Sunday, March 04, 2012

Suggestions for controlling Dollarweed in the landscape...

Unusually warm temperatures and frequent rainfall have created ideal conditions for an explosion of Dollarweed (DW) - a very common problem here in Galveston and throughout the Texas Upper Gulf Coast area. There are many different thoughts and philosophies when it comes to weed control in turf and landscape beds. Most folks are looking for an easy, low-cost, non-chemical solution to the problem. However, some weeds, like DW, aren't that easily managed. The following suggestions cover a variety of tactics that may be employed in the battle against DW.

An IPM Approach:
I believe in an Integrated Pest Management (IPM) approach to controlling any landscape pest - including DW. IPM begins with the proper identification of the problem (see the DW picture). Some folks confuse DW with dichondra - another pesky weed. The best way to tell these 2 apart is that DW has it's stem in the center of the circular leaf. Dichondra doesn't.

The next step in an IPM approach is selecting a control tactic(s) that poses the least threat/impact to the environment. This can include: doing nothing if the problem isn't bad enough to warrant a control tactic, mechanical, cultural, biological and/or chemical control(s).

Mechanical Control:
DW is one tough cookie in the weed-world. It can spread by seed, rhizomes and/or tubers. That's why the BEST control is not letting it get started in the first place. Pull even the smallest plant the minute it shows up in turf areas or beds. BUT - that can be more challenging than it sounds. If you don't get the entire plant (rhizomes and all) you're just helping it spread. It's better to "dig" these plants up with a trowel than to pull them.

Cultural control:
DW is a plant that thrives in wet soil. If you have a lot of DW, there's a high likelihood that something, somewhere in the yard is being over-watered. Or the irrigation system is not being properly operated. That being said - we're coming off one of the worst droughts in Texas History and I saw plenty of DW in non-irrigated areas. So this reduced moisture thing can only get you so far in controlling DW.

Healthy growing turfgrass helps prevent DW from getting established better than stressed out, under-nourished, insect/diseased infested turfgrass. A good case for spring/fall fertilization. Also "proper" mowing height is important. Don't "scalp" when mowing. This practice helps DW become established and spread. 

Chemical control:
Generally speaking it's much easier to control DW in turfgrass than it is in landscape beds. That's because DW is classified as a warm season, perennial, broadleaf weed. This enables the use of a broadleaf herbicide. However, these same herbicides can have lethal consequences in landscape beds containing broadleafed annuals and herbaceous perennials OR when applied near/around trees and shrubs.

(NOTE: Here are a couple of terms to become familiar with in the chemical warfare battle against DW. Pre-Emergence Herbicide = controls weeds before they germinate. Post-Emergence Herbicide = controls weeds after they germinate)

Historically - the broadleaf herbicide of choice for DW has been atrazine. It works great! Atrazine provides both pre and post emergence control of DW - that's what makes it so effective. Problem is, this stuff is highly soluble and it's widespread use has resulted in atrazine showing up as a contaminant in surface and groundwater resources throughout the US. That's particularly bad news in areas with sandy soils - like an island...

Because of this environmental threat, EPA has restricted the use of atrazine by homeowners. Some liquid formulations of atrazine are still on retailer's shelves but not for long. Licensed/certified pesticide applicators will still be able to apply soluble atrazine but homeowners will soon lose access to liquid products. A plus for the environment.

There are numerous other atrazine products on the market for DW control in turfgrrass - including weed and feed fertilizers. Generally speaking, I don't use or recommend weed and feeds simply because of the potential damage they can cause to trees, shrubs and other broadleafed plants in the landscape.  Most experts agree - fertilization and weed control are 2 very separate activities and the risks of applying weed and feed products outweigh the benefits. 

There are also products on the market that combine several different herbicides together for DW control on bermudagrass, zoysiagrass, centipedegrass and St. Augustinegrass. The active ingredients in these combo herbicides may contain several different broadleaf weed killers including: 2,4- D, dicamba, MCPP, MCPA, etc.

Examples of combo herbicides are Ferti-lome Weed-Out, GreenLight Wipe Out, Bonide Weed Beater for Southern Lawns, Bayer Advanced Southern Weed Killer for Lawns, Spectracide Weed Stop Weed Killer for Lawns, Southern Ag Lawn Weed Killer with Trimec®, and Lilly Miller Lawn Weed Killer Concentrate.
The active ingredient penoxsulam (Fertilome Dollarweed Control Plus) is another product that's receiving a lot of attention for DW control. The jury is still out but early indications suggest that it will be a more environment-friendly replacement for atrazine. 

Imazaquin or Image is another popular broadleaf herbicide for use on DW. The reason it has been used so widely is because it is somewhat "selective" and can be used around certain other broadleaf plants in the landscape. BE SURE TO READ THE LABEL to make sure that the Image-tolerant plants are on the label. Many users have reported poor control of DW with Image. Remember - the DW plants have to be actively growing for Image to work at its best, so temps need to be in the 80's. Oh, BTW, Image also works on Nut Sedge - another very challenging landscape weed.

Glyphosate (often referred to generically as RoundUp) can also be used for spot DW treatments. Glyphosate is a non-selective herbicide and basically kills any and everything it comes in contact with. Avoid drift and over spray when applying Glyphosate. This is our product of choice for  spot applications in landscape beds. We make up a small container of material and apply it to both sides of the DW foliage uisng a foam paint brush. Time consuming - yes but very effective.

Glyphosate, like Image, works best when plants are actively growing - again, temps in the 80's. We sometimes water the weeds a few days before applying Glyphosate to ensure the active ingredient will be translocated throughout the plant.

Lastly...
Read all label(s) carefully and follow instructions to the letter! These products can be extremely effective for controlling DW but can have serious consequences to you, plants and the environment if handled, applied and/or stored improperly!!!

Of course there are always new products coming out and label changes occur regularly. So review the labels carefully before purchasing any product. Also - BE SURE to bring your reading glasses when shopping for lawn and garden chemicals because the info you really need is usually written so small it's impossible to read without some magnification.

Dollarweed is very challenging to control in the landscape - hope these suggestion help get you started in the right direction.

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