The integrated control of Armillaria mellea 2. Field experiments

Several isolates of Trichoderma harzianum, T. viride and T. hamatum, and an isolate each of Dactylium dendroides and Chaetomium olivaceum, found antagonistic in vitro and under glasshouse conditions against several isolates of the root rot pathogen, Armillaria mellea, were evaluated for their ability to suppress root rot of young apple trees under field conditions. Some of these antagonists were selected for integration with two systemic fungicides, fosetyl-Al and fenpropidin. The antagonists were applied on mushroom compost with dead mycelia of Agaricus bisporus either before or after a 2000 mg l(-1) dose of the fungicides, with a time interval of 40 days. Some isolates of the Trichoderma spp. and D. dendroides reduced the extent of infection as compared with that on control plants inoculated only with A. mellea. A significant interaction was found between the antagonists, fungicides and their sequence of application. D. dendroides was significantly (p < 0.05) more effective in reducing the rot when applied 40 days before fosetyl-Al. Conversely, T. harzianum isolate Th23 showed greater efficacy when introduced 40 days after fenpropidin. T. hamatum isolate Tham1, however, exhibited a greater effect when applied before fenpropidin. Changing sequence of application of the other antagonists with either of the two fungicides had no significant effect on the extent of the root rot. Trees treated with Trichoderma viride isolate Tv3 and fenpropidin had a greater increase in number of branches > 30 cm, but Chaetomium olivaceum caused a greater increase with fosetyl-Al than with fenpropidin. Similarly, increase in branches > 30 cm was significantly greater on trees treated with fosetyl-Al only, compared with those treated with fenpropidin only. Whereas dose rates of fosetyl-Al did not cause significant differences, a dose rate of 8000 mg l(-1) of fenpropidin resulted in significantly fewer branches < 30 cm, compared with the lower dose rates of 2000 and 4000 mg l(-1).