Tuesday, June 4, 2019

Friday, February 17, 2017

Plant growth regulator.  That may sound scary to some, and counterintuitive to others.  Why would we want to intentionally stop a tree or shrub from growing, and how does that even work?  Believe it or not, there are many reasons why it may be beneficial to slow the growth of a plant, which include economic factors, environmental factors, and overall plant health factors.

Before we delve in to the specifics of plant growth regulators, or as I like to call them ‘plant growth managers (PGMs),’ it’s important to know that many of us come in contact with this technology quite often.  PGMs first became popular in the floriculture industry to get uniform plants that would be merchantable when they made it to the garden centers.  Have you ever noticed your house plants start becoming leggy and a bit yellow after they’ve been in the house for a few weeks?  That is because the growth regulator applied before you bought them is wearing off.

Early versions of PGMs, Type I growth regulators, were closely related to herbicides, and actually blocked cell division to accomplish reduced stem elongation.  While Type I growth regulators work very well at reducing growth there can be some unintended consequences of using them.  Namely, Type I growth regulators may cause leaf yellowing and distortion.  If applied above certain temperatures Type I growth regulators may also cause slight defoliation. 

Modern PGMs, Type II growth regulators, work within the plant to regulate the hormone (gibberellin) which is responsible for cell elongation.  This means the plant is still producing the same amount of cells, leaves, buds, etc. just those stems are extending 30%-70% less than normal.  This reduction in growth can lengthen time between pruning cycles for trees and shrubs growing in close proximity to infrastructure.  For example, the oak tree planted 10-feet from the corner of your executive building, the line of trees planted underneath those utility lines, or that hedge that needs to be trimmed a few times a year so you can see out of the first floor windows.  

Less pruning means less wounding for the plant (bonus for the plant), less time your crews need to spend managing your shrub and tree resources (bonus for labor), and also means less ‘green-waste’ your crews need to dispose of (bonus for the environment). In 2016, Rainbow Scientific, in cooperation with our partners, performed a series of trials to determine labor savings when incorporating Trimtect into their pruning operations.  Trimtect is a foliar spray-applied Type II plant growth regulator.  The sites selected contained highly manicured shrub hedges ranging in length from 50-180 feet long and 4-8 feet tall.  Over a twelve week period we found pruning time was reduced by an average of 62% when compared to shrub hedges not treated with Trimtect.  In another trial we found green waste removed from the site was reduced by 50% over a 12 week period.  Managers and crew leaders involved in the trials were unanimous in their positive response to the reduced need to prune.  Landscape crews were able to focus on getting more detail work accomplished (e.g. weeding, flower bed maintenance, trash removal, etc.), in addition to getting caught up on turf mowing and edging.  They also had less ‘call backs’ and complaints in areas where Trimtect was applied.

While plant growth managers reduce the amount of above ground growth by 30%-70%, they are also promoting responses in the plant that can encourage plant health. One positive side effect of growth control is the stimulation of another plant hormone, abscisic acid (ABA). ABA helps with preventing cell dehydration, and regulating leaf water loss by allowing stomata in the leaves to respond faster to drought conditions.  When PGMs are applied as a soil drench we see energy resources being diverted to the promotion of fine root growth. This allows a tree to mine more resources from the soil, and increases drought tolerance.  PGMs can also increase the amount of chlorophyll the plants produce.  Chlorophyll is, of course, what gives a leaf its green color, and plays a major role in photosynthesis.  Disease resistance to certain fungal leaf and canker diseases has also been recorded with the application of PGMs.  So, not only can you employ PGMs as a growth management tool, but they can also be employed as a plant health care tool.

The use of plant growth managers can often be overlooked, but when used correctly, can be a substantial tool to help reduce time spent on pruning while also benefiting plant health.  Next time you’re walking through your site think of those hedges, ground covers, trees, and vines that seem to need constant attention.  Now imagine, instead of the plants dictating your pruning schedule, you dictate the plants growing schedule.

Tuesday, February 7, 2017

What's limiting your trees's growth?

What limits plant growth?

Have you ever experienced a tree or woody ornamental that just doesn't want to grow?  Overall plant health and vitality depend on several factors, and if just one is out of whack, you may end up with an under performing plant.

It begins in the nursery
Starting with a quality plant is key for long term success.  Occasionally there are breakdowns in how the plant is cared for in the nursery that can affect how it thrives in the landscape.  During production, if a baby tree is kept in a pot for too long it may eventually form a distorted root system.  If these conditions aren’t addressed, the deformed root system will remain with the plant for it's entire life.

One common root distortion that may form is circling roots.  Circling roots are roots that grow around the stem of the plant instead of perpendicularly away from the plant.  In the nursery this happens when young roots contact the side of the pot in which the plant is growing, and start growing along the outside of the container.  Circling roots can affect plant stability.  If these roots are in contact with the stem they can lead to a condition called girdling roots.  Girdling roots have the potential to cut-off portions of a stem’s vascular system, interrupting nutrient and water flow through the plant.

At planting
There is an old saying, “you only get one chance to plant a tree.”  While planting a new tree or shrub seems intuitively easy, there are some caveats to proper planting.  All woody plants should be planted so their root flare is  at grade level and exposed, not covered by excess soil or mulch.  The root flare is the transition zone between the trunk and the roots.  Buried root flares may result in bark damage which lead to vascular system issues.  Buried root flares may also lead to girdling roots.   Note, sometimes root flares are buried due to poor nursery practices.

It’s also important to dig a hole large enough for the tree/shrub.  Standards state digging a hole at least 1.5 times the diameter of the plant’s root ball. The larger the planting hole the better.  This is so newly emerging roots have an easy time of colonizing the native soil.  The more soil that can be loosened around a newly planted tree, the faster the tree will be able to become established.

Site, site, site
Matching the right tree to the site and site preparation is paramount to overall performance of trees and woody ornamentals.  Different species have unique light, soil, and water needs.  Let’s take our native flowering dogwood as an example.  According the USDA NRCS plant materials program: “Flowering dogwood is adapted to most upland sites but grows best on rich, well-drained soils on middle and lower slopes. It develops best as an understory species in association with other hardwoods.”  So, if we are to plant a flowering dogwood in a poorly drained clay soil in full sun, it goes without saying the tree will not be healthy vigorous specimen.

One major issue we run into, especially in our urban/suburban landscapes, is damaged soils.  During new building construction the top layers of soil, which forest trees roots thrive in, are removed.  What remain are compacted subsoils.  Compaction destroys soil pore spaces that air, water, and plant roots occupy.  This is direct stress on woody ornamentals, and one of the greatest reasons trees and shrubs fail to thrive in our landscapes.  Accompanying compaction in urban/suburban soils are also nutrient deficiencies, soil chemistry imbalances, and inadequate amounts of soil organic matter.

Another major issue for plants in our landscapes is water issues.  Too little or too much water is often the difference between green and growing plants or yellow and dying plants.  Combine improper watering with poor soils and you have a recipe for disaster.

All's not lost
Fear not.  While the issues we discussed may sound overwhelming the arboriculture industry has developed some innovative protocols and tools for mending these common problems.  Laboratory soil analysis, soil decompaction treatments, and root collar excavations utilizing compressed air-tools are just a few methods available to mend adverse plant growing conditions.  If you have a tree that just doesn't seem to be growing, call your friendly neighborhood qualified arborist for a thorough assessment.

Saturday, April 4, 2015

Cankerworms among us...

In the Charlotte, NC Metro area we have a big problem with cankerworms.  These inching little menaces emerge every spring to wreak leaf consuming, poop raining havoc on the populous.  Treatment for these wringing pests comes, usually, in a few forms.  Banding in the fall and early winter to capture flightless females on their trek to mate high in the canopies of trees, and foliar spraying once the chomping little caterpillars have hatched.  Both of these methods have their pros and cons.  Bands certainly do not catch every female, and in the spring newly hatched cankerworms can easily blow from trees not banded to banded trees.  Foliar sprays to control the munching larva have their own host of issues, namely getting adequate coverage on 60 - 100 feet tall trees is tough even in the best of conditions.

It is debatable how much damage is done to trees defoliated by cankerworms.  In most instances, defoliated trees create a new full canopy by the end of May/beginning of June.  This allows trees almost a full season of photosynthesis to create the energy they need and build reserves.  And hey, a few weeks of additional sunlight helps out the grass, and all of that worm poop hailing down is like free fertilizer, so look on that bright side.

Outside of being a tree pest, cankerworms can be a real nuisance.  They are constantly falling from trees attached to silk threads, and of course all that pooping.  This can make for an uncomfortable experience if your back yard is completely covered by the canopy of large trees.  My house has 2 large (+50-inch DBH) willow oaks in the rear yard.  Two years ago the cankerworm population was high enough to defoliate both of the trees by the 1st week of May.

Last year I put bands on the trees, specifically the Bug Barrier product, only to have squirrels rob the bands of the fiber used to help catch climbing females.  Once again my trees were defoliated, minus what I could reach with a foliar spray of Conserve (active ingredient spinosad).

This year I am opting for a new strategy.  Soil injection with Lepitect (active ingredient aceaphate).  Lepitect has shown great results on a host of tree pests.  It works fast to get in the tree, and has a residual of only +/- 30 days.  I like the idea of a short residual because I don't want to kill other caterpillar species that emerge later on in the season.  But here is my question, will Lepitect work well on large trees with high populations of cankerworm pests?  Hence the penning of this article.

 Follow the saga of the cankerworms below:

  • March 24th
    • The 1st cankerworm is spotted.  Willow oak leaves just beginning to break bud and expand.
  • April 1st
    • Lepitect applied at high rate, 10oz per 25-inches of diameter applied at 250ml per inch DBH.  Willow oak leaves are expanding
  • April 4th
    • Signs of dead cankerworms falling from trees.

  • April 11th
    • Approx. 18-days after emergence, and 11-days after treatment.
    • Once again, a very high population of cankerworms are affecting the trees.

  • April 18th
    • Significant amount of dead cankerworms falling from the tree.

  • April 27th
    • Peak cankerworm feeding has concluded.


Once again the cankerworm population was very high on the trees in my backyard.  Because some leaf feeding is required for the insects to be exposed to the product, we expect a certain amount of defoliation.  Inevitably, with instances of very high pest population we will have more leaf matter consumed.  All said and done, there was probably 40%-50% canopy defoliation when using the Smitley Scale for Defoliation.  This sounds high, but is much better than the fully defoliated trees I had the two previous years.  Additionally, the product is no longer present (or at least should no longer be present) with in the tree or the soil, so any benign leaf feeding arthropods or soil dwelling organisms should be allowed to go on with their natural life cycles.

Additional Notes/Thoughts:

I would have liked to make the application a week earlier, but my equipment for making the application had yet to arrive.  One wonders if the product had a week longer to move in to the tree, would the defoliation been less?

There were a significant amount of dead cankerworms falling over the course of three weeks.  Will this hammering of this years population have any effect on next years population?

It has been noted that the fiery searcher beetle was in greater numbers the past two springs.  These beetles are voracious predators of caterpillars and especially cankerworms.  Did these predators significantly reduce, or aid in the reduction, of the cankerworm population that in turn lead to the decrease in defoliation noted from last season?

Sunday, January 4, 2015

It's all in the phenology......

Below is an article I wrote for my friends at Limbwalker Tree Service in Louisville, KY. Enjoy:

Though it may seem hard to believe, the first flowers of spring will soon be upon us.  It doesn't take a horticultural aficionado to appreciate these brightly colored petaled reproductive organs of angiosperms. The yellows, whites, blues, reds, and purples are a welcomed site after a gray cold winter.  But, the emergence of certain plant species floral displays can be the warning signs for  the appearance of diabolical plant damaging pests.  The study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation) is called phenology.

Smoke bush flowers coincide with Japanese maple scale crawlers.

Monitoring the life cycle of plants (leaf expansion, flowering, color change, etc.) has been used for centuries in agriculture to determine the appropriate timing of when certain crops should be sown.  In fact, the first record of phenology dates back to 974 BC *.  Complementing phenology are growing degree days (GDD).  GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature (usually 50°F). GDD are a measure of heat accumulation used to predict plant and arthropod development rates, such as, when flowers of a particular species may bloom, or when a particular insect will become active.

                             GDD      =        (daily high + daily low)     -   50

Growing degree day charts highlighting common tree/shrub pests have been developed by the Ohio State University and Cornell University to name a few.

The use of phenology and GDD is an important monitoring tool for integrated pest management practices in the landscape.  The activity of many plant damaging pests coordinates to either the flowering or leaf expansion of common shrubs and trees, some of which may be in your backyard.  When the hanging white racemes of black locust flowers appear (500 GDD +/-), the invasive emerald ash borer adults are beginning to emerge.  The first flight of the adult dogwood borer corresponds to about 2 weeks after peak dogwood bloom (850 GDD +/-). Eight weeks after the full leaf expansion of red maple (1000 GDD +/-) the most vulnerable stage of gloomy scale appears.  These are just a few examples of using phenological indicators to predict the emergence of tree damaging arthropod pests.

Being in tune with phenology and growing degree days can be invaluable when developing a plant health care plan for our landscapes.  Knowing when insect pests are active allows arborists to make precise treatments, which limit the amount of products applied in landscapes.  This also reduces the chances of harming beneficial, or benign, critters that make our plants their home.  Happy hunting!

*University of Wisconsin


Sunday, May 4, 2014

Don't worry, it's not that complicated.

I'm constantly amazed at the over simplification of plant maladies that most people subscribe to.  If a tree or shrub is looking 'sick', then it must be some inauspicious bug or disease causing the problem, and a one time spray of something should solve the problem.  If not some magic spray, then the obvious solution is to 'feed' the poor starving plant.  Often we can find a tree damaging pest or signs of nutrient deficiency on our sickly patient, but it's the greater predisposing factors which are leading to the plant's decline.
Recently I was asked to look at some sickly shrubs.  Within a few moments I learned the following; when the property owners purchased the plants they got a good deal because the shrubs were old stock and not looking great (in some cases dead bark was peeling from the trunks), when installing the shrubs the planting holes were over amended with compost, and they’d been applying a complete fertilizer liberally to the root zones.  In the mean time the root balls of most of the shrubs had settled to several inches below grade.  After the shrubs started to look really bad, the property owners assumed some unknown but malevolent pest was attacking their plants, and began spraying them with horticultral oil.  My assignment was to identify what was wrong with the shrubs and develop a plan for their improved health.
The diagnosis? What was wrong with the shrubs is everything.  Substandard plants, installed incorrectly, with soil chemistry all mixed up.  There was no baleful insect or disease, just a series of preventable cultural mishaps, which so often after having occurred are left to an unsuspecting arborist to diagnose.  The remediation plan? Basically, start the planting process from the beginning, which included removing and replacing a handful of the previously installed plants.
The results of this encounter was a dissatisfied property owner left doubting the diagnoses of the consultant that was subcontracted through their primary tree care provider.  At the end of jobs like these I almost feel guilty charging my fee, and I know the clients are never too happy to pay.  Maybe next year there will be a magic potion for this.
What could be going on with this sad looking plant?

Sunday, April 13, 2014

What could it be? I hope it doesn't suck....

Take a look at the picture of the Nelly Stevens holly below.  You'll notice the top of the tree is in decline.  What could it be?  Root rot? Nutrient deficiency? Perhaps straps where left around the stem and are now girdling the tree...

Now let's take a closer look...

Upon closer inspection we see the top die back is being caused by coalescing sap sucker wounds.  The yellow belly sap sucker drills holes in over 1000 species of trees.  The purpose of this behavior is to feed on the high sugar content tree sap, and any insects that may get caught in it. Sap suckers form two kinds of holes.  The first is a round hole that extends far into the tree and is not enlarged.  These are the holes that are commonly associated with species like sugar maple.  The second is a square hole that is shallow, but which needs to be be constantly maintained for sap flow.  It's this square hole that I've seen kill whole branches of trees over the years, most notably holly species. 

There aren't any good ways to prevent sap suckers from enjoying your trees.  Repellent sprays on the market seem to not be effective.  For high value trees I've seen burlap being wrapped around trunks during times of sap sucker activity.  This provided some modicum of protection, but can be unsightly and labor intensive.  In the interest of political correctness, I'll refrain from any BB-gun jokes.