Cylindrocladium buxicola is a fungal pathogen that causes a severe leaf and twig blight on Buxus spp. Laboratory experiments were carried out to study the in vitro effect of 13 fungicides on mycelial growth and conidia germination of the fungus. Based on the values of the effective concentration at which mycelial growth was inhibited by 50%, the fungicide Stroby (kresoxim-methyl) and the combined fungicides Opponent (epoxiconazole + kresoxim-methyl + pyraclostrobin), Opera (epoxiconazole + pyraclostrobin), and Signum (boscalid + pyraclostrobin) were the most effective at inhibiting mycelial growth and conidia germination. Pathogenicity assays showed that the host range of the fungus was not limited to the genus Buxus because Sarcococca sp. also was susceptible. None of the 10 boxwood species and cultivars tested were immune to the disease, although Buxus balearica as well as Sarcococca sp. showed significantly lower levels of infection as measured by the expression of leaf symptoms and the number of conidia produced on host tissue, the latter probably contributing to the apparent resistance of these species in the field. Microscopic observation showed that disease development was very rapid and aggressive on B. sempervirens ‘Suffruticosa’ where it was able to survive at least 5 years on decomposing fallen leaves.

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The effect of allicin (a stabilized garlic extract product) at five different concentrations (0, 20, 30, 50 and 100 mg/l) was studied in vitro on the growth rate of 100 isolates of Armillaria gallica and A. mellea. Isolates were obtained from 41 host genera growing in gardens located in 39 counties in the United Kingdom. Agar plugs of the actively growing Armillaria isolates were added to the centre of malt agar plates infused with allicin, and radial mycelium growth was measured on days 7, 14 and 21. The total number of rhizomorphs and length of rhizomorphs were also measured. Relative growth rates were calculated as the growth rate relative to the controls (0 mg/ l). The relative growth of each isolate at each allicin concentration was used to estimate EC 50 values for A. mellea and A. gallica populations as well as individual isolates. EC 50 values for both Armillaria spp. increased over time. The mean EC 50 values for A. mellea of 16.0, 26.4 and 102 mg/l (days 7, 14 and 21, respectively) were higher than those for A. gallica (8.8, 7.9 and 11.0 mg/l) and probably relate to the more aggressive nature of A. mellea. Isolates with higher EC 50 values were also more likely to produce more rhizomorphs. At allicin concentrations of 20 and 30 mg/l, the production of rhizomorphs and the growth rates of A. mellea isolates were stimulated, when compared to the control treatments. From this study's findings, it appears that the field use potential of allicin is limited, due to better inhibition of the less virulent A. gallica, than the more aggressive A. mellea.