If gardens weren't full of insects, gardeners would have to pollinate flowers by hand for every fruit, vegetable and seed they wanted to harvest. In addition to pollinators, the garden contains bugs that are beneficial, threatening and plain old nuisances. Although one of the most pest-free plants in the garden, the lily hosts some bugs from each type.
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Nuisance --- Aphids, Whiteflies and Thrips
Lilies attract the usual nuisance insects. The aphid, a tiny green or brown insect with a soft, watery-looking oval body, is the most common. Two long tubes, called cornicles, trail behind aphids, depositing a waste, called honeydew, as they suck out the carbohydrates and nutrients that travel in the plant's vascular system. Aphids reproduce rapidly, forming colonies on leaves and stems. Large colonies leave stunted leaves and shrivelled flower buds in their wake but aphids do not often pose more than a nuisance.
A sharp stream of water or treatment with insecticidal soap dislodges aphids. Other possible sapsuckers, whiteflies and lily thrips, (Liothrips vaneeckii) may enter the lily patch on greenhouse-grown plants but seldom rise to nuisance levels out of doors.
Nuisance -- Mites and Bulb Flies
Two types of mites chew on lilies above and below the soil level. Tiny spider mites form colonies under leaves and larger bulb mites attack weakened or infected bulbs. Spider mites (Tetranychus spp.) may appear as red or brown dots encased in webbing as they work under leaves, sheltered from rain and wind.
In areas where winter brings freezing temperatures, they spend the winter in the bark of neighbouring trees. Controls include water and insecticidal soap for these nuisance bugs. Bulb mites (Rhizognyphus echinopus) are cream-coloured "secondary" pests that only target tissue that is already damaged. By the time bulb mites set in, a bulb is too compromised to produce healthy plants. Lesser bulb flies (Eumerus spp.) attack compromised bulb tissue as well.
Dangerous Bad Bugs
Lilies host one insect that threatens them whenever it lands. The lily leaf beetle (Lilioceris lilii), first sighted in the Northeastern U.S. in the early 1990s, eats lily leaves and buds both as immature larvae and as adults. Adults are bright orange-red and consume leaves quickly, according to the University of Massachusetts, sometimes leaving only the stalk.
Neem has been found effective against young populations but gardeners should hand-pick any of these aggressive and dangerous pests as soon as they spot them. Chemical controls for adult infestations containing imidacloprid are under study. The lily weevil (Agasphaerops nigra) affects West Coast lilies, consuming stems and laying eggs in them. Imidacloprid-containing systemic controls manage weevils.
Several common garden insects eat aphids, mites and more but no natural enemy has been found for the lily leaf beetle. Green lacewings and parasitic wasps both gobble up aphids. Both beneficial insects are sold by garden supply companies. American hover flies (Eupeodes americanus) are common in American gardens; they pollinate ornamentals including lilies and eat aphids.
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- University of California Extension; Pests in Gardens and Landscapes
- University of Vermont Extension; Aphids; G.B. MacCollom; 1997
- University of Massachusetts Extension; Lily Leaf Beetle; Tina M. Smith; 2009
- The Lily Flower Store; Common Lily Pests; Kenn Parry
- University of Maryland Extension; Production of Hybrid Lilies as Cut Flowers; Stanton Gill, et al.; 2006
- Bug Guide: Eupeodes americanus - American Hover Fly