Bizarre Lumps, Bumps, and Growths in Your Yard!
You are particular about the appearance of your property and notice spent flowers, withered leaves and broken stems that need to be picked up as you want everything to be neat and tidy! But, you come across odd round things on maple and oak twigs and strange bumps on leaves.
These growths are called galls. Galls are abnormal growths that occur on leaves, twigs, roots, or flowers of many plants. Most galls are caused by inflammations due to feeding or egg-laying by insects such as aphids, midges, wasps, or mites. Some galls result from infections by bacteria, fungi, or nematodes and are difficult to tell apart from insect-caused galls.
The insects and mites that cause galls are very specific to the kinds of plants they attack and to the types of galls they produce. The majority of gall-making insects are wasps. Just remember, most wasps do not sting people. It is just a few bad tempered ones that give a bad reputation.
In addition to the unusual structure of galls, they draw attention due to their range of colors: red, green, yellow, or black. Factors such as weather, plant susceptibility, and pest populations affect the occurrence of galls on plants from year to year. Oaks are most susceptible to hosting insects that cause galls on leaves and twigs. Oak deformities are of various sizes, shapes, and colors on leaves, twigs, flowers, acorns and buds. Galls are so commonly found on oaks that many people think the galls are typical parts of the plants.
Another familiar plant gall is the maple bladder-gall often seen as bright red bead-like growths on upper leaf surfaces of silver and red maple. Caused by the eriophyid mite, they feed inside these galls. The galls are green at first, turning a reddish color and then almost black by the end of summer. By fall, the mites have left the foliage to overwinter on the twigs, usually at the bases of the buds.
As noted by the Morton Arboretum in Illinois, crown gall is one of the most studied plant diseases. The disease is caused by a soil-inhabiting bacterium. More than 600 plant species in over 90 plant families are susceptible to this disease, although relatively few species sustain significant damage. Galls form on roots and stems, especially at the root collar – the junction of roots and stem. Young plants with large or numerous galls tend to be stunted and predisposed to drought damage or winter injury. Galls continue to enlarge as plants grow and can disfigure woody stems
Managing the Ugly
Galls, while strange and sometimes even disturbing in appearance, fortunately cause little permanent injury and rarely cause the plant to die. Plant gall damage is usually an aesthetic problem and is not considered serious. Affected trees ordinarily show little injury, although foliage of young trees is sometimes completely deformed. On ornamental trees this condition can be unsightly. Chemical sprays are rarely necessary or recommended to treat gall infestations because by the time the galls become noticeable, the insect or mite causing the injury is protected from chemical sprays. If only a few galls are present, the affected part of the plant may be simply removed.
Keeping the Beauty
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