Posted by
Mary Small
State Colorado Master Gardener Coordinator
I went to the Longs Peak Scottish-Irish Festival in Esters Park
this past weekend. So colorful! And so many tartan patterns identifying the
different clans.
My mind wandered. Instead of thinking about my ancestry, it hit me that clan tartans are similar to some classifications in the plant disease world. Patterns of damage help us identify what “clan” a
plant's problem belongs to.  |
| Lupines |
 |
| Apple scab on crabapple |
Look at the crabapple leaves here on the right. A number of them have scattered
spots. You can also see that some of the leaves in the background don’t have
spots. The spotted pattern on the two main leaves is not identical, either. This
problem is apple scab, which is a fungal disease. An interesting feature of
these leaf spots is that they have “feathery”, not solid margins. Apple scab
also belongs to the biotic clan.
 |
| Fireblight on crabapple |
Can you see the random pattern of damage in the crabapple to the left?
Most of the leaves look normal, but there are some scattered twig tips with
dead leaves. This is fire blight, which was a huge problem in 2019 largely due
to the late spring/early summer rains that helped splash the bacteria around. The
disease belongs to the biotic clan.
 |
| Leaf scorch on linden |
What do you think about the pattern of damage on this linden (right)?
All the leaves have the same damage – brown leaf edges and tips. The pattern is
uniform on all of the leaves, which points to the abiotic (non-living) clan. The poor tree had two major strikes
against it. It was growing in a non- irrigated area (I hesitate to even call it
a “lawn”). On top of that, much of its already struggling root system was severed
during driveway and street construction. No (or few) roots to absorb water and
hydrate the canopy and you get the pictured leaf scorch.
What happened to this oak (below)? All of the newer leaves (near the twig
tip) look dark green and healthy. But all of the older ones are distorted, paler
and have some cool-looking fringe at the tips. The leaf damage was caused by herbicide
injury. The older leaves were exposed to herbicide, but the newer ones were
not. It’s another member of the abiotic clan.
 |
| Herbicide injury to oak |
Next time you’re out and about, see if you can
identify which "clan" a plant problem belongs to. By the way, I belong to Clan Ross (tartan below).
 |
| The Ross tartan |
