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: https://read.dmtmag.com/i/64785
FieldScience | ByBrad S. Fresenburg, PhD weed control for sports fields >> DANDELION Post-emergent O >> CRABGRASS >> GOOSEGRASS stand of turfgrass. Culturally, we can reduce our potential for weeds if a dense stand of turf- grass can be maintained at the highest cutting height possible. While most sports fields are mowed at relatively close mowing heights as compared to a home lawn, we do know that going from 1½ inches to 3½ inches can reduce annual weeds by 80%. Weed seed requires light for germination and a dense turfgrass canopy mowed taller creates a shade effect. Obviously we are not saying that all sports fields should be mowed at 3½ inches. How- ever, in some situations, keep in mind that if we can get by with a higher mowing height every additional ¼ to ½ inch does help; we can reduce weed infestations. Often weeds are properly identified and the first question asked is, "What do I spray to kill it or control it?" Most extension spe- cialists or weed scientists can give a short- term solution to that question. What we would like you to ask yourself first is, "Why is this weed there?" Knowing why weeds exist outside of having a weakened turfgrass can sometimes dictate changes in our cultural practices that may impact the level of infesta- NE GENERAL COMMENT that can be made about weeds is the fact that they are there due to a weakened Other Reasons Weeds Exists Low Mowing Compaction >> PROSTRATE KNOTWEED Images above >> DANDELION is a perennial broadleaf weed that is best controlled in early fall. >> CRABGRASS is a summer annual grassy weed. Best control for post-emergent herbicides is at the 1 to 3 leaf stage (left). Products containing quinclorac are best in the early tiller stage (right). >> GOOSEGRASS is a summer annual grassy weed that will emerge after crabgrass. >> PROSTRATE KNOTWEED is a summer annual broadleaf weed that is an excellent indicator weed for soil compaction. 8 SportsTurf | May 2012 Drought Poor Drainage/ Wet Soils Low Soil pH High Soil pH Low Nitrogen High Nitrogen Low Fertility Low Calcium Shade Weeds Annuals such as annual bluegrass, chickweed, crabgrass, speedwell; also plantains Annual bluegrass, crabgrass, dandelion, goosegrass, pineapple weeds, prostrate knotweed, prostrate spurge, speedwell Black medic, cinquefoil, clovers, crabgrass, curly dock, goosegrass, prostrate spurge, speedwell, yellow wood sorrel Barnyardgrass, buttercups, nutsedge, plantains Common mullein, English daisy, hawkweed, knawel, red sorrel, wild strawberry Broadleaf plantain, hop clover, wild carrot Black medic, clovers Annual bluegrass Foxtails, henbit Dandelion Chickweeds, moss, speedwell, wild violets tion we have. Understanding that some weeds favor compacted soils, droughty or poorly drained soils, low or high soil pH, low or high nitrogen, low fertility and/or shade can help identify needs for perhaps aeration, grade work, proper fertility and irrigation, and soil testing (see table below) Treating weeds after they emerge allows for proper identity of the weed species. However, several weed species are difficult to identify in the seedling stage. It's only after they become more established and unsightly before correct identification can be made. Controlling weeds when they are young and actively growing will provide the best post-emergence control. Grasses are best controlled prior to tiller. Broadleaves are best controlled in the 2 to 4 leaf stage, sedges usually in a 3 to early 6 leaf stage. Avoid mowing within 24 to 48 hours before or following applications of post-emergence herbi- cides. The goal here is to provide maximum leaf area for maximum plant uptake. Irrigation within 24 hours after post-emergence applica- tions should be avoided. Note that many new formulations of post-emergence herbicides are rain-fast within 6 hours. Be sure to check the label. Drought stressed weeds should be irri- gated 24 hours before applications of herbicides for improved efficacy. www.sportsturfonline.com