Pathogen Prevention

Accurate identification, rotating modes of action, and proper watering practices are key.

The air-water balance in the soil is key in preventing destructive soil pathogens such as Pythium, Thelaviopsis, and Phytophthora. Conditions where there is low oxygen and high moisture content are stressful for the plant, but ideal for these problem pathogens. A well-aerated soil media will drain well and provide air space for roots to respire. In addition, injury to the roots from overfertilization or from allowing the soil to become excessively dry can make plants vulnerable to root diseases. Roots damaged from drought cannot take up as much water, so if watering is resumed at the original frequency, damage from overwatering can occur.

A poinsettia with roots damaged by excess soluble salts and infected with Pythium. After leaching with clear water and treatment with a fungicide, healthy new white roots are beginning to grow.
Photo: Tina Smith, University of Massachusetts Extension Greenhouse Crops and Floriculture Program. New England Greenhouse Update Photo Library:

Cultural Controls: A well-drained media with good porosity is essential to preventing soil pathogens. Of equal importance, and closely tied to it, are careful watering practices and a balanced fertility program that keeps plants strong and healthy and bolsters their natural defenses.

Several of the major soil pathogens spread through water, and careful sanitation is also key. While subirrigation allows watering without wetting the foliage, therefore helping to limit spread of foliar disease, it can be a culprit in spreading soil pathogens, especially if the water recirculates. Regular disinfection of these systems is important.

Chemical Controls: Despite growers’ best efforts to keep things clean, it is nearly impossible to avoid using chemical controls for pathogens in a commercial greenhouse environment. There are many fungicides that can be used to control root diseases before they start. But there are some factors that have to be taken into account when considering what to use and when:

  • Know your enemy. Make sure your diagnosis is correct. Call in a consultant or send a soil sample to a commercial lab if you need assistance. It’s expensive to waste time and money on a product that isn’t designed to control the disease you actually have.
  • Keep records. Know when the conditions are right for possible disease problems and if they have occurred in your greenhouses before.
  • Apply the appropriate fungicide two or three weeks before the disease might appear.
  • Rotate modes of action. Pathogens can develop resistance if the same mode of action is used too many times in a season. FRAC (Fungicide Resistance Action Committee) codes group products by mode of action. Find out the codes of the products you use; if two products have different codes, you know it is safe to use them in rotation. Information is available at
  • Know the length of the residual activity of your products. Why apply another product when the first one is still working? The details can save you money.

Fortunately, growers have a variety of effective fungicides from which to choose. Pageant® Intrinsic® Brand fungicide is one of them. As a broad-spectrum fungicide, Pageant controls major soil pathogens such as Phytophthora, Pythium and Fusarium, in addition to numerous foliar diseases. Pageant is also the first-ever crop protection product in the ornamental market to include “plant health” on the label.

While Pageant’s primary purpose is as a fungicide, it has been proven to provide plant health benefits. Pyraclostrobin, the active ingredient, provides increased efficiency of plant processes, namely, conserving carbons, the source of plant energy, in the roots. This enables plants (specifically geraniums, impatiens, pansies, and petunias) to better withstand disease and a multitude of stresses, whether drought, cold, or shipping, resulting in improved plant performance and attractiveness.