Hostas have fewer insect and pest problems than many ornamental plants in the garden. They are an easy-to-grow, perennial shade plant known for its beautiful foliage. Leaves are solid or variegated in color combinations of blue, green, white and gold. Over 2,500 varieties are available. Despite their hardiness, though, insects such as the black vine weevil and foliar nematodes are known to occasionally infect hostas.
Symptoms of an infestation of the black vine weevil include yellowing, wilting and irregular notches chewed from the leaf edge. The weevil larvae that feed on the crown and roots do the most damage to the plant. Black vine weevils are similar to grubs. They are ¼-inch long, off-white with a brown head, and are slightly "C"-shaped.
A brown streak appears on the leaf vines in July or August when hosta plants are infested with foliar nematodes. They are microscopic-size worms that infect the leaves. Nematodes stay in the ground in winter and move to hosta leaves when the weather warms. They feed between the leaf veins. Symptoms typically show up in older leaves first.
Slugs and snails are the most common problem for hostas. They are nocturnal, making them difficult to eradicate. Slugs and snails eat small, round holes in the leaves. They leave slimy silver-colored trails on the plants. Thin-leafed hostas, or those with leaves growing close to the ground, are the most susceptible to these pests.
Slugs and snails may be hand-picked off plants in the daytime by using a flashlight. Common snail abatement methods are to put a wet newspaper over the ground at night to catch them, or put out saucers of beer--slugs crawl in and drown. Some types of leaf-cutter bees also chew holes in hosta leaves.
Leaves chewed at the edges may be the result of squirrels, voles, rabbits or deer rather than insect damage. Deer are likely to eat the entire plant. Some gardeners use bitter tasting sprays to deter deer, but they need to be re-applied after rainfall. Voles eat the roots of hostas and occasionally kill the entire plant.
The "Hosta Virus X" first appeared in 1996 on plants in large nurseries. The virus causes mottling, twisting and stunting of leaves. These can appear to be insect problems. Ring spots or small yellow dots on the leaves are also indications that a virus has infected the plant. Symptoms can take up to 3 years to appear. If plants show these symptoms they should be dug up and thrown away. Clean and disinfect garden tools used on these plants.