How To: Identify Crown Gall

img 0268 300x248 How To: Identify Crown GallLooking over some garden hedges recently, I discovered a type of gall on all six of the identical shrubs. The gall growths were hard, irregularly shaped, and about two inches in diameter. I looked over the area that the galls were attached to, and noticed that the galls were mostly growing in areas that had been pruned within the last one or two years, a sign that pointed to a bacterial gall instead of an insect gall.  I snapped the gall off of the plant to have a closer look.

There are many types of gall with several specific causes, but they can generally be broken down into two categories: disease caused, and insect caused.  Insect caused galls come in all shapes and sizes, both soft tissue growths, fuzzy growths, and firm growths. All of them hold either the eggs or larvae of a specific type of wasp or mite inside, and can contain hollow areas inside the gall where the creature lives and feeds.  Insect caused galls may look strange and detract from the outward appearance of a plant, but they do not damage plants. Disease galls do damage a plant, and are initially caused by a bacterium that lives in the soil, although they are commonly spread from plant to plant by pruning, or grafting, when hedge shears have come into contact with an infected plant. The true damage caused by a bacterial gall is actually in and around the gall growth, where the unchecked growth of cell tissue distorts, or chokes off the flow of water and nutrients through the plant.

How To Discern Between Insect And Disease Caused Galls:

With the above pictured gall, I investigated the cause of the growth visually from the exterior appearance, and by dissecting the growth, to check for hollow areas inside the gall that would be a sign of insects.  I found that the gall was solid throughout, with layers of disorganized tissue, and concluded that the gall was in fact Crown Gall, a bacterial infection. If you find a gall on one of your plants you will need to do these two things to determine the root cause. Identifying the shape of a gall is important, the shape and appearance of a gall can most often tell you what the root cause is. If you are unsure, or just curious, you can then dissect the gall to check the inside for insect life.

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