Since there are still over 4-weeks before the official start of summer, the accumulation of growing-degree-days (GDD) will continue to accelerate over the next several weeks. Many of our landscape insect pests will be rapidly emerging and be entering their best control windows before they potentially cause feeding symptoms. This writing contains part 2 of 2 parts of only a handful of the many late spring landscape insect pests that require monitoring. Some could more properly be called mid-spring pests, especially in southern NJ. Those included within part 2 of this blog are: Taxus mealybug; Boxwood leaf miner; Aphid species and Bronze birch borer.
The late spring weeks in the landscape means full plant leaf emergence & many flowers plus increasing insect activity. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Taxus Mealybug (Dysmicoccus wistariae) =(246-618 GDD = adults/crawlers): Some may find it surprising that mealybugs are categorized as a family of scale insects. Although yews have relatively few insect problems, this pest is sometimes found in significant numbers. They are present now in the branch forks and nodes. The adults are covered with a white cottony wax. They produce honeydew, so look for the shiny sticky substance on the leaves and for the black sooty mold that will grow on the honeydew. The feeding will cause yellowing and dieback of branches. Stunting of younger plants can occur with high infestations.
Taxus Mealybug body has 15 to 17 pairs of waxy tuffs with the last pair about one-fourth the length of the body. Look for white adults & crawlers feeding in clusters at nodes & branch forks on yew plants where foliage is sparse & yellow. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
The Taxus Mealybug infested plant on right shows obvious stunting & discolored symptoms. Although this insect prefers yew, they also can be found on Rhododendron, dogwood, maple & Prunus species. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Mealybugs are generally recognized as among some of the more difficult to control insects in the landscape. Their waxy covering can be difficult to penetrate. Monitor for the presence of beneficials. If a large population of beneficials are present, then attempt to preserve them by spraying with horticultural oil or insecticidal soap. Orthene and some of the pyrethroids are examples of other labeled insecticides. Unexpectedly, the neonicotinoids may not provide satisfactory efficacy.
Boxwood Leaf-miner (Manarthropalpus flavus) =(~290+ GDD) = adult emergence) & (448-700 GDD = early feeding larvae): Adults of this imported pest are orange-yellow mosquito-like flies about 1/8 inch in size. They can be seen swarming around boxwoods for a two-week period during mid-May (shake bushes to detect flying adults). In the southern half of NJ, this adult emergence period is coming to an end or has already expired.
Dozens of Boxwood Leaf Miner adults are captured in the pre-planned spider’s webbing. The spider appears to have anticipated the BLM adult emergence. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Delicate pupal skins of emerged Boxwood Leaf Miner adults are ephemeral & will break apart easily. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Yellowish, blister-like blotch mines on the under surface of leaves are caused from larvae feeding inside the leaves of American boxwood. Heavily mined foliage turns yellow and drops prematurely. Damage to new season growth does not become readily apparent until later in the season since the heaviest feeding is done in the later months of the season. In fact, during warm winter periods, the leaves can be snapped in half & peeled back to expose the actively feeding yellow boxwood leaf miner larvae.
Symptoms of over-wintering Boxwood Leaf Miner larvae feeding within leaves. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Removing the lower leaf epidermis on boxwood exposes the active yellow-colored larvae. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
When the egg-laying adults are seen, contact insecticides can provide good suppression. If numerous mines are found during the summer and fall, a systemic spray, acephate (Orthene) or imidacloprid (Merit) can be applied to kill larvae within the mines. Spinosad (Conserve) & abamectin (Avid) are other locally systemic materials that can give good controls. The overwintering larvae are also susceptible to these applications during the late winter-feeding period. Replace susceptible plants with resistant cultivars.
Aphid species (Aphididae) / Beneficials =(spring weeks): Within the landscape, the numerous aphid species probably receive too much attention and should more realistically be classified as “junior-varsity pests.” Many of the aphid species that are present this spring on the new growth of certain plants (e.g., burning bush, rose and spirea), will eventually migrate to feed on alternate hosts (often weeds) during the summer.
High density aphid populations on upper, new shoot growth of Spirea plant. Presence of winged-adults indicate the aphid cluster will begin to spread to new areas. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Stealthy aphids can often be found feeding on leaf undersides resulting in smaller populations going undetected. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Furthermore, lady beetle, green lacewing & hover fly predators are becoming active & will be feeding on soft bodied insect pests (e.g., aphids, scale crawlers, mites). Look carefully among aphid populations to find either the larvae or adults of predators somewhere on the plant. If there are sizable predator populations or if aphids are not significantly harming the plant, consider not spraying. Continue to monitor and knock down the aphid population with horticultural oil if aphids are outproducing the predators. Insecticidal soaps will only give suppression at best.
Lady Beetle larvae will often be more voracious predators than adults. One larva can successfully feed on 50 aphids. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Green Lacewing larvae are sometimes referred to as the “psychopaths of the insect world.” They have been observed killing prey for sport. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Parasitoid wasps have also started becoming active & their presence can be detected by the circular exit holes on the swelled grey-colored dead aphid bodies. These holes are created by emerging adult parasitoid wasps. Healthy leaves produced later in the season after aphid populations wane will hide any leaves damaged now.
However, many shade trees (e.g., maples, oaks, lindens, birches, tulip poplars, etc.) will continue to have populations of aphids during the mid-weeks of summer. When encountered, first consider if the pest is presenting an aesthetic problem. Maybe the various beneficials are too slow to build-up & the client is upset or inconvenienced by the presence of honeydew or sooty mold. Is the honeydew/sooty mold an eyesore on the tree or is it a nuisance, appearing on objects under the tree such as a car, patio furniture, decks, or sidewalks? Aphids rarely threaten the health of the tree, particularly later during the season. If left alone, predators will often eventually maintain the population within acceptable levels.
Black bean aphids with some having been infested by parasitoid wasps. The swelled-up gray colored aphids have been killed. The black colored aphids are still active. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Dead empty shells of parasitized aphids showing exit holes created by the emerging parasitoid wasp adults. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Foliar predators of aphids, such as ladybeetles, green lacewings, and big-eyed bugs, cause aphids to drop off plants as a self-defense mechanism. Almost 25 years ago, researchers in Wisconsin showed that up to 60% of aphids will tuck their legs and drop to the ground within 1 hour of exposure to ladybeetles. Meanwhile, there are ground predators of aphids just waiting for a snack, including carabid ground beetles, spiders, ants, and tiger beetles. This combination effect of predators in different habitats is synergistic. Without the foliar predators causing aphids to drop, the ground predators ate few aphids. Alternatively, when foliar predators were present, ground predators ate many aphids. An experiment caging predators and aphids showed a 50% control of aphids with only ground predators, 75% control with only foliar predators, and almost 100% control with both.
Bronze Birch Borer (Agrilus anxius) =(440-800 GDD = egg -laying adults): Wood boring insects can have devastating effects on trees & shrubs. Borers are the “true assassins” within the landscape. Although many plants are relatively tolerant to leaf feeding herbivores, they cannot tolerate extensive feeding within their vascular systems. For example, bronze birch borer (BBB) beetle larvae feed within the phloem of birch and typically girdle branches or trunks. The resultant interference of the translocation of photosynthates (e.g., carbohydrates/starches) from the phloem to the roots results in tree starvation. Declining roots subsequently cause a reduction in the absorption of water and nutrients that results in the death of the top of the tree. The tree declines from the top-down because of hydraulic resistance. It is a myth that the bronze birch borer attacks the top of a birch tree first. This wood boring species attacks anywhere on the tree where branches exceed one inch in diameter but are especially attracted to bark wounds.
Bronze Birch Borer female adult laying eggs on surface of tree bark. After hatching, larvae will bore through bark & begin to feed on vascular tissues. (Photo Credit: Ohio State Coop. Ext.)
D-shaped exit holes created by the emerging Bronze Birch Borers. Larvae are shallow feeders just under the bark. They destroy vascular tissues & kill the tree if it is girdled. (Photo Credit: Steven K. Rettke, Rutgers Ext.)
Since it is still only third week of May, the adults of this metallic beetle will not become active for another 10 days or more in many areas within the northern half of NJ. Nevertheless, it is important to take the time to monitor susceptible birch species that may require protective treatments. During the month of June this beetle will lay eggs on birches (primarily European white, Asian white, paper, and gray birch) that are under stress (drought stress, heat stress, compacted soil, etc.). The bullet shaped, metallic black adult beetles (1/2”) lays eggs on branches as well as the main trunk. Monitor for adult activity and last year’s exit holes, which are shaped like the letter “D” (1/4”). Symptoms include dieback from the upper branch tips, working down the tree toward the base. Sometimes “ripples” are noticed beneath the bark.
Remember, a wood borer is present because the tree is already under stress. Relieve stress as much as possible by watering during drought conditions, mulching, fertilizing, controlling birch leaf miner, and pruning out dead wood (but not just prior to adult emergence, since adults are attracted to wounds to lay eggs). Pesticide bark sprays are effective when timed to target newly hatched larvae as they chew through the bark into the tree. Pyrethroid insecticides treatments offer good control (i.e., provide 3-week residual) if the bark is wet thoroughly, since eggs are laid in many small cracks and crevices. Systemic insecticides (e.g., neonicotinoids) applied to the soil or as bark sprays/trunk injections offer excellent protection. BBB will often be more severe the year following a drought that occurred during the previous summer. European and Asian birch species are highly susceptible to invasion by the BBB. Our native birch trees (e.g., paper, gray, yellow) have some resistance (i.e., if not under stress) against this native wood borer. The River birch var. ‘Heritage’ is highly resistant to the BBB.
Birch trees with Bronze Birch Borer infestation will often show initial symptoms at the top of the canopy. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
The River Birch species var. ‘Heritage’ is a native species & is highly resistant to the Bronze Birch Borer. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
