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18 Landscape and Irrigation January/February 2014 www.landscapeirrigation.com Landscape and Turf Maintenance By Jeffrey Borger F or many turf managers, spring is the end of a long hibernation away from the outdoors. You most likely notice the aftermath of the winter in some of the turf you maintain — tree limbs, gravel from plowing roadways, and leaves that were never collected before the onset of cold weather. You also know that crabgrass germinates in the spring. But it can be controlled with a range of differing preemergence chemistries. The following are some preemergence crab- grass control strategies. Crabgrass plant's developmental stages Knowing the particulars about how the crabgrass plant germinates, develops, and ex- pires is essential. Crabgrass germinates in the spring (Figure 1). The experienced turf manager knows, on average, when this hap- pens in their respective regions. One should never rely solely on the calendar to determine the germination patterns each year. Nature has a phenological indicator to assist in pre- dicting crabgrass germination. A phenological indicator can be defined as any recurring bi- ological phenomena such as one plant growth stage that happens at a similar time another seasonal action is occurring. For example, where I live, the Mid- Atlantic region, when the forsythia plant drops its yellow flower petals can be a phe- nological indicator of the start of the germi- nation of crabgrass. This timing can still prove to be a bit ambiguous. When exactly in the petal drop process will the crabgrass germi- nation happen? Refer to Figures 2 and 3 to see some stages of forsythia petal drop. To more accurately predict crabgrass ger- mination in the spring, soil temperature and moisture should be monitored and recorded. Crabgrass germination happens when the soil temperature at a 1/4-inch depth maintains a temperature of 50 to 55 degrees Fahrenheit for three consecutive days and nights, and moisture is present. Crabgrass germination begins sometime from late March to mid-May in our region. Generally, the majority of the crabgrass will stop germinating about mid-July. The crab- grass plant will mature and be eliminated from the sward at the first heavy frost. Some- times, a late heavy frost in the spring can also eliminate newly germinated crabgrass popu- lations. However, following a heavy frost in the spring, crabgrass will continue to germi- nate and still be a problem if not attended to in some fashion. Formulate a management strategy A strategy to control crabgrass using pre- emergence material can seem simple. The dif- ficult part of most strategies is the implementation phase. There are many things that can be controlled by the turf manager and equally as many that cannot. Although the list of things that cannot be controlled is long, the most unpredictable is the weather. Remember, formulate the management strat- egy and be prepared to change it often. There are really two distinct preemer- gence crabgrass control strategies — apply preemergence materials only once or apply them twice. There are several additional things to consider. If the materials will only be applied once, the rate and the longevity of them must be evaluated. For example, one product may have a five-week residual when Preemergence Crabgrass Control Strategies Fig 1. Newly germinated crabgrass in the spring of the year. All photos and graphics provided by Jeffrey Borger Left: Fig 2. Forsythia is in full bloom. The yellow petal drop has not started. Right: Fig 3. Forsythia yellow pedal drop has begun. About this time crabgrass will start to germinate.