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On a recent garden tour, I noticed several boxwoods in a relatively newly planted garden showed signs of leaf distortion on some branches. The leaves on the branch tips were cupped, but showed no sign of insects or surface damage when viewed through my 10 power lens — a valuable piece of swag I picked up at a trade show.

A professional grower on the tour identified the leaf cupping as damage from the boxwood psyllid (Psylla buxi) that the Missouri Botanical Garden says is the most common insect pest of Buxus sempervirens, but they report all boxwoods are susceptible.

The damage from these insects is caused by piercing and sucking sap from the buds and young leaves of the plants that results in the cupping of the leaves. This takes place when the insects are in the nymph stage. The weakened leaves usually fall off after a year or so, and terminal growth may be affected a year or so later.

The psyllids hatch and begin feeding in spring and at that time they will be visible inside the cupped leaves. Another sign of attack is the waxy filaments and secretions these insects produce. This gunky stuff forms a shield that protects them as they mature into adults.

To control these insects, be aware of their life cycle and take action at the right time. The knee-jerk reaction is to break out the insecticide and spray away whenever damage is discovered. To do so now would be a waste of time because the boxwood psyllid hatches and does its dastardly deed of feeding in the nymph stage in early spring when new growth emerges. So that is the time the plants can be effectively treated and protected from damage.

The Missouri Botanical Garden’s website at missouribotanicalgarden.org (search for boxwood pests) gives an excellent explanation and photos of this insect, the damage it causes and various methods of control including OMRI listed products. The mature insects lay their eggs on the branches between the leaves at the tips of the plants, so clipping off the cupped tips is another method of damage control.

According to the Missouri Botanical Garden, treatment time for these insects is around the beginning of May. However, we are further north where our growing season begins later and in today’s ever-changing climate we can no longer pinpoint time sensitive projects on the calendar. So I suggest if you see cupping of the leaves on your boxwood keep an eye on them next spring and be ready to act when you see new growth emerge.

Nancy Szerlag is a master gardener and a Metro Detroit freelance writer. Her column appears Fridays in Homestyle. To ask her a question go to Yardener.com and click on Ask Nancy. Read previous columns at detroitnews.com/homestyle.

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