The recent weather conditions, periods of hot and dry, followed by much cooler, more humid stretches have created the ideal vectors for turf disease. Red thread, rust and especially leaf spot are being observed in a large percentage of our Clark County and Portland Oregon area lawns.

The most serious of these diseases is leaf spot, a very common fungal disease we see year-round in turf. Generally, we can control leaf spot (as well as red thread and rust), with regular, proper fertilization. However, when conditions are right, as they are now, leaf spot often progresses to the damaging melting out phase. This melting out phase typically starts as irregular shaped purplish, brown or straw-colored spots in the lawn, with distinctive spots of seemingly healthy green grass (this is called frog-eye) within the patches.

People often mistake this condition for dry spots, which it closely resembles, and apply extra water. Unfortunately, this actually makes the disease worse and helps it spread. If you notice areas in your lawn that have this appearance, dig into the soil with a knife or screw driver. If the soil is moist, you almost certainly have this disease and need a fungicide application ASAP.

It's important to note, fungicide will stop the spread of the disease, but does not restore damaged turf. In most cases the turf will gradually recover over several weeks, but, if the damage is severe enough, aeration and over-seeding may be necessary.

See photos: The first is leaf spot melting out in the early stage of infection. The second shows more advanced damage.