Pythium Root Rot or Blackleg of Geranium

Disease Information

Pythium Root Rot or Blackleg

Pythium spp.

Symptoms and damage

Usually more serious on cuttings during propagation but can occur on plants of any age; brown, water and soaked lesions develop at the base of cuttings or at wounds; they become coal-black and watery; plants collapse when girdled;


 • Practice good sanitation by using a clean house and equipment and a sterile, welldrained medium

• Use disease-free cuttings

 • Avoid overwatering (disease is favored by high moisture and low oxygen levels)

• Rogue and remove symptomatic plants

 • Maintain good insect control, esp. fungus gnats and shore flies

• Fungicides: among those registered for use are metalaxyl, mefonoxam, fosetyl-al, etridiazole, and etridiazole plus thiophanate-methyl; also registered is the biocontrol agent, Trichodermaharzianum T-22

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