Hostas Unhealthy: Are they saying “Hosta La Vista”?

(Question)

I’ve attached a picture from the top view of the front yard hostas, which appear to be perforated with holes from some insect, probably. I may have to transplant them during a renovation before winter, but I may not. Please comment on their health, and the method of transplanting them.

 

 

 

 

 

(Answer)

Thank you for providing this picture. You are correct in speculating that the holes in the leaves are caused by an insect, as hostas can be attacked by slugs, snails and other chewing insects such as black vine weevils. It is important to identify the pest you are dealing with before you take action. Try to get a close enough look to make certain if you can.  If you notice silvery trails leading along your paths and under the plants the most likely culprit will be slugs or snails.  If the leaves have notching wounds along the leaf margin then the culprit may be the black vine weevil. The black vine weevil adult is dark gray or black snout beetles, about 1/2 inch long with wing covers marked with gold flecking.  They spend the winter usually as larvae, in the soil around the root zone of the plants on which they feed. The females lay eggs around the base of plants. Eggs hatch midsummer, and the legless larvae feed on plant roots until cold weather temporarily stops development.

All of these pests are more active at night and prefer warm, moist conditions.

Your best chance of catching slugs and snails in the act is just after rain. If you find snails, throwing them over the garden fence will not help to get rid of them as researchers believe that snails have a strong homing instinct and will do their best to get back to the garden they originated from!

Although not looking as handsome as they could do, your hostas can survive these attacks with a little help from you. There are many remedies to deter slugs and snails, these include organic approaches such as handpicking (go out at night with a flashlight, wear gloves if you do not like the slimy feel! and drop them into a pail of salty water). There are special slug traps sold at garden centres that you could consider or buy some copper tape, slugs and snails do not like crossing it . This would be a good solution if you have to transplant your hostas and store them in containers because you could wrap a length of copper tape around the containers. In fact if you are persistently bothered by slugs, growing your hostas in containers would be a good way to go. Another option is diatomaceous earth, coffee grounds, salt, wood ash, or crushed up eggshells sprinkled around the base of the plants.

There are some slug baits available. Avoid those containing metaldehyde, which can cause kidney damage in kids and pets. Varieties containing iron phosphate are less harmful. Also remember that birds dine on slugs, and will ingest the poison too.

If you suspect black vine weevils keep the soil clear of debris and litter, which offers hiding places for adult female insects. Cover the soil or compost with a layer of grit to deter egg laying. You could also treat the soil around the susceptible plants with parasitic nematodes (Heterorhabditis megidis and Steinernema carpocapsae), which parasitize and kill the pest. If you choose to grow your hostas in containers avoid crocking the base and also keep the soil clear of debris.

With regard to transplanting your hostas you can do this ideally in spring or summer as fleshy rooted perennials need time to make new roots before winter sets in. If and when you transplant you could take advantage of this opportunity to divide them if you wish. Large hostas with tough rootstocks should be divided using a spade. Include several buds on each division and trim any damaged parts with a knife. If your hostas have looser, fleshy rootstocks you may be able to separate them by hand or with back-to-back forks and again each division should have at least one eye.

Looking ahead, if you want to add to your hosta collection keep a look out for slug resistant varieties. Encouraging birds to visit your garden would be a useful (and enjoyable) strategy also.

Good luck with your hostas!