As discussed on the previous page, the life cycle is short, perhaps only a few days in some cases. Since you would have to spray every 2 or 3 days over 2 weeks, we think this control strategy is futile.
The best control method would be a systemic insecticide applied just after the eggs hatch, around mid to late June in central Virginia. Since the larvae are alive, eating, and growing all during the summer and fall, we have found these systemic insecticides to be effective until temperatures turn cold, which in some years is not until Thanksgiving. When these chemicals are applied properly and thoroughly to all boxwood in a given area, you can expect control for up to 2-3 years to bring that population back up to noticeable levels.
The best products we have tried are those that contain the active ingredients imidacloprid, Thiomethoxam, or dinotefuran.
We advise any nurseryman or homeowner to contact a local full-service garden center or Extension personnel for recommendations. With any pesticide, read and follow the label.
Another strategy that Sounder Brother, Inc. is exploring is finding varieties that are resistant to boxwood leafminer. We have experimented with about 85 varieties over the years and have found moderate to good resistance in some cultivars. We continue to research new varieties and attempt to understand why some cultivars are more susceptible than others.
| Resistant* | Moderately Resistant* | Least Resistant* |
| ‘Franklin’s Gem’ | ‘Dee Runk’ | ‘Chicagoland Green*’ |
| ‘Grace H. Phillips’ | ‘Elegantissima’ | ‘Green Beauty’ |
| ‘Golden Dream’ | ‘Fastigiata’ | ‘Green Gem’ |
| ‘Green Pillow’ | ‘Jensen’ | ‘Green Mound’ |
| ‘Insularis Nana’ | ‘Jim Stauffer’ | ‘Green Mountain’ |
| ‘Morris Dwarf’ | ‘Morris Midget’ | ‘Green Velvet’ |
| ‘Suffruticos’ | ‘Rotundifolia’ | ‘John Baldwin’ |
| ‘Vardar Valley’ | Sempervirens | ‘Justin Brouwers’ |
| ‘Winter Gem’ | ||
| ‘Wintergreen’ |
The astute gardener should take into account many factors when choosing a boxwood cultivar for a particular application including varietal susceptibility if neighboring landscapes have high populations of leafminers or if he desires to minimize control measures.
Boxwood Psyllid
Boxwood Physllid occurs wherever boxwood is found. There is only one life cycle per year and the nymph emerges in mid-April or as new growth starts in the spring. The nymph lives for about 2 months chewing on the new foliage resulting in the upward cupping of the leaves.
The cupping of the leaf protects the feeding psyllid. A sticky white deposit is often left on the foliage by the psyllid. Minor damage is mainly aesthetic but heavy infestations can eventually cause some defoliation. The winged adult typically appears in June. After mating, the female flies over the canopy of the plant and then lays her eggs under the bud scales of the plant. The eggs remain there until the following spring when they hatch. Control measures, if desired, should be taken immediately after new boxwood buds break dormancy. Once the psyllid has cupped the leaf, the pest may be controlled but damage to the leaf cannot be corrected. Use insecticidal soap, horticultural oil, and other insecticides to control the nymphs. Consult your local full-service garden center or Extension personnel for recommendations for control of psyllid.
Mites
The boxwood mite is a spider mite. Mites generally begin hatching in late April to May and become most active in hot, dry summers. A typical mite has a life span of 1 to 3 weeks; thus in hot, dry summers, there are many generations of this pest.
The boxwood mite is very small and difficult to see with the naked eye. Gently hitting a branch over a piece of white paper will often allow you to see the mites when they fall onto the paper. Mite-damaged leaves appear to have tiny creamy-white spots and marks on them. Damage is often superficial but can become a problem if the mite population becomes too great.
Control measures include natural predators and the use of horticultural oils, insecticidal soaps, and other chemicals. Consult your local full-service garden center or Extension personnel for recommendations. Unfortunately, some of the insecticides used for control of boxwood leafminer seem to cause an increase in mite populations because they kill predators of the mites. There appear to be some cultivars that are more resistant than others to boxwood mites. Microphylla Cultivars seem to be more resistant, while some Sempervirens cultivars seem to be more susceptible.
Pets and Boxwood Odor
Dog urine will kill boxwood branches. Buxus sempervirens cultivars are the favorite targets of dogs.
Some boxwood cultivars exhibit a strong odor in early summer when the sun shines directly on them, especially when the humidity is high, particularly Buxus sempervirens ‘Suffruticos’. Some people believe this may be what attracts dogs. Some gardeners relish the aroma of boxwood while others say it smells like cat urine. Fortunately for some and unfortunately for others, this is the odor of boxwood and it is more intense with some cultivars than others and cannot be controlled.
