WICHE: Various causes of plant distortions

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By Jeneen Wiche

I am starting to appreciate anomalies in nature in ways I had never considered.

I suppose I am getting more acquainted with things not going as you plan. I can’t expect a season in the garden to unfold in seamless perfection if nothing else in life does.

So I am embracing an attitude of wonder instead of one of dismay when things start to distort, twist, stunt, grow nipples, galls or any other odd appendage.

Plant anomalies come in many different forms, take, for example, witches’ broom, which causes stunted, yellow, tightly clustered growth.

Witches’ broom had long been described as some sort of hormonal reaction within a plant caused by insect feeding or disease. Basically no one really knew what was going on; but as observation continued and technology advanced so did the theories about what was causing the distortion.

It is true that there are some hormonal reactions going on but the cause varies between plant species. Rutgers University states that, “witches’ brooms are created on plants when the transfer of growth hormones is disrupted (perhaps caused from the introduction of a foreign substance). Insects (e.g. mites or aphids), fungi, bacteria, phytoplasmas and herbicides have all been implicated in causing the formation…”

Now witches’ broom is the generic term for a variety of different chronic conditions that cause distortion including the most common vector, the eriophyid mite. 

Leaf galls often look like something out of a Dr. Seuss story. My favorite is the wool sower gall that appears from time to time on our scarlet oak because it looks like a little round fur ball on the leaf.

And because leaf galls cause no measurable damage, why not delight over it? Our hackberry always gets nipple gall, the spindle-like protrusions on the leaves are caused by mites that gather around buds in the spring of the year and enter the leaves as they unfurl.

As the mite enters the leaf, it injects a growth hormone that causes irregular tissue growth, which creates the gall where the mite lays her eggs.

Galls come in many forms.

There are root, crown, trunk, twig, flower and leaf galls; and the causes vary including mites, non-stinging wasps, flies, aphids and fungi. It really just depends on the plant because certain insects will only lay their eggs on certain plants and certain plant parts.

I think the galls that most people are familiar with are those golf-ball-sized growths that appear on the branches of many oak species. These oak galls are caused by non-stinging wasps (called gall wasps).

There are different species of gall wasps that cause different shapes and sizes of galls.

The galls begin to form when the insect lays her eggs on the twig. First she injects a growth hormone, then the eggs, and as the eggs hatch into grubs, the gall forms around them as a hard, protective encasing.

The grubs continue to feed and mature to either emerge to produce additional generations or over winter in the gall until the following spring. It is a quite amazing feat.

These types of galls typically don’t cause damage to the tree but they may cause tip die back if the galls form on newer tip growth.

Our best bet it to cut away galls as soon as we see the first signs of them. Years of going ignored can result in a tree covered in galls.

Fasciation is an odd distortion that causes the plant to elongate or flatten as it grows.

A bacterium causes it in herbaceous plants but it is not completely understood in woody plants. I actually have a succulent that is prone to fasciation that I enjoy for its extra unusual appearance.

If you can’t beat them, join them, I suppose.