Tan patches in an otherwise green lawn at this time of the year are likely due to either slow-greening warm-season grasses or snow mold. The most common tan patch right now is warm-season grasses like nimblewill or zoysia (photos). Time, warming temperatures, and rainfall are the cures for most of these patches and they should green up in mid-May. These grasses maintain their structural integrity with stiff leaves and stems during dormancy. Some would classify these grasses as “weeds” and try to control them, but control is extremely difficult. In 99% of the cases, it’s best to just leave the patches alone and not try to control them. If you prefer to torture yourself trying to control these weeds, there’s information at http://www.agry.purdue.edu/turf/publicat.htm under AY-11: Control of Perennial Weedy Grasses in Turf. Snow mold is the other candidate for causing tan patches in lawns and this is more common in Fort Wayne and farther north. Pink snow mold will form 12” or smaller circles, which sometimes coalesce to damage large areas (photo). Often these patches have a tinge of pink. Pink snow mold rarely kills turf in Indiana, but a light raking could help the grass recover more quickly. Fertilization in September and November does not encourage snow mold, but actually helps the turf recover faster from an infection. However, an October application of nitrogen will keep the turf too succulent and may encourage snowmold. More information can be found in BP-102-W Turfgrass Disease Profiles: Pink Snow Mold at the same web page mentioned earlier.
