Plant Health Page 2

BT – natural toxin that kills caterpillars when they eat it on a treated leaf (Dipel).  Some formulations kill fly-type larvae like mosquitoes (Mosquito Dunks) or fungus gnats (Gnatrol).
Pyrethrins- Kills anything it contacts, including lady bugs and predators.

Plant Diseases:

  • There are 2 kinds of diseases: environmental and infectious
  • Environmental are caused by a difficult environment (too wet, too hot, too sunny, too little fertilizer, wrong pH, someone did something unfortunate like spray herbicides nearby or dump chemicals too close, or hit plant with a weed-whacker).
  • Infectious are caused by fungi, bacteria or virus
  • Infectious disease:
    • Virus is like the flu.  It can’t be cured with medicine.  Throw away the plant.
    • Bacteria can’t be cured but it has some rules:
      • Bacteria must enter through a wound.  Prune susceptible plants as little as possible.
      • Bacterial diseases may appear after hard rains (raindrops make wounds).
    • Fungi are usually the culprits.  A tiny spore enters the leaf, injures plant and then spreads itself to other leaves by air or moving water.

Fungal disease control:

  • Crowded plants and those in too much shade cannot dry off well in the morning and are more susceptible to fungal attack.  Improve air movement (get plants away from the wall or remove some plants if too many were placed in a small space).  Improve sun exposure by thinning overhead branches.  Transplant those in too much shade.
  • Removing the first spotty leaf or 2 will often stop the disease.
  • Use a mulch to stop rain splashing soil onto leaves.  Use drip irrigation if possible.
  • Use a fungicide preventively:
    • Fungicide provides a layer of protection to keep spores OUT.
    • Only use on plants with expected problems, not on everything.
    • Reapply according to directions, sooner if heavy rain washes it off.
    • Damaged leaves will not repair themselves, but uninfected leaves will be protected.                Page 1