HomeResearchBacterial Wilt of Cucurbits

Bacterial Wilt of Cucurbits

Research was initiated in 1999 because bacterial wilt had been increasing in importance in New York and was seen affecting crops previously thought to be moderately to highly resistant (summer and winter squashes, some gourds, and pumpkin, in particular some recently commercialized powdery mildew resistant varieties).

Field experiments were conducted under natural infestation of striped and spotted cucumber beetles, vectors of the causal pathogen of bacterial wilt.  Cucurbit crop types and varieties were compared for their attractiveness to beetles and susceptibility to wilt in five experiments conducted in 1999, 2000, 2001, 2003 (just pumpkin), and 2006 (cucumber).  The insecticide Admire (applied to soil at seeding) and the plant activator Messenger (applied as seed soak and/or foliar spray) were evaluated in separate experiments in 1999 and 2000.  Harpin, the active ingredient in Messenger, is a protein originating from Erwinia amylovora discovered by Cornell Professor Emeritus Steven Beer that has been shown to induce SAR (systemic acquired resistance) to several diseases and to reduce insect attractiveness of treated plants.  Control achieved with Admire applied over or in furrow was compared to weekly applications of the insecticides Avaunt and Sevin.  Striped cucumber beetles were dominant in all experiments.

Results.

1. Susceptibility to bacterial wilt and attractiveness to cucumber beetles varies among cucurbit crop types and varieties:
– Ornamental gourd variety Turk’s Turban (Cucurbita maxima) was highly attractive to cucumber beetles and very susceptible to wilt.  The gourd Pear Bicolored (C. pepo) was less susceptible.
– Pickling cucumber variety County Fair was less susceptible than Calypso or Dasher II, a slicer type.  Wilt incidence was 7% versus 100% in 2000.
– Pumpkin varieties Harvest Moon and Howden were less susceptible than Merlin and also Magic Lantern under high disease pressure.
– Winter squash varieties Waltham Butternut and Table Ace had fewer beetles, less feeding injury, and lower incidence of wilt than Golden Delicious and Blue Hubbard.

cucumber plants in field with bacterial wilt symtpoms
Cucumber variety Dasher II exhibited high susceptibility to bacterial wilt in the cucurbit crop type and variety comparison study.
healthy cucumber plants in field
Plants remained healthy of the pickling cucumber variety County Fair, which was bred to be resistant. This resistance is difficult to breed for which is why there are few wilt resistant varieties available.
Ornamental gourds in field with bacterial wilt symtpoms
The ornamental gourd variety Turk’s Turban (in front) was more attractive to cucumber beetles and more susceptible to bacterial wilt than Pear Bicolor (in back).
Zucchini plants in field with bacterial wilt symtpoms
The zucchini variety Seneca (in front) was more susceptible to bacterial wilt than Ambassador (in back).

2. Generally, varieties with the most beetles per plant and the most feeding damage had the highest incidence of wilt.  However, beetle attractiveness did not completely account for variation in susceptibility.
– Watermelon Crimson Sweet and winter squash Waltham Butternut did not develop wilt although beetles and their feeding damage were observed on these plants.
– Pumpkin varieties Harvest Moon and Howden had slightly higher beetle infestations than Merlin, but they had lower wilt incidence (3, 13, and 89%, respectively, in 1999).

3. Heightened susceptibility to bacterial wilt exhibited by the powdery mildew resistant variety Magic Lantern is not genetically linked to this resistant trait based on the fact similar wilt incidence was observed in two closely-related varieties: Sorcerer, a susceptible variety, and Magician, which has two copies of the  resistant gene in Magic Lantern (one from each parent).

4. Among cucumber varieties evaluated in 2006, County Fair exhibited the best resistance.  The Cornell experimental did not have significantly more symptoms.

5. Plants of pumpkin variety Merlin (previously shown to be highly susceptible to wilt) that were treated with Messenger (with or without seed soak) had lower wilt incidence than untreated plants on 21 and 28 July, but not on 17 Aug when 99-100% of plants were wilting.

6. Plants of cucumber variety Dasher II and pumpkin variety Merlin treated with Admire in furrow at seeding had lower wilt incidence than untreated plants.  Treated Dasher II plants also had less beetle feeding injury.  Sevin XLR Plus applied weekly was only effective in the pumpkin experiment.  Avaunt applied weekly was ineffective in both.  Movement of beetles among the small, closely spaced plots probably interfered with detection of differences among treatments in both experiments.  Wilt incidence was high in untreated plants in both experiments (86 and 64%) although beetle density remained below the action threshold for applying foliar insecticide of 1 beetle/plant.

A pumpkin plot
Pumpkin variety Merlin treated with Admire applied in furrow at seeding, 2000.
A pumpkin plot
Pumpkin treated with Admire applied in 2-inch band over the row after seeding, 2000.
A pumpkin plot
Pumpkin treated with Sevin 9 times on a weekly schedule, 2000.
A pumpkin plot
Pumpkin not treated with any insecticide for bacterial wilt, 2000.

 

Publications listed below have more information about research results summarized above, including table with results.  To download report click on publication year, which is year after study was done; most are available at Plant Disease Management Reports website.

  1. McGrath, M. T., and Shishkoff, N.  2000.  Comparison of cucurbit crops and cultivars for their attractiveness to cucumber beetles and susceptibility to bacterial wilt, 1999. Biological and Cultural Tests 15:154.
  2. McGrath, M. T., and Shishkoff, N.  2000.  Evaluation of Messenger for the control of cucumber beetles and bacterial wilt of pumpkin, 1999.  Fungicide and Nematicide Tests 55:252.
  3. McGrath, M. T., and Gilrein, D.  2001.  Evaluation of Admire for the control of cucumber beetles and bacterial wilt in cucumber, 2000. Arthropod Management Tests 26:E33.
  4. McGrath, M. T., and Gilrein, D.  2001.  Evaluation of Admire for the control of cucumber beetles and bacterial wilt in pumpkin, 2000. Arthropod Management Tests 26:E74.
  5. McGrath, M. T., and Shishkoff, N.  2001.  Comparison of cucurbit crop types and cultivars for their attractiveness to cucumber beetles and susceptibility to bacterial wilt, 2000. Biological and Cultural Tests 2001:V86.
  6. McGrath, M. T., and Shishkoff, N.  2001.  Evaluation of Messenger for the control of cucumber beetles and bacterial wilt of pumpkin, 2000.  Fungicide and Nematicide Tests 2001:V74.
  7. McGrath, M. T.  2001.  Variation among cucurbit crop types and cultivars in susceptibility to bacterial wilt and attractiveness to cucumber beetles. Phytopathology 91:S60.
  8. McGrath, M. T.  2001.  Susceptibility to bacterial wilt and attractiveness to cucumber beetles varies among cucurbit crop types and cultivars. Phytopathology 91:S196.
  9. McGrath, M. T.  2002. Attractiveness of cucurbit crop types to cucumber beetles and their susceptibility to bacterial wilt. Pages 222-227 in Cucurbitaceae 2002. D. N. Maynard, ed. ASHS Press.
  10. McGrath, M. T.  2002.  Comparison of cucurbit crop types for their attractiveness to cucumber beetles and susceptibility to bacterial wilt, 2001.  Biological and Cultural Tests 17:V11.
  11. McGrath, M. T.  2004. Attractiveness to cucumber beetles and susceptibility to bacterial wilt of pumpkin cultivars, 2003. Biological and Cultural Tests 19:V017.
  12. McGrath, M. T., and Davey, J. F. 2007. Bacterial wilt resistant cucumber cultivar evaluation, 2006. Plant Disease Management Reports 1:V127.