“Irregular weather patterns will not only affect the severity of weed infestations in warm- and cool-season turfgrasses but the efficacy of several herbicide treatments as well.”
While we are still continuing to study these populations, implications of this research to turfgrass managers everywhere are significant, particularly in regard to herbicide selection. Te current recommendation from University of Tennessee Extension is to target Poa annua infestations of warm-season turfgrass with a mixture of pre- and postemergence herbicides in October. Tis approach is an optimal resistance management strategy in that it facilitates using multiple modes of action for control. Additionally, delaying treatment until October increases the likelihood of turf remaining devoid of Poa annua throughout spring, compared to making a single application of a preemergence herbicide in late August or early September. Keep in mind that these timings may vary amongst producers in other geographies; however, the benefits of using pre- and postemergence herbicide mixtures for resistance management is applicable everywhere. Poa annua management is critically important in sod production considering that material can be distributed over a wide geographical area; those not already implementing a resistance management program should do so as soon as possible in 2019.
Lesson #3 - Soil Moisture Affects
Goosegrass Control Postemergence goosegrass (Eleusine indica) control is a challenge every season. In 2018, we learned that the growing environment in which goosegrass is commonly found could be a reason why herbicide applications often struggle. We evaluated several different herbicides for postemergence goosegrass control in the greenhouse including: Speedzone, Acclaim Extra, Tribute Total, Pylex, and Revolver. Tese treatments were applied to multi-tiller goosegrass maintained in soils varying in volumetric moisture content (VMC) from <12 percent to >20 percent. When applied at maximum labeled rates to plants growing in soils measuring <12 percent VMC, none of the herbicides tested controlled goosegrass greater than 25 percent.
When soil moisture increased, goosegrass control increased dramatically as well. For example, Tribute Total only controlled goosegrass 20 percent when applied to plants growing in soil measuring <12 percent VMC compared to 93 percent when applied to plants growing in soil measuring >20 percent VMC.
To that end, we are recommending that sod producers measure soil moisture content before making postemergence herbicide applications for goosegrass control in 2019. Use of a moisture meter can aid in determining if adequate soil moisture is present prior to treatment. It is important to remember that goosegrass needs time to acclimate to changes in soil moisture; simply applying irrigation prior to herbicide treatment likely will not improve efficacy.
“Weed control programs can incorporate different herbicide applications along with timely cultural practices to deliver an
integrated approach to weed control.”
Lesson learned #3: Interesting results in our ongoing research looking at soil moisture effects on herbi- cides for goosegrass control. Checking soil moisture before treatment in 2019 might not be a bad idea.
TPI Turf News May/June 2019 35
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