Hostas: the 10 most common diseases and pests

Initially punctiform and later up to five millimeters large leaf spots can indicate leaf spot disease. The brown or reddish-brown spots are roundish or oval and appear on the entire leaf blade and on the leaf margin. You are surrounded by a bright courtyard. Its interior is lighter, dries up and cracks open. An infestation is favored by damp weather conditions and temperatures above 20 degrees. Corresponding damage occurs around May.

combat

• Treat infestation as early as possible
• Remove all affected leaves
• Also leaves and plant debris that have fallen off in autumn
• Dispose of in the household waste, not on the compost
• Preventively strengthen particularly susceptible plants when they sprout
• Treat with herbal products in spring

chlorosis

One of the most common diseases of hostas is chlorosis. It is manifested by yellowing of the leaves, with the exception of the leaf veins. Causes can be soil that is too calcareous or heavily compacted, but also the use of immature compost. A good soil preparation, the loosening of the subsoil and a humus-friendly soil care can help.

Drawstring Effect

With the so-called drawstring effect, the green part in the center of the leaf grows faster than the edge of the leaf. The result is a curling, warping or splintering and tearing of the sheets. This phenomenon does not occur with all types of hostas, but mostly with white-edged ones. Since it can recur every year, it is advisable to remove affected plants and avoid particularly susceptible varieties as a preventive measure.

Grauschimmel (Botrytis)

One of the diseases that can endanger hostas is gray mold, caused by botrytis, a putrefaction pathogen with a particularly high risk potential. Plants whose plant tissues are weakened are mainly affected. Plants that are too dense and excessive nitrogen fertilization also promote infestation. Too much nitrogen softens hosta plant tissue and makes it more susceptible to disease.

symptoms and countermeasures

• Brown, later rotting leaf spots
• Late grey, furry moldy lawn
• Severely affected plants die
• Remove and discard infected parts or entire plant
• Also lying on the ground
• Fungus overwinters on dead plant parts on the ground
• In the future, pay attention to location and fertilization

nutrient deficiency

Yellow streaks on the leaves can be a sign of nutrient deficiency. There is usually a magnesium deficiency. It can be the result of too low or too high a pH value. In both cases, the hosta cannot absorb magnesium, although it is present in the soil. It needs a neutral to slightly acidic pH. If there is a magnesium deficiency, it can be remedied with magnesium fertilizer (Epsom salt).

snails

Slugs are very voracious pests, especially nudibranchs . Hostas are practically their favorite food. The red and Spanish slugs can cause particularly great damage. In very humid weather, they can eat plants bare in a very short time. These pests are more common in spring. Various biological means can be used to combat it. Chemicals should be avoided if possible.

biological control

Collect

The simplest but also the most unpleasant method is the consistent collection. Due to the nocturnal activity of these pests, dusk and dawn are the best times to do so. It is particularly effective in damp weather or after heavy rainfall.

Use treats

A suitable lure is the marigold (tagetes), which magically attracts these pests. They are best used for border planting. A good bait should be a mixture of moistened dry dog ​​or cat food and wheat bran. Of course, the bait has to be collected regularly, otherwise there will soon be more snails than before. Coffee grounds mixed with some sand are also said to be an effective attractant.

Set up beer traps

One often reads that beer traps should help against snails. You sink a small vessel into the ground and fill it with beer. The snails are attracted by the smell, fall into the jar and drown. However, the smell of beer is also irresistible to snails from the area and attracts them.

Organic slug pellets

Organic slug pellets are the ecological alternative to conventional chemical slug pellets. It is ideally applied to moist soil. This is how the small pellets swell up and become even more attractive for the slime. After ingesting the remedy, they retreat to their lair, where they perish. They don’t defecate.

floor care

Good and regular tillage can keep snails away. It gives the soil a crumbly structure and thus offers fewer places to retreat. Mulch should only be applied in a thin layer. It should also contain a high proportion of strongly scented herbs such as peppermint, oregano, lovage or tomato leaves. Conventional bark mulch is less suitable.

Settle natural predators

A very good support in the fight against slugs are natural predators. These include hedgehogs, moles and shrews as well as predatory beetles and spiders. They feel particularly comfortable in a natural garden, because it offers sufficient living space. In such a garden, trees for feeding and protecting birds, areas with stones, wood or foliage, dry stone walls or a garden pond can be integrated.

Not every variety is susceptible to snails

Hostas with fragrant flowers are particularly popular with slugs. Their leaves are high in sugar, making them a treat for snails. The bluish varieties, on the other hand, are largely spared thanks to their wax-coated leaves. Other varieties with firm, leathery leaves are also mostly spared. These include ‘Snowden’, ‘Regal Splendor’, ‘Sum and Substance’, ‘Ben Vernooij’, ‘Halcyon’ and ‘June’.

vine weevil

The vine weevil also causes leaf damage. This nocturnal beetle sits on the edge of leaves where it leaves semi-circular feeding tracks. Its larvae are much more dangerous. They live in the root area, where they eat the important fine roots. This in turn can lead to an infection with soil fungi and thus to further diseases of hostas.

To protect against these pests, you can place a flower pot filled with wood shavings upside down at the infested site. The bugs hide in the wood shavings during the day so you can collect them. Another effective means of control are nematodes of the genus Heterorhabditis, which are spread over the irrigation water.

Nematodes – leaflets

In addition to useful nematodes, there are also harmful ones, such as aphids. They penetrate the leaf tissue through wounds. Shortly thereafter, elongated, glassy spots appear there, which later turn brown to black. When an infestation begins, it may be sufficient to remove affected leaves. If it is already advanced, the hosta must be dug up and disposed of.

virus problem

Many diseases in hostas are caused by viruses, which generally cannot be combated directly. You can only prevent spread by completely disposing of diseased perennials. An accurate diagnosis is often only possible under laboratory conditions. Hosta virus (HVX) and tomato ring spot virus are particularly worth mentioning in hostas.

Hosta-Virus (HVX)

This virus is a very special pathogen. An infection with this virus does not necessarily cause hostas to die, but it does cause pathological changes in the plants. The risk of spreading is low because it cannot be transmitted via pollen, insects or fungi as is normally the case. After a transmission, several years can pass before the first symptoms appear on the plant concerned.

symptoms

• The most common sign of infection is bleeding
• Heavily discolored tissue along a leaf vein
• Stands out from the surrounding tissue
• Green leaves show brightened areas
• Yellow and light green leaves have dark discolorations
• With a stronger infestation, discolored tissue collapses
• Possibly additional speckles or stains
• Then discard the hosta completely

transmission paths

The hosta virus (HVX) can be transmitted during vegetative propagation of infected plants or through the use of unsterilized tools. Another transmission route is maintenance, because transmission can also occur when cutting or transplanting if plant sap gets on hands or tools. Infection should also be possible if infected plant parts remain in the soil and healthy hostas are then planted there.

preventive measures

It is important to prevent the transfer of plant sap by disinfecting used tools and thoroughly cleaning hands. In addition, there are a few things to keep in mind when it comes to maintenance work.

• Do not cut off injured leaves, tear them off
• Leave leaves until they dry up
• When dividing, do not touch broken or cut surfaces
• Use only sufficiently sharp cutting tools
• When doing garden work such as mowing, do not injure hostas
• Completely dig up the infested hosta and dispose of it in the household waste

Tomato ring spot virus

This virus is primarily transmitted by thrips. These are animal pests that are often difficult to combat. An infestation can be recognized by yellow spots forming between the leaf veins. There are no bulges like the hosta virus. In the case of a mild infestation, remove all infested leaves. If it is already too late and the whole plant is affected, you should dispose of it.