|White rust (Albugo candida) on spinach leaves|
Aecidium candidum Pers. (1797)
White rust (Albugo candida) is a common but usually not serious disease.
Local infection appears as pustules or "blisters" filled with sporangia on leaves, smaller stems, and floral parts. Pustules measure approximately 1-2mm in diameter and are white or creamy yellow. Systemic infections result in abnormal growth, distortion, and sterility of flowers or inflorescences. These abnormalities (or hypertrophy) are known as stagheads and consist mostly of thick-walled oospores.
Plowing or disking diseased plants and plant parts results in rapid decomposition of infected tissues and helps to significantly reduce future white rust infection. Crop rotation with noncruciferous host plants is also effective. Weed control and other sanitary methods are necessary too.
Resistance has been successfully deployed with mustard and rutabaga, however, with Asian vegetables such as Chinese mustard, Chinese cabbage, pak choi, and diakon, resistant varieties have not yet been identified.
The development of the acylalanine fungicide metalaxyl (Ridomil; Subdue) greatly improved the ability to control while rust with fungicide application. Metalaxyl provides limited curative activity and some control of systemic infection.
Applications should be made to the soil and subsequently applied to the foliage. Frequency of application would vary according to the length of crop and amount of rainfall experienced. In temperate environments a soil application and a minimum of 1-2 foliar applications during the crop cycle is suggested.
With the possibility of developing fungicide tolerant pathogen strains associated with metalaxyl, growers should consider using Ridomil MZ58 formulations with foliar fungicide applications. This formulation adds a second fungicide to the tank mix.
Older fungicides used, but less effective, for white rust control include: Dithane Z-78, Blitox, wettable sulphur, fixed copper compounds, Bordeaux mixture, chlorothalonil, captofol, captan, dodine, mancozeb, metiram, maneb, and zineb.
White rust most commonly occurs on:
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