Pests and the Guara Perennial

White blooms floating above grass-thin stems like hordes of dainty butterflies make perennial guara (Guara lindheimeri), commonly known as wandflower, a garden mainstay in U.S. Department of Agriculture plant hardiness zones 6 through 9. The showy blossoms of the 3- to 6-foot sun-lover appear from late spring until fall, deepening to pink as they age. A couple of leaf-feeding pests join friendly nectar-collecting bees and hummingbirds in flocking to these graceful ornamentals.

A few tiny, soft pear-shaped aphids pose no threat by draining the nutritious sap from a wandflower's stems and foliage. As the yellow, green, red, brown or black pests multiply, however, their feeding wilts the plants, yellows their foliage and often leads to shoot dieback. During mild weather, individual females of many aphid species produce a dozen live offspring each day, and each of these larvae has the potential to reproduce asexually a week later. The expanding colonies remain attached to the stems and leaf undersides until their sheer numbers force winged adults to migrate to less crowded hosts. Aphids also cover the wandflowers with a transparent, gooey substance called honeydew. Wind-carried sooty mold fungi attracted to this sticky excrement disfigure the plants with unsightly layers of black mold.

With regular inspection, you may halt aphids when their numbers are low enough to control by pruning the affected leaves from your wandflower without damaging its appearance. For larger populations, blasting the stems and leaves with a strong blast of water with the garden hose may suffice. Treat particularly stubborn infestations with a spray containing 5 tablespoons of detergent-free liquid soap in 1 gallon of water, aimed directly at the pest colonies. The insecticidal soap kills only the insects it reaches, so reapplying it once or twice over the next few days ensures minimal survival. Spraying on a cloudy day and rinsing the plants with water after a few hours protects them from sun damage.

Wandflowers share their evening primrose (Onagraceae) family's vulnerability to flea beetles. In their case, the culprit is the apple flea beetle (Altica foliaceae LeConte), a shiny, green to blue-green 1/6-inch insect. Thanks to its long, spring-coiled hind legs, this pest avoids trouble by jumping like a flea. The winged adults overwinter beneath leaves, emerging in spring to feed on foliage and lay their orange eggs. Their black larvae chew telltale grooves on the backs of the leaves before dropping to the soil to pupate and mature over the next two weeks. Serious flea beetle infestations may come close to defoliating their hosts.

To practice nontoxic flea-beetle removal, place an open jar partially filled with beer near your wandflowers to lure and drown the pests. For a chemical solution, spray your plants with a solution of between 3 and 5 tablespoons of beetle-paralyzing pyrethrin insecticide concentrate and 1 gallon of water, saturating both sides of the leaves to the runoff point. Avoid exposure to the chemical with protective clothing and eyewear.