Watch for “Melting Grass”

As the temperatures warm into the 60’s (or greater) and the rain chance remains good, keep an eye open for disease in your lawn.  Large patch disease is common in turfgrass this time of the year.  It is caused by the fungus Rhizoctonia solani.  The fungus is present in the soil and thatch layer year-round.  When the temperatures rise into the 60’s and 70’s it begins to spread.  Large patch thrives under these conditions, especially when the soil is wet.  With frequent showers the disease spreads quickly.  The first symptom of large patch is circular, discolored areas within the lawn.  The outer borders of the patches are orange to yellowish in color.  In the center of the circle there are grass blades trying to green up again.  They are usually unsuccessful, resulting in odd-shaped patches of dying grass that begin to connect to each other.

A simple field diagnostic techniques to confirm large patch disease is to pull on the diseased grass shoots near the edge of the circle.  The blades will come loose from the stolon easily.  At the base of the leaves the stem and sheaths will appear dark brown and rotten.  Yes, it is large patch.

If the weather gets colder or hotter very quickly, the disease will go back into dormancy.  Looking at the long-range temperature predictions, the rest of February will be going up and down.  Remember, the groundhog said six more weeks of winter.  So, start looking for a fungicide or two or contact your pest control service.  However, remember fungicides don’t cure existing problems.  They are utilized as a protectant for the unaffected portions of the grass.  When favorable conditions are present, the turf should be sprayed in order to keep the fungus from penetrating the grass blades.  Repeat applications will be needed for as long as the weather is cool and wet.  Check the product label for the correct intervals.  Several cultural practices promote large patch infection including over-fertilization, over-irrigation, low mowing height, poor drainage and excess thatch.  This spring, after the grass has greened-up on its own, is a good time to look at these factors and make corrections.  Keep a close eye because as soon as the temperatures drop again in the fall, large patch can reappear if the corrections were not complete.  For more information: https://edis.ifas.ufl.edu/lh044