Tree fungi

With all the rain we have received, we have several fungi having a big time splashing around on leaves. These fungal pathogens manifest as spots on leaves, a powdery look, or even odd shaped blotches.

On my morning stroll, I noticed that many of the neighborhood trees have polka-dotted leaves. What is that? Why is it happening? When should we freak out? Thus, I decided to write about things to worry about and things to not worry about (probably).

Every year, the joy of gardening includes disease or insects attacking your tree. As I mentioned in an earlier column (you are collecting them all, right?) everything was just perfect for oak leaf blister to show up in all the live oaks. This caused deformity of the leaves, but otherwise not a big deal.

With all the rain we have received, we have several fungi having a big time splashing around on leaves. These fungal pathogens manifest as spots on leaves, a powdery look, or even odd shaped blotches. If you have a healthy tree, these diseases aren’t anything to worry about too much. If you did get a very severe case, there are fungicides available to use. One way to keep your tree healthier is to avoid watering the leaves of trees. Watch where those sprinklers hit, the spores of the fungus literally bounce around with water. Best practice also recommends to remove fallen leaves and branches so there is not a safe harbor for overwintering. Be careful with fertilization; lush growth is more appealing to both disease and insects.

If every year you seem to have the same spots, a preventative fungicide in the spring might be helpful. However, as I’ve mentioned, if conditions hit just right, you probably can’t prevent it nor should you fret over it.

It’s not unusual to have insect damage on trees. They’ve gotta make a living, too. Most of the time, they come do a little snacking (maybe not even noticeable) and either they move on or get eaten by something else. Make sure you aren’t killing the beneficial insects that are there to eat the bad guys. Also, keep in mind that butterflies and moths come from leaf-chewing caterpillars. Caterpillars cause damage, but aren’t they so pretty when they grow up?

I know you are thinking, but what can I worry about? Here are a few things.

Look at your trees and the way the trunk goes into the ground. If it looks like a telephone pole going straight into the ground, that’s a problem. Trees need the root flares exposed.

If you have mulch (proud of ya for having mulch) around your trees, make sure it is not touching the trunk of the tree. It may be fashionable to create these monstrous volcanoes of mulch around the tree, but it is absolutely devastating for the tree. Don’t do it.

What’s your lawn look like? If you have lush vibrant green St. Augustine or even Bermuda grass, you may be overwatering the trees. Or watering them too shallow and frequently. Our native post oaks are the fussiest trees around. Nothing makes them happy, really. They don’t live well with disturbance around the roots or overwatering. If you have post oaks in your landscape and they are thriving as is your lawn ... don’t change a thing. It’s working, it doesn’t make sense, but don’t fix what ain’t broke.

If you can reach any limbs of your tree, look at the very newest growth. The new growth will be on a little branch that may look a different color or be less woody. That little branch of new growth is how much your tree has grown this season. If you see several inches, you’ve got a robust tree. If it is stubby or less than two inches, you may have a stressed tree. This is not a hard and fast rule; trees grow at different speeds. But it can be an indicator of health and vigor.

Speaking of reaching limbs, I venture a guess that most trees are not pruned correctly. Trees don’t need to be pruned, so you can take that off your annual to-do list. Young trees can be pruned in order to establish a good structure. If limbs are crossing or broken or dead, they need to be removed. What I see, though, are mature trees with no limbs except at the top. We call it lion’s tail.

This particular style of tree trimming is especially bad for Bradford pears. They already have a bad branching structure with narrow crotch angles that are weak. Surely you have noticed that when we get wind or hail, somebody’s gonna get a split pear tree. Part of the tree splits off, and what do we do? We cut it off and leave the rest of the tree in even worse condition. Maybe we even limb it up more to “take the weight off” or some nonsense.

On my neighborhood walk, there are several pear trees that I do not walk under or near. Seriously, getting killed by a falling tree branch cannot be the way I go. But if I do, you have my permission to make all the dark humor jokes you want about it; I’ll be sad to miss out on them. Anyway, we have created these trees that are top heavy so often when we get a lot of rain or wind, they can topple over.

I understand that you want to remove a few branches because your kid is getting taller and complaining about it when they mow. (I don’t think that’s a kid’s chore anymore. Lucky generation.) So take some branches off. Start at the bottom and remove one or two. But do not remove every horizontal branch on your tree. You want to create a triangular looking tree but with just a little more trunk showing. You do not want to have a long, scrawny trunk with a poof of branches at the top. Unless it’s a palm tree. That’s how palm trees should look. Not oak trees.

Also trees have a life span. Some have shorter ones than others (looking at you, Bradford pear). Sometimes there is nothing to be done other than make the tree comfortable and start looking for a replacement. When you get this opportunity, select trees that like our area; how about some natives?

But some insects and diseases are very, very bad and fatal. Typically, these insects or diseases are host specific. Think: oak wilt, emerald ash borer, rose rosette virus — and we need to be on the lookout for them. Worry level panic.

Overall, trees want to thrive, and we want to help you help them. Give us a call or an email at 940-349-2892 or master.gardener@dentoncounty.com. Check out Aggie Horticulture’s Gardening 101 videos at bit.ly/3dT9szk to learn more about succulents and vegetables and all sorts of topics.

JANET LAMINACK is the horticulture county extension agent with Texas AgriLife Extension. She can be reached at 940-349-2883 or via email at jelaminack@ag.tamu.edu.

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