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Wild West District Extension Blog

Tag: Herbicides

Fall is the Best Time to Control Dandelions and Perennial Weeds

Posted on by Kylee Harrison

Fall is the Best Time to Control Dandelions and Perennial Weeds

By Ron Honig

Mid-October to early November is a great time to treat perennial broadleaf weeds such as dandelion and field bindweed.  With shorter days and cooler temperatures, these perennial weeds are moving nutrients from their foliage down to their root systems.  A fall herbicide application applied to the foliage will move a dose of herbicide down to the roots as well and improve chances of satisfactory weed control.

For many perennial broadleaf plants, including dandelion, a fall application of the herbicide 2,4-D in amine or ester form will provide good to excellent control. The best response may be seen when using the herbicide products which are a combination of three or more active ingredients such as Trimec Classic or one of the Weed-B-Gon or Spectracide brand products.  These products usually include the active ingredients 2,4-D and dicamba, plus additional herbicides such as quinclorac or mecoprop (MCPP).

Dandelion is a perennial plant and will survive the winter and green up again in the spring.  New dandelion plants often sprout and emerge in late summer and thus are vulnerable to a fall herbicide application.

University tests show a fall herbicide treatment on dandelions often yields over 90 percent control the following spring verses only 50 percent or less control from a single treatment performed in the spring or summer.

Field bindweed is a perennial vine with whiteish-pink flowers and arrowhead-shaped leaves.  Bindweed produces an extensive root system that once established, can be difficult to decrease.  Kansas State University research shows fall herbicide applications containing the chemicals dicamba and quinclorac provide the best control of field bindweed and the best chance of weakening and reducing the root system.

Chemical premixes containing dicamba and quinclorac are readily available at your garden supply store.  To find these products you must read the portion of the label indicating the active ingredients in the product and not just the product’s brand name.

Henbit is a winter annual and sprouts in the fall up until sustained cold temperatures stop its emergence. When temperatures warm again, henbit then continues to emerge in late winter to mid-spring.  In fertile lawns, henbit can grow a foot high or more with bright purple flowers.  Unlike dandelion and bindweed, henbit will eventually die back when hot weather arrives.

Once henbit begins to grow in the spring and produce flowers, it becomes significantly harder to control with herbicides.  Fall and early spring herbicide treatments with one of the combination products will provide the best control.

The recommended use rates provided on the herbicide product labels are normally sufficient to provide excellent control when applied in the fall.  For best results, choose a day when the temperature is at least 50 degrees F during the daytime.

The one weed we see so much of in late-summer and fall is prostrate spurge.  It is that circular, low growing weed that seems to grow out of every sidewalk crack and when its stems are broken, produces a white, milky sap.  The good news is prostrate spurge is a summer annual and will freeze in the coming weeks. Thus, it will not require any herbicide treatments.

Selecting a Crabgrass Preventer for Your Lawn

Posted on by Kylee Harrison

Selecting a Crabgrass Preventer for Your Lawn

By Ron Honig

If you can find a day when the wind is not howling, now is the time to be applying crabgrass and broadleaf herbicides to cool and warm season lawns. Crabgrass preventers are simply preemergence turf herbicides that prevent crabgrass seeds from developing into mature plants.  As the name suggests, preemerge herbicides must be applied before the grass germinates and begins to grow in order to get control.  With a few exceptions, they have little to no effect on existing crabgrass plants.  Early to mid-April is the recommended application period in Kansas.

Crabgrass, however is not the only common weed controlled by crabgrass preventers thus selecting the right herbicide can be a handy aid to controlling a number of other grasses and broadleaf weeds in your lawn such as dandelion and sandbur.

Following are four common active ingredients found in crabgrass preventers along with their common trade names: Prodiamine (Barricade), dithiopyr (Dimension), pendimethalin (Halts or Pendulum), and a combination of trifluralin and benefin (Team or Hi-Yield Crabgrass Control).

Of the four herbicides, prodiamine has the longest residual in the soil and provides the longest control of weeds listed in the product label.  Because of this long residual, prodiamine is a good choice for applying in the late summer or fall for preemerge henbit (the spring weed with square stems and purple flowers) control.  Henbit germinates in the fall or winter months and begins growth early in the spring.

Prodiamine also controls kochia which may germinate in late winter or early fall as well as pigweeds, shepherdspurse and prostrate spurge.  Dandelions, however, are not on the label’s control list.  Products vary, however a full-rate application of prodiamine can provide over six months of crabgrass control.

A fall prodiamine application, at the full application rate, should still provide weed control into the summer.  A split application of a half-rate in early fall and another in the spring may extend weed control through July.

Dithiopyr, when applied at the full rate, also has a long residual of 3 to 4 months.  Dithiopyr has the advantage of controlling many of the same weeds as prodiamine but with the addition of dandelion and sandbur.

Dithiopyr may also be applied in the fall like prodiamine, but if used in the fall, a second application in early summer will be needed to get season-long weed control from dithiopyr.  If applied in the spring at the full application rate, expect weed control throughout much of the summer.

Pendimethalin controls a wide range of grass and broadleaf weeds including sandbur, henbit, kochia and a broadleaf weed called Redstem Filaree which we are seeing more and more of in this area.  Dandelion is not on the label however, and henbit, filaree and kochia may emerge before pendimethalin is normally applied in mid-April.

Pendimethalin, unfortunately, has a shorter residual than either prodiamine or dithiopyr and will require a second application about six weeks of the first, even if applied in the spring. The product label will provide exact retreatment recommendations based on the concentration of the active ingredient.

The trifluralin and benefin combination in Team products control a smaller list of both grass and broadleaf weeds.  Purdue University rates the level of crabgrass control from Team lower than that of the other products discussed previously.  Team provides control of pigweed, prostrate knotweed and some foxtails along with crabgrass.

The four crabgrass herbicides mentioned do not control emerged weeds.  These products are intended for preemerge control of weeds and are soil applied herbicides.  The exception is that dithiopyr will control small, early-tillered crabgrass when applied post emerge.

After application, all of these herbicides need to be watered into the soil with either rain or approximately ½ inch of irrigation.

The addition of a 2,4-D- or dicamba-based herbicide either in dry or liquid form will help control emerged broadleaf weeds such as dandelion.

Most crabgrass preventers are marketed to homeowners with fertilizer in the product mix.   The four herbicides discussed in this article can be ordered without fertilizer from garden stores or from online vendors.  Follow label directions for the correct application rates and for the recommended timing of reapplications.

Now is the Time to Treat Deandelions and Perennial Broadleaf Weeds

Posted on by Lacey Noterman

By: Ron Honig, Crop Production and Horticulture Extension Agent

Late October to Early November is a great time to treat perennial broadleaf weeds such as dandelion and field bindweed.  After a few shots of cold weather these perennial weeds, if not damaged by sustained hard freezes, are moving nutrients to their root systems this time of year.  An application of 2,4-D or a premix containing 2,4-D and dicamba herbicides (such as Trimec or one of the Weed-B-Gone products) is easily absorbed by the weeds and translocated throughout the plant and roots.

Dandelion is a perennial plant and will survive the winter and green up again in the spring.  New dandelion plants often sprout and emerge in late summer and thus are vulnerable to a fall herbicide application.

University tests show a fall herbicide treatment on dandelions often yields over 90 percent control the following spring verses only 50 percent or less control from a single treatment performed in the spring or summer.

Field bindweed is a perennial vine with whiteish-pink flowers and arrowhead-shaped leaves.  Bindweed produces an extensive root system that once established, is difficult to decrease.  Kansas State University research shows fall herbicide applications containing the chemicals dicamba and quinclorac provide the best control of field bindweed and the best chance of weakening and reducing the root system.

Chemical premixes containing dicamba and quinclorac are readily available at your garden supply store.  To find these products you must read the portion of the label indicating the active ingredients in the product and not just the product name.

Henbit is a winter annual and sprouts in the fall up until sustained cold temperatures stop its emergence. When temperatures warm again, henbit then continues to emerge in late winter to mid-spring.  In fertile lawns, henbit can grow a foot high or more with bright purple flowers.  Unlike dandelion and bindweed, henbit will eventually die back when hot weather arrives.

Once henbit begins to grow in the spring and produce flowers, it becomes significantly harder to control with herbicides.  Fall and early spring herbicide treatments will provide the best control.

The recommended use rates provided on the herbicide product label are normally sufficient to provide excellent control when applied in the fall.  For best results, choose a day when the temperature is at least 50 degrees F during the daytime.

The one weed we are seeing so much of this time of year is prostrate spurge.  It is that circular, low growing weed that seems to grow out of every sidewalk crack and when disturbed produces a white, milky sap.  The good news is prostrate spurge is a summer annual and will freeze in the coming weeks and thus, will not require any herbicide treatments.