Plant Marks
What's Wrong With This Picture?
Look closely. What kind of plant is this and what could cause those marks on the
leaf?
Refining the issue:
The lines are actually in the leaf, not on it. Note how they begin small and, as the trail progresses, gradually widen with a darker spot that may be found at the
wide end of the trail.
Clue:
This plant receives its common name from the coarsely jagged edge of the leaf. It
evidently reminded some of the teeth of a lion, hence the name in French: dente-de-
leon.
Answer:
The plant is a dandelion. The common weed gets its name as a corruption of dente
de leon - tooth of the lion, referring to the coarse cut edge of the leaf.
The channels in the leaf are caused by leaf miners. This is actually an umbrella
name for the larvae of a fly, moth, or beetle that lives inside the leaf. Regardless
of exactly which insect causes this, the result is essentially the same.
Upon hatching from the egg, the creature tunnels through the leaf, growing as it
eats. Hence the tunnels get progressively larger as it eats and grows. The dark
blotch is the larva, or the insect pupa transforming into its adult stage, or the
hole where the adult emerged.
There is really very little that can be done about leaf miners. They are inside
the leaf and not easily reached by any sort of control attempt. About all one can do
is pick off affected leaves, if they are not too numerous, and dispose of them to
prevent new adults from affecting more plants.
Fortunately, the damage is usually not very serious and more cosmetic rather than
actually harming the plant. But a few years ago the leaf miners were so numerous on
citrus that I thought it was all over for my trees. A friend 20 miles away also
reported devastating leaf miner on his citrus. I did nothing (and my friend also did
nothing) and we were very pleasantly surprised when the following year there were
very few leaf miners.
Note that the leaf miners in this picture are found in a dandelion leaf. This is
quite significant as it points out a serious aspect of weeds. Often I have heard the
attitude of "So what if I leave the weeds. They don't really bother me."
Unfortunately, the dark side of weeds is that they often are hosts for pests that
will then travel from the weeds to your garden plants. Ouch!
So getting rid of weeds is a very great tool to keeping down the pest population
in your garden. In this case, no dandelions would mean no leaf miners. Keep your eye
open for weeds and see if they are unwanted guests hitching along.
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