Eight Tips for Better Disease Control in the Greenhouse

The Disease Triangle: Where Growers Fit In

The interaction between a susceptible host, a virulent pathogen and a favorable environment determines the severity of plant diseases in the greenhouse. Eliminate one of these three factors and you lower the probability of disease occurrence.

The “human component” is an additional, but rarely talked-about factor that can be added to the disease triangle. Growers have more influence than they think on disease prevention. The management decisions they make, from the choice of cultivar to the amount of water they apply, have the potential to intensify, alleviate or eliminate conditions that favor disease.

  1. Be obsessive-compulsive about sanitation. Start clean and stay clean to prevent a majority of disease-related problems. Clear away dead plant materials, eradicate weeds, start with clean stock material and disinfect equipment and benches.
  2. Dry out. Saturated pots, water film on leaves and puddles on benches are open invitations for several nasty pathogens to come calling. Avoid overwatering and late-day watering. Do everything necessary to keep plant leaves dry and roots slightly moist.
  3. Monitor for problems. Check plants regularly for insect, disease and root problems, as well as for overall plant health. Keep detailed records of when problems occurred and what conditions were present at the time. Pictures are also useful for preliminary identification.
  4. Combine chemicals with cultural controls. A two-pronged disease program that combines both cultural and chemical controls is necessary to maintain crop uniformity and marketability. Carefully read and follow labels. Rotate products to slow down resistance.
  5. Choose growing media carefully. Make sure your growing media has excellent drainage and good porosity. Never re-use soil or use non-sterile soil from outdoors.
  6. Maintain good air circulation and control humidity. Be aware of high humidity conditions and maintain good air circulation during the evenings, on rainy, overcast days or anytime water use efficiency is at a low. Vent late afternoon air and heat incoming air to reduce relative humidity. Space plants appropriately for good air movement through the canopy.
  7. Quarantine incoming stock. Isolate new plants until they can be inspected for disease symptoms and insect problems. Use a reputable supplier for purchasing non-rooted cuttings, plugs and liners.
  8. Use disease-resistant cultivars. Healthy, disease-resistant plants help minimize disease outbreaks and can reduce pesticide use.
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