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/101565
FieldScience | By Brad Park >> HIGHLY TRAFFICKED sports fields that receive little or no overseeding during fall and subsequent spring months may consist almost entirely of summer annual weeds such as prostrate knotweed in field centers during summer months. Photo by Brad Park. Managing summer annual weeds on high traffic sports fields HERE IS AN OLD ADAGE that the best form of weed control is a healthy, dense stand of turfgrass. Is it any wonder that high traffic sports fields virtually absent of turf cover are often with riddled with summer annual weeds? Solving these weed problems requires more than a phone call to schedule a contractorperformed herbicide application. A long-term seeding program that may involve strategically-timed herbicide applications, or perhaps even sodding, must be employed to fill-in the voids in turf cover caused by traffic. T THE PROBLEM Sports field locations that are heavily trafficked during fall and receive little to no overseeding during that period typically enter winter as bare soil. These voids in the turf cover are ideal conditions for summer annual weeds to germinate during the following spring months, mature in summer, and produce large quantities of seed in late summer. The weed seed is returned to the soil creating a seed bank that will replenish weed populations for years to come. As temperatures cool and mother nature brings the first frost during fall, summer annual weeds are reduced to fragile skeletons and continued field use quickly reverts the surface back to bare soil���an unsafe surface that can lack stability when wet (i.e. mud) and be hard-as-concrete when dry. Crabgrass (Digitaria spp.), goosegrass, (Eleusine indica L.) and prostrate knotweed (Polygonum aviculare) are summer annual weeds that are routinely present on high traffic sports fields. Crabgrass is among the most common summer annual grassy weeds that invade turf areas. It germinates when soil 12 SportsTurf | January 2013 temperatures have been 55 degrees F for 4 to 5 consecutive days, typically corresponding with early April to early May in the Northeast United States. Goosegrass, sometimes referred to as silver crabgrass, is a grassy weed, has a recognizable zipperlike seedhead structure and geminates later in spring compared to crabgrass when soil temperatures in the upper ��-inch of soil are 60-65 degrees F for 12 to 15 consecutive days. Often observed in goal creases, field centers, and footpaths where pedestrians cut-across turfgrass sites, goosegrass tends to be more tolerant of compacted soil conditions compared to other grasses and broadleaf vegetation. The earliest germinating summer annual weed that affects sports fields in the Northeast is prostrate knotweed, a weed in which seedlings have been observed in northern New Jersey in the first week of March. Prostrate knotweed seedlings are often misidentified as newly germinated turfgrass; however, prostrate knotweed is a broadleaf weed (i.e. dicot) and has two seed-leaves (i.e. cotyledons). In contrast, grass species (i.e. perennial ryegrass, crabgrass, etc.) are monocots and have a single initial seed-leaf. Similar to goosegrass, prostrate knotweed is a common problem on heavily trafficked sports fields constructed out of compaction-prone native soils. While summer annual weed lifecycles and the season-specific timing of much sports field use presents an inherent challenge, an added dilemma is that some sports fields are routinely treated with conventional preemergence herbicides (i.e. pendimethalin, prodiamine, or dithiopyr) in March and April yet are predominantly bare soil in field centers and goal Similar to goosegrass, prostrate knotweed is a common problem on heavily trafficked sports fields constructed out of compaction-prone native soils. www.sportsturfonline.com