[Baltimore Sun] Garden Q&A: What’s the best way to manage Japanese beetles?
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Q: Japanese beetles have been ravaging my yard. I heard Milky Spore can be a natural way to treat them. Is that right?
A: Japanese beetle grubs feed underground on plant roots, and the adults feed on foliage and flower petals on perennials, shrubs, and trees. Only one of those two life stages may pose a problem for a gardener while the other does not, so you won’t necessarily have to tackle both. In fact, a lot of lawn grub treatments are unnecessary, because any grubs encountered are not abundant enough to create noticeable lawn damage, or someone mistakenly blamed grubs for turf dieback caused by other factors.
Milky Spore, the product name for a biological control agent for Japanese beetle grubs, is a naturally occurring bacteria that infects the grubs and kills them. Unfortunately, University of Maryland field trials have found it is not reliably effective. Microbial levels might require several years of build-up from annual applications of the product to reach populations sufficient to reduce grub numbers, which can be costly.
You do have other options; the adults of this species won’t be out for a month or so. Beneficial nematodes can be applied to a lawn where white grubs feed, which will infect them with deadly parasites.
Lower-toxicity insecticides can be used as a last resort, though check with local government rules about applications to turf since some areas restrict pesticide use on home lawns. It may be best (or necessary, for certain ingredients) to hire a certified pesticide applicator to make such treatments.
Residents who have a lawn dominated by tall fescue will rarely have serious Japanese beetle grub issues because this is not the turf type they prefer. (Kentucky bluegrass, fine fescue, and perennial ryegrass are those at risk.)
Adult beetles are simpler to deal with. Simply hand-picking them off of shrubs is an immediately effective tactic. These beetles like to congregate, so removing them in the morning, before they can produce a waft of aggregation pheromone to attract others to the banquet, will reduce the plant’s risk of damage.
Don’t worry too much if damage sneaks up on you: even heavily chewed shrubs may surprise you by rebounding well on their own, once the adult beetle activity has ended later in the summer. More information about their life cycle and management options can be found on our White Grub Management on Lawns and Japanese Beetles on Trees, Shrubs, and Flowers pages.
Q: I received some flower bulbs (gladiolus) from a memorial event and have never grown summer-flowering bulbs. Do I plant them now?
A: Yes, May air temperatures should be frost-free enough and the soil temperatures high enough (55 degrees or warmer) to plant now for most of the state. If you stagger plantings by a week or so, you can get a longer season of bloom by having some plants come into flower before others, especially if you want a more steady supply of stems for bouquet use.
Choose a site in full sun with well-drained soil for best growth and flowering. Plant corms (the bulb-like structure of gladiolus) about 4 to 6 inches deep, with the more pointed end of the corm facing up (roots grow from the blunt end). The plants might need staking as they mature since some varieties can get quite tall. Blooms should appear around two months after planting. If new plants don’t bloom and are receiving full sun, they might be too young (small corms) and need a season of growth to mature.
These are tender perennials, which means they can live for several years if protected from freezes. The hardiness zone of commonly grown gladiolus varieties is such that they might survive Maryland winters if left in the ground in central and shore counties. Otherwise, it might be safer to assume they need added protection.
Bulbs can be dug up at the end of the growing season and stored indoors until next spring. Come autumn, let a frost kill the foliage, if it hasn’t yellowed and withered already, cut off most of the old leaves, and dig up the corm(s). Store the dormant corms in a cool, dry spot and replant next May.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.
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