Management
of Phytophthora Blight of Cucurbit Crops in Illinois
M. Babadoost
Universtiy of Illinois
Illinois
Cucurbit Industry. Illinois produces approximately 30,000
acres of cucurbit crops, including 12,000 acres jack-o-lantern pumpkins, 10,000
acres processing pumpkins, 2,500 acres squash, 2,000 acres cucumber, 2,000
acres watermelon, and 1,500 acres cantaloupes and muskmelons. Due to implementation
of effective horticultural practices and disease management strategies, acreage
of processing pumpkins in Illinois in 2002 increased by 65% compared to that of
2000.� Approximately 90% of processing
pumpkins produced in the United States are grown in Illinois.
Phytophthora Blight.
Phytophthora blight, caused by Phytophthora
capsici, has become one of the most serious threats to production and
industry of cucurbit crops in Illinois. Also, P. capsici infects bean, beet, carrot, eggplant, okra, onion,
pepper, tomato, and several weed species in cucurbit fields. In the past four
years, Phytophthora blight has been epidemic in Illinois, causing up to 100%
yield losses.
P. capsici
is a soilborne pathogen and is also disseminated by air currents.� It survives in the soil indefinitely. P. capsici can strike host plants at any
time from planting through harvest. Symptoms produced by this pathogen include
pre- and post-emergence damping-off, root rot, crown rot, stem lesions, leaf
spots, foliar blight, and fruit rot. Until 2001, there was no method available
to provide adequate protection of vegetables against P. capsici.
Disease Management.
Three methods were developed to manage Phytophthora blight on cucurbit crops,
which are: (i) seed treatment, (ii) foliar fungicide spray, and (iii) red-light
treatment.
Seed
treatment. Seed treatment with mefenoxam (0.64
fl. oz/100 lb seed) and metalaxyl (1.5 fl. oz/100 lb seed) significantly
reduced pre- and post-emergence damping-off of seedlings caused by P. capsici in pumpkins. In greenhouse
studies, 31 days after seeding, at inoculum level 600 cfu/g soil, the average
seedling stands were 88.3, 85.8, and 45.7%, for Apron, Allegiance, and
untreated control, respectively. In field trials, the average seedling stands
35 days after seeding were 76.7, 74.7, and 44.9% for Apron, Allegiance, and
untreated control, respectively. Seed treatment with Apron or Allegiance did not
have any significant effect on either seed germination or seedling vigor.
Foliar
Fungicide Spray. Five application of dimethomorph (6.4
oz Acrobat 50WP/acre) plus copper sulfate (2.5 lb Cuprofix Disperss/acre), at a
weekly schedule, provided effective protection against foliar blight and fruit
rot, caused by P. capsici,
in pumpkin fields. Application of the fungicides was begun at the first sign of
the disease. Fungicide spray reduced yield losses from 100% to less than 10% in
the commercial fields.���
Red-Light
Treatment. A study was conducted in the
greenhouse to investigate the effects of red light (600-700 nm) on the
subsequent occurrence of seedling infection of pumpkin caused by P. capsici. Four-week-old seedlings were
inoculated with zoospores or transplanted into pots filled with artificially
infested soil mix. Only 21% of the
seedlings treated with red light became infected. In comparison, 78% of control
seedlings, either grown under white light or under natural daylight, were
infected and died. Investigations are underway to evaluate the effectiveness of
red-light induced resistance on controlling Phytophthora blight in commercial
fields of cucurbit crops.
IPM
of Phytophthora Blight.
Seed treatment (Apron or Allegiance) along with foliar spray of
dimethomorph
(Acrobat) provided effective protection to pumpkin plants against P. capsici in
commercial
fields. Investigations are underway to develop effective methods of integration
of
seed
treatment, red-light treatment, and foliar application of fungicides for management
of Phytophthora infection on cucurbit crops.
