For many turfgrass managers in Western Canada take-all patch (TAP) can be one of the most damaging diseases on creeping bentgrass putting greens. What makes this disease so difficult to detect and manage is the fact that the above ground symptoms often occur long after the infection has started. Research has shown that when soil temperatures are cool and moist TAP begins to infect the plants roots. Based on this knowledge now is the time to use the fire extinguisher before the flames reach the ground floor as the curative options for TAP are generally ineffective.
Figure 1. Take-all patch on a bentgrass fairway. Note the healthy annual bluegrass colonizing the affected areas.
The pathogen (Gaeumannomyces graminis var. avenae) infects creeping bentgrass roots when soil temperatures are cool (10-16 °C) and moist. Soils high in pH can often lead to greater disease development.
Take-all symptoms usually appear in late spring to early summer during the time period coinciding with first wilt stress. Initial symptoms can develop as reddish-brown to bronze patches a few centimetres in diameter. In time, individual patch size will increase, eventually reaching 1 metre or more in diameter. A primary indication of take-all patch is that only bentgrass is affected whereas other turf species inside the patch remain unaffected and healthy. In severe cases, the patch interior thins significantly. Often, weeds or other grasses will colonize the thinned patches of bentgrass.
Figure 2. Signs of pathogen infection. Lobed hyphopodia on left and dark runner hyphae on the right.
Roots of infected creeping bentgrass are colonized by dark brown to black ectotrophic runner hyphae. The hyphae then produce mats of mycelium and lobed hyphopodia which are useful for microscopic identification of Gaeumannomyces species. Infected roots change in appearance and the central root cortex loses its transparent colour and becomes darkened, with roots turning dark brown to black as the infection advances.
Cultural practices that are successful in reducing take-all patch rely on maintaining soil pH between 5.5-6.0. For this reasons, using ammonium sulfate in spring and fall may be helpful in reducing soil pH. Liming and use of nitrate forms of nitrogen should be minimized as both can enhance disease. Take-all patch severity can be reduced by applications of manganese sulfate (2.2 kg per ha in the spring). Fungicides are often used in conjunction with cultural strategies because soils deficient in manganese or high in pH can be difficult to correct in the short term.
DMI and QoI fungicides are most effective against take-all. The most effective control of take-all patch occurs when fungicides are applied preventively in the fall (Sep-Nov) when soil temperatures are 7-16 °C at a 5 cm depth. In situations of chronic take-all, fungicides should be reapplied preventively in the spring when soil temperatures reach >13 °C for 5 days at a 5 cm depth with 2-3 applications every 21 to 28 days required. Fungicides must target infected roots, so apply at high label rates with flat fan nozzles in 8-20 L of water per 100 m2 (or use 0.6-1.3 cm of irrigation immediately after application) to ensure fungicide contact with the root zone.