CO-Horts Blog

Monday, September 10, 2018

Plant Diseases Have Tartans, Too!

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.

For example, to the left is a picture of lupines. Can you see how some of the plants look  okay and others don’t? The pattern of damage is random – pointing us to the biotic clan. This means that the cause of the damage is probably a living one – like fungi, bacteria or viruses. I think it’s probably a fungal root rot and I would love to look at the roots more closely to help confirm that. But I don’t think digging up plants in this garden would be appreciated, since it’s a public one.

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

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