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 17 as crabgrass germinate from seed present in the uppermost layers of soil. Like all plants, these seeds require sunlight for ger- mination. Practices to maximize turf cover during the season will minimize the amount of sunlight reaching the soil surface ultimately lowering crabgrass pressure. Practices to maximize turf cover include everything from the selection of traffic tolerant cultivars, management of sum- mer diseases that can reduce turf cover, to changes as simple as increasing mowing height. Recent research has shown that increasing turf mowing height during the summer can improve the efficacy of several PRE herbicides including dithiopyr, oxadiazon (e.g., Ronstar), pendimethalin, prodiamine (e.g., Barricade), and prodiamine + sulfentrazone. Increasing mow- ing height will also improve the ability of turf to compete against weeds for essential water, nutrient, and light resources. Research has shown that increases in mowing height as small as 1/64 of an inch can increase photosynthesis as much as 13%. Thus, increasing mowing height not only improves PRE herbi- cide efficacy but also helps turf produce carbohydrates needed for growth and vigor during fall sports. Acknowledge thAt resistAnce is reAl Perhaps the biggest step field managers can take in maximiz- ing PRE herbicide efficacy in 2015 is to acknowledge that herbicide resistance, particularly to PRE chemistry, is a very real phenomenon that can compromise weed management programs. Biotypes of annual bluegrass and goosegrass with resistance to commonly used PRE herbicides are being identi- fied, with increasing frequency, throughout the transition zone southward. In most cases, these biotypes have evolved following repeated use of the same PRE herbicides over consecutive years without rotation to different herbicides that make use of vari- able mechanisms of action to control weeds. Many mistakenly assume that herbicides with different trade or active ingredi- ent names work differently—this is not the case. For example, prodiamine, dithiopyr, and pendimethalin all control weeds in the same manner (inhibiting cell division). Therefore, if resis- tance evolves following exclusive use of one of these products then weeds will be resistant to the others as well. Failure to rotate herbicides with different mechanisms of action or implement diverse weed management strategies (other than spraying) can lead to severe consequences should herbicide resistance manifest. Case studies of facilities suffer- ing from herbicide resistance have shown that the cost of weed control can increase three-fold once resistance is apparent. For example, the cost of annual weed management at a facility with resistance to dinitroaniline herbicides (e.g., prodiamine, pen- dimethalin, etc.) was $143 per acre compared to ~$50 per acre before resistance reached a critical level. In addition to econom- ics, resistance can drastically reduce the number of herbicide options available for effective weed management regardless of price. This is concerning given that no new herbicidal mecha- nisms of action have been introduced into the agricultural marketplace since the late 1980s. Fewer tools available for weed management coupled with an increased implementation cost is troubling considering that the presence of weeds on athletic fields can directly compromise athlete safety. PRE herbicides can be a highly effective tool for managing weeds on athletic fields. Always refer to the product label for specific information on proper use, tank-mixing compatibility and turfgrass tolerance. Mention of trade names or commercial products in this publication is solely for the purpose of provid- ing specific information and does not imply recommendation or endorsement by the University of Tennessee's Institute of Agriculture. For more information on turfgrass weed control, visit the University of Tennessee's turfgrass weed science web- site at www.tennesseeturfgrassweeds.org. ■ ST Dr. Jim Brosnan is the head of the turfgrass weed science research and extension program at the University of Tennessee. Greg Breeden is a weed science extension assistant at the University of Tennessee. Biotypes of annual bluegrass and goose-grass with resistance to commonly used Pre herbicides are being identified, with increasing frequency...