SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: http://read.dmtmag.com/i/448298
www.stma.org February 2015 | SportsTurf 13 In our opinion the key predictive criteria for crabgrass ger- mination and infestation is soil temperature. Other predictive methods can be used to determine crabgrass germination like growing degree days (GDDs), phenological events like forsythia bloom drop, calendar dates, weather consultant services, his- torical experience, etc. but soil temperature monitoring is by far the most reliable qualitative method. Crabgrass typically ini- tially germinates in late winter/early spring when nighttime soil temperatures reach 50-55F for several consecutive nights (Table 1). It continues to germinate throughout the spring and early to mid summer period. Monitoring soil temperatures at a 2" depth is one of the best ways to predict when crabgrass will initially germinate. The temperatures listed in Table 1 refer to the low nighttime soil temperatures over a period of several consecutive nights. Any method that assists in monitoring soil temperature within your region can be used like a simple soil thermometer or a website weather database; a weather monitoring technology like the Spectrum Technology Watch Dog weather system also can provide a wide variety of other climatological data in addi- tion to soil temperature, local weather consultants, etc. Our Ohio Agricultural Research and Development Center at the Ohio State monitors climatological data at 20 different loca- tions across the state and provides weather data via the OARDC weather system web-site every 5 minutes 24 hours a day 7 days a week. Sports field managers can log onto the site anytime and retrieve past and current nighttime soil temperatures at the 2" and 4" depths every night and day during the late winter/ spring. As soil temperatures begin to move into the 50-55F range for several consecutive nights, just like a clock, crabgrass will initiate germination. The OARDC weather system is a great soil temperature monitoring tool. Check with your closest land grant university or state turfgrass specialists to see if such a weather-based system is available to you in your state. The sec- ond best attribute of this system is that it is FREE. I think most of us like valuable things that are free. The relatively new GDD tracker program/model (www. GDDTracker.net) developed at Michigan State University is another good way to assist you in monitoring crabgrass ger- mination timing based on growing degree days. It is set up for monitoring in four mid west states at the present time. In Ohio, GDD tracker program use is being financially sponsored by John Deere Landscapes and the Ohio Turfgrass Foundation. You may want to consider working with sponsoring agencies, associations and foundations in your state to bring this pro- gram on board. Most turfgrass managers continue to rely on the use of preemergence herbicides as a standard preventative control for crabgrass and other annual grasses (an "offensive" strat- egy). Preemergence herbicides provide a chemical barrier or blanket at the soil surface intercepting the young seedling weed and preventing it from emerging/developing (Figure 1). Thus, proper application timing is a key factor in its effec- tiveness. Many agronomists consider improper (i.e. missing the initial window of crabgrass germination) as the primary reason for preemergence herbicide failure. Emerged crabgrass plants are not controlled by preemergence herbicides, except for Dimension, which exhibits early post and pre activity. The basic "offensive" principle is that the preemergence herbicide be applied before the onset of crabgrass seed germination. It is fairly simple if you engage the "offensive" principle and moni- tor soil temperatures and/or GDDs. Crabgrass can germinate at significantly different times from year to year. In Columbus (a great example) crabgrass germinated at its typical time of April 20-25 in 2013, but in 2012 crabgrass surprised most turf managers by germinating March 15-20 (4 weeks earlier than normal). Sports turf managers monitoring for soil tempera- tures and/or GDDs where well ahead on the "offensive" side of the game plan whereas many other managers lost the game in the first quarter (March/April 2012). Really can't recover when the initial germination window has long passed (like a wide receiver 30 yards down the field and wide open!). Preemergence herbicides that can be routinely used in the "offensive" plan of most turfgrass managers for both cool and warm season grasses are listed in. The most effective preemergence herbicides are those ranked good (G) to excel- lent (E) for crabgrass control. The "offensive" strategy for sports turf managers is confounded by the fact that most of these preemergence herbicides will severally damage, kill and/or prevent the emergence of desirable turfgrasses as well as weeds. Sports turf managers have several choices of preemergence herbicides based on species tolerance and efficacy where NO seeding or overseeding programs are planned. Most of the her- bicides listed for standard preemergence use cannot be used on turfgrass areas at the time of seeding or within a certain time interval after a preemergence application. Please note that there are major differences in the tolerance/ Figure 1: Preemergence herbicides form a chemical barrier or blanket at the soil surface. New annual grassy weed seedlings like crabgrass contact and absorb the herbicide during emergence and are killed. See table for restrictions on seeding and overseeding with preemergence.