absolutely hate the sharp edges of the stones.
You can use rat poison as vole bait. If you can see the runways, put the bait in there, otherwise apply it throughout the infested area. Make sure the bait is covered, because voles like the dark. Repeat this process exactly two weeks later.
Another way is to put mouse trap in the runways. No bait required. Just put two mouse traps together in the runway, the triggers facing away from each other.
About foliar nematodes
Over the last couple of years, foliar nematodes (Aphelenchoides spp.) have become a serious problem for hosta growers in the USA. I don't have any data about the situation in Europe, but as significant numbers of hostas cross the Atlantic every year, I guess it's just a matter of time before we'll have the problem over here to.
Foliar nematodes are very small worms, that feed on leaf tissue, flowers end buds. In hosta they cause a brown coloring of parts of leaf tissue in between veins. Although not lethal to the plant they make it look ugly and affect it's vigor.
They are highly infectious and are carried from plant to plant by water in the form of rain, dew, sprinklers, wet tools, etc.
Always bare in mind that not only hostas, but a large variety of garden plants can be infected, and even some weeds. It may even be a good idea to grow some of these ornamentals, like Solomon's Seal, as an indicator plant, because they will show signs of infection much earlier than it shows in hostas.
How do you know if you have foliar nematodes ?
The damage to hosta will show in late August. If you suspect nematodes in a plant, there is an easy way to verify. Take small pieces of possibly infected plant tissue and place them in a container. Add water until the pieces are just covered. The next day, with the help of a strong light and a 10X hand lens., you should be able to see the tiny worms in the water.
Methods of controlling foliar nematodes
Create a nematode unfriendly garden
- Keep the part of the garden your hostas grow in completely clean of weeds and debris. All debris and weeds from infected areas should be destroyed, certainly NOT composted.
- Hope for a cold winter, as this will decimate nematode populations.
- Keep the foliage as dry as possible. Avoid overhead watering.
Take action to avoid spreading of the infection
- All infected plant should be isolated.
- It's best to destroy very heavily infected plants. An alternative is to give them the warm water treatment (repeatedly throughout the growing season)
- Individual plants can be soaked in warm water (50 °C = 120 °F) for about 15 minutes. Dig them out, clean of all the earth, remove all the leaves and soak them. Afterwards, put them in isolation, but keep them apart from untreated infected plants
- When dividing, repotting or otherwise handling hostas, take all
- Avoid working with plants when they are wet;
- Sterilize your tools in between plants;
- Work with clean soil and containers, on a clean surface.
- Pesticides treating nematode infections are not available for home use.
Foliar nematodes can be treated with Insecticidal Soap and ZeroTol
(BioSafe Systems). This reduces levels of A. fragariae in leaves
and soil by 70% after 45 days. Insecticidal Soap is used by many
gardeners to control insects like aphids and spider mites. ZeroTol
is a fungicide used to disinfect greenhouses. The active ingredient
is Hydrogen Dioxide. The main drawback is it is toxic to birds,
fish, honeybees and other beneficial insects.
If you've had foliar nematodes the previous year, it's good to give the hostas a preventive treatment:
- Apply a 2% ZeroTol solution as a drench at the crown stage
- Spray 2% ZeroTol when the leaves emerge
- Repeat the spray application 2 to 3 times at weekly intervals, no more.
When symptoms start to (re)appear during the growing season:
- Apply ZeroTol daily for three consecutive days.
- This application may be repeated once a month if new symptoms continue to appear.
- A 1.5% concentration of insecticidal soap can be used in place of the ZeroTol as both a soil drench and foliar application.”
Is currently being developed.
Only purchase disease free plants
- This may seem like a simple advice, but it's hard to live up to it, because the symptoms show late in the season, and most hostas are purchased earlier in the year.
- This not only goes for hostas, but for all garden plants you acquire.
Deer can eat all your hosta plants in one evening, leaving just the stalks standing.
There's only one deer-proof solution to this problem, and that's keeping them out. And this requires extremely high fencing, guarded by guard dogs.
All other solutions (deer repellant, a bitter-tasting chemical that is sprayed on the leaves; predator urine; ...) may have some results, but they have to be re-applied after several rainfalls and will not deter a really hungry deer.