The uncharacteristically warm weather has brought many diseases earlier than we would expect and has left many scrambling to either identify the pathogen or make a curative fungicide treatment. Copper spot (caused by Gloeocercospora sorghi) is one of the diseases (along with dollar spot, brown patch, take-all) that have made an early appearance this year. Copper spot was recently observed on a bentgrass/Poa golf course fairway in Eastern Massachusetts and is not typically observed this early in the year. Creeping and velvet bentgrasses are the most susceptible hosts (Fig. 1). The warm nights and wet conditions that occurred in the early portion of last week provided ideal environmental conditions for this pathogen to infect turfgrass. Symptoms typically include small red to brown lesions that may coalesce to blight the entire leaf and form 1-3 inch copper colored infection centers unlike the bleached infection centers of dollar spot (Fig. 2). Copper spot is not typically a major problem, because most fungicides (chlorothalonil, DMIs, strobilurins, and thiophanate-methyl) at 14 days interval that control dollar spot will also control copper spot. If damage has been observed, avoid applications of water-soluble nitrogen.
Submitted by: Jay Popko and Dr. Geunhwa Jung