Leaf beetles

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(HOST) Now that the leaves are out, so are the critters that like to nibble on them. Commmentator Charlie Nardozzi has some advice for dealing with two exotic leaf beetles.

(NARDOZZI) I’m a big advocate of growing native and well-adapted plants in the landscape. Not only are they tailored for our climate, most have few insect problems. Well, just when I thought I had Nature figured out, she throws me a curve ball. Two plants that I thought of as being relatively pest-free are under attack by exotic leaf beetles.

Viburnums are great, trouble-free landscape shrubs. Depending on the variety, they grow from three to ten feet tall and produce flow- ers in summer and colorful berries in fall that birds love. Some, such as the Korean spice viburnum, are extremely fragrant as well. Viburnum can be planted in mixed flower borders, as a hedge and as a specimen shrub in the lawn.

However, these shrubs are being attacked by the viburnum leaf beetle. This European native has been established in Canada for years and now is making its way into the Northeast United States. Last year, there were many reports in Vermont of viburnum plants being defoliated by the beetle, and gardeners are seeing damage again this year.

Eggs laid the previous summer hatch in May. The one-half-inch long, light brown colored caterpillar-like larvae feed on viburnum leaves until the end of June. Then they crawl to the ground and pupate. Adult flies emerge in July to feed on leaves, mate and lay eggs on viburnum twigs. The eggs look like slight brown bumps on the viburnum branches.

Not all viburnum species are susceptible to the leaf beetle. The Korean spice viburnum, Viburnum juddii and the double-file viburnum are resistant. However, the leaf beetle loves the Amer- ican cranberry, European cranberry and Arrowwood viburnums. To control this pest, spray pyrethrum in May and June to kill the larvae and again in late summer to deter the adults. Prune off twigs with the egg bumps in late summer to reduce next year’s population.

Another beetle that’s made its way to Vermont is the lily leaf beetle. It attacks the Asiatic, Oriental and other lilium family bulbs, but doesn’t attack daylilies. This pest was first reported in Massachusetts in the 1920s and has slowly migrated throughout New England.

The one-half-inch long, bright red colored adult beetle emerges in April and May to feed and mate. They lay reddish-brown eggs on the underside of lily leaves. The slug-like larvae feed on the leaves and flower buds for three to four weeks, after which they pupate. Adults emerge in late summer to continue the life cycle. If only a small number of lilies are affected, just handpick and destroy the adult beetles. For more severe infestations, spray neem oil on the larvae to kill them.

With a little diligence and observation, you can keep your viburnums and lilies free from these new pests this summer.

This is Charlie Nardozzi in Shelburne.

Charlie Nardozzi is an all-around gardening expert with a special fondness for tomatoes and roses.

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