Although it is only January, it has been a mild winter with a severe lack of rain in the desert southwest. Typically, there will likely be some precipitation during February and March that can result in early germination (mid to late March) of many summer grassy weeds such as cupgrass, crabgrass and watergrass (junglerice or barnyardgrass). This update will discuss preemergence weed control options in overseeded, non overseeded and native areas for grassy and broadleaf species as well as a tip on postemergence control of troublesome winter weeds.
Preemergence weed control for grassy weed species in the desert southwest
Weeds such as cupgrass, crabgrass and watergrass generally will begin germinating in mid to late March and that means the preemergence herbicide application window is only a few short weeks away. If the bermudagrass was healthy prior to overseeding and plant samples in the field reveal healthy stolons and rhizomes then move forward with products such as prodiamine, dithiopyr or pendimethalin. For non overseeded and native areas, some turf managers are using alternatives such as simazine and oryzalin. Newer products such as flumioxazin can control grasses as well as some broadleaved weeds.
Preemergence weed control options where bermudagrass health is poor
The chemical options discussed above can be detrimental to the ability of the bermudagrass to recover where turf health is poor. In such cases, an alternative, although more expensive option is oxadiazon. Oxadiazon will not inhibit the ability of the bermudagrass stolons to establish in the soil and can be applied safely on ryegrass in the granular form.
Broadleaf preemergence weed control
The smart option for broadleaf weed control in overseeded, non-overseeded and native areas is isoxaben. Isoxaben will control (or suppress) many common broadleaf weeds in the southwest that will be germinating within the next 6-10 weeks such as Russian Thistle, purslane, plantain, fleabane and spurge.
Postemergence control of winter weeds
If the preemergence window for grassy and broadleaf weeds was missed in the fall season, act now to remove pesky winter weeds before they mature and outgrow their ability to be controlled with herbicides. Several combination herbicide products such as combinations of 2,4-D, MCPP, and dicamba or 2,4-D, dicamba, carfentrazone and mecoprop will control common mallow, London rocket, and mustards that are common winter weeds in the desert southwest.
Preemergence weed control in most cases will be more efficient and cost-effective when compared to postemergence management. Plan now and be prepared to apply the appropriate chemicals prior to grassy and broadleaf weed germination during mid to late March.
A special thank you to Kai Umeda, Area Extension Turfgrass Specialist with the University of Arizona for his assistance with this update.
Source: Brian Whitlark (firstname.lastname@example.org)
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