When it comes to plant abnormalities, the most common show up as curled or cupped leaves.
Insects, mites, disease organisms, herbicides and weather events can lead to malformation of leaf, stem, flower and fruit tissue.
Examination of the leaves is the first step in diagnosing the problem.
Insects, such as aphids, can be seen unaided, but viruses and mites that cause distortion are often too tiny to see without a tissue analysis or microscope.
If you suspect a virus or mite problem, you may need to send a sample to a diagnostic lab.
Weed killers, such as 2,4-D or Weed-N-Feed, sprayed in the affected area can volatilize and drift. Such drifting can curl and cup the foliage on nontargeted plants.
Weather events, such as cold temperatures when leaves are emerging from the bud, also can cause leaf malformation.
Distorted, abnormal growth occurring in the flowers of a plant, is likely caused by aster yellows.
Aster yellows is a disease caused by phytoplasma, which are somewhat like bacteria and cause a variety of unusual and strange symptoms.
The heads of flowers may be deformed or lopsided and the flowers may remain yellowish-green, regardless of the variety’s normal color. Leaves may also be yellow and the veins pale white.
Distorted leaves can be picked off a plant, if insects are the cause.
Plants tend to outgrow damage caused by cold injury and low doses of herbicide.
If virus or aster yellows is the cause, entire plants must be removed to control the disease.
Control of abnormal, distorted plant-growth problems depends on the actual cause.
A glimpse at Insect and Mite Galls
— Galls are abnormal growths of plant tissue caused by a wound, infection by a microorganism, or the feeding and egg-laying activity of certain Insects and mites.
— Although galls are conspicuous and unattractive, they rarely cause serious damage.
— Once galls start, formation is largely irreversible.
— Under most circumstances, control is not recommended.
How Galls Are Formed
Galls are abnormal growths of plant tissue that form in response to a wound, infection by various microorganisms, or the feeding and egg-laying activity of certain Insects and mites.
Galls occur on almost any plant tissues.
The most common are leaf, stem and flower galls produced by insects and mites.
Galls often are unusual in form, conspicuous, and frequently cause considerable concern.
Galls produced by Insects and mites rarely cause serious threat to plant health.
Most gall-maker populations fluctuate from season to season.
The occurrence of many in one year usually is followed by few the next.
Galls are produced by plant cells stimulated to abnormal growth.
Galls from Insects and mites usually result from chemical secretions produced during feeding or egg laying.
The chemicals act like natural plant growth hormones.
Galls also may form following mechanical injury from insect feeding.
Insect and mite galls are produced when plants are growing rapidly, when new leaves are expanding or shoots are lengthening.
Mature plant tissues are insensitive to various gall-making stimuli.
Consequently, most galls start in late spring and early summer when adult Insects become active and lay eggs.
On a few plants that produce new foliage over a period of several months, multiple generations of the gall-making insect can occur, such as honeylocust podgall midge. In general, gall makers have only one generation per year.
The gall-making insect or mite develops within the plant gall.
The gall continues to expand as the gall maker feeds.
Once formed, galls may remain on the plant for long periods, even though the insect may leave it shortly after the gall develops. Many galls are not seen until after the insect or mite leaves the gall, as with Cooley spruce galls.
Although galls are conspicuous and unattractive, they rarely do any real damage to plants.
Gall-making is cyclical and problems often subside with natural controls.
Furthermore, once galls start, formation is largely irreversible.
Under most circumstances, control is not recommended.
Occasionally, heavy infestations that occur repeatedly over several seasons may slow the growth of the plant or make the appearance unattractive.
The eriophyid mites and a few gall-making Insects that overwinter on the plant may be controlled with dormant oils.
However, most galls are produced by Insects that move to the trees as new growth develops in the spring.
They can be controlled only with sprays that cover the leaves during the egg-laying period.
Repeat applications often are needed.
Insecticidal control of plant galls can be difficult to achieve because sprays usually must be timed to coincide with periods when the gall-makers are laying their eggs.
Also, for some gall-making insects, such as the poplar twiggall fly, there are no effective controls. ❖