Jeff Dodson, MG 2014
Greetings from the Clinic Desk,
Spring has officially sprung as can be attested to by the wide and varied problems that have crossed the clinic desk. Luckily, we have an outstanding group of clinicians (more about them as individuals in next month’s entry from the Clinic Desk) that can be found each morning of the work week poring over the problems that have arisen in Whatcom County’s gardens. Interns from this year’s Master Gardener class are putting in volunteer hours with the veteran clinicians that inevitably turn out to be learning experiences for all involved.
Something we see a lot of and that can be somewhat confusing
to home gardeners are galls on plants.
If you would indulge me, I would like to go from general to specific and
write a little about galls. These are
growths that occur on all parts of plants and are usually in response to a
certain stimulus. Bacteria, fungi and
insects can all be contributors to the initiation and continued growth of plant
galls. Although galls are usually quite
distinctive to the organism that causes them, I find insect galls particularly
interesting because of the gall’s extreme specificity and appearance to a
certain type of plant depending on the insect.
It all begins with the deposition of an insect egg into the plant tissue
(leaf, stem, root, flower bud). The presence
of the egg generally initiates the plant to produce tissue, but as it hatches
and the larva grows, things really get curious.
Hormones from the insect stimulate the plant to make more and more
tissue. These tissues become increasingly unique until the gall produced takes
on an appearance that is distinctive to the insect that caused it. Skilled individuals can often identify the
insect to genus (and sometimes species) just by the appearance of the
gall. Examples of insect galls include….
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Surprisingly, these insect galls prove to be almost totally
harmless to the plants upon which they appear.
Eventually, the insect (wasp, bee, fly, etc…) pupates, matures and
leaves the gall via a small round hole.
The presence of this exit hole is the way one can tell whether or not
the gall is still occupied.
Anybody want to start an insect gall collection? I’ve seen some pretty impressive ones.
Specifically, however, I want to highlight a sample that was
brought into the clinic by one of this year’s
Master Gardener trainees.
This appeared on one of her azaleas, a plant that was hidden
in a protected spot under a rhododendron.
It was a place that was humid with very little air circulation. These are perfect conditions for the fungus Exobasidium vaccina, commonly known to
cause azalea leaf gall. The best
non-chemical control for which is the removal of the galled tissue before the
appearance of the white powdery spores.
As the weather warms, better air circulation is supplied and lower
humidity occurs, this disease goes away all on its own. Remember the disease triangle?
Best Regards to All,
Jeff