How Does One Kill Ladybugs on Lilies?

Appearing in a stunning range of colors and sizes, lilies (Lilium spp.) brighten gardens and borders in U.S. Department of Agriculture plant hardiness zones 3 through 10, depending on species. These tough perennial plants emerge yearly from freeze-resistant bulbs, bringing low-care fragrance into the landscape. If you spot ladybugs crawling on your lilies, this isn't cause for alarm -- the ladybugs are most likely there because aphids are quietly feeding on your plants.

Ladybugs are a gardener's best friend, voraciously destroying pest insects wherever they go. Although ladybugs have been known to feed on nectar, they prefer soft-bodied aphids, a common pest of lilies. Ladybug larvae can consume up to 400 aphids before pupating and another 300 before they lay their eggs -- in a lifetime, a single ladybug can consume up to 5,000 aphids. For this reason alone, ladybugs are considered a beneficial insect and control is not recommended. If you want to banish ladybugs from your garden, your best bet is to destroy the aphids they're eating.

A single ladybug sighting might just be an insect that's passing through, but if several ladybugs are congregating on your lilies, you should check them carefully for aphids. Look for tiny, pear-shaped insects feeding in groups on the undersides of leaves and inside blooms. Lilies host a variety of aphids, so these pests can be any color from nearly clear to black and shiny -- some may even have wings. Look for a clear, sticky fluid below feeding sites -- this honeydew is a byproduct of the aphids' aggressive feeding. As aphid colonies expand, the feeding pressure causes leaves to yellow, curl or drop -- if your lily foliage is damaged, blame the aphids and not the ladybugs.

Aphids growing on widely spaced lilies can be blown from the plants with a garden hose, but if your plants are tightly spaced, do this with care because it may just spread aphids to other lilies. Some gardeners simply cut out heavily infested sections of plants and destroy or double-bag them immediately, eliminating significant numbers of pests at once. Always apply fertilizer carefully to discourage aphid feeding -- they prefer the new, succulent growth that may be exaggerated by excessive nitrogen.

Aphids that aren't controlled well without chemicals respond to weekly sprays of insecticidal soaps or horticultural oils. These safer insecticides preserve beneficial insects like ladybugs by killing on contact, leaving plant surfaces safe to any bugs not directly sprayed. Before using horticultural oils or insecticidal soaps, test a small, inconspicuous area on each lily plant's foliage at least 48 hours prior to treatment for signs of phytotoxic reactions. If the test area yellows, dries up or appears brown or tan, erect a shade cloth to protect your plants from the sun before spraying your lilies; make sure to leave the shade in place until the chemical is completely dry.