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.

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.

Conclusion:

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?

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

             2

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

http://hort.uwex.edu/articles/phenology

I smell something ferty.

Something often forgotten is that our NPK fertilizers and recommendations are based mainly on agriculture.  Most often farmers plant multiple acres of the same crop.  The crop grows from seed to maturity in these fields, absorbing all the elements essential for plant growth from the soils.  When the crop is ready for harvest the entire plant is removed from the site leaving bare soil.  Even when fields are rotated this process happens often enough to burden the soil.  In these situations, complete fertilizers with high NPKs are necessary to replace elements robbed from the soil when plants are taken from the site.

Landscape trees and soils are managed in completely different ways.  While top soils are usually stripped and vegetation removed during the construction process, it's usually a one time event.  Most soils are still able to retain many of the elements essential for plant growth.  Trees, shrubs, and other plants also produce exudates.  Though still not fully understood, exudates promote soil micro-organisms which produce available soil nutrients over time. 

Many studies comparing fertilizers and methods of fertilization often show trees respond best to simple correct mulch applications.  Trees have evolved in forests where leaves, branches and trunks are left to decay.  Correct mulch applications mimic this dynamic.

If you suspect nutrient deficiency in a tree you're managing, it's important to identify which nutrients are lacking.  Misapplication of the wrong fertilizer can be a waste of time and money, and may hurt the tree further if one element is raised to damaging levels.

Typical Soil Analysis 

Getting to the pH of the problem

When we fertilize, our goal is to make nutrients available in the soil.  Plants may then absorb and use these nutrients in biological processes.  By taking soil samples we may determine what nutrients may be lacking, or what nutrients may be in such abundance they are creating an antagonistic environment for the plant.  Most soil samples will also return pH.

Soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm (base 10) of the activity of hydronium ions (H+ or, more precisely, H3O+ aq) in a solution. It ranges from 0 to 14, with 7 being neutral (I copied all of that from Wikipedia).

Soil pH is important. Nutrients can be made unavailable in soil at different pH ranges. Classic examples are iron (Fe) will get tied up in soils at higher pH, while phosphorous (P) will get tied up at lower pH. The pH scale is logarithmic, so there can be a big difference in availability between 5.5 & 6.

Chart of soil pH and Nutrient Availability

When managing trees in a man-made landscape, pH ranges can vary within a few feet of each other. Removal of soil layers, exposure of soil layers, and type of building material can all effect a 'micro pH environment.' Most trees enjoy a pH of around 6 (give or take). Again, depending upon multiple factors, adjusting pH to an ideal range for trees may be difficult. In addition, depending on which way you are trying to tip the scale, and which product you are using, results may take months and may be fleeting.

Take soil samples and pay attention to pH.  All of the nutrients required for growth may already be in the soil and just tied up.  Knowing this information will help arborists choose the correct soil amendments and reduce the chances of creating an antagonistic environment from over applying fertilizers.

The Scourge of Imidicloprid

If you're like me, then while your wife is looking at power tools at Home Depot, Lowes, or wherever, you are looking at the active ingredients on pesticides in the garden aisle.  Which means you have probably noticed that many general purpose over the counter insecticides are now imidacloporid based.

As an industry, we have relied on imidacloprid, Merit in its most popular form, for more than a decade.  Applied properly it is a great product.  It is in the neonicotinoid family of chemicals, and its mode of action is kind of neat.  The chemical interferes with an insects nervous system which results in death. Imidacloprid can be applied as a foliar spray, soil application, or directly injected into the trunk.  It is nontoxic to mammals, has a long residual, and can be quite effective.

However there are some things we need to consider when using this pesticide.  Studies have shown that with repeated use the molecule can make its way into the flowers of plants.  For trees and shrubs that are not wind pollinated this exposes pollinators to the product, and may lead to civilian casualties in the war against plant pests.

The other issue is pest resistance to imidacloprid.  In some areas imidacloprid has been so heavily used that it is no longer effective against targeted pests.  With imidaclolprid now being readily available to the public at large, and continued reliance on the chemical in many professional PHC programs, we may only assume that this pest tolerance will grow.

There are few 'silver bullets' in pest management.  Product/chemical diversity is an important part of an IPM program.  Imidacloprid may still be part of your chemical arsenal  but pest monitoring and investigating different products for use on target pests should be on the forefront.

The molecule