Hostas are perennial landscaping plants known for their attractive foliage. Sometimes hosta leaves fall victim to insects and small pests. According to the University of Minnesota Extension, slugs are the most common hosta leaf chompers. Earwigs (long bodied insects with pincers), cutworms (small caterpillars that curl up), leaf beetles and grasshoppers also chew holes in hosta leaves. Foliar nematodes cannot be seen with the naked eye, but they may reek havoc on your hosta leaves, leaving yellow or tan vertical stripes in between the leaf veins, resulting in foliar death. Several methods exist for preventing and getting rid of these pests.
Remove any leaves or organic debris from your hosta flower bed in early spring. This action will eliminate material that slugs and earwigs like to spend time in during the day. If you must add mulch to prevent weeds from growing around your hostas, do not use wood chips or leaf matter. Instead only use two to three inches of pine straw, cocoa mulch or spruce needles, states Perfect Perennials.
Prune the lower branches of hostas if they become too dense or crowded with neighbouring plants because earwigs and slugs like to take refuge in sheltered areas.
Water the hostas in the morning, so that the soil is dry by evening, since nocturnal earwigs and slugs thrive in moist environments.
Set up traps for slugs, earwigs and cutworms at night. For slugs, fill a tin can with beer or a mixture of one tsp of yeast and three ounces of water. Place tin cans in the soil so that the top of the can is at the soil's surface. For earwigs, use moistened newspaper or a tin can filled with vegetable oil as a trap. For cutworms, place a mixture of equal parts of sawdust and bran onto a plastic tray. Pour molasses on top to create a sticky texture. Check traps every morning and remove all trapped pests.
Encourage birds to come into your yard, such as house wrens, that will keep cutworm, leaf beetle and grasshopper populations in check, says the American Hosta Society. Set up bird feeders and bird baths.
Prevent potential invasion of foliar nematodes by watering the soil around your hostas rather than getting water on the foliage, because foliar nematodes thrive on moist leaf surfaces.
Remove any leaves damaged by foliar nematodes that are marked by yellow or tan vertical stripes. Immediately destroy and dispose of the leaves.
Heat treat your entire hosta plant if it is severely infected by foliar nematodes. Dig up the plant. Heat up water to approximately 123 Fahrenheit and pour it in a large bucket or pot. Submerge the entire plant in the hot water bath for between four and eight minutes. Fill another bucket with cold water and submerge the plant in the cold bath after the hot bath. Replant the hosta immediately.
If you see cutworms or slugs on or near your plants, you can handpick them. Drown slugs in a soapy water and crush cutworms and dispose of them in a plastic bag. You can force the cutworms to the surface by adding a spoonful of dish soap to a watering can full of water and pouring it on the soil.
Use pesticides only as a last resort since the chemicals could kill natural insect predators that will prey on your hosta pests. Hostas do not always survive after a heat bath treatment, thus it should be used in extreme situations.
Tips and warnings
- If you see cutworms or slugs on or near your plants, you can handpick them. Drown slugs in a soapy water and crush cutworms and dispose of them in a plastic bag. You can force the cutworms to the surface by adding a spoonful of dish soap to a watering can full of water and pouring it on the soil.
- Use pesticides only as a last resort since the chemicals could kill natural insect predators that will prey on your hosta pests.
- Hostas do not always survive after a heat bath treatment, thus it should be used in extreme situations.
- University of Minnesota Extension: Hostas
- Iowa State University Extension: Hosta Diseases and Pests
- University of Minnesota Extension: Slugs in Home Gardens
- Perfect Perennials: All About Hostas
- The American Hosta Society: Cut Worms, Leaf Beetles and Grasshoppers
- The University of Wisconsin, Department of Entomology: Controlling Earwigs