Hole-y leaves! What’s the problem — or is there one?

Holes in leaves can have many causes. From top left clockwise: Hollyhock rust, leaf tatter, Japanese beetle damage, hail damage.
Holes in leaves can have many causes. From top left clockwise: Hollyhock rust, leaf tatter, Japanese beetle damage, hail damage.

Mother Nature sure is in her usual fickle mood with her hot flashes and cold dips, but lately she has been throwing nature spitballs — hail. And I have had several people ask me about what is eating their leaves. Is it hail? Bugs? Disease? There are some easy tell-tale signs to give you a clue — and what to do, or not to do.

Holes on leaves can be from almost anything. Even before a leaf is fully, as they say, “leafed out,” the tender new green foliage is easily torn with high winds. I often get reports in early spring that oak leaves look “pre-eaten” as they start to come out. What often has happened is the weather warms enough to signal the bud opening, but as the protective sheath cracks open, high/low temperature variations, or strong winds or rains can tear the new leaves, resulting in the “pre-eaten” look. And often difficult to diagnose.

It could be hail damage, too. Hail is an obvious phenomenon, I mean, who doesn’t have a little bit of awe at balls of ice falling from the sky on a hot day? But it is also extremely sporadic. Like these last few hail events we have had. Some people literally had to shovel their decks, while others, like me, had just a bit of small pea-sized hail that melted almost as quickly as it hit the ground.

So, you might have had hail at home where your plants are, but you weren’t. I had several photos submitted of plants with tears and holes, and the homeowners wanted to know what was eating them, and what to do. And the answer was simple: Do nothing. Or prune off the severely damaged leaves, as we are early enough in the season and the plant has enough stored energy to put out a fresh growth.

There are also diseases that cause holes in leaves as the disease progresses. Take hollyhocks, the large fan-shaped leaves can look like they were riddled with a BB gun with dozens of holes. Bugs? No. Fungus. Hollyhock rust is an airborne common fungus that won’t kill your hollyhocks but can decimate your leaves.

Hollyhock rust fungus starts on the underside of leaves as rust-colored pustules, which look like a bad case of teenage acne. As the fungus progresses, the leaf tissue becomes fragile and breaks out, leaving the holes. No amount of bug spray will stop this “bug,” because it isn’t a bug/ A preventive fungicide like chlorothalonil is a recommended treatment. But you can also just pull off damaged leaves and remove them from the area.

As I have mentioned several times in the past, another amazing part of nature is that most plants have a new leaf waiting in the “batter’s’ box.” If you don’t follow baseball, while there is one person up to bat, the next batter is standing in a spot preparing to bat.

So. it is with nature. Plants have a new leaf waiting in their “armpit,” now that is a real image you can’t get out of your mind. Where the leaf attaches to the stem, there is a new leaf just waiting to start growing once the current leaf is removed (all the way to the stem).

People are often amazed when I tell them to pull off damaged leaves, and within a short time, new clean, undamaged leaves will reveal themselves. With leaves damaged by physical issues –like hail, wind rain — and plant-diseased leaves, when you remove the injured foliage, a new clean leaf will emerge. If the disease is still present (like if you didn’t clean up the diseased foliage), the disease can reoccur. But if the disease triangle is broken, meaning the right temperatures and amount of pathogen are no longer right, and the disease will not recur.

Somewhat same for when the holes are caused by the usually assumed suspect –bugs. Japanese beetle damage looks like leaves that your grandma made out of lace. Those prolific (not plant harming) beetles will eat all the leaf tissue out from between the veins, but not the veins, hence the lace-like foliage.

But if you remove those damaged leaves, new leaves will emerge. The question is, will you still have more Japanese beetles present to do their damage on them? It is all about timing as to whether bug damage in some plants is actually that harmful.

We preach the Integrated Pest Management (IPM) model of how to handle problems: Do the least amount of intervention that gets you what you determine to be adequate control for the plant outcome. For example, bean leaf beetles can make Swiss cheese holes out of bean leaves, but that damage doesn’t effect harvest, and then you replant for a second harvest.
Determining hole cause is like being Sherlock Holmes sometimes. Here are my tips:

First, look at the whole plant. Plants show you their history in their leaves. Say if there are holes in a certain area, but the leaves below those and above those are clean, it might have been a discrete event, like hail or wind.

Second, pests tend to leave clues. Since bugs are cold-blooded, if you are home in the day, just look at both sides of the leaves. The night pests, like earwigs and slugs, need to visit after sundown. Or as in the case of slugs, since they have no feet, and they slime along, look for a slick trail on leaves to determine their presence.

As always, if you can’t figure it out, that is why we are here, to help homeowners answer their gardening questions. Email me pics anytime at [email protected],A and I will help you figure it out, and if anything need be done.


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