Red Thread Needles
Red Thread on cricket square in Jersey
Red Thread
RED thread is an extremely common turfgrass disease that can develop at any time of the year during cool, wet weather, but frequently appears most severely during late spring and autumn. It can develop on most turfgrasses but ryegrasses, meadowgrasses and fescues appear to be more commonly affected. This disease is often referred to as an indicator of low fertility and symptoms will often develop more severely if nitrogen or potassium is limited. Red thread is caused by the fungus
Laetisaria fuciformis. The initial symptoms of infection are water-soaked areas of leaf tissue, but these often go unnoticed. As the infection progresses, the infected leaves rapidly dry, become straw-coloured and appear as irregular patches across the sward. Patches can range in size from 5 to 50 cm in diameter and will often develop characteristic red needles (sclerotia) throughout the damaged area. The sclerotia are aggregations of countless strands of very pale pink fungal mycelium which grow out of the
infected leaf tissue and become wound tightly together appearing pink or red when complete. The development of these ‘needles of
mycelium’ allows the infection to progress by enabling the fungal mycelium to spread over the turf under humid conditions. Once the sward is dry or the relative humidity around the turf is reduced, the needles become desiccated and brittle. They then become dislodged from the infected plants and fall to the base of the sward where they will remain until favourable conditions return. The disease can be spread by infected clippings and direct movement of the sclerotia but the fungus also produces arthroconidia (fragmented mycelial strands) that can be windblown over long distances. Red thread is almost invariably a foliar disease and although the causal fungus has the ability to enter and damage the crown tissues, it very seldom does. Because of this, the symptoms of the disease can frequently be reduced by light
Bibionid Flies
THERE are two Bibionid flies that are common to amenity turfgrass
areas. One is the St Mark’s Fly and the other is the Fever Fly. These flies cause no damage in their adult form and are thought to be beneficial pollinators of fruit and other crops. However, their larvae do cause damage to turf by feeding on the roots and reducing water and nutrient uptake. The adult St Mark’s Fly (Bibio marci) and the slightly smaller Fever Fly (Dilophus febrilis) are relatively small (6 mm or less), stout, black flies. The St Mark’s Fly appears between the end of April and May but the Fever Fly appears between March and October. After mating, the female lays around 30 eggs at a time and this results in small clumps or pockets of larval activity in the
rootzone. The eggs are laid between May and August/September and hatch from late summer, producing larvae that will feed on the organic matter in the rootzone or the roots themselves. Damage is often seen either in November/December or in January/February as small yellowing patches throughout the sward. If the damage to the turfgrass roots is extensive enough, the yellowed plants will eventually die. The adult fly will emerge from the pupal stage to initiate a new life cycle.
Although these pests are flies in their adult form, their larvae have a small dark head with well-developed mouthparts, similar at first glance to that of the chafer larvae. However, the Bibionid larvae do not have either legs or pro-legs and their body is relatively
long and thin. The larvae will vary in size depending on their age but will grow to around 11mm long and 1.5-2.0 mm wide. Identification of the different Bibionid species requires microscopic analysis of certain details on the larval segments.
Insecticides that are used to control leatherjackets (larvae of the Crane Fly, Tipula sp.) will also have an effect on Bibionid larvae. However, timing of the insecticide application is important because during November/December, the larvae are relatively small and closer to the surface of the rootzone whereas during January/February, the larvae will have grown significantly in size and will start to move deeper in to the profile.
nutrient applications and removal of the diseased tissue by boxing off the clippings. However, there are increasing reports of this disease developing on turf that has been maintained under adequate nutrition and in such instances, symptoms will not be satisfactorily reduced by nutrient application alone. Where red thread regularly causes damaging symptoms, it would be worth considering over-seeding with grass cultivars that have been bred with reduced susceptibility to the disease. Many of the fungicides that are currently
available for use on managed amenity turf have shown efficacy against this turf disease and, where necessary, can be used as part of an integrated programme to manage red thread. Always ensure that the disease is correctly identified prior to the application of any plant protection product.
Dr Kate Entwistle The Turf Disease Centre Tel 01256 880246
OF THE MONTH
pest
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