This year has been extremely humid and warm. We have seen a summer full of warm temperatures during the day that cool down in the nighttime to the dew point, which has been causing a high number of turf diseases. We are also now experiencing a great deal of crabgrass and other summer annual weeds in our lawns. These are things that decrease the overall appearance of our lawns but they are not long lasting this late in the summer.
Brown patch is a fungal turf disease showing up in our lawns right now. This disease often shows up in lawns that were overwatered or were fertilized heavily in the summer months as brown patches in an otherwise green lawn. Upon closer investigation, you may notice that the leaves may have long tan-colored spots that are surrounded by a dark brown margin. You can avoid this disease by avoiding over-irrigation and over-fertilization of the lawn.
Summer patch is also showing up in our lawns right now. This fungal disease also leaves brown patches in your lawn, but usually they are in a circular pattern with an area of green turfgrass in the center, like a frog-eye appearance. The leaves do not have a distinct marking on them but the roots will be brown. The best control for summer patch is to follow fertilization and watering requirements to reduce the stress to your lawn.
The diseases that we see in our lawns this time of the year are mostly environmental. You can help to reduce the incidence of these diseases if you take good care of your lawn. Keeping the lawn mowed at 2-3 inches high, correct fertility, and correct watering, will help keep your turf healthy and able to compete with these diseases. Fungicides can be used, but they need to be applied as a preventative and are not usually necessary in home lawns. Home lawns can tolerate a low level of damage without the need for fungicides. If this is a problem that is seen in the same location of your lawn year after year, you may need to use a fungicide, but that should be used in the spring or in the summer as the first signs begin to appear in your lawn. At this time of the year, fungicides will not fix the damage that is already seen in the lawn this year. So in the late summer and fall, fungicides are not recommended.
Crabgrass and other summer annual grasses are also becoming more problematic now. In addition to the maturation of plants that germinated earlier in summer, incidence has also increased from recent rains and warm weather that allowed more seed to germinate where a sufficient herbicide barrier is not still present, especially in full sun or thin turfgrass canopies. Control is not necessary this time of the year because the crabgrass present in your lawn now, will die with the first fall frost in a few weeks. It is the best environmentally and economically for you to use a pre-emergent herbicide next spring.
Lawn fertilization should occur with the holidays: Arbor Day, Memorial Day, Labor Day, and Halloween. Applications for Labor Day can be done anytime now. Apply 1 pound of Nitrogen per 1,000 square feet on your lawn. Once the temperatures cool down, you can begin using 2,4-D products to combat broadleaf weeds such as dandelions, clover, and henbit. The fall is the best time to treat for the perennial weeds so that the chemical is taken into the roots with the nutrients the weeds have in their leaves that they store in their roots over the winter months. For henbit, it is best to treat this in the fall as well to kill it before it sets seed next spring.