Cucurbit Genetics Cooperative Report 14:18 (article 7) 1991
Michael Havey
U. S. D. A. / A. R. S. and Department of Horticulture, University of Wisconsin, Madison, WI 53706
In 1989, Wisconsin ranked fifth in the U. S. for production of cucumbers for pickling, producing 642,700 tons (8% of U.S. production) valued at $9.4 million (1990 Agriculture Statistics, Wisconsin Dept. of Agriculture, Trade and Consumer protection, Madison, WI). In addition to acceptable yield and quality, cucumber growers and processors are concerned with protecting the crop from economically significantly damage by diseases and pests.
The primary diseases of cucumber in northern production regions are scab (Cladosporium cucumerinum), cucumber mosaic virus (CMV), and angular leaf spot (Pseudomonas syringae). Bacterial (Erwinia tracheiphila) and fungal (Fusarium oxysporum or Verticillium species) wilts are not commonly observed. Bacterial wilt is controlled effectively by eliminating spotted and striped cucumber beetles, and resistance to Fusarium wilt appears to be linked with scab resistance (M. Palmer, personal communication). Since scab resistance has been incorporated into most cultivars, both diseases have been controlled with genetic resistance.
Target leaf spot (Corynespora cassiicola), anthracnose (Colletotrichum orbiculare), and downy mildew (Pseudoperonospora cubensis) are diseases more commonly found in warmer production areas, so are generally not a problem in Wisconsin. Late season leaf diseases such as Alternaria occur sporadically on older leaves, but fungi isolated from lesions are only weekly pathogenic (Harvey and Palmer, unpublished).
Wisconsin growers do not adhere to a weekly spray schedule to control diseases in their cucumber crop. Scab, CMV, and angular leaf spot are primarily controlled by genetic resistance. Resistance to scab and CMV appears to be effective. However, angular leaf spot may occur, even on cultivars listed as resistant. Cucumber fields are scouted and occasional sprays of copper-based chemicals to control angular leaf spot may be recommended. In Illinois, belly rot (Rhizoctonia solani) may become prevalent late in the season as cooler nights allow heavy dew formation. Application of a fungicide (e.g. Bravo 720) may be needed. Overall, it appears that genetic resistance offers acceptable control of the diseases of northern-grown cucumbers and only occasional sprays are necessary.