Goldenrods might have caught your attention back in August and September with their showy yellow flowerheads. And they may still catch your attention during the winter.
If you happen to see a plant stem in a road ditch, prairie, or similar area with a spherical growth in the stem a little smaller than a golf ball, it is likely a goldenrod plant with a goldenrod gall. They are quite common.
Plant galls are swollen abnormal growths on a plant caused by invading organisms such as insects, mites, fungus, bacteria, etc. Galls may form on stems, leaves, leaf stalks, twigs, and branches, and provide both protection and nourishment for the invading organism.
The round stem gall on goldenrods, specifically Canada goldenrod and giant goldenrod is one of the more common plant galls. They are caused by a species of fly. In the spring, the females will lay an egg on the stem of a goldenrod. The egg then hatches and develops into a small creamy white larva which burrows into the stem.
In the case of the round goldenrod gall, the gall is smooth, round, and often a bit smaller than a golf ball. During much of the summer may have the same color as the stem but have some red or purple color. When fall comes around the larvae will chew an exit tunnel but will leave a small covering about the size of a pinhead that may be readily observed. The larvae will subsequently pupate and exit as an adult the following spring.
Some observers might think that the gall is a plant’s defensive response to isolate a pathogen or invading organisms from accessing the rest of the plant. But the plot thickens. The shape of a gall is determined, not by the plant, but by the particular invader species. In this case, the larva produces saliva which contains a substance that causes the plant form a mass of protective and nutritious tissue around it (a gall).
So, as you travel about, be on the lookout for goldenrod galls. By the way, the larvae of goldenrod galls are reportedly good fish bait. If you are an angler and you are really ambitious, you could collect a few, open them, collect the larvae, and go fishing.
