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The use of potato and maize disease prediction models using automatic weather stations to time fungicide applications in KwaZulu-Natal.

Maize grey leaf spot (GLS), caused by Cercospora zeae-maydis, and potato late blight







(LB), caused by Phytophthora infestans, are foliar diseases of maize and potato, two







of the most widely grown crops in KwaZulu-Natal (KZN), after sugarcane and timber.







Commercial maize in KZN accounts for just on 4.3% of the national maize crop. This







is worth R563 million using an average of the yellow and white maize price for the







2001/02 season (at R1 332.87 ton(-1)).







In 2003 KZN produced about 5% of the national







potato crop (summer crop: 7531 300 10kg pockets from 2243 hectares). This equates







to a gross value of R89.4 million based on an average price of R1 188 ton(-1) in 2001.







Successful commercial production of maize and potatoes depends upon control of these







diseases by translaminar fungicides with highly specific modes of action.







This study extends an existing model available for timing of fungicide sprays for GLS







and tests and compares two LB models for two calendar-based spray programmes. The







study also evaluated the use of an early blight model which is caused by Alternaria







solani, and over the single season of evaluation showed potential for use in KZN. For







the GLS model it was found that a number of refinements are needed, e.g., the amount







of infected maize stubble at planting and not the total amount of maize residue at







planting.







Based on two years' data, it was found that for the LB models there are no significant







differences in levels of control between using a predicted fungicide programme and a







calendar-based programme. The importance of knowing initial infection sites, and







hence initial inoculum, was demonstrated. This led to the creation of a KZN LB







incidence map, now being used to more accurately time the start of a preventative spray







programme and to time the inclusion of systemic fungicides in the preventative spray







programme.







This study has contributed to the further development and expansion of the Automatic







Weather Station Network (AWSN) at Cedara, which now comprises 15 automatic







weather stations in KZN. The AWSN is currently used to aid farmers and advisers in







decision-making regarding fungicide spray timing for GLS and LB. / Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2003.

Identiferoai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/6259
Date January 2003
CreatorsVan Rij, Neil Craig.
ContributorsCaldwell, Patricia May., Savage, Michael John., Quinn, Nevil W., Laing, Mark D.
Source SetsSouth African National ETD Portal
Languageen_ZA
Detected LanguageEnglish
TypeThesis

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