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Beginner

Scientific Name
Phytophthora capsici

Identification

• Phytophthora symptoms include foliar blight, fruit rot and stunting
  
• The foliar blight/crown rot phase often starts at the growing point
  
• Dark green lesions form on the crown, eventually girdling it and causing the entire plant to turn brown, collapse and die
  
• Fruit infections begin as a large water-soaked lesion
  
• White spores resembling powdered sugar develop on the surface of the lesion 

Often Confused With
Pythium fruit rot
Fusarium wilt
White mould

Period of Activity
Phytophthora spreads rapidly during warm, wet weather. Ideal conditions for infection are moist soils above 18°C (65°F) and air temperatures between 24°C and 29°C (75 and 85°F).  Levels of soil inoculum build up over time, especially under intensive cucurbit and/or solanaceous crop rotations.

Scouting Notes
While monitoring for other diseases, take note of any wilted or stunted plants.  Record the number and location of the infected plants.  Inspect fruit for lesions or fungal growth.

Thresholds
None established.

Advanced

Scientific Name
Phytophthora capsici

While Phytophthora has not been a significant problem in cucurbits in Ontario in the past, this disease has caused serious losses in Michigan, Illinois and New York. Once established in a field, Phytophthora is extremely difficult to control.

Identification
Depending on the crop affected and time of infection, Phytophthora symptoms include foliar blight, fruit rot and stunting.  While the symptoms listed below are most common to that crop, infections are not necessarily limited to one type of symptom.

FOLIAR BLIGHT/CROWN ROT	FRUIT & STEM LESIONS	STUNTING
Squash Pumpkin Zucchini Peppers	Cucumbers Melons (musk & water) Eggplant	Tomatoes Cucumbers

Phytophthora problems often follow field drainage patterns.  They are most likely to occur in low lying, or poorly drained areas of the field. 

The foliar blight/crown rot phase often starts at the growing point.  Dark green-to-brown lesions form on the crown, eventually girdling it and causing the entire plant to collapse and die.  Later infections may begin with stem lesions, progressing down the vine and causing rot symptoms at the stem end of the fruit.

Foliar blight is uncommon in cucumbers and melons.  In these crops the rot usually goes straight to the fruit.  Fruit infections begin as a large water-soaked lesion.  White spores resembling powdered sugar develop on the surface of the lesion.  Symptoms often first appear where the fruit has direct contact with the soil surface.  Muskmelons are less susceptible to infection after netting. 

Often Confused With
Pythium fruit rot
Fusarium wilt
White mould

Biology
Phytophthora survives between crops as a thick-walled oospore or as mycelium on crop residue.  The oospores can survive in the soil for five to ten years.  Under intensive cucurbit production and short crop rotations, the levels of inoculum build up over time, potentially becoming a significant production problem.

Sporangia are formed on the roots, stems and leaves of infected plants.  They are spread long distances by air and splashing water.  Under saturated conditions, the sporangia will release motile zoospores.  The zoospores move on the plant surface and in the soil water.  They are capable of directional mobility and are attracted by the root exudates of host crops, allowing the infection to spread from plant to plant, and from field to field.  Irrigation water may also be an additional source of zoospores.

Period of Activity
Phytophthora spreads rapidly during warm, wet weather. Ideal conditions for infection are moist soils above 18°C (65°F) and air temperatures between 24°C and 29°C (75 and 85°F).

Scouting Notes
While monitoring for other diseases, take note of any wilted or stunted plants.  Record the number and location of the infected plants.  Inspect fruit for lesions or fungal growth. 

Thresholds
None established.  Early diagnosis will allow growers to manage it through crop rotation, before the inoculum builds to potentially devastating levels.

Management Notes

• Rotate fields for a minimum of 3 years away from all host crops. 
  
• Do not plant cucurbit crops in a field that has a history of Phytophthora infections. 
  
• Select well-drained fields.  Where drainage problems do exist, use a grassed waterway to divert surface water away from the crop. 
  
• Minimize soil compaction and avoid excessive irrigation, especially in overhead systems.
  
• Raised beds can significantly reduce Phytophthora capsici infections in the bush-type cucurbits (zucchini, mini pumpkins, gourds etc.).  Beds must be dome-shaped. 
  
• Ensure that the planter does not leave a depression at the base of the plants.
  
• Clean farm equipment if traveling between infected and non-infected fields.