The summer of 2019 has seen an explosion in disease activity on area lawns. The high temps and high humidity along with heavy downpours have created the perfect environment for lawn fungus development.
The worst hit grasses this summer are the hybrid Bermudas. First seen in 2017, a lawn disease called Bipolaris is doing extensive damage to area residential lawns and golf courses. It was not until we sent samples to NC State that we got a definitive identification. The initial infection looks a lot like Dollar Spot fungus with small brown circles. Examination under magnification does not show the hour glass shaped lesion on the leaf associated with Dollar Spot, but shows tan leaf spot lesions very similar to Helmenthasporium on Blue Grass. The initial browning occurs after mowing. It is especially bad when the grass is long and cut down short. Based on our research, there are contributing factors. The lawns infected the worst have low PH (acidic soil). Lawns with a PH of 6.0 or lower are the hardest hit. Lawns with a thatch layer greater than 1/2″ will see extensive damage as the fungal spores reside, over-winter and reproduce in the thatch layer. The third common denominator is low available Potassium in the soil. The shorter mown Bermudas (1″) resist the disease better because the surface soil can dry out quicker.
NC State, Clemson and Georgia Have given recommendations on fungicide treatment for this disease. We have tried every combination of the recommended products over the last two summers, We are getting acceptable results with a systemic/contact combo treatment. Once applied the spread of the disease stops and allows the damaged turf to fill in. It takes two treatments 21 days apart for efficacy. The results are not great and the treatments are very expensive. Over fertilizing with quick release Nitrogen to stimulate growth is the worst thing you can do for this disease. Controlled release, organic based fertilizer high in Potassium is what is required.
We recommend an aggressive lime treatment plan to get the soil PH up quickly. Aerate the Bermuda twice per year if you can and address the thatch layer with verti-cutting. Years ago (many) it was legal to burn off your Bermuda lawn in the spring. It eliminated thatch, disease spores and added carbon to the soil. Please cut the lawn at the proper frequency and height. If you have the lawn cut every other week versus weekly your lawn will be infected under current weather conditions. Once this pathogen infects a Bermuda lawn, we will fight it basically forever.