The Effect of Chlorophenoxy Acid Herbicides on Growth and Rhizomorph Production ofArmillariella mellea

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Abstract
Rhizomorph production by A. mellea from dead oak [Quercus spp.] roots in the field was assessed on trees that had been killed 2-14 yr before sampling. More rhizomorphs were produced from roots of trees killed by herbicides than from roots of trees killed by hand-girdling. The maximum quantity of rhizomorphs was recovered from root systems 10 yr after trees were treated with herbicides. In culture, 2,4-D stimulated the growth rate or the production of rhizomorphs of 4 A. mellea isolates. The range of growth-regulating activity for 2,4-D was 10-250 .mu.g/ml. Picloram, 2,4,5-T and 2(2,4,5-trichlorophenoxy)propionic acid (2,4,5-TP) either had no effect on the fungus at any concentration or were inhibitory at and above 10 .mu.g/ml. The addition of 2,4,5-T or 2,4,5-TP to an equal quantity of 2,4-D negated the stimulatory effect of 2,4-D. GLC was used to detect 2,4-D and 2,4,5-TP in root-collar phloem of oaks treated with aerial applications of the herbicides. Traces of both compounds were detected as early as 2 days after treatment and as late as 39 days after treatment. In general, less than 2.5 .mu.g/ml of 2,4-D and 0.5 .mu.g/ml 2,4,5-TP were present in analyzed tissue. Under field conditions, these herbicides were not present in root phloem at levels high enough to have a direct effect on A. mellea.

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