Natural Notes: Plant Healthcare

This post consists of my notes from a lecture on plant healthcare as part of my training to become a certified arborist by the International Society of Arborculture.  The speaker was Rob Klamcynski, a natural resources specialist with the Forest Preserves of Cook County and his lecture took place on February 6, 2015 at the Salt Creek Resource Management facility in Willow Springs, Illinois.  

 When discussing plant health, there is some important terms to distinguish:  vitality versus vigor.  Vitality is a plant's ability to deal with stress.  Vigor  is a plant's adaptability to various environmental conditions such as soil conditions, moisture, and cold or heat.  

 An example of vitality in trees are trees planted in parking lots.  These trees often have reduced growth, their stomata close more frequently, and their leaves shed early.  

 Trees exhibit resource allocation among four primarily functions:  (1) maintenance, (2) growth, (3) storage, and (4) defense.  Limited resources = stress!  Much of the stress is related to soil and environmental conditions.  

 Plants have defense mechanisms to deal with this stress.  Some may have physical deterrents such as thorns, spikes, and hairs.  Others have tough cellulose and lingins (dense cell walls with "chain-like" molecules that provides strength to the tree's leaves and shoots).  

 Chemical deterrents in trees are known as allelochemicals.  Walnuts and sunflowers, for example, release allelochemicals in the form of tannins and phenols. . Some of these allelochemicals are found in pesticides (e.g. Rotenone).   Moderate drought stress can increase allelochemical levels.  Sun-adapted trees planted and grown in shade have reduced levels of allelochemicals.  

 It has been shown that rapidly growing trees can be less resistant to some insects and diseases.  

 The decline of tree health occurs in a morality spiral (see figure 1).  The further down the spiral, the harder it is to treat the tree.  Timing is important (address tree health early in the spiral if possible).  
Figure 1:  Tree morality spiral.  
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The process of plant health care includes monitoring and early detection is key!  It is best to gather info from the site prior to determining a response.  This involves using the appropriate response process (ARP):

  • Gather information
  • Access Severity.  
  • Determine client expectations
  • Determine course of action
Determining a course of action could include an integrated pest management (IPM) approach.  This involves a cost-benefit analysis that has been adapted from agricultural crops where the cost of using herbicides to reduce crop mortality is determined (see figure 2).  
Figure 2:  Cost-benefit analysis for using herbicides to reduce crop mortality.  
IPM could also include the use of disease resistant varieties of trees as well as cultural control.  Selecting trees or varieties of trees that are resistant to or tolerant of changing conditions are examples of using IPM strategies.  There are many hardy varieties now of crabapples and elms.   

Cultural controls include cleaning tools prior to and immediately after pruning.  Always clean tools between each cut on infected tissue or on plants that are highly susceptible to disease transmission.  Prune during the dormant season if possible, as well.  Identify infected plant material and take precautions to limit its spread.  It should be noted that the use of "wound sealer" is not recommended unless oak wilt has been identified in the area and growing season pruning is the only option.  

The right tree in the right place at the right time is ideal!  

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Chemical controls (pesticides)
Fungicides are typically applied as a protectant to prevent infections (e.g. apple scab, cedar rust).  

Insecticides kill pest animals on contact.  Contact insecticides are what gets affected is the area that is contacted by the insecticide.  Systematic insecticides get soaked up through the whole root system.  Insecticidal soaps disrupt cell membranes of soft-bodied insects and mites.  Dormant and summer products are available.  Insecticidal soaps are effective on scale crawlers and others.  

Botanical pesticides are plant extracts used for insecticidal purposes.  They can be toxic to humans, animals, and other plants.  

Insect growth regulators (IGRs) mess up insect life cycles.  

IPM also includes biological controls.  

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