While out walking I noticed that leaves are changing color on many trees and dropping to the ground but the young oak trees in the neighborhood are keeping their leaves. Are they sick?
Not all hardwood trees lose their leaves in a display of fall color. Young oak (Quercus) and beech (Fagus) trees may hang on to some of their leaves until spring. This phenomenon is called marcescence (sounds like mar-CESS-enss) and it’s a real mystery. It is most commonly observed in young trees and on lower branches.
Scientists are unsure as to the reason why leaf drop doesn’t occur until spring for these trees. One thought is that newly dropped leaves in spring provides a fresh layer of mulch adding nutrients and conserving moisture for growth in the new year. Another idea is that leaves on the tree will slow down the falling winter snow directing it to the base of the tree for much needed moisture. The leaves may offer frost protection for buds and new twigs while discouraging browsing deer and protecting the new buds especially on younger trees. So whether the young oak and beech trees are hanging on to some of their leaves to use as spring mulch, to stay hydrated, or as defense, they are not sick but showcasing one of nature’s mysteries – marcescence.
The goldenrod in my pollinator garden has a stem with a marble-sized ball in it. Is something living in it?
Yes. You’ve spotted a gall, the home of the goldenrod gall fly (Eurosta solidagnis.) There are nearly 1500 insect species that create galls on plants. Galls can vary in shape from bumps to balls, cones to stars, from stiff to fuzzy, from green to brown, even orange and red. The female fly inserted her eggs into the goldenrod (Solidago) stem. After hatching, a chemical in the larval fly’s saliva mimics plant hormones causing the goldenrod to grow abnormally forming the hard, spherical chamber or gall. The maggot feeds on plant tissue in the gall, molting twice and growing to about 1/4 inch long. In the fall to prepare for its spring exit, it chews a tunnel to the surface leaving a thin layer over the outside. The grub overwinters in the gall protected from the rain, wind and cold and in the spring, the adult fly emerges. Because it has no chewing mouthpart, it inflates a balloon-like structure between its eyes to push open the thin covering to the outside world. Amazing!
You can also find galls on trees. Over 800 insect species create galls on oaks (Quercus). The greenish tan oak apple gall is the size of a golf ball and forms on leaves. In a central seed-like chamber, a single larva of a wasp develops. The chamber is lined with tissue that the larva eats. Check for a small hole where the insect bore its way out of the gall. Look closely at oak tree twigs. You might notice a cluster of brown marble-sized galls. A tiny gall wasp laid eggs inside the leaf bud. The oak responded to the foreign tissue by growing a gall around the expanding egg sac to protect the plant. If you discover a stiff, brownish orange blob on the leaf, it could be the creation of the furry oak leaf gall wasp, a small, harmless cynipid wasp. While strange looking, galls are usually not harmful to their host plant. 
Gardening advice, information and commentary from the Capitol Hill Garden Club. Send your questions to capitolhillgardenclub@gmail.com. Want to learn more about gardening or spend time with people who like plants? For more information, go to the Capitol Hill Garden Club website at capitolhillgardenclub.org.
