Although hostas are usually not affected by diseases that inflict other plants, snails and slugs can cause considerable damage to these plants. However, as the conditions in different gardens vary greatly as the population of the hostas, it has often been found that some plants are almost never affected by these pests. While there are several remedies to this problem, our understanding of the situation suggests that it can be avoided best by watering the plants as well as the ground around the hostas with a liquid formulation known as metaldehyde during the beginning of spring, when the shoots just begin to emerge from the ground.
The timing of treating the plants with metaldehyde formulation is extremely vital, as early spring is the time when snails and slugs come out of their hibernation. Moreover, for best results, you need to use this treatment once in a week or fortnight for about six to eight weeks. When you do this, you have successfully applied the fluid metaldehyde formulation to the developing as well as spreading leaves, which may be the hiding place for small slugs during the day time. When you begin the treatment early, it is effectual in wiping out the black keeled or little dark brown slugs that thrive just below the soil surface and are responsible for most of the initial damages to the tender hosta leaves. Once the slugs are successful in damaging the young leaves, the harms are usually noticeable throughout the remaining season.
Subsequently, gardeners may make use of slug pellets to get rid of the pest. As nearly all slug pellets contain a chemical compound that allures slugs, random or excessive use of the substance may worsen the problem further instead of resolving it. In fact, a very small amount of this chemical is present in the pellets and this is enough to eliminate a slug. Hence, you do not require too many pellets to get rid of the slugs in your garden. The ideal way to deal with the problem is tracing the hiding places of the slugs during the daytime and scattering the pellets in moderation as well as very carefully in those places. Usually, slugs have a preference for cool, moist places for hiding. Many a times, you may find them hiding in the gutter located between a lawn and a border in your garden. Scattering just some pellets in the trench or drain will prove to be more effective compared to pouring a dense circle of pellets in the region of hostas. However, it is important to apply the pellets on a regular basis because they remain effective just for three to four days. Moreover, it has been found that the slug pellets are most effective when you apply them following a rain as well in moist and clammy conditions when the slugs are usually very vigorous.
Typically, pellets either enclose methiocarb or metaldehyde. Although it has been found that methiocarb is more effective compared to metaldehyde, many gardeners prefer to use both alternatively. It is important to note that as far as humans are concerned, both these chemicals are extremely poisonous and, therefore, they need to be used with great care. In addition to these two varieties of slug pellets, there are others that contain aluminium sulphate. Although aluminium sulphate pellets are more environment friendly, they are not as effective as metaldehyde or methiocarb pellets in eliminating snails and slugs. Normally, pellets come in blue color, as it is believed that birds are unable to see this color. In case you have pets at home and are apprehensive that they may consume the pellets, you should place them in the middle of little clay land drains, underneath a slate sheet or plastic guttering with a view to prevent the pets from reaching the pellets easily.
However, there is an alternative method of controlling slugs and it is much cheaper as well as more effective. This method involves going around your garden with a bucket full of saline water during the dusk, when you can scoop up hundreds of slugs very soon, particularly after rain. Several gardeners also make use of slug pubs, crushed eggshells, grapefruit halves turned upside down and several other traditional remedies to get rid of these pests. However, employing these methods does not help to enhance the attraction of your garden.
Of late, a new and biological substance that helps to control slugs is available in the market. It is called a nematode, which is particularly meant for controlling slugs and has no affect whatsoever on snails. The nematode is mixed in water and the then the water is applied to the ground in the region of the hostas using a watering can. Subsequently, the nematode thrives as a parasite on slug that is exposed to the biological control; reproduces inside the body of the slug and eventually kills the pest. In addition, it infects all other slugs that try to eat the deceased slug.
There is another alternative or corresponding method of controlling snails and slugs in your garden. This method involves understanding the role of these organisms in the environment and not creating an environment in your garden or in the place where you are growing hostas with a view to prevent these pests from prospering. Slugs and snails have a vital role in clearing the environment of decomposed vegetation. In the absence of snails and slugs, decaying garbage would soon inundate your garden. You may prevent these pests from hiding in your garden provided you regularly clear all the drying leaves as well as other rubbish like stones and old bricks from the backyard. Actually, these not only provide an ideal hiding place to the slugs and snails, but also serve as perfect breeding ground for these pests.
Moreover, you should ensure that you remove the hostas leaves as well as those of other plants in the region immediately when they start turning yellow or begin to show any sign of mouldering. However, doing this may pose a problem for gardeners who prefer to use these organic substances for mulching their hostas. In fact, there is no doubt that mulching the hostas with these substances helps to retain the moisture of the soil at the base of the plants and also encourage them to grow healthily. At the same time, you need to keep in mind that mulching hostas with such organic substances also provide a calm and moist place for the snails and slugs to hide and thrive. Cultivating the borders on a regular basis and thoroughly will help to bring the slugs as well as their eggs to their natural killers, but if you adopt this procedure, you will have to do away with using mulch.
You can control the damages done by snails and slugs more easily if you are growing hostas in containers and pots compared to cultivating them in open gardens. These pots and containers should never be placed directly on the ground, as the soil underneath them will be cool as well as moist, providing these pests with a perfect habitat and encouraging their multiplication. It is advisable that rather than placing the pots directly on the ground, you put them on a raised platform roughly 4 cm (1 1/2 inches) above the soil using small feet, broken tiles or broken bricks. If you are able to achieve this and if the foliage of one hosta does not come in contact with the foliage of another plant, they will be able to pass through the entire season without any damage by slugs and hostas. However, you may be required to take additional measures to ensure this. In this case, hiding the slug pellets in the form of a ring encircling the pot will be effective in preventing damage to the plants. Nevertheless, you should place the pellets in such a manner that the pets cannot find them. If you smear a thin strip of fruit tree grease or petroleum jelly roughly 4 cm (1 1/2 inches) wide in a circular manner somewhat between the top and base of the pots it will go a long way in preventing the slugs and snails from climbing up to the hosta.
The ability of the hostas to defend themselves against damages caused by snails and slug differs greatly. Hosta varieties like H. "Green Sheen" and H. "Sum and Substance", which have comparatively thicker leaves, suffer less damage due to these pests. On the other hand, hostas having slender leaves, like H. sieboldii and H. "Undulata", suffer major damages from slugs and snails.
Actual damage to the hostas is done by the vine weevil larvae, also called grubs, which eat up the roots of the plant. The shape of the vine weevil larvae is similar to the alphabet "C". They are fat and have a creamy-ivory color, while their length is half of that of a thumbnail. You should essentially destroy them immediately when you notice these pests. These grubs can be crushed easily under your foot. Interestingly enough, goldfish find these larvae delectable. The adult pests or sluggishly moving beetles consume the leaf edges, leaving behind typical indentations. You can control the adult pests by using organophosphates (a variety of organic compounds containing phosphorus and having strong neurotoxic activities). However, it is more important to obliterate these grubs altogether. Currently, a parasitic nematode, which is basically a biological control, is available and this substance is extremely effectual. Similar to using the slug nematode, this control is also applied using a watering can.
In fact, vine weevils create more problems for hostas grown in containers than those grown in the open garden. Nevertheless, they can also be a major problem for hostas grown in marshy soil or soils that lack a proper drainage system. The vine weevils have a propensity to swarm the containers or pots, which contain the same compost for more than a year. Therefore, you may control these pests to some extent by repotting the plants once in a year.
Provided hostas are cultivated in favourable conditions, they are generally free from diseases. However, they may still be troubled by some diseases that may occur from time to time. Usually, the plants are initially affected by viruses and the viral infection generally develops into a yellow mosaic seen on the surface of the leaves. The major as well as minor veins of the plant turn yellow and occasionally the infection is obvious in the form of yellow blemishes on the leaves. Sometimes the entire surface of the leaf also becomes yellow, often dwarfing as well as congesting the growth of the leaves. Tobacco rattle virus and arabis mosaic virus are the two viruses that affect the hostas. Usually these viruses are transmitted through aphids or when you divide the hostas using garden tools that have already been used on some infected plants. The leaves of the infected hostas manifest chromosome or mineral deficiency in the form of blemishes or mottling. Occasionally, people mistake these signs to be virus infections.
As such virus infections are not curable, it is advised that you dig up the affected hostas and burn them immediately so that the infection does not spread to healthy plants. While the H. "Tardiflora", H. "Sea Sprite" and H. "Crispula" are the hosta varieties that are most commonly affected by the above mentioned viruses, even plants producing glaucous blue leaves are prone to such virus infections.
Apart from virus infections, hostas are also affected by a disease known as crown rot. Only hostas growing in warm climatic conditions or under glass are affected by this condition. However, sometimes this disease may occur when the growing media is excessively compact. When a hosta is affected by this disease the leaves of the plant turn yellow and eventually drop to the ground from the rootstock. In such cases you need to dig up the affected plant, separate the diseased parts and throw them away or burn them, keeping only the healthy and firm pieces. As crown rot occurs due to infections by fungi, it is essential to immerse the healthy parts in a fungicidal solution prior to potting them again.
There is another disease that causes problems to people growing hostas. This condition is known as leaf spot and it is attributed to three fungi - Colletotrichum omnivorum, Alternaria and Plyllostricta. You can treat leaf spot by spraying the affected leaves with fungicides called Thiram or Benomyl twice or thrice every fortnight.
Wrong use of synthetic garden sprays as well as various air-borne contaminants may also cause leaf spots in hostas. Sometimes brown spots of the size of a pinhead are evident on hosta leaves either during the end of spring or beginning of summer. Such spots are usually attributed to the bursting of leaf cells owing to mild frosts that occur occasionally after the leaves have opened out. This type of leaf damage is not noticeable immediately. Damage due to frosts can also change the color of the leaves to brown. Another condition, known as leaf scorch, also affects the hosta leaves. Although this condition, somewhat akin to leaf spotting, is not harmful, it does make the leaves appear ugly. This condition is attributed to drops of cold water that fall on the leaves that grow in very bright sunlight.