Grey leaf spot is a serious yield-reducing disease of maize (Zea mays) in many parts of the world where this crop is cultivated. The causal organism associated with the disease is Cercospora zeae-maydis. Two potential sibling species have been recognized as Groups I and II. The DNA sequences for the internal transcribed spacers (ITS1 & ITS2), the 5.8S rRNA gene, elongation factor 1-α, histone H3, actin and calmodulin gene regions suggest that Groups I and II are two distinct species. Furthermore, Cercospora zeae-maydis (Group I) can be distinguished from C. zeina sp. nov. (Group II) by its faster growth rate on artificial media, the ability to produce cercosporin, longer conidiophores, and broadly fusiform conidia. A PCR-based test that distinguishes the two species was developed using species-specific primers designed from the histone H3 gene.

These results demonstrate the disease control activities of glyphosate against rust diseases in GR wheat and GR soybeans.

The effects of the application of 0, 60, and 120 kg N ha-1 and of 0, 25, 50, and 150 kg K ha-1 on final disease severity, standardized area under disease progress curve, and grain yield were investigated at Cedara, South Africa, on a maize (Zea mays) hybrid susceptible to gray leaf spot (GLS), caused by Cercospora zeae-maydis. The trial was a randomized 3 × 4 factor design, split for fungicide treatments, and replicated three times. With increased N and K levels, final percent leaf blighting and the standardized area under disease progress curve were higher. In fungicide-treated maize, grain yields increased with increasing levels of N and K, as expected. In non-fungicide-treated maize, grain yield increased significantly with increased levels of N, despite increased disease severity. This was in contrast to small increases in grain yields from non-fungicide-treated maize with increased K levels, which were not significant. This was probably because grain yield response, which should have occurred at higher K applications, was reduced by increased disease severity. The effect of N, P, and K on GLS wasinvestigated at Ahrens. Maize was grown in a 4 × 4 × 4 N-P-K factorial, in a randomized complete block design. Fertilizer was applied at 0, 60, 120, and 180 kg N ha-1, 0, 30, 60, and 120 kg P ha-1, and 0, 50, 100, and 150 kg K ha-1. No fungicides were applied. A single disease assessment at physiological maturity showed that final disease severity increased with increasing levels of N, P, and K. These results have implications for small-scale farmers who are encouraged to fertilize for increased grain yields but may not have the resources to apply fungicide sprays to control fungal diseases.

Pareuchaetes aurata aurata (Butler) from Chromolaena jujuensis in northern Argentina was tested as a biological control candidate for the composite weed C. odorata. The larvae feed voraciously and complete their development on C. odorata. The host-plant feeding range of P. a. aurata is limited to the genus Chromolaena. It is suggested that the egg-laying behaviour of P. a. aurata, which scatters its eggs around the base of the host-plant, will help to overcome the problem of ant predation which prevented the establishment of Pareuchaetes pseudoinsulata Rego Barros, which lays its eggs in batches, in South Africa. Any possible benefits of the new association between P. a. aurata and C. odorata may also contribute to the success of this biological control programme.

No abstract