Tree insect pests and diseases are part of this area’s forestry world.
It seems like whether the previous summer was scorching or temperate, whether the winter was severe or mild, and whether our spring is wet or dry; we always see a few problem spots when our area trees grow their leafy canopies for the summer.
It’s true weather conditions play a role in the appearance of some tree problems, but it’s equally true that the appearance of tree pests and tree diseases are annual events in the Ozarks. Tree problems have been in this area as long as we have had trees.
The effects these problems have on trees can vary. 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.
Before we get to the solutions, here’s more information about a few of the common tree problems we encounter in this 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 U.S.
Many trees are afflicted by their own specific species of fungi (sycamore anthracnose, oak anthracnose, maple anthracnose, etc.). Weather conditions also impact 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 out-growing 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, with favorable moisture conditions, they infect tender buds and young, unfolding leaves.
• Galls — Galls are tumor-like growths that appear on leaves or small 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 surrounding plant material.
The digestive fluids used by the larva in the feeding process 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 pock-mark surrounded by damaged leaf material show where the gall had been. Other types of galls remain attached to the tree after the insect has emerged.
Due to the prevalence of oak trees in this region, the most commonly seen galls in southwest Missouri are the ones 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 over-aggressive use of lawn-mowers and weed-trimmers are notorious canker-causers but some trees still suffering from the drought stress from previous years can also be subject to canker diseases. Canker diseases become serious when dead areas expand, eventually girdling the branch or trunk and causing die-back or death to the tree.
These are just three of a long list of problems that can afflict Missouri trees. A sound, across-the-board remedy to these many maladies is good, 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 a little water in times of drought can make a huge difference in the health of your tree.
(Francis Skalicky works for the Missouri Department of Conservation in southwest Missouri. He can be reached at 417-895-6880.)