Case of the Browning Oaks Solved!

25 June 2014 Idea of the day “Wherever you go, there you are.” Confucius

I had now made two trips to this subdivision on the far southeast side of Tampa to try to uncover why 20 oaks had suddenly gone brown. This one is completely dead, with a partially dead one behind it.
a completely dead laurel oak at Camden Woods

The first trip I discovered the too deeply planted condition, the poor volcanic mulching procedure and noticed the synthetic plastic straps from the original root ball bag from ten years ago not decaying but biting into the roots and acting like a tourniquet to water and nutrient delivery on some of the trees. I had also clipped off leaves, branches and roots for lab samples. I sent those samples to the University of Florida Plant Pathology lab. They found no pathogen present.

The technician at the lab said sometimes there are vascular microorganisms clogging up the vessels of the inner trunk, especially the phloem vessels which deliver the carbohydrate energy from the leaves down to the woody reserve parts of a tree and roots. So she suggested I get another sample of sapwood just under the bark to see if there was a vascular wilt problem. Texas has a rampant disease called Oak Wilt of this type and in California they have Sudden Oak Death, another vascular wilt, both which fortunately have not been seen in Florida yet. Unless this is it.

I made a second trip with some knives and plastic sample bags, making the smallest incisions I could and sent those chips to the lab. When no primary causative pathogens showed up with these either, (only some secondary fungi which simply feed on decaying wood) I was both happy to know Oak Wilt and Sudden Oak Death had not gotten to Florida and was still mystified.

Having noticed that some of the oaks were still doing fine and having been there for ten years, I ruled out nutrition deficiencies. Pathogens and insects had been ruled out. What was left? As the lab indicated, only something environmental – from drought (we hadn’t had any, if anything it had been a little more rainy than usual this spring) to mechanical damage (I hadn’t noticed any signs of mowers or weedwackers or vandalism on the bark) to construction damage (there had not been any of that) to possibly . . . herbicides.

Right as I was coming to think that might be the culprit, the lab tech suggested I talk to an expert in the Forestry Division. He knew of a very knowledgeable associate professor of forestry who got to see a lot of things going on with trees all over the state and was on top of these sort of unusual situations. I thanked him and gave the doctor a call.

I explained the mysterious browning I was running into and all the testing I’d done and answered some of his questions. Yes, all the leaves were remaining on the trees but had gone from 10% to 100% brown – and about 20% had not been affected at all. After a little more discussion, he had the most amazing thing to say.

“I can’t say with 100% certainty, but I’d say pretty close to it, that this is MSM. These exact symptoms are something I’ve seen 27 different times just this year and they all traced back to it.”

“Really?!” I said surprised. “Wow. What is it?”
“It’s a selective herbicide with the active ingredient Metsulfuron Methyl, MSM for short, that is used a lot for dollar weed and other broadleaf weeds. It doesn’t affect every weed but the ones it does die quickly because it inhibits cell division in shoots and roots. It is even specifically used in forestry to kill oak trees when they need to be cleared! I’ve seen it affecting all sorts of oaks in developed communities like this because the landscapers are using it around the base of the oaks.”

“So this could account for both the minimal browning and the total killing of other trees?” I asked.

“Yes,” he responded, “it’s very biologically active even in very low concentrations so if only a little gets absorbed by a few roots, there goes a fourth of the canopy. If more was applied at the base of a tree “to really get rid of weeds” it could easily kill the entire tree. They could have run out before they got to those in the front you said weren’t affected. Or perhaps they were in such good overall health they resisted it.”

“What’s the product brand name that’s most common?” I asked.

“It was originally created by Dow Chemical but their patent expired recently and so some twenty different chemical companies are now producing it cheaply as a generic. That’s why we’re seeing all these effects all of a sudden, they’re all pushing it.” He rattled off a list of common products I knew landscapers were using for weed killers. “Just go online and punch in Metsulfuron Methyl brands in a search engine and you’ll see them all. And the landscapers and pesticide people need to be aware of this because it’s creating extensive, expensive damage to oaks all over.”

“Well thank you for the information,” I said sincerely. “This certainly seems to solve the mystery. But what do you recommend for trees that are partially damaged by MSM? Can they be saved?”

“I think so. But I wouldn’t use any heavy synthetic fertilizers. The salts might be too much for them at this point.”

“What about a natural liquid organic compost with trace minerals that I use all the time?” I offered.

“Yeah that would be good. And I’d prune out the dead material so it doesn’t encourage canker (dead bark and tissue) or fungal decay. And normal watering. That’s all. You may have to remove some of them. And you can’t plant another oak in the same spot safely for almost two years.”

“Got it. Thanks for the info.” I knew that at least two or three were going to have to come out. But at least I had something I could offer as a possible fix for the rest.

I called up the property manager and told her the story. I said I wasn’t a licensed pesticide applicator so I couldn’t say anything in writing that implied I had the correct diagnosis, but I was just passing on the strong circumstantial evidence from the University to help out the community. I told her she ought to check to see which weed killers the landscape company was using.

She did that in the next few days and came back to me. Of the two they were using, one was one of the most common MSM weed killers.

“Wow,” she said. “Thanks for all your detective work Bob! They’ll just have to change their product. The guy said he couldn’t believe it because there are lots of weeds it doesn’t handle.”

“That’s true. Out of 70 in one study I saw I remember there were about 15 it didn’t affect. So I can see why he feels that way. But honestly as a pesticide applicator he should know that this stuff kills oaks,” I reasoned. “I sure would have found that out if I were a licensed pesticide applicator.”

“Yes, it’s not going to be a simple solution to figure out who pays for all the damaged trees.”

“Remember too,” I reminded her “that the soil can be contaminated for up to 22 months after application so you can’t safely plant another oak in these spots for a while.”

“Yeah, that’s right. Sheesh, this information needs to be gotten out to the public!”

“Well we are on a plant and gardening radio show many Sundays. We’ll bring it up on the show – the host has a pesticide license so he’ll be glad to pass that on to the public – and his employees!”

“Hey that would be great! Well I’ll certainly be using you in the future. Thanks again!”. I smiled and nodded. It had been a productive bit of detective work.

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