Adelgids – @%$#!!!
If you grow Japanese black pines for bonsai, then you are most likely aware of a common and persistent pest that plagues the most diligent tree caretakers; adelgids. These tiny, almost invisible, insects feed from the sap of evergreens and are similar to aphids. They excrete a white waxy substance from their abdomens, which is generally your first sign of an infestation. Their presence can be harmless in forests where entire trees can be coated white with their excretions. Other harmful infestations of Asian adelgids have devastated native hemlocks in the Great Smokey Mountains and the northeastern United States. Closer to home, our precious bonsai can be susceptible to adelgids where they can harm the candle and needle formation on your pines. A heavy infestation of adelgids can overwhelm your tree and cause it to die.
Adelgids are sucking insects similar to aphids. They use a tubular proboscis to penetrate into the phloem tissue of the tree where they extract carbohydrate-rich sap of evergreen trees. The insects typically concentrate on the fresh and tender needles and new candles but can sometimes invade under the bark of the tree to access the phloem.
An adelgid’s life cycle is complicated. Typically, adelgids have two generations per year. However, this may vary according to the climate and species. Populations of adelgids are all females that reproduce asexually. In spring, females emerge from their winter hiding spots and lay up to 300 eggs each along the branches of trees. The larvae hatch and crawl to feeding spots (a.k.a. the candles of your prized black pine bonsai). Once they find a juicy spot on your tree to feed, they become immobile nymphs. Adult adelgids emerge from the nymphs in early summer. These new adults may be winged or wingless. The winged adults leave to start new infestations, while the wingless adults start the next generation in your garden.
The problem with adelgids on Japanese black pine is two pronged. First, the tree is weakened by the loss of fluids and food at the new growth. Second, the release of sap and excretions by the insects provide the perfect environment for sooty mold to form. New candles or advantageous buds can be covered in white cottony excretions and mold. The constantly moist area can lead to deformation of the new candle/needles and loss of the buds. In either case, the tree is weakened and loss of the branch or entire tree can occur.
So how do you fight an infestation? To rid your trees of adelgids requires complete diligence and commitment. If the infestation is limited, you should try spraying the candles with a direct stream of water to blast away the white excretions and hopefully most of the eggs. Organic treatments of insecticidal oils or soaps can be applied afterwards. This treatment must be repeated weekly. Try this treatment in the morning of a warm/hot sunny day so the water will evaporate from the candles before night. I have found that if the candles stay relatively dry, the infestation can be limited. Do not forget to avoid wetting the candles with daily watering, especially in San Francisco where we may experience moist and cold fog for an entire week or more.
John Boyce suggests using a pet’s flea collar to kill adelgids. John cleans the plant as described and then places the entire tree in a plastic bag. Toss the flea collar into the bag and seal the top. Keep the tree in a cool shaded area for a day or two. The fumes from the insecticide will fill the bag and kill the insects. Some people have reported decent success with this technique.
If the infestation is serious, your next course of action is to try systemic pesticides. We as conservation- and environmental-minded gardeners/members/citizens are well aware of the hazards associated with using synthetic chemical pesticides. Please follow the instructions, use correctly, and dispose of properly. Malithion and Orthonex have shown only limited success when battling aldegids. A new product from Bayer chemical called Bayer Advanced Tree and Shrub Care specifically claims to kill adelgids. Early reports are extremely positive.
Because the insects are dormant in the winter, consider a dormant spray such as dilute lyme sulfur. By applying the spray in the winter months, you may kill wintering aldegids before they have a chance to lay eggs in the spring.
Despite which treatment you choose, you must continue with regular applications of the product. So,pay close attention to the buds of your pines for signs of an infestation and treat as needed.