University of Minnesota Extension
www.extension.umn.edu
612-624-1222
Menu Menu

Extension > Garden > Yard and Garden > Vegetables > Diseases of cucurbits > Phytophthora blight

Back to Diseases of cucurbits

Phytophthora blight

Michelle Grabowski, University of Minnesota, Extension Educator

photo-26

Clemson University, Bugwood.org

photo-28

P. Bachi, University of Kentucky, Bugwood.org

Phytophthora blight is caused by Phytophthora capsici. This pathogen can infect all cucurbit crops as well as peppers, tomatoes, eggplants, and infrequently beans. Infection is most common in squash and pumpkin. Phytophthora capsici infects every part of the plant including roots, crowns, leaves, vines and fruit. Phytophthora has only been reported in a few fields in Minnesota.

Identification

photo-29

H. F. Schwartz, Colorado State University, Bugwood.org

Important biology

Phytophthora capsici is an oomycete, often referred to as a water mold. Oomycetes are not true fungi, but are more closely related to certain kinds of algae. Phytophthora has swimming spores known as zoospores that can swim through films of water and saturated soils to locate a new host plant. As a result, new infections often appear in the direction in which water drainage occurs. Phytophthora thrives in warm (75-85F) wet conditions. Disease is commonly seen first in low lying poorly drained areas of the field, but can spread throughout the field if environmental conditions are right. Spores can be blown on windblown rain or carried in soil stuck to equipment that was used in an infested area.

Phytophthora overwinters in soil and plant debris. There are two different mating types of Phytophthora capsici. If only one mating type is present in a field, the pathogen can survive for 2 years. If both mating types are present, the fungus will create oospores, a hard walled resting structure that can survive 5 or more years. It is unknown if both mating types occur in Minnesota.

Management

photo-30

P. Bachi, University of Kentucky, Bugwood.org

  • © 2014 Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy