Cucurbit Genetics Cooperative Report 14:15-17 (article 6) 1991
Paul C. St. Amand and Todd C. Wehner
Department of Horticulture Science, North Carolina State University, Raleigh, NC 27695-7609
The North Carolina State University Department of Plant Pathology Disease loss committee issues annual state-wide reports (1, 2, 3, 4, 5, 6) on crop loss estimates due to plant diseases and nematodes. Data on cucumber was available for the years 1983 to 1988, but so far, has not been examined for trends or ranking of pathogens. The objective of this report was to review the data for trends and ranking of cucumber pathogens according to their severity in North Carolina.
Data from the reports reviewed here were estimates. Data were collected each year from collaborators with firsthand knowledge of each crop and its diseases. The data were also assigned a confidence rating indicating how the data was obtained and its reliability, but were not based on surveys or tests, only educated guesses.
The estimated incidence of most pathogens has remained constant for the years 1983 to 1988 (Table 1). The estimated incidence of downy mildew however, has increased by five fold for the last three years compared to the first three years. The estimated incidence of target spot and belly rot have both increased, but only slightly. There are strong decreases in the estimated incidence of both angular leaf spot and scab. Gummy stem blight was estimated to have the highest incidence of all pathogens for all six years followed by belly rot and anthracnose. Tomato ringspot virus had the lowest estimated incidence. It is important to note that most cultivars being grown in North Carolina have moderate to high resistance to anthracnose, angular leafspot, downy and powdery mildew, scab, and cucumber mosaic virus.
Table 1. Estimated incidence of 14 diseases on all field grown cucumbers (slicing and pickling cucumbers) in North Carolina from 1983 to 1988 (ranked by mean).
Rank |
Disease |
1983 |
1984 |
1985 |
1986 |
1987 |
1988 |
Mean |
| 1 | Gummy stem blight | 80.0 | 80.0 | 80.0 | 80.0 | 80.0 | 80.0 | 80.0 |
| 2 | Belly rot | 70.0 | 70.0 | 70.0 | 70.0 | 75.0 | 75.0 | 71.7 |
| 3 | Anthracnose | 50.0 | 75.0 | 75.0 | 75.0 | 75.0 | 75.0 | 70.8 |
| 4 | Air pollution | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 |
| 5 | Cottony leak | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 | 50.0 |
| 6 | Root knot | 40.0 | 40.0 | 40.0 | 40.0 | 40.0 | 40.0 | 40.0 |
| 7 | Target spot | 25.0 | 33.4 | 42.4 | 42.3 | 42.2 | 42.1 | 37.9 |
| 8 | Damping-off | 30.0 | 30.0 | 30.0 | 30.0 | 30.0 | 30.0 | 30.0 |
| 9 | Downy mildew | 10.0 | 10.0 | 10.0 | 50.0 | 50.0 | 50.0 | 30.0 |
| 10 | Angular leaf spot | 30.0 | 30.0 | 30.0 | 30.0 | 5.0 | 5.0 | 21.7 |
| 11 | Alternaria leaf spot | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 |
| 12 | Powdery mildew | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 | 8.8 | 9.8 |
| 13 | Scab | 5.0 | 5.0 | 5.0 | 2.0 | 1.0 | 1.0 | 3.2 |
| 14 | Tomato ringspot | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Mean | 32.9 | 35.3 | 35.9 | 38.5 | 37.0 | 36.9 | 36.1 |
The estimated percentage loss in crop value caused by 9 of the 14 pathogens has remained fairly constant for the years 1983 to 1988 (Table 2). Downy mildew and target spot increased fivefold, and root knot decreases slightly for the last two years reported. Root knot caused the greatest loss of all six years, accounting for nearly one third of all diseases losses. Root knot was followed in importance by gummy stem blight, belly rot, and target spot.
The average incidence by year for all 14 pathogens indicated slight increase in the estimated incidence of pathogens (R2 = 0.46) (Tables 1 and 3). Estimated percentage loss of crop value by year also indicated a slight increase (R2 = 0. 51) (Tables 2 and 3). The increase appears related to the strong increases in downy mildew and target spot and, to a lessor degree, belly rot.
Table 2. Estimated percentage loss of value by 14 diseases on all field grown cucumbers (slicing and processing cucumbers) in North Carolina from 1983 to 1988 (ranked by mean).z
Rank |
Disease |
1983 |
1984 |
1985 |
1986 |
1987 |
1988 |
Mean |
| 1 | Root knot | 12.0 | 12.0 | 12.0 | 12.0 | 8.0 | 8.0 | 10.7 |
| 2 | Gummy stem blight | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 |
| 3 | Belly rot | 3.5 | 3.5 | 3.5 | 3.5 | 4.0 | 4.0 | 3.7 |
| 4 | Target spot | 1.0 | 3.3 | 3.8 | 3.8 | 5.0 | 5.0 | 3.6 |
| 5 | Downy mildew | 0.4 | 0.2 | 2.0 | 5.0 | 5.0 | 5.0 | 2.9 |
| 6 | Anthracnose | 2.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 2.8 |
| 7 | Cottony leak | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 |
| 8 | Damping-off | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 |
| 9 | Powdery mildew | 0.4 | 0.4 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
| 10 | Air pollution | 1.0 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.4 |
| 11 | Angular leaf spot | 0.3 | 0.3 | 0.5 | 0.5 | 0.1 | 0.1 | 0.3 |
| 12 | Scab | 0.1 | 0.1 | 0.5 | 0.3 | 0.1 | 0.1 | 0.2 |
| 13 | Alternaria leaf spot | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| 14 | Tomato ringspot | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| Total | 28.9 | 31.3 | 34.3 | 37.1 | 34.2 | 34.2 | 33.3 |
z Estimated percentage loss of value calculated as the percentage dollar loss due to yield and quality reduction.
Table 3. Coefficients of determination (R2) for estimated incidence, estimated percentage loss of crop value, estimated cost, and year of estimate for field grown slicing and pickling cucumbers due to 14 diseases in North Carolina from 1983 to 1988.
Variable |
Year |
Incidencez |
Lossy |
Costx |
| Year | 1.0000 | 0.4624 | 0.5105 | 0.7816 |
| Incidence | 0.4624 | 1.0000 | 0.9228 | 0.5274 |
| Loss | 0.5105 | 0.9228 | 1.0000 | 0.7310 |
| Cost | 0.7816 | 0.5274 | 0.7310 | 1.0000 |
z Estimated incidence calculated as the average incidence of 14 pathogens by year.
y Estimated percentage loss of value calculated as the total dollar loss due to yield and quality reduction by 14 pathogens by year.
x Estimated cost calculated as the total dollar loss due to yield and quality reduction and cost of prevention and control by 14 pathogens by year.
Literature Cited
- Main, C. E., S. M. Nusser, and A. W. Bragg (eds.). 1984. 1983 Crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 3, North Carolina State University, Raleigh, NC. 146 pp.
- Main, C. E. and S. M. Nusser (eds.). 1985. 1984 Estimates of crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 4, North Carolina State University, Raleigh, NC. 152 pp.
- Main, C. E. and S. V. Byrne (eds.). 1986. 1985 Estimates of crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 5, North Carolina State University, Raleigh, NC. 183 pp.
- Main, C. E. and S. V. Byrne (eds.). 1987. 1986 Estimates of crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 6, North Carolina State University, Raleigh, NC. 183 pp.
- Main, C. E. and S. K. Gurtz (eds.). 1988. 1987 Estimates of crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 7, North Carolina State University, Raleigh, NC. 209 pp.
- Main, C. E. and S. K. Gurtz (eds.). 1989. 1988 Estimates of crop losses in North Carolina due to plant diseases and nematodes. Department of Plant Pathology Special Publication No. 8, North Carolina State University, Raleigh, NC. 209 pp.