box elders and anthracnose disease
Thank you for using Ask an Expert. You have presented three questions here, so let's start with the easiest one to answer. The Western Box Elder bug is indeed very visible right now, congregating especially on warm surfaces and the bark of maples in the sun. In other parts of the U.S., the eastern form of this lined plant bug does a lot more damage, targeting Box Elder trees, especially damaging the female tree's seed pods. In the west, where we have mainly hybridized versions of red maples, native big-leaf maples and vine maples, and many versions of "Japanese" style maples, this insect is more of a nuisance than a real threat. They do overwinter under rocks, in cracks, etc. They may cause some leaves to curl. You an use a hand- held vacuum to dispose of them, or if they are grouped together on the side of the trunk or house, use a shop vac. In summary, they are pesty nuisances unlikely to seriously damage your tree.
Your second question was about anthracnose on the surface of maple leaves. Yes, maples of most kinds are subject to this fungal disease. You can not do much about it at this point, except to keep any fallen leaves swept up and disposed of. Keep lawn sprinklers or other sources of water from spraying on the leaves (unfortunately, we have spring rains in southern Oregon and you can't do much to protect the leaves from rain). Once the tree is dormant (in autumn after leaf fall), do a thorough job of cleaning up all the fallen leaves and dispose of them (not in the compost pile, however). You can prune back infected twigs (they will be spotted and sometimes cankered) to 6 inches below any damage. Sterilize your pruning equipment with alcohol or a solution of 10% bleach (1/2 cup bleach to 4 1/2 cups water) so you do not transmit the disease to other plants. Then, in spring, when the buds swell and shoots begin to form, you can spray a fungicide on the tree.The PNW Disease Handbook (see pnwhandbooks.org ) recommends using Bonide Fung-onil Multi-Purpose at 2 1/4 tsps. per gallon of water. Follow the directions on the label carefully. There are no recommended biological or organic controls for this disease. You may have to repeat this process for successive years until all of the disease is controlled.
Your third questions pertains to trunk damage on a Japanese maple. There are many possibilities here: mechanical injury from mowers or contact with objects thrown by humans or blowers which has allowed disease (viral or fungal) to penetrate the trunk; frost damage which has similarly caused splitting and peeling; or the possibility of a bacterial blight such as Pseudomonas spp. which has caused splitting and rot. Unfortunately, despite your good photos, we cannot make a diagnosis without examination. If only a few branches are affected, you might prune them off below the damage. If it is the main trunk which is affected, the tree is probably on the way to dying. We suggest you take additional photos and perhaps a sample of the peeled away bark to the OSU Extension Office in Central Point for the Master Gardener Plant Clinic technicians to examine. They are located at 569 Hanley Road (Rte. 238) with hours daily 10 to 2.
The above response is NOT A CANNED RESPONSE. it is the result of several hours of research so please do not disregard it. Thank you.