Timing crabgrass pre-emergence applications
There is still time to make pre-emergence herbicide applications to control crabgrass.
Spring 2016 has been a roller coaster ride of temperature peaks and valleys. What started as an early spring with warm temperatures melting snow and some golf courses opening the second week of March has since slowed. The weekend forecast is even mentioning that four-letter word for frozen precipitation. For those looking to make a pre-emergence herbicide application for crabgrass control, there is still time.
Summer annual grasses such as crabgrass require proper soil temperature and moisture to germinate and establish. Eighty percent of germination will occur when soil temperatures at the 0-2 inch depth are consistently between 60-70 degrees Fahrenheit. For pre-emergence herbicides to be effective, they need to be applied before the soils reach this optimum temperature range. March 31 was the first day the maximum soil temperature at a 2-inch depth hit 50 F at the Hancock Turfgrass Research Center on Michigan State University’s campus.
A growing degree day (GDD) model to predict application timing is available at GDD Tracker. The model uses GDD to indirectly measure soil temperatures in a turf situation (enter your zip code under the map and then click on the Crabgrass PRE button). The optimum application window for the model attempts to predict when the 0-2 inch depth soil temperatures consistently reach 50-55 F and therefore provides adequate time for the pre-emergence herbicide to be applied and watered in before crabgrass germination occurs.
This year, the GDD model for crabgrass pre-emergence in mid-Michigan reached the optimum application timing window on March 25. Currently, a line from approximately Mt. Pleasant, Michigan, south is in the optimum timing window while to the north is still early. Based on the forecast, it appears the optimum application window will last at least another week if not possibly two.
A good environmental indicator for pre-emergence timing is when forsythia bushes are blooming with their bright yellow flowers. Every year I watch a forsythia bush near my office, it happens to be located on the south side of a building so it’s a warm site and usually blooms a little early. This bush just started blooming in the last couple days. Remember the practices that encourage a healthy, dense turf stand, such as mowing high, returning clippings and adequate fertilization, are all part of an effective crabgrass prevention strategy.
Dr. Frank’s work is funded in part by MSU’s AgBioResearch.