Fungicide levels and arbuscular mycorrhizal fungi in golf putting greens

1. Annual meadow grass Poa annua is the most problematic weed within sports turf in temperate climates. It is so abundant that herbicides cannot be used against it because almost total loss of the sward would occur. Arbuscular mycorrhizal (AM) fungi can be used as biological control agents of P. annua, acting to reduce its growth while increasing that of desirable perennial grasses. However, natural levels of AM fungi in amenity turf are very low. Sports turf is characterized by high fungicide usage, so this study tested the hypothesis that levels of toxic elements (derived from historical fungicide applications) and/or organic fungicides are related to the low mycorrhizal abundance observed. 2. Records of fungicide applications to putting greens at four golf courses in south-east England were collected for the period 1993-2000. Soils from all 18 putting greens on each course were sampled during spring 2000. Levels of arsenic, cadmium, copper and lead were recorded, as these elements formed part of the fungicidal compounds applied in the past. Of the organic fungicides in current use, chlorothalonil, fenarimol and iprodione were found to comprise more than 70% of all compounds used and soil levels of these three chemicals were also measured. Levels of AM colonization of P. annua were recorded at every putting green. The rates of AM colonization of desirable grasses could not be obtained because these were too rare in all the swards examined. 3. There was little evidence that the abundance of AM fungi, as measured by arbuscular colonization of roots, was affected by the presence of any of the chemicals. Levels of all elements were below the ambient levels for UK soils. 4. Chlorothalonil, fenarimol and iprodione were applied to a single putting green over a 6-month period but no effects on AM colonization were found. 5. Synthesis and applications. We have demonstrated that the low levels of AM fungi in putting greens are unlikely to be a consequence of excessive fungicide application. Levels of compounds applied in the last 20 years are very low and modern fungicides do not reduce existing AM colonization when applied to turf. Therefore, if AM fungi are added to sports turf to control P. annua, their effectiveness will not be compromised by current or past fungicide use.