TURF magazine has been getting reports from lawn care friends and readers of the very early appearance of weeds on clients’ lawns. Fortunately, many companies could get on the lawns earlier than they usually do because of the very mild winter in most of the country. Unfortunately, on many properties the weeds are beating them to the punch. 
Here’s some valuable information regarding this spring’s weed issues from Dr. Aaron Patton, Turfgrass Extension Specialist at Purdue University in West Lafayette, Ind.
With warm temperatures this winter many are questioning how to adjust their turf management practices in 2012. In the past 90 days, Indiana (editor’s note: indeed, most of country east of the Mississippi) has experienced warmer than normal temperatures. The forecast also shows that we will likely continue to be warmer than normal during the next 30 days.
Although I do not foresee the need to make significant changes to your management program, it will be necessary to start making preemergence applications earlier this year in my opinion. Here are some things to consider as you adjust.
How will the warmer conditions affect my preemergence timing?
Some believe that despite the warmer weather, that it is not necessary to make preemergence applications early in 2012 because we will very likely get a "killing" frost in April which could kill all the crabgrass that germinates early. While I think this is possible, my experience is that many warm-season grass seedlings (whether crabgrass or bermudagrass) are largely unaffected by spring frosts.
The reason for this is not completely clear, but it is likely that these seedlings are insulated from frosts that occur at the top of the turf canopy because the emerged seedlings, such as crabgrass, are protected next to the warmer soil surface. Since I do not believe that there is a guarantee that a late spring frost will kill emerged crabgrass, then I recommend making sure that you apply your preemergence herbicide early this year prior to emergence. Just how early is uncertain, but it would not hurt to target making applications 7-10 days earlier than normal. To track crabgrass germination and the optimum window for preemergence applications, check the following website http://www.gddtracker.net/.
How can I get extended crabgrass control?
Split or sequential applications are a strategy for improving crabgrass control with preemergence herbicides. The general strategy is to split the application from one application into two applications using the same total amount of product. The first application would be applied before crabgrass germinates at a one-half rate at the normal application timing and the second application would be made approximately 60 days later at a one-half rate. For example, Dimension 2EW would be applied at 1 pint/acre (0.25 lb a.i./acre) on April 1 and a second application would be made with Dimension 2EW at 1 pint/acre (0.25 lb a.i./acre) on June 1. This would equal a total of 2 pints/acre or 0.5 lb a.i./acre. Research at Purdue shows that crabgrass control can be increased by about 20% using a split application strategy compared to a single preemergence application.
