Timely tree tips — insects and diseases can indicate other problems

Cherry trees on the Capitol Campus Photo: Micki McNaughton, DNR
Cherry trees on the Capitol Campus       Photo: Micki McNaughton, DNR

Trees that are damaged, stressed, unhealthy or in decline are far more susceptible to insect infestation and diseases for two reasons:

1) Physical injuries damage a tree’s protective bark tissue, providing easy access to the tree’s core for insects and pathogens; and,

2) Stressed, unhealthy or declining trees have fewer available resources to provide active defenses against insect and disease attacks.

Unhealthy trees are attractive to insects and pathogens for the same reasons that a sickly zebra is attractive prey for a predatory lion: sickly prey is weaker, easier to attack and less likely to fight back, skewing the odds in the predator’s favor.

Prescriptions for treating insect and disease problems often come in the form of pesticide applications. Pesticides can be powerful tools to address symptoms, but do little or nothing to mitigate underlying causes of a tree’s decline, and nor are they helpful in returning the tree to health.

The best antidote to tree disease is similar to the advice given to us humans: proactive attention to stress reduction and good care. Here are a few recommendations to get you and your trees started down the road to good health:

  • Plant the right tree in the right place. Choose trees that are well-suited to local soils and other site conditions with adequate growing space above and below ground.
  • Plant the tree properly with the root flare at grade. Planting too deeply is one of the leading causes of long-term tree decline, and one of the easiest to avoid.
  • Provide supplemental water when needed. Dehydration is incredibly stressful but also preventable when trees, especially newly planted ones, are provided adequate water during hot summer months.
  • Mulch trees deeply. 2″- 4″ of organic mulch in a nice, wide ring around the base of your trees can do wonders to reduce plant stress by decreasing moisture loss from the soil and cooling the rooting zone of the tree. Physical damage from mowers and string trimmers may also be lessened by keeping grass and weeds away from the tree trunk.
  • Prune trees according to best practices. Good pruning practices not only reduce the risk of storm damage, but may also limit the spread of some pests and disease organisms.

Pause before breaking out the chemicals and look for opportunities to improve tree health instead; it’s cheaper and friendlier to the environment, and the positive effects are longer lasting. Healthy trees will reward your care by fending off nasty pests and diseases on their own, as well as looking more beautiful in the landscape.

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