Potato Research 46 (2003/4) 27-37
Early blight in South Africa: Knowledge, attitudes and control practices of potato growers JACQUIE E. VAN DER WAALS *1'2, LISE KORSTEN 2 and ED.N. DENNER 3 1 Gold Fields Computer Centre, University of Pretoria, Pretoria, 0002, South Africa 2 Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, 0002, Pretoria, South Africa 3 Roodeplaat Agricultural Research Council, Pretoria, South Africa * Corresponding author;
[email protected] Accepted for publication: 2 June 2003 Additional keywords: Alternaria solani, Solanum tuberosum, farmer perceptions, survey, fungicides, research needs
Summary A survey of control practices and grower perceptions of early blight in South Africa was conducted from May 2001 - July 2002 using an informally structured questionnaire. Questionnaires were collected from the 10 largest of the 14 potato production regions in South Africa. The predominant control method for early blight was the use of fungicides with mancozeb or chlorothalonil as active ingredient. Most respondents commence spraying at flowering and spray at 7-10 day intervals thereafter. BP1, Up-to-date and Mondial were the most commonly planted cultivars. The majority of farmers indicated that they would be willing to use an early blight decision support system if an accurate and cost-effective one was available, and that they believe more research is necessary on early blight in South Africa. Estimated economic losses ranged from 1-60%, with the average being approximately 20%. This is the first such survey to be conducted in South Africa.
Introduction Potatoes (Solanum tuberosum L.) are an important crop in South Africa, with production exceeding 1.4 million tonnes annually, produced on approximately 47,000 ha (Potatoes South Africa, 2002). The potato production areas in South Africa are divided into fourteen main regions, namely Limpopo (formerly Northern Province), North-West, Gauteng, Mpumalanga, Northern Cape, Western Free State, Eastern Free State, KwaZulu-Natal, Sandveld, Ceres, South-Western Cape, Southern Cape, Eastern Cape and North-Eastern Cape (Fig. 1). Early blight, causal agent Alternaria solani Sorauer, is one of the major foliar diseases of potatoes and causes premature defoliation of potato plants almost everywhere they are grown (Rotem, 1994). Disease symptoms are characteristic dark brown to black lesions with concentric rings, which produce a 'target spot' effect (Rands, 1917). Symptoms are initially observed on older, senescing leaves (Jones, 1893; Rands, 1917; Pscheidt, 1985). In South Africa, early blight is a vastly underestimated disease (Nevill, 1985; McKenzie, 1991; Denner & Theron, 1999), and has Potato Research 46 (2003/4)
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JACQUIE E. VAN DER WAALS, LISE KORSTEN AND F.D.N. DENNER
Fig. 1. Potato growing areas of South Africa. been shown to cause yield losses of 20-50% if not adequately controlled (McKenzie, 1991). The purpose of this study was to determine the impact of early blight on the South African potato industry and to evaluate knowledge, attitudes and control practices of potato growers concerning this disease. This study will help to highlight misconceptions and gaps in farmers' knowledge of the disease, and find disease management practices that will approach the socio-economic optimum, considering farmer income and needs. Materials and methods
A survey was conducted from May 2001 to July 2002 among potato growers in South Africa using an informally structured questionnaire (Table 1). A random sample of growers in each region completed the questionnaire, with the number of growers in each region between 3 and 30 and approximately proportionally equal to the percentage potato production for that region out of the South African total. The questionnaire was divided into four main sections. Section 1 concerned the environmental conditions (average daily maximum temperatures during summer and winter, and rainfall) in each region. Section 2 was about crop production practices, including irrigation, propagative material used and cultivars planted. The third sec28
Potato Research 46 (2003/4)
EARLY BLIGHT IN SOUTH AFRICA
Table 1. Categories of information included in the informally structured questionnaire on cultivation of potatoes, control and importance of early blight in South Africa. Category of information
Questions on:
Growing region
Summer and winter temperatures Rainfall
Crop production
Irrigation Propagative material Potato cultivars planted
Crop protection (early blight control)
Control measures Fungicides used Spray schedule Perceived susceptibility of potato cultivars Willingness to use forecasting model Estimated economic loss
Other
Opinion on need for research on early blight Areas of research required (open-ended question) General comments about disease
tion contained questions pertaining to crop protection, including fungicides used, fungicide spray schedule and estimated economic losses due to early blight. Growers were asked to rate the potato cultivars they are familiar with for susceptibility to early blight on a scale of 1 to 5; with 5 being highly susceptible; 4, susceptible; 3, moderately susceptible; 2, moderately resistant; and 1, resistant. In order to determine the possibility of implementing a decision support system (DSS) for early blight in South Africa, growers were asked about their willingness to use one. Section 4 was used to ascertain whether growers believe research on early blight is necessary. In two open-ended questions, growers were allowed to make suggestions for research and general comments about the disease. The frequencies of answers from the questions pertaining to irrigation frequency, spray commencement date, spray schedule, the use of a forecaster and susceptibility of cultivars were tested using the chi-square one-sample test. A one-way ANOVA was used to test for differences in mean economic loss between the Sandveld, Eastern Cape, KwaZulu-Natal, Limpopo, Eastern Free State and North-Eastern Cape regions (where n>5). Results
A total of 127 questionnaires were collected from l0 out of the 14 potato growing regions, with these 10 regions representing 95% of potato production in South Africa. The regions from which questionnaires were collected were (the number of respondents in each region is given in parentheses): Limpopo (29), Mpumalanga (2), Northern Cape (4), Western Free State (4), Eastern Free State (9), KwaZulu-Natal (25), Sandveld (23), Ceres (1), Eastern Cape (16) and North-Eastern Cape (16). Potato Research 46 (2003/4)
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JACQUIE E. VAN DER WAALS, LISE KORSTEN AND ED.N. DENNER
Questionnaires were not collected from North-West, Gauteng, South-Western Cape and Southern Cape, due to the low numbers of growers in these regions and difficulties in reaching them. Because only one response was received from Ceres, this was left out of all calculations. The two responses from Mpumalanga were combined with those from Limpopo, which has similar climatic conditions. Crop production. Sixty percent of the respondents irrigate their potato crops; of these, 31% irrigate twice a week, 33% once a week and the remaining 36% follow other irrigation schedules. These frequencies were not significantly different (~2 =0.496; p=0.783; dr=2). Other irrigation schedules that were mentioned were: daily; 2-3 times per week; every 6 days; when necessary; only in the early part of the season or four times per season. Ninety-seven percent of respondents use certified seed. Control practices. The predominant method for control of early blight in all regions was through the use of registered fungicides. The most widely used (65% of respondents) fungicides were those with mancozeb as active ingredient 1. The second most widely used (53%) active ingredient was chlorothalonil. Tebuconazole, difenoconazole, azoxystrobin and cymoxanil/famoxadone were used by 25%, 23%, 21% and 18% of respondents, respectively. Active ingredients used by between 5% and 10% of respondents were cymoxanil/maneb, captab, mancozeb/zinc oxide and various copper compounds. Less than 5% of respondents used fungicides with the following active ingredients: mancozeb/metalaxyl, propineb, bupirimate/hexaconazole, fentin hydroxide, flutriafol, cyproconazole, propamocarb hydrochloride, procymidone, cymoxanil/propineb, fentin acetate/maneb, dimethomorph/mancozeb and phosphorous acid equivalents. None of the respondents listed the use of biological control agents (These percentages do not tally to 100, as many respondents listed more than one active ingredient). Fungicide spraying for the control of early blight commences at flowering for 49% of the respondents, at symptom appearance for 19% and at other times for the remaining 32%. The frequencies were significantly different ()~2=16.528; p
