Hurry Up and Wait. Now Go!

At the beginning of March we were potentially a week or two away from annual bluegrass seedhead emergence thanks to an extremely warm February. Cooler temperatures prevailed and significant snowfall across much of the Northeast brought soil temperatures down and put the brakes on annual bluegrass development for a few weeks. It’s now the beginning of April and we are very close to annual bluegrass seedhead emergence on putting greens in central New Jersey. Parts of northern New Jersey appear to be about a week behind the New Brunswick area.  If you haven’t already applied ethephon (i.e., Proxy, Ethephon 2 SL, Oskie) for seedhead suppression, this week might be ideal (see previous post for more information) for most courses in New Jersey.

Warmer temperatures this week will likely bring average 24-hour soil temperatures (one inch depth) into the 50s and turf will begin to grow more rapidly. Emergence of summer annual weeds is not far away. I first noticed prostrate knotweed emergence in mid February. These early germinating plants survived the winter weather and will continue to develop this week.

Prostrate knotweed seedlings

Note that knotweed seedlings will have two seed leaves and crabgrass will have only one.

Prostrate knotweed seedling with two seed leaves


Smooth crabgrass seedling with one seed leaf

I have not observed crabgrass emergence, even on south-facing slopes. I spent the latter part of last week in Washington D.C. and could not find any crabgrass along sidewalks and bare areas there either.

Crabgrass emerging with one seed leaf (in a previous year)

Depending on your location, forsythia may or may not be a reliable phenological indicator for crabgrass germination this year. In a normal year, pre-emergent herbicides (except for dithiopyr (Dimension), which can control crabgrass up to the pre-tiller stage) should be applied when forsythia is in full bloom because crabgrass germination will occur shortly thereafter. However, extremely cold temperatures killed or injured many forsythia flowers in central Jersey and areas south.

In northern New Jersey I’ve observed forsythia plants still in the bud stage and in this case they are likely to be effective indicators. Especially this year, it is important to use multiple forsythia plants because the bloom timing is affected by location among other factors. Plants that bloomed early were injured by the winter weather, but others were unaffected as this photo from @samcamuso demonstrates.

Soil temperature at a 1-inch depth has been reported as a reliable indicator of crabgrass germination assuming soil moisture is adequate. In a three-year study, Fidanza et al. (1996) found that crabgrass began to emerge when the soil temperature at a 1-inch depth averaged 57 to 63 degrees during a 7-day period. Soil temperatures at our research center in North Brunswick have been well below this threshold as of this writing. At this time we are holding off on making pre-emergent applications to our research trials. However, in southern New Jersey soil temperatures are warmer and crabgrass will germinate sooner. In these areas, making a pre-emergence herbicide application soon would be timely. If you are worried you may be too late, scout bare areas with crabgrass carcasses, especially those on south-facing slopes, as crabgrass will germinate earlier in these areas.

Making pre-emergent herbicides applications early is not thought to reduce efficacy. However, if you are using dithiopyr (i.e., Dimension) it’s a good idea to wait until shortly after emergence and take advantage of the early post-emergence efficacy this product provides against crabgrass.

Of course don’t forget to consider your potential renovation/seeding projects this spring. If you are planning on seeding, do not apply any pre-emergence herbicide.

Literature Cited

Fidanza MA, Dernoeden PH, Zhang M (1996) Degree-days for predicting smooth crabgrass emergence in cool-season turfgrass. Crop Sci. 36:990-996.

Crabgrass Emerging

Crabgrass has been emerging for several weeks now, depending on the exposure. Warmer and more open turfs will likely have more advanced (larger) plants while cooler and denser turfs will have smaller plants.

Relatively small crabgrass plants  (most pre-tillering stage) emerging from a footpath on June 11th.

Relatively small crabgrass plants (most pre-tillering stage) emerging from a footpath on June 11th.


Management options for this weed at this point in the season range from doing nothing to [Read more…]

Crabgrass Emerging

Back on May 24, I posted about my observation of crabgrass emerging in areas that had very thin turf cover and very high levels of crabgrass seed in the soil. Crabgrass is now emerging from areas with healthier turf and good density (and has not received a preemergence herbicide application). Recent and forecast rains are likely to [Read more…]

Crabgrass is Emerging

Very small first and second leaves of emerging crabgrass can be seen now in open turf areas.

During the last couple weeks, we have seen crabgrass emerging from open turf areas that were previously infested with crabgrass. Crabgrass emergence will probably occur later than this on better maintained turfs with a dense canopy.

If crabgrass is emerging, it is too late for most preemergence herbicides to be useful. However, dithiopyr (trade name Dimension) is a commonly used preemergence herbicide that also provides effective postemergence control of crabgrass (but not goosegrass). For postemergence control, dithiopyr should be applied [Read more…]

Crabgrass Continues to Emerge

Recent rains have stimulated more crabgrass to emerge. This will probably continue through the end of the month. If applied preemergence herbicides, especially early in the spring, you may start to see “breakthrough”. If have decided to control crabgrass postemergence (manually or with postemergence herbicides), you should scout for emerging plants after each rain or irrigation event. Water will stimulate more emergence of plants. See previous post for more information.

Recently emerged crabgrass seedling plants (taken 20 July).

Crabgrass Emerging

I have been observing the emergence of crabgrass since late April (see image above). Some crabgrass has now entered the tillering stage of growth.

As a general rule, most people begin to notice crabgrass in turf around the 4th of July (Independence Day). At that time, the crabgrass plants are large enough that the leaves stick-up above the desired grasses and the lighter (yellow) green color is highly noticeable from a distance. However, the crabgrass plants will be relatively large (tillered) by that date.

For those that want to control crabgrass postemergence, the next few weeks is the time for action because, regardless of the control tactic, crabgrass becomes more difficult to remove as it matures (get larger).

For those interested in non-chemical options, hand-picking the crabgrass is easiest when the plant are relatively small seedlings. As the plants grow, the enlarged root system makes it more difficult to pull these plants without snapping off the leaves and leaving the crown attached to roots. If this happens, the plants will re-grows its leaves. Hand-picking crabgrass plants is only practical for small turf/lawn areas.

There is limited detailed information the application and efficacy of “organic” herbicides to control crabgrass postemergence. So specific recommendations, other than make treatments to small plants, are not available.

For those interested in conventional postemergence herbicides, these are most effective when applied to seedling crabgrass plants. Two, sometimes more, treatments are often needed, especially when crabgrass plants are relatively large. Apply at 7-to 10-day intervals. Do not apply to drought stressed plants. Discoloration may occur on the desired turfgrass after the treatment is applied. Discoloration is generally more noticeable if the grass is under stress from heat or drought. Spraying the herbicides will be more effective than applying as a granular product. Do not irrigate for 24 hours after the appliation and do not apply if rain is forecast within 24 hours after the application.

Herbicides with postemergence activity on crabgrass that is less than the 4-tiller growth stage include: quinclorac (Drive, SquareOne ), mesotrione (Tenacity), and fenoxaprop (Acclaim Extra). Dithiopyr (Dimension) is primarily used as a preemergence herbicide but it does have postemergence activity on crabgrass plants in the 1- to 4-leaf growth stage.

The use rates and tolerance of desired turfgrasses varies among these herbicides, so consult the label for specific use information. You can also read more at: Crabgras and Goosegrass Control in Cool Season Turfgrass.