Introduction
Eradication Tactics
   Disinfectants
   Water Treatment
   Soil Fumigation
Prevention Tactics
   Contact Fungicides
   Systemic Fungicides
      Phenylamide
      Phosphonates
      Cinnamic Acids
      Quinone Outside Inhibitor
Resistance
Summary

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Disclaimer: The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products implies no endorsement by the authors. Criticism of products or equipment not listed is not implied or intended. Due to continually changing laws and regulations, we can assume no liability for the suggested use of chemicals contained herein. Pesticides should be applied according to the label directions on the pesticide container.

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Chemical Control—Prevention Tactics (continued)

Systemic Fungicides—Phosphonate Group

The phosphonate group includes fosetyl-Al and phosphorous acid. These can move both up and down in the vascular system (both xylem and phloem movement).

A plant can take up these chemicals through roots, leaves, and stems and then move the chemical to other parts of the plant. Trunk, soil, or foliar applications can effectively control Phytophthora root diseases; however, soil microorganisms can degrade some of these chemicals quickly, so foliar applications are preferred. Application can be any time during active plant growth.
    
The mode of action in this group is a bit different from other groups’, because it acts directly on Phytophthora itself. However, chemicals in this group also stimulate host plant defense responses.

The phenylamide and phosphonate fungicides do not kill Phytophthora. They can either prevent the organism from becoming established the plant, or, if the organism is already inside the plant, the chemicals can  prevent its continued growth. As a result, the chemicals can delay the appearance of symptoms. Once chemical activity has subsided with time, however, Phytophthora can resume growth within infected plants.

For this reason you may choose to—or be directed to—AVOID use of these chemicals when producing susceptible plants. Avoiding use of these chemicals would allow you to identify infected plants that need to be discarded. This practice also would avoid the shipping of infected nursery stock to places where they do not have the disease.

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