Annual Weeds

Posted by Kara Harders, Regional Small Acreage Management Specialist, Peaks and Plains Region

Cheat grass, gone to seed

 Getting rid of weeds sounds like a simple idea but most of us know it is easier said than done. This post talks about controlling annual weeds, not perennials. Always try to identify the weeds you are dealing with so you can plan the most effective attack plan.

As I take my socially distanced walks around the neighborhood I am always disheartened at the sheer volume of annual weeds I see taking over peoples yards, gardens, rocked areas, and flower beds. It isn’t that I think my neighbors don’t care, I think many of them do, it is just such a hard problem to cure.

The annual weeds are some of the worst because they come up in the spring when we are all dying to see green. They give us hope that the dead patch in the back alley or next to the driveway is finally filling in with the grass we want, and just a few months later we are irritated by the nasty seed heads stuck in our socks and pet’s fur or the dead brown patch they become.

Often times killing the annual weeds (be it Blue Mustard, Yellow Mustard, Cheat grass, Green Foxtail, Henbit, Kochia, Russian Thistle, or others) won’t do anything in the overall control of the weeds. Annuals are the quick and dirty plants of the world because they go to seed so quickly, often before we really have the chance to find and identify them all.

Foxtail, gone to seed

Instead of having it in your mind to kill annual weeds, have it in your mind to keep them from spreading seed. Since an annual weed only lives for a year and then dies, it’s entire specie depends on producing enough seeds to repopulate next year. This can be achieved (or at least attempted) in several ways.

Weed Early: If you can pull or otherwise root up the weeds when they are very small (less than 3 inches, and no sign of seed heads) they will likely die without reproducing (win!). If you don’t mind the look of little weed bodies all over, you can even leave them on the ground. No bagging for you! Herbicides are also an effective choice at this point (always read the label on herbicides! The Label is the Law).

Weed Often: Sometimes with cold and warm weeks and spring rains we will have “flushes” of new weeds coming up. So take a walk around your yard or property fairly frequently, it’s good for your health and also lets you keep on top of what is sprouting up.

You say you see weeds with seeds? It is easy to fall behind on weed watching. I know it happened to me this year. If you start seeing taller weeds or weeds with seed heads you know you have missed the easy window. I really am sorry for you because things get a little more labor intensive now.

Herbicides: If you were all for using herbicides, that window has closed, put down the sprayer. If you kill a happy green weed with seeds you will have the satisfaction of seeing it get sad and brown and die, but the seeds will survive your chemical assault and next year you will be back where you started.

Don't leave a pile of weeds with seeds!

Pulling: Pulling is a solid option. Annual weeds are usually easy to pull up and can be bagged and thrown away. Since the seeds exist try not to shake the pulled plants too much. You have to bag and throw them away at this point.

Mowing with a bag: If you just can’t possibly pull all the weeds consider using a lawn mower with a bag to collect your cuttings (and throw the mowed contents away). This method is sloppier than hand pulling and bagging but will collect more weed seeds than doing nothing. This works from some weeds but less on others, Kochia for example will just grow lower to the ground and form a mat of seed producing weeds.

Keep Weeding: You will likely need to do some level of weed control every year. Seeds from deeper underground will start to grow, wind will bring seeds from your neighbors, a rogue Kochia tumble weed will make its home in a corner of your fence and rain seeds on the ground, the possibilities are endless. But keep your head up, after the first year or two of keeping the seeds at bay you will probably see a good reduction in the weeds that come up, and after that hopefully you can work proper weed management into your schedule.

For more information and links to fact sheets visit: https://planttalk.colostate.edu/topics/weeds-cultural-problems/2117-landscape-weeds-control/

Blue Mustard with seeds

Young Kochia, not seeded yet

Young Cheatgrass, not seeded yet

Tansey or Yellow Mustard with seeds

Prickly lettuce, no seeds

Crabgrass is Here - Finally!

Tony Koski, Extension Turf Specialist

Seedling crabgrass (May 22) in Fort Collins.
Notice the young plants are coming up in a dead
plant (a weed "cadaver") from last year. This is
why it's important to encourage healthy grass
growth in weedy lawns in the fall - to break the
cycle of seed germination the following year.

The up and down spring – periods of above normal heat and below normal cold spells – has delayed crabgrass seed germination by about 2 weeks. That’s a good thing if you were a little late putting out your crabgrass pre-emergence herbicide (aka crabgrass preventer).

But now that crabgrass HAS germinated, control efforts (if you want to control crabgrass and its warm-season weedy cousins – foxtail and barnyardgrass) should be focused on post-emergence herbicide products. Once you can see these annual grassy weed seedlings, it is too late to use a pre-emergence product.

As with any landscape pest, it is absolutely essential that you accurately identify the pest in question before purchasing and applying the control product. It makes no sense – environmentally, financially, and for your precious time – to apply a product that won’t work because you haven’t correctly identified the pest.

This is not crabgrass! Crabgrass and other seedling
grassy weeds are still very small now. This is a
clump of tall fescue - which will not be killed by
crabgrass control products containing quinclorac.

For example, crabgrass and the other just-germinating warm season grassy weeds are still very tiny now. If you have large, fast-growing, “ugly” (coarse, clumpy, wide-bladed) grass growing in your lawn NOW it is NOT crabgrass – which means that none of the herbicides labeled for control of crabgrass will eliminate these unsightly, undesirable grasses. We have blogged previously about grasses that people mistakenly refer to as “crabgrass”. These unattractive, perennial grasses can’t be controlled with either the pre- or post-emergence crabgrass control products.

What to use NOW for young/seedling crabgrass, foxtail, and barnyardgrass? The following products are available in the garden product aisle at big-box and hardware stores, and at better nurseries and garden centers. What they all have in common is the ingredient “quinclorac” (and all contain herbicides for broadleaf weed control as well, like 2,4-D, dicamba, MCPP, etc.). Quinclorac provides excellent control of the most common summer annual grassy weeds: crabgrass, foxtail, and barnyardgrass in bluegrass, ryegrass, and fescue lawns.

Bayer Advanced Lawn Weed & Crabgrass Killer (quinclorac, 2,4-D, dicamba)
Ferti-Lome Weed Out with Crabgrass Killer (quinclorac, 2,4-D, dicamba)
Monterey Crab-E-Rad Plus (quinclorac, 2,4-D, dicamba)
Ortho Weed B Gon Max plus Crabgrass Control (quinclorac, 2,4-D, dicamba)
Roundup for Lawns - Northern Lawns (make sure it’s the Roundup FOR LAWNS!; quinclorac, dicamba, MCPA, sulfentrazone)
Spectracide Weed Stop For Lawns Plus Crabgrass Killer (quinclorac, dicamba, 2,4-D, sulfentrazone)

Crabgrass and its cousins are much easier to
control now - when they are small plants- than
in a couple of months when they have grown to a
plant of this size. Large crabgrass plants are very
difficult to kill.

It’s much easier to control crabgrass and its cousins this time of the year, when they are small. These grasses grow larger very quickly as we get sustained warm/hot temperatures. Large crabgrass plants are much more difficult to kill.

Make sure that you are spraying the right product for the weed in question! If you need help with the identification of weedy grasses – or any weed – in your lawn, you can bring a sample to your county Extension office. Or email me a high resolution photo of the grass (tony.koski@colostate.edu). 

We've blogged about crabgrass and other weedy grasses before...go here and here to see more photos of crabgrass and other weedy grasses, with hints on how to identify and control them.

And, as always, read the label for any pesticide you use and follow all instructions to ensure effective weed control and to avoid injury to your lawn or other non-target plants in your landscape.

Don't Bug Out! Educate Yourself!

Posted by: Sherie Caffey, Horticulture Coordinator, CSU Extension-Pueblo County

I’m sure at some time in most of our lives, we have reached for a pesticide to help us out with a yard or garden pest. Being a new homeowner, I found that I had a lot to learn about the proper use of pesticides. Here’s some of the most important things I have discovered:

The new EPA advisory box

 Most people think of pesticides to be insecticides, but the actual definition of a pesticide is any chemical that controls a pest, whether it is an insect, a weed, a fungus, a rodent, or any other thing that is “pest”ering you.

There are many categories that pesticides fall into. One of the broadest is natural or synthetic. Natural pesticides are derived from biological ingredients, and synthetics are man made. If keeping your garden organic is important to you, look for an OMRI (Organic Materials Review Institute) label on the product you are using, this means it is certified to be used in organic production. Even though a product may be natural or organic, it may still be harmful to humans and beneficial critters in high concentrations, which brings me to the most important point about using pesticides, ALWAYS read the label! We will come back to this…

Too late for pre-emergents on this guy

There are a couple of other categories that pesticides are separated into. For herbicides in particular, they may be pre-emergent, meaning they can only control weeds before they germinate, or post-emergent, meaning you use them after the weeds have sprouted. Broad spectrum products are not picky, they kill everything, whereas selective products are meant to control one certain pest. Some pesticides are soil applied, and others need to be applied to the actual plant. Finally, protective pesticides prevent the pest of interest, and eradicants get rid of pests that are already present.

Signal words

The most important information that you can get about safely and properly using a pesticide is on the label. It is against the law to use any pesticide in a manner inconsistent with its labeling. There are many things that you will generally find on the product label. First of all, there will be the product name. There is usually a brand name (e.g. Roundup), and a common name (e.g. Glyphosate).

The next thing you should look for is the signal word, which tells you how hazardous the product is. These are the signal words you will see, in order from least toxic to most: Caution, Warning, and Danger/Poison. 1 to 3 drops of a product labeled Danger/Poison can kill an adult. You should also pay attention to any hazard or precautionary statements. These statements are meant to protect the applicator and the environment.

Last but not least, you will see the directions for use. You must use the product as directed on the label. The directions will tell you which plants it can be used on, which pests it is for, application rates, re-application times, and how long to wait until you harvest if you are using it in a vegetable garden.

So next time you reach for a pesticide to control a pesky garden problem, educate yourself before you use it, and remember, the label is the law!

The Annual Weeds of Summer

Posted by: Alison O'Connor, Larimer County Extension

Though we're approaching the end of the gardening season (I know...I don't want to think about it either!), most of us are still battling the sea of weeds on our gardens. As I was walking Maple the other day, I took photos of a few persistent and common annual weeds that we see in our gardens, lawns and landscapes.

It's important to note these are annual weeds and germinate in spring and complete their lifecycle in one growing season (just like petunias or geraniums). Most summer annual weeds will germinate after soil temperatures warm to above 60 degrees. This year, we had a slow start to spring...and our soils stayed cool, so we didn't see weed growth as early as normal. But once temperatures heated up--BAM! Weeds. Everywhere.

There's a few approaches to weed control. One is to pull the weeds. Persistent and regular pulling will prevent the weeds from going to flower and seed (very important) and help keep the weed seed bank at bay. I'm sure most gardeners do their share of pulling weeds throughout the year. Another control option is to use an organic mulch (wood chips, grass clippings, leaves). Granted, this isn't possible in all areas of the landscape, but a thick layer of mulch in planting beds and vegetable gardens does wonders to prevent weed growth. Most weed seeds need light and exposed soil to germinate. Take away these two things and you'll have fewer weeds.

Using chemical options is also an option. For post-emergence weeds (those that have germinated), there are only a few options in our landscape areas (far more in lawns). These options include glyphosate and some organic products (like acetic acid (vingear) and oils). These tend to be non-selective products. Glyphosate is absorbed via the foliage, which does kill the root of the plant. Acetic acid and oils are burn-down products, which means that the foliage dies back. It also means that repeat applications may be necessary.

There are pre-emergence herbicides that you can use in the early spring, such as treflan (sold in Preen), isoxaben (sold in Ferti-Lome Broadleaf Weed Control with Gallery) and corn gluten meal. All  of these products can work, but may need to be reapplied. Always follow the label on the product you plan to use. And a note about corn gluten meal: While it has VERY LIMITED, SHORT-TERM weed control capabilities, it has proven, by research, to be a much better fertilizer than herbicide.

So let's look at the Weeds of Summer:

Crabgrass (Digitaria sanguinalis)

Large crabgrass

Good ol' crabgrass. Here it is in all its glory. Other plants get called "crabgrass" but this is the one and only. Crabgrass won't germinate until soil temps are above 60 degrees. In a lawn, the best defense against crabgrass is to keep the lawn healthy (well-watered and fertilized). In this situation, crabgrass found a great place to grow in rock mulch along the sidewalk. It's nice and hot and ideal for growth. Crabgrass has a very distinct seedhead, which is finger-like (hence the genus Digitaria).

Finger-like seedhead of crabgrass.

Prostrate spurge (Euphorbia maculata)

Prostrate spurge

Prostrate spurge has had a very good summer. It's everywhere. This mat-forming weed can reach impressive size by late summer if left uncontrolled. Fortunately, it's easy to pull. The one caution is that like other plants in the Euphorbia genus, the plant has a milky sap, which oozes when stems are broken. The sap can be caustic and an irritant. If you have sensitive skin, wear gloves and be sure to wash your hands following weeding.

White latex sap of prostrate spurge

Close up of prostrate spurge...you can make out the teeny-tiny flowers, which all form viable seeds!

Purslane (Portulaca oleracea)

Purslane is a pretty mild weed...it's edible, after all! And I haven't seen as much purslane this summer, but I might not be looking that hard. Purslane can be confused with spurge, but there is no milky sap...and this weed has thick, red stems. It's a succulent, so it can tolerate dry conditions with occasional moisture. I see it most often in my vegetable garden, near the drip irrigation lines.

A very mature purslane plant.

Puncturevine (Goatheads) (Tribulus terrestris)

Ugh! By far the WORST of the summer annuals. This beastly plant is just nasty and mean. If you aren't familiar with puncturevine, consider yourself lucky. The seedheads can pop bicycle tires, injure dogs' paws and wreck havoc on bare feet. This is one weed that you should 100% remove and prevent from growing. It can reach widths of feet if left to grow undisturbed...yikes!

One (yes one!) puncturevine plant.

That same plant pulled from the ground.

Puncturevine has yellow flowers and the seedheads start off green, hardening into sharp, pointed, vicious seedheads by late summer.

Yellow flowers of puncturevine.

Nasty, mean and cruel seedheads. The plant is called "goathead" because the seedhead resembles a goat's head.

And poor Maple, my faithful beagle pal and gardening buddy, was afflicted by a stray puncturevine seed on our walk. Poor thing hobbled for a few feet before sitting down, lifting her paw in the air. It's because of this that I just despise this weed. So pull it already!

Maple's paw with puncturevine seed stuck in the pad.

There are many other weeds of summer that I didn't mention, like kochia, but we can cover those another time. Happy late summer weeding, folks!

Weed of the Moment: Crabgrass and its look-alikes

By: Tony Koski, Turfgrass Specialist

Guess what? You might actually be seeing crabgrass in your lawn this time of year! It was late germinating this spring (we didn't see it in Fort Collins until late May), but now it's large and in charge. This is crabgrass in late May:

Young crabgrass

Now it looks like this (late July):

Small (smooth) crabgrass (Digitaria ischaemum)

Small (smooth) crabgrass--growing in concrete!
(That's a joke)

Small (smooth) crabgrass near sidewalk

Crabgrass seedhead

Many think they have crabgrass, but they don't. Here are some other crabgrass look-alikes that are often called crabgrass, but misidentified...

This is not crabgrass; this is bromegrass (wide, coarse blade; often a "W" watermark on upper tip of leaf):

Bromegrass in a bluegrass lawn

This is not crabgrass; this is annual bluegrass (characteristic apple green color; often with seedheads):

Annual bluegrass in a Kentucky bluegrass lawn

And this is not crabgrass; this is tall fescue (clumps of grass with rough edges on the leaf blade):

Tall fescue in a bluegrass lawn

 This isn't crabgrass either; this is orchardgrass (flat "stems" and tall white ligule):

The ligule is located like a collar on the inside of the leaf

Orchardgrass in the lawn

And no, this isn't crabgrass either; this is yellow foxtail (characteristic red base, yellow-y color):

Yellow foxtail, which can easily be confused with crabgrass.
The great news is that the same products that work on crabgrass
will work on foxtail.

Yellow foxtail--look at that distinctive red color!

Finally, this isn't crabgrass--this is bermudagrass (forms runners, invasive, pointy leaf tip):

Bermudagrass

Crabgrass is characterized by its prostrate growth habit, especially after mowing and a light, apple green leaf color. The seedheads are digitate (finger-like) and will begin forming in earnest in August. Crabgrass is a warm season grass (and a summer annual), so it will die with the first frost.

If you want to control it now, use any herbicide product containing quinclorac (such as Ortho Weed Be Gon Max Plus Crabgrass Control, Fertilome Weed Out Plus Q or Bayer All-in-One Lawn Weed and Crabgrass Killer). Be aware it may take more than one application to completely kill this persistent weed. It's much easier to control when it's a seedling or use preemergence products in early spring.

The big point to make, with the exception of foxtail and crabgrass, is that quinclorac will not work to selectively remove tall fescue, bermudagrass, bromegrass or annual blugrass from your lawn. So identification of grasses that LOOK like crabgrass is essential before you start spraying herbicides willy-nilly.