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Little bugs and black sticky stuff all over my crepe myrtles. Help!

Your crepe myrtles likely have a relatively new problem called crepe myrtle bark scale (CMBS). CMBS came over from Asia in a shipping container, possibly through Mexico, first arriving in Texas a few years ago. It has slowly moved East from there. The actual scale insects look like tiny pieces of puffed white rice. Though the male of the species is quite mobile, the female, which causes most of the problems, is relatively immobile, leaving us a little puzzled as to how the disease/pest spreads. Our thinking now is that it might spread by wind or birds but more likely spreads through mulch, bought in bulk from mulch yards, made of limbs and debris dumped at the mulch yard by landscapers, i.e. crepe myrtle bark pruning byproduct (think of the crepe murder that so many practice every year). Another possibility is that it gets on the clothing of landscapers themselves who travel from yard to yard. Regardless, it’s here!

The insect hurts the crepe myrtles in two ways. First, it feeds off of the tree, getting its nutrients from the outer cambium layer, depriving the tree of much needed nutrients, causing it to deteriorate. Second, it excretes a clear sticky substance, euphemistically called ‘honey dew,’ which becomes a perfect host for sooty mold, turning the tree black, coating the leaves and inhibiting photosynthesis, and often coating nearby plants too.

Currently, we are recommending a two-pronged approach, a systemic insecticide in the form of a soil drench, absorbed through the roots and moving throughout the tree, killing the insects when they feed on the tree. This is a slower but more thorough approach, slower because trees have a passive circulatory system and the substance is only pulled up through the tree as moisture transpires from the leaves during the night. The second prong is a contact pesticide or oil to provide a quicker knock-back, but a less complete kill. The important thing to remember is that a single pregnant female insect introduced on a crepe myrtle can have the entire tree covered in CMBS in just 2-3 weeks! So, act with a reasonable degree of haste.

We are currently recommending Fertilome Tree & Shrub Systemic Insect Drench (containing imidacloprid in a very high concentration) as the systemic, which may stay in the tree up to one year, combined with either horticultural oil or the liquid version of Sevin.

Environmental concerns: We prefer organic and natural approaches where possible, but there doesn’t seem to be an effective organic/natural control/kill for CMBS yet. Though this is debatable, with good arguments on both sides, we currently think the systemic, imidacloprid, despite being a neonic, has minimal impact on pollinators and other beneficial insects, because of the difficulty it has traveling into the flowers of the crepe myrtle. We do, however, caution that one should be cautious in using it near other plants that pollinators utilize, like perennial gardens. Additionally, we do know that any contact pesticide will kill any insect it comes in contact with. Therefore, out of respect for the benefits pollinators like butterflies, bees, etc., provide us, we urge you to only use the liquid Sevin, for example, closer to dark, when pollinators are less active. Finally, we urge that you consider cultural changes like switching to pine-straw mulch rather than wood mulch or at least getting the wood mulch in bag form, not planting crepe myrtles or removing and replacing the ones you already have with other trees, asking that your landscapers not come to your yard right after pruning infected crepe myrtles and making sure they are educated about the disease, making sure the trees are adequately watered and fertilized because we know that healthy trees are less attractive to harmful insects, etc.

Unfortunately, though we initially thought the CMBS species would limit itself to crepe myrtles, there is some evidence that it is attacking beauty berries, hawthornes, and maybe even other plants.

Each year, Greg Touliatos gives a seminar on this new disease and other pest problems. To learn more, check our facebook page or email us for a schedule of our free classes and attend them on Saturdays.

Caution! Don’t forget to read the label carefully and follow all procedures. The label is the law. Although we are told that imidacloprid is not easily absorbed transdermally, wear gloves and take other precautions necessary to keep it off of your skin and certainly keep it away from your face, i.e. not allowing it to splash as you are pouring. Further, remember that it is more harmful to pets than to humans. Therefore water it in heavily after applying it to the soil and keep your pets away until it has had a reasonable amount of time to sink below the surface.


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Mulch Ado About Nothing

When I first started as a landscape contractor, I loved hardwood mulch. The market rate for it, delivered and installed, was anywhere between $55 and $75 per cubic yard, with a 3-yard minimum. With landscaper discounts, I was able to get it for anywhere between $5 and $20 per cubic yard and the skill required to install it was not great, meaning that any properly motivated friend or recently unemployed person or teen, with 30 minutes training, could do it at a rate of about 3 cubic yards per hour. Properly shaken with a pitchfork, mulch provided a uniform appearance, covered up imperfections in the surface, blocked sunlight from penetrating to the dirt and promoting the germination of weed seed, and slowed the evaporation of moisture from the surface.

And, you should have heard my arguments for how beneficial it is for the environment! They were, of course, arguments I had heard elsewhere and believed. Mulch manufacturers take debris from cut-down trees, construction, and pruned limbs, etc., and grind it up until it has a uniform appearance. They sell it in bulk as a gardening product, rather than dumping it in a landfall, where it would degrade much more slowly.

Memphians love and like to pay for a fresh mulched yard. And, it creates jobs! How could one not love such a product?

I remembered growing up in my native South Carolina low country, where my stepfather and others would have me raking up “pine straw” (called pine needles by Memphians) to put in beds. After moving to Memphis, I found double-stamped “hardwood” mulch and could only pray that one day South Carolinians would discover it.

Pine straw mulch lays beautifully and is good for all plants!

Pine straw mulch lays beautifully and is good for all plants!

But, as they say, that was then and this is now. A decade later, after a few visits back to South Carolina and some careful reflection and listening to people like Caroline and Arthur Nave and Greg Touliatos, I now know why the azaleas, hydrangeas, camellias, and other plants are so much more beautiful along the Carolina and Georgia coast. It is likely, at least in part, because of pine straw.

But, what’s wrong with wood mulch? Well, a lot.

1. Wood mulch works best as a weed deterrent when it is in large chunks, but Memphians don’t like their wood mulch in big chunks any more than they like shredded pork sandwiches without slaw.They like their mulch at least double-stamped or even triple-stamped (referring to the number of times mulch is passed through a wood grinder). Though this mulch does prevent seeds below it from germinating, it is a perfect host for weed seeds dropped by birds. By having the wood more finely ground, they reduce its efficacy as a weed deterrent. (Memphians are right about barbecue, however. Theirs is much better than South Carolina’s.)

2. Wood mulch promotes termites. Every termite inspector I have met in Tennessee says that wood mulch should be kept at least 12 inches away from the foundation of a home, and some say it should be kept further away than that. Having recently taken a Tennessee chemical applicators licensing exam, I can tell you that official Tennessee guidelines for keeping termites at bay comport with this commonly held opinion. Listen to the experts. Termite damage is incredibly expensive and Memphis has the perfect climate for them.

But, I’ll just keep it 12 inches away from my house! Will you? With a tape measure? Won’t that look odd? Will you put down gravel in the 12 inch zone? Will the gravel mix with the dirt and the mulch? Do you expect the hourly summer employees of landscape companies to keep it exactly 12 inches from your house? Do you trust your spouse to get this right? Your teens? What happens if you pay to have your home treated for termites and your termite company points to a clause in their indemnity contract about wood mulch being too close to the home, and it turns out you missed a spot where a little was up against the foundation? Will they still honor the indemnity agreement.

But, I’ll just use cypress, or cedar, or redwood mulch and it will keep the termites away! Hardly. Mulches are rarely as pure as they are labeled. It is expensive and difficult to keep the types of wood used for mulch entirely separate. Most suppliers can, at best, warrant that it is mostly one type of wood. Second, opinions (the legitimate ones that count) vary about the degree to which these woods really repel termites. We know, for example, that only old-growth cypress heartwood has the resins in it that repel bugs, and there isn’t much old-growth cypress left in the United States. And, if we keep cutting down young-growth cypress, there won’t be any old-growth cypress, eventually. Remember the vague, pro-environmental, recycling argument I used above? If you use one of these kinds of mulches, you can pretty much forget that argument.

3. Wood mulch competes with your plants for nitrogen. This is because all organic matter, in its early stages of decomposition, is nitrogen robbing, only releasing the nitrogen back into the environment late in the process of decomposition. So, either you have to put down more fertilizer or you will see a slowing of new canopy growth, and a reduction in the plant’s ability to shake disease. One might rightly point out that pine straw is also organic matter and is also nitrogen-robbing in its early stages of decomposition, but, pine straw is far less dense. The nitrogen-robbing effect of hardwood mulch is exponentially greater than with pine straw.

4. The wood used in wood mulch didn’t end up in the mulch pile because someone made a great sacrifice. It ended up there because someone wanted it gone. And, very often, though not always, they wanted it gone because it was infected with a pathogen of some kind.

Hardwood mulch is a product of whatever landscapers unload into the mulch pile, all types of wood, all types of pathogens.

Hardwood mulch is a product of whatever landscapers unload into the mulch pile, all types of wood, all types of pathogens.

I used to tell my customers, “Oh, don’t worry. Because it’s in big piles and gets so hot, all the bad stuff gets cooked out.” Maybe, sort of, sometimes. (In my defense, I honestly believed that to be true for many years.) Consider, for example, the recent widespread spread of crepe/crape myrtle bark scale in the Mid-south. As Greg Touliatos has rightly pointed out, since the female of the species only moves a short distance in her entire life, a distance measured in inches, at most, we have to ask, how is it spreading? Could it be wind? Birds? Maybe, but it is still spreading awfully fast for that to be the only source of transport. The more likely explanation is landscapers and the wood mulch from mulch yards, bought in bulk. Can Greg prove that assertion? Not without a lot of time and money, but I regard it as probable, and you would be wise to do so, as well, until more data and a good competing explanation is presented.

I maintained this home for years as a landscape contractor, regularly using wood mulch.  It looked great but there were some problems.  The green mountain boxwood replaced two diseased American boxwood and the snow white Indian hawthorns in the background had frequent fungal infections.  In retrospect , these problems might have been prevented by using pinestraw mulch instead.

I maintained this home for years as a landscape contractor, regularly using wood mulch. It looked great but there were some problems. The green mountain boxwood replaced two diseased American boxwood and the snow white Indian hawthorns in the background had frequent fungal infections. In retrospect , these problems might have been prevented by using pinestraw mulch instead.

I suppose landscapers could change clothes and sanitize all of their equipment between yards, and pre-treat your wood mulch, but what consumer is willing to pay for that?

5. Wood mulch is heavy; unless you buy it in bags, you must transport it with a pickup or dump truck or pay someone else to deliver it. And, if you buy it in bags, you have to pay a lot more. In contrast, my source (read: the google) says the average bale of pine straw weighs less than 12 pounds. No wheel barrow or pitchfork required. Gloves are advised, but not strictly necessary.

6. If wood mulch is piled against the trunks of woody plants it promotes damage to the outer cambium layer, the thin outer ring of recent growth. It is the main, in some cases, the only highway for nutrients to move up and down the trunk of a plant. If this layer is damaged and/or rendered non-working, the plant dies, every time.

Wood mulch holds water, like a sponge, and, though the roots of plants absorb and utilize moisture very well, the trunk wood does not. Although good landscapers and gardeners know to keep the wood mulch off of trunks, this is not done as often as it should be. And, heavy rains can move mulch, leaving it in drifts piled up against trunks, even if the person who originally installed the mulch did so with great attention to this detail.

7. Bulk mulch can have a ph problem. Ph is the measure of alkalinity/acidity, the middle of the scale being 7 and most plants thriving at various points along the ph scale between 5.5 and 7.5. Anything below 7 is regarded as acidic and anything above that number is considered alkaline. Once, early in my career, I bought 20 cubic yards of wood mulch and had it delivered by dump truck from a mulch yard to a property owned by two scientists in Cordova. They were new clients, with willingness and ability to pay, so, I was not only pleased to be making the profit from the mulch install but also hoping for more business from them in years to come. The next day, all of the perennials they’d recently planted, several hundred dollars worth — perennials that were in perfectly good shape when I arrived on the scene — were all in a wilted and browned-out state. Saying they were annoyed was an understatement.
How could this be my fault? My assistant promised he had heavily watered it in to counter any moisture robbing effects. And, we had done a nice underlayment of composted leaf mulch to counter any nitrogen-robbing effect. I denied any wrong-doing on my part. But they, being scientists, tested the mulch’s ph and said that it was under 4 in nearly every spot — highly acidic — and, smelled like rotten eggs.

So, I began to research. Turns out that mulch not turned regularly at the mulch yard, though it cooks out many pathogens, promotes anaerobic organisms. Anaerobic organisms excrete compounds that are highly acidic and toxic to plants. Further, the excretions give off a rotten egg smell.

It cost hundreds of dollars to replace their perennials and I never again received any business or referrals from them.

Now, the supplier of mulch Urban Earth uses is very conscientious about this issue and, even if they weren’t, our mulch sits for some time in a smaller pile after transport to our garden center before being sold, allowing it to air out and get access to oxygen.

Even after I have explained all of this to my customers at Urban Earth, I still sometimes hear two arguments: 1) I’m sure pinestraw carries diseases too. 2) Your pine straw costs $9 per bale and I can get hardwood mulch for less than $5 per bag, and even cheaper by the truckload.

Let’s address these in reverse order. Depending on density of plant matter in your beds and how thick you put it on, the pine straw covers anywhere from 20 square feet to 50 square feet, with 30 square feet being about the median coverage factor, in my experience. Wood mulch covers about 10 square feet per bag. That means customers end up paying between 18 cents and 45 cents per square foot for pine straw and 25 cents to 50 cents for bagged wood mulch. So, if anything, pine straw is cheaper.

As for the disease argument, it is possible for anything to carry disease, but it is far less likely that pine straw will and, even if it does, it is less likely that the particular disease will effect your plants. Pine needles are shed by trees naturally and regularly. Even if the source pine tree is diseased, most diseases are pretty specific to a plant. So, unless you’re using it to mulch around other pines or closely related species, you’re in the clear.

So, there are a few things to learn from this. First, hardwood mulch is for chumps and you should stop using it. Second, the advice I give you may later turn out to be terrible and it does not offend me in the least if you double check it with other sources, including soliciting competing opinions from other staff at Urban Earth. Third, I am willing to admit I was wrong and I owe all of my old clients from my days as a landscape contractor an apology (but don’t try to get any money out of me). Fourth, Urban Earth carries bales of pine straw and you should buy from us when you need it. Fifth, Urban Earth also carries double-stamped wood mulch in bulk, sold by the cubic yard, but will likely discontinue carrying wood mulch in bags once our current supply runs out.

Unless our customers decide I don’t know what I’m talking about and continue to demand it.

— John Jennings, Manager