University of Maryland Lecturer and Turfgrass Management Advisor Geoff Rinehart answers your questions about lawn weeds and fall fertilization.

Q: What is this “grass” and is it possible to eradicate it from our lawn? It has been spreading down the hill from our neighbor’s property. What’s the best way to bring our lawn back to a nice quality grass?

Answer: Japanese stiltgrass (Microstegium vimineum) is an invasive summer annual grass that is becoming more pervasive in Maryland. While it used to be more limited to just woodland areas, we are getting more reports of it infesting lawn areas in recent summers.

As is the approach with any weeds, practicing good turfgrass cultural practices to encourage a healthy, dense stand of grass is the cornerstone of any lawn management program. Mowing taller (3”-3 ½”), fertilizing based on University of Maryland recommendations, and overseeding annually with improved turfgrass cultivars are three practices that will help create greater density.

This summer has been a particularly difficult one for controlling summer annual grasses like crabgrass, goosegrass, and, of course, Japanese stiltgrass since these weedy grasses are favored by wet, hot conditions like the weather we had in July-September. Since Japanese stiltgrass is a summer annual, it can be deterred by applying a pre-emergent herbicide in the spring at forsythia bloom (which is a similar approach to crabgrass control). When watered-in, pre-emergent herbicides form a soil barrier to seed germination. However, most of these products only last 6-10 weeks (the lower part of this range when it is wet and/or hot, the upper part when it is dry and/or cool). This May was rather rainy, so if you applied a pre-emergent in early April, another should have been applied in June. Usually, two applications are enough to get us to early August and then summer annual weed pressure decreases as early cooler weather is usually a month around the corner.  Continue reading →