While 'jumping oak gall' is infesting white oaks in southwest Missouri, galls also showed up on a hickory branch brought into the tree clinic by a concerned owner. / Mike Penprase
Blast-furnace heat and bone-dry drought were the weather conditions that dominated the news last summer. Consequently, it’s odd to be talking about problems caused by cool and wet weather only a year later.
However, those two meteorological conditions are the root of many of the tree problems appearing in the area.
Many of our native trees, once they reach maturity, can weather these fungal or insect invasions and bounce back with little damage. On occasion, steps can be taken to improve a tree’s recovery. Here are a few common tree problems in the area:
• Anthracnose: Anthracnose is a name for a group of diseases caused by several closely related fungi that affect a number of hardwood tree species in the eastern and central United States. Many trees are afflicted by their own specific species of fungi. Weather conditions also affect disease development. As a result, symptoms of anthracnose vary. Sometimes these fungi cause small dead spots on a leaf while in more severe cases, an entire tree can be defoliated. Some types, such as sycamore anthracnose, also affect twigs, buds and shoots. Anthracnose fungi overwinter in infected leaves (and sometimes twigs) on the ground or in the crown of the tree. Spores are produced by these fungi in the spring and are carried by wind or water to other trees where they infect tender buds and young, unfolding leaves.
• Galls: Galls are tumorlike growths that appear on leaves or twigs. Gall formation begins in spring when a female wasp, midge or mite (depending on the type of gall) lays an egg in the developing plant material (either leaf or woody part) of a tree. A larva hatches from this egg and begins to feed on the plant. The digestive fluids used by the larva in feeding are foreign to the tree’s system and thus initiate a protective response from the tree. This consists of the formation of hard plant material — the gall — around the feeding larva. This mass of hardened vegetative material creates a barrier between the larva and the rest of the tree, but it also serves as a cozy shelter for the larva to complete its development. Some types of galls fall from the leaf and the adult insect eventually emerges from the gall on the ground. Meanwhile, back on the leaf, a pockmark surrounded by a damaged leaf shows where the gall had been. Other types of galls remain attached to the tree after the insect has emerged. Because of the prevalence of oak trees, the most commonly seen galls in southwest Missouri are those caused by cynipid wasps, which because of the galls they form on oak leaves, are appropriately called gall wasps.
• Cankers: Canker is a term used to describe an area on a tree that is infected with a fungus or bacteria. Though localized to begin with (often around some type of nick or wound), this infection can spread and cause problems for the rest of the tree. Nicks from mowers and weed trimmers are notorious for causing cankers. This year, some trees still suffering from the drought stress of previous years are also the subject of canker diseases.
These are just three in a long list of problems. A sound, across-the-board remedy to these many maladies is basic tree care. As simple as it sounds, putting the right species in the right location, keeping cutting and digging activities away from the roots, trunk and branches, and providing water in times of drought can make a huge difference.
Information on tree diseases can be found at your nearest Missouri Department of Conservation office or at www.missouriconservation.org.
Francis Skalicky is media specialist for the Missouri Department of Conservation’s Southwest Region. For more information about conservation issues, call 417-895-6880.