Evaluation of the Efficiency of Two Fungicides on the Control of Almond Leaf Blotch Disease on Two Cultivars in Along Zayanderood

Polystigma amygdalinum Sacc (Cannon sp nov.) causes almond leaf blotch and is reported from various countries. The pathogen is widely distributed in the Mediterranean region and often causes premature defoliation of its host. Based on morphology, P. amygdalinum has been assumed to be a member of the order Phyllachorales and is consid¬ered to be a close relative of the genus Phyllachora, but phylogenetic analyses indicated that P. amygdalinum did not group with Phyllachora species (Phyllachorales) which have been thought to be its close relative. Polystigma amygdalinum show to be a relative of Trichosphaeriales and Xylariales and placed in the Xylariomycetidae. Almond leaf blotch is the most important disease on the leaf in almond (Prunus dulcis) in Iran. Ascospores are believed to be the only inoculum of this pathogen. Ascocarp initials develop in infected leaves in contact with, or in close proximity to, filamentous spore-bearing bodies, which are the first to appear. Environmental factors were affected ascocarp formation and development in P. amygdalinum. Mature ascocarps were formed in leaves from July to October (leaf fall). Ascocarps were produced under field conditions in infected leaves buried in soil at the depths of 0 to 40 cm with maximum mature ascocarp formation at 5 cm and minimum at the soil surface. Based on the appearance of disease symptoms under natural and greenhouse conditions the incubation period was estimated about to be 40-45 and 35-40 days respectively. The peak of ascospore discharge was 2-3 weeks after petal fall and was dependent on rain fall. Various chemicals were applied to control P. amygdalinum on almond. Spraying with Mancozeb and Bordeaux mixture is the most effective with four applications after petal fall in East Azerbaijan. Over a 4-year study period, it was found that ascospore discharge began at flowering and continued for 4-5 weeks in Maharloo of Fars Province. The maximum discharge occurred at petal fall. The incubation period was estimated to be 4-5 weeks under experimental conditions. Although the mature ascospores could produce short germ tubes in distilled water or water agar, the fungus could not be cultured or grown on conventional media from either ascospores, pycnidiospores or stromatic tissues under laboratory conditions. Of several systemic and non-systemic fungicides evaluated under field conditions, triforine at 100-400 µg /ml was most effective. Other fungicides which significantly reduced leaf infection were, in order of efficacy, copper oxychloride (2000µg/ml), copper hydroxide (2000 µg/ml), Bordeaux mixture (10000 µg/ml) and mancozeb (2000 µg/ml). Carbendazim and thiophanate methyl (500 µg/ml) increased the level of infection. One application of the fungicide at petal fall and then at two at 14-day intervals were found to be effective in reducing the disease. Two applications of Bordeaux mixture at 2 and 4 weeks after petal fall was found to be the most efficient control treatment in Chahar Mahal and Bakhtiari. A single spray two weeks after petal fall also reduced the disease significantly.
During 2012-13, the efficiency triforin (Saprol® 30%) (500 µg /ml) with three timing of applications, in comparison with Bordeaux mixture (10000 µg /ml) on two local cultivars (Sefid and Mamaee), was tested in a completely randomized block design, in along Zayanderood of Chahar Mahal and Bakhtiari province.
According to the results, two applications of triforin at two and four weeks after petal fall, a single spray four weeks after petal fall and two applications of Bordeaux mixture were found to be the most efficient control treatment in both cultivars, respectively. All applications of fungicides on both cultivars reduced the disease significantly. Infectivity percent and disease severity on Mamaee cultivar were more than Sefid. In general, it can be said Triforin was more effective in terms of decreasing infectivity percent and disease severity in comparison with Bordeaux mixture.
The results of this study, previous researches and surveys in Chahar Mahal and Bakhtiari province and other parts of Iran show that some of the almond cultivars cultivated in the country are susceptible to P. amygdalinum, so the only method to manage this disease is using the chemical control on these cultivars. Two applications of fungicides at two and four weeks after petal fall was found to be the most efficient control treatment in Chahar Mahal and Bakhtiari, these results are recommended for all regions of Iran.