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Matthew Elmore

What Does the Fling with Spring Mean for Weed Emergence?

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The region enjoyed warmer than average temperatures last week and into the weekend before things cooled off on Monday and now remain seasonal. While warmups like we saw last week are not uncommon in March, the extended 5- to 6-day duration of warm weather has Forsythia in full bloom across much of the region. What does this mean for emergence of summer annual weeds like crabgrass?

Forsythia in full bloom.
Forsythia in full bloom

The science on this topic is not settled, but found phenological indicators like Forsythia are as good or better than using soil temperatures or growing degree-days (calculated from air or soil temps) to predict crabgrass emergence. When Forsythia is in full bloom, it is a warning that crabgrass emergence is near and it is a good time to start making preemergence herbicide applications, particularly for those not using dithiopyr and others that need multiple weeks to get applications completed. I suspect that for most of us, except potentially in southern NJ, we will need another warm period of high temperatures in the 60s and 70s to see crabgrass emergence. For those relying on prodiamine and pendimethalin, it is not too late, but also not too early to make applications. That said, forecasting crabgrass emergence is less certain than predicting the weather.

In combination with using uncertain predictions, check sentinel areas for crabgrass seedlings to see if emergence has started. Sentinel areas I go to are thin turf on south-facing slopes since they warm faster than other turf areas. Areas near paved surfaces warm too rapidly compared to turf and are not useful. If you see emergence in sentinel areas, make preemergence applications ASAP.

A crabgrass seedling

Japanese stiltgrass emergence

While I have not seen crabgrass seedlings, Japanese stiltgrass has emerged in central NJ. Stiltgrass emerges before crabgrass, although temperatures that trigger emergence or phenological indicators are not understood. Typically have seen it emerge 3 to 4 weeks before crabgrass.

Japanese stiltgrass seedlings in lawn on March 18, 2024 in East Brunswick, NJ.

Particularly in central and southern NJ and the NY metro area, do not expect complete control of Japanese stiltgrass if you have not applied your preemergence herbicide and had rainfall to get it into the soil. For more information on Japanese stiltgrass control in lawns, see this blog post.

Summer Weeds

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It finally feels like summer in New Jersey. Rain, humidity, and warmer temperatures, especially at night, mean that warm-season weeds are growing quickly. Of particular concern are summer annuals like crabgrass, goosegrass, and spurges. Yellow nutsedge and false-green kyllinga are warm-season perennials are also enjoying the weather. These weeds are now growing more quickly than the turfgrass so they are easier to spot a few days after mowing.

Notice the light green leaves of crabgrass in a lawn in early July. Plants this size are still relatively immature and easier to control.

Particularly for summer annuals, walking the area and looking carefully for these weeds will allow you to control them while they are still immature. In this weather these weeds will mature quickly, and once they do herbicide programs are less successful and hand weeding becomes more difficult.

For more information on crabgrass and goosegrass control for professionals see: https://njaes.rutgers.edu/fs1309/

For information on crabgrass control in the home lawn for non-professionals see: https://njaes.rutgers.edu/fs1308/

For more information on false-green kyllinga control see: https://njaes.rutgers.edu/fs1290/

For more information on yellow nutsedge control see this previous blog post: https://turfblog.rutgers.edu/?p=1431

The broadleaf weed spurge (Euphorbia spp.) in a lawn in early July.

Time to Control Yellow Nutsedge

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Now is the ideal time to control yellow nutsedge (Cyperus esculentus). This plant is a perennial that grows best during the heat of summer and survives the winter through underground tubers. While the drought may have limited nutsedge emergence in unirrigated areas, it is visible and rapidly growing in irrigated beds and lawns.

Yellow nutsedge and other sedges look similar to grasses, but sedges have a unique triangular stem. This triangular stem results in a three-ranked leaf arrangement. While many sedge species can be found in the lawn and garden, yellow nutsedge is the only perennial sedge found in New Jersey and is far more difficult to control than annual sedges.

A cross section of a yellow nutsedge stem. This triangular shape is unique to sedges.
A yellow nutsedge plant from above. Notice the leaves at 120-degree angles from one another forming a three-ranked leaf arrangement.

Yellow nutsedge is a perennial through tubers. The aboveground plants and rhizomes are killed each winter and the tubers are the source of the infestation each spring. Initiating nutsedge control measures now will prevent the formation of new tubers and make this weed less problematic in the future.

Yellow nutsedge tubers.
Yellow nutsedge tubers. The brown tubers are mature while the white tuber is immature.

Lying dormant during winter up to several inches below the surface, nutsedge tubers sprout in spring, giving rise to new plants aboveground. These plants then produce rhizomes (underground stems) that form more plants and tubers for next year (and beyond). If left unchecked, a single tuber sprouting in spring can produce thousands of new tubers by the end of the summer.

A severe yellow nutsedge infestation.
A severe yellow nutsedge infestation in a recently mulched landscape bed. The open space between ornamental plants allows ample sunlight and nutsedge thrives.
Yellow nutsedge in a lawn in early June.
Yellow nutsedge in a lawn in early June is relatively inconspicuous. The thin and light green leaves are the nutsedge. The nutsedge will become more obvious as temperatures increase through the summer.

Implementing strategies to control nutsedge now before it forms tubers is critical to get rid of this weed. Right now in early June, yellow nutsedge shoots are producing rhizomes but have probably not yet begun producing tubers. Treating nutsedge with herbicide now and again in 6 to 8 weeks (if green shoots are visible) is an ideal strategy.

Yellow nutsedge rhizomes.
Yellow nutsedge rhizomes

The herbicide halosulfuron can be used for selective sedge control in both lawns and ornamental beds. It is safe to the turfgrass and can be applied around ornamental plants. Numerous formulations are available for professionals. A user-friendly product for non-professionals is Sedgehammer®+, which is widely available and sold in small pouches with the exact amount to mix into a gallon of water for a pump sprayer. This product also contains the surfactant halosulfuron needs for best nutsedge control. Halosulfuron is systemic (moves in the plant), but slow to work, so it will be 2 to 4 weeks before there are noticeable results.

Nutsedge tubers can persist for several years in the soil, so one year of herbicide treatment will not eliminate yellow nutsedge. But treating now and once more later in the season will reduce the severity of the problem in future years. This approach is better than waiting until mid or late summer for the first application.

Combine herbicide programs with non-chemical management to improve control. More than other weeds, nutsedge is poorly competitive in shade and in dry soils. You may notice nutsedge in thinner areas of the lawn. Focusing on turf management practices that increase lawn canopy density during the autumn (e.g. N fertilization and seeding) will result in fewer herbicide applications the future. Do not apply halosulfuron sooner than 4 weeks before seeding turfgrass. Modifying landscape beds to reduce large spaces between plants can be similarly combined with herbicide programs for better long-term control. Fixing poorly drained areas and being careful not to over irrigate may also help manage nutsedge.

It is possible to eliminate yellow nutsedge by hand weeding or by using OMRI-approved herbicides (which are non-systemic). But keep in mind, pulling shoots or killing with non-systemic herbicides usually signals the tubers to produce many new shoots. So, hand-weeding or spraying more frequently than with systemic herbicides like halosulfuron is necessary. Digging the tubers is not practical as they are several inches underground and many are too small to be easily seen.

Weeds of Early Spring

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With warmer weather comes plant growth. The most conspicuous plants in the lawn and landscape right now are winter annuals such as hairy bittercress (Cardamine hirsuta), henbit (Lamium amplexicaule), purple deadnettle (Lamium purpureum), and chickweeds (Stellaria media and Cerastium fontanum ssp. vulgare), to name a few. In lawns, these winter annuals are typically found in areas where the lawn was thin in September and October when these weeds germinated. Most winter annuals do not establish readily where the lawn canopy is dense. In ornamental beds they can be prolific unless the beds were recently mulched (which buries the seed), as there is plenty of open space and little competition from other plants.

Henbit flowering.
Henbit flowering
Purple deadnettle flowering in early spring.
Purple deadnettle flowering in early spring
Common chickweed in an ornamental bed.
Common chickweed in an ornamental bed

In the lawn, these winter annual broadleaf species can be easily controlled by herbicides that contain 2,4-D, MCPA, mecoprop, or dicamba. But keep in mind that these winter annual weeds are near the end of their life cycle and will be dead within 3 to 4 weeks even if no herbicide is applied. Exceptions include mouseear chickweed (Cerastium fontanum ssp. vulgare) and corn speedwell (Veronica arvensis) which can persist farther into the summer.

Corn speedwell in an ornamental bed.
Corn speedwell in an ornamental bed

Perennials such as wild garlic (Allium vineale), star-of-bethlehem (Ornithogalum umbellatum), and lesser celandine (Ranunculus ficaria) are also noticeable this time of year. They are ephemerals that will return to dormancy within the next few weeks where they reside as bulbs for the summer, emerging again in late fall or mid-winter.

Star-of-bethlehem.
Star-of-bethlehem. Notice the white midrib on the leaf.
Star-of-bethlehem in turf.
Star-of-bethlehem in turf
Lesser celendine in a lawn.
Lesser celendine in a lawn

Another ephemeral winter perennial is bulbous bluegrass (Poa bulbosa). This also emerges from bulbs in late fall and is dormant all summer. It is most conspicuous when in mid spring it produces what looks like an inflorescence, but is actually a collection of bulbils (small bulbs) and not flowers. Bulbous bluegrass is occasionally widespread in extremely low input lawns, but is more commonly found in small patches where disturbance and competition from other plants is low. I commonly see this at the base of tree trunks or between the sidewalk and road.

Bulbous bluegrass bulbils. Photo courtesy of Aaron Patton.
Bulbous bluegrass bulbs and leaves.
Bulbous bluegrass bulbs and leaves

Roughstalk bluegrass (Poa trivialis) is a perennial grass that is obvious this time of year due to rapid growth and light green color. There are no selective herbicide options for roughstalk bluegrass control. Except in wet and shaded areas where it is well-suited, roughstalk bluegrass growth tends to slow by late spring and it goes dormant in summer. If it is mixed well with other turfgrass species, this slow decline to dormancy is not noticeable. For more information about roughstalk bluegrass, see this recent blog.

Patches of roughstalk bluegrass in a lawn.

While winter annuals are nearing the end of their life cycle, summer annual weeds are just getting started. Japanese stiltgrass emergence (discussed in a recent blog) has been noted in several locations in central and southern NJ. It may be too late for preemergent herbicides to control stiltgrass. For more information on stiltgrass control, see this RCE factsheet.

Forsythia in full bloom.
Forsythia in full bloom

Soil temperatures and Forsythia full bloom we are now seeing suggests crabgrass (Digitaria spp.) emergence will begin within two to three weeks. Now is a good time to begin making preemergence herbicide applications. Based on what we know about crabgrass and other summer annual species, the mild winter is not likely to accelerate germination, since the seed is not active until soil temperatures are in the 50s. Other than using Forsythia spp. full bloom as an indicator, soil temperatures can be monitored, but the science doesn’t provide precise guidance on this. But as a general rule, once soil temperature consistently exceeds 55 °F at a 2” depth for at least few days, crabgrass seed germinates and emergence is often noted a few days later. Live soil temperatures can be found on the Rutgers NJ Weather Network. The 24-hr rolling average at locations we monitor in North Brunswick, NJ is between 48 and 54 degrees F, depending on sun exposure. See these links for more information on crabgrass control in the lawn for professionals, and homeowners.

Japanese Stiltgrass Control in Turf

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Japanese stiltgrass (Microstegium vimineum) is a C4 summer annual grassy weed commonly invasive to forests. It can be problematic in lawns. Often it is problematic in shaded areas adjacent to an infested forest. But we have observed infestations in full sun turfgrass areas where you would normally expect crabgrass to be the predominant summer annual. It seems this weed is becoming increasingly problematic in lawns. But why I am I writing about a summer weed in February?

Japanese stiltgrass in a lawn during late summer.
Japanese stiltgrass in a lawn during late summer.

Japanese stiltgrass is the first summer annual grassy weed to emerge. Preemergence herbicides commonly used to control the summer annual crabgrass (dithiopyr, prodiamine, and pendimethalin) were effective for Japanese stiltgrass control in our research. However, stiltgrass emerges sooner than crabgrass and these preemergence herbicides are only effective when applied before stiltgrass emergence. In our 2022 research we applied these preemergence herbicides on March 11, 2022 in Pittstown, NJ. Stiltgrass typically emerges in March, often about a month before crabgrass. Germination of the seed and subsequent emergence is probably highly variable from year to year and depends on soil surface temperatures. Do not expect seedlings to be killed by frost. While Forsythia full bloom can be used as an indicator to apply crabgrass preemergence herbicides, there is no information available regarding soil temperatures or phenological indicators for stiltgrass emergence.

Japanese stiltgrass seedlings.
Japanese stiltgrass seedlings emerged in tall fescue turf in March

Our research found that while preemergence herbicides applied before stiltgrass emergence (in early March) were effective, those same treatments applied around crabgrass emergence in early May were not effective. A mixture of the postemergence herbicide Acclaim Extra (9 fl oz/A) and a preemergence herbicide was effective for stiltgrass control when applied in early May at crabgrass emergence. For stiltgrass control in June, July, and August, higher rates of Acclaim herbicide will be necessary for control. Acclaim Extra is the only product registered for postemergence stiltgrass control in turfgrass. Field research found it to be the most effective control option. See this RCE factsheet for more information about Japanese stiltgrass identification and other control options in non-turf areas.

https://njaes.rutgers.edu/fs1237/

In summary, to control Japanese stiltgrass, preemergence herbicides need to be applied a month earlier than is typical. If this is not feasible, tank-mixing preemergence herbicide with low rates of Acclaim Extra is an effective option.

Please Help: Annual Bluegrass Survey

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Conditions for good annual bluegrass growth have returned. Whether you adore or despise Poa annua, consider completing a survey which will allow us to collect valuable insights regarding the turf industry and opinions about managing this pesky grass. The results of this survey will inform a national project team of turfgrass weed scientists working to develop improved solutions for annual bluegrass control.

This survey is being conducted to investigate attitudes and actions related to the management of weeds, in U.S. turfgrass operations, including

golf courses,
sports and recreation turfgrass (athletic fields, schools, parks),
sod production, and
turfgrass seed production.

Your participation in this survey is completely voluntary and responses will be anonymous. Please click the link below to begin. The survey may be difficult to navigate on a smartphone device and is best completed on a PC or tablet. Thank you for your time and insight.


https://confidential-survey.com/datafile/Turfmanager12.htm

 

Annual bluegrass

Roughstalk bluegrass

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Roughstalk bluegrass (Poa trivialis) is a cool-season perennial grass often considered a weed. Light green in color it is most obvious in the early spring when it grows more rapidly than other turfgrasses. As temperatures rise in the summer its growth will slow and it often goes semi-dormant until cooler temperatures and rainfall return in the autumn.

A roughstalk bluegrass plant in a lawn.
A roughstalk bluegrass plant in a lawn in spring.
A small roughstalk bluegrass plant with purple stems.
A small roughstalk bluegrass plant with purple stems.

Infestations usually begin as small plants, but over time these plants spread via stolons and form patches that don’t tend to mix well with other cool-season grasses. These patches form as small plants expand from stoloniferous growth. These stolons (in addition to the lighter green color) can be used to differentiate roughstalk bluegrass from other bluegrasses such as annual bluegrass (no stolons or rhizomes) and Kentucky bluegrass (rhizomes only). Unlike Kentucky bluegrass, roughstalk bluegrass also has a long membranous ligule with a pointed tip.

Patch of roughstalk bluegrass in a lawn.
Patch of roughstalk bluegrass in a lawn.
Patches of lighter green roughstalk bluegrass amongst Kentucky bluegrass.
Patches of lighter green roughstalk bluegrass amongst Kentucky bluegrass

Currently there are no selective herbicides you can use in a home lawn to control roughstalk bluegrass. For many years Velocity herbicide was an option for professional turf managers, but it is no longer being manufactured and is not registered for use in home lawns (golf courses and sod farms only). Xonerate herbicide can provide some suppression, but should be used carefully to prevent injury to desirable turfgrass.

To control roughstalk bluegrass in cool-season lawns and athletic fields, nonselective control with glyphosate (Roundup and others) followed by reseeding is the best option. Apply glyphosate at this time in early spring, before summer stress, for best control. Glyphosate will kill any plant the spray contacts so apply carefully. If the areas are small, consider removing them with a shovel or a sod cutter. Be sure to remove the patch and at least 12 inches of turf surrounding the patch. Removing soil to a 0.5-inch depth should be sufficient to remove the stolons and all growing points. Reseed or sod the area with a desirable turfgrass species after removal.

These recommendations are based off of the 2019 Turfgrass Weed Control for Professionals guide. I highly recommend this guide for professionals managing cool-season turfgrass.

Weed Control in Spring Seedings

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The recent warm weather means its time to started on lawn and landscape projects. You may have plans to seed bare spots in the lawn that you didn’t get to in the autumn. These bare spots may be the result of fungal diseases, which were aplenty due to heavy rainfall in 2018. Summer annual weeds such as crabgrass or Japanese stiltgrass can out compete desirable species in the summertime and leave bare areas as well. While autumn is the ideal time to seed lawns in New Jersey, spring seedings can be successful if you have a plan to control summer annual weeds.

Crabgrass in a lawn

 

Weed competition from summer annual weeds is much more intense and is the main reason spring seedings are unsuccessful. In a mature lawn, you can apply a pre-emergence herbicide (crabgrass preventer) to manage weeds such as crabgrass and stiltgrass. If you recently seeded or have plans to, these crabgrass preventers are not an option.

If you are planning to seed this spring, using a starter fertilizer product that also contains the active ingredient mesotrione is an effective option when applied at seeding. It will control weed seedlings as they emerge without harming the grass you’ve seeded. One product for home lawns that contains mesotrione is Scotts® Turf Builder® Starter® Food for New Grass Plus Weed Preventer. Mesotrione is available for professional applicators as Tenacity® and other trade names. Products that contain siduron (Tupersan) are also an option for crabgrass control at seeding. Mesotrione and tupersan are not as effective as other pre-emergent herbicides such as pendimethalin, dithiopyr, and prodiamine that can be used on mature, well-established lawns.

After mesotrione is applied, weed seedlings and sometimes the turfgrass will appear bleached for 7 to 21 days after the application. The turfgrass will recover but most of the weed seedlings will not. Read the label carefully especially when using mesotrione and seeding fine fescue. Do not over apply mesotrione as it can damage grass you’ve seeded, especially perennial ryegrass. In areas of heavy weed pressure, mesotrione and siduron will likely not provide season-long crabgrass control. A second mesotrione application can be made 4-6 weeks after the initial or post-emergence herbicides that conitain quinclorac or fenoxaprop are also options if crabgrass develops mid-summer. Sprayable products sold for crabgrass control usually contain quinclorac or fenoxaprop.

Insane Rain

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The summer of 2018 isn’t going away quietly for many in New Jersey. August 2018 will be remembered for a steady dose of torrential rain that has made turfgrass management extremely difficult, especially in the northern half of the state. In the last 30 days, over 12 inches of rain have fallen across several counties in Northern NJ. This is almost triple the 30-year average of approximately 4 inches of rain for this period in a normal year.

Map generated by the national weather service.

These rains have produced saturated soils during an already difficult time of year for cool-season turfgrass (examined by Dr. Murphy in a previous post). High humidity and extended periods of leaf wetness have provided ideal conditions for diseases as well. Desirable turfgrass is thinning out and giving the competitive advantage to certain weeds. If you have weed problems right now you are not alone!

Nutsedge, false-green kyllinga, and creeping bentgrass (where it is a weed in poorly drained areas) are very competitive perennial weeds in wet soils and I’ve noticed they have become more prevalent in recent weeks. Even roughstalk bluegrass has awoken from summer dormancy in some spots.

Amongst annual weeds, crabgrass and goosegrass seem to be especially prevalent this year. Plants that escaped pre-emergence applications matured very rapidly through warm and wet conditions in late July through mid August and made post-emergence control difficult. Crabgrass and goosegrass are much more difficult to control as they mature beyond the 5-7 tiller stage of growth. With heavy rainfall and warm temperatures in late July it was difficult if not impossible to make post-emergence applications in time for optimal weed control.

Goosegrass plant with 4 tillers. Difficult, but not impossible to control.

Goosegrass plant with too many tillers to count. Extremely difficult to selectively control.

In a perfect world, post-emergence herbicide applications are not necessary due to an effective pre-emergence herbicide program. But grass, soils, and weather are not perfect and pre-emergence breakthrough in problem areas is expected. Pre-emergence herbicide programs were pushed to, or past the limit after heavy rainfall this spring. Late May was especially wet in the Central NJ where some areas received almost 10 inches of rain which fell during 11 days of a 17-day period (see CoCoRaHS for statewide maps). These conditions may have increased dissipation of pre-emergence herbicides, especially in sandy soils. Crabgrass breakthrough may be especially evident on slopes, high traffic areas, compacted soils, or where only a single pre-emergence application was made. Research consistently demonstrates that split application pre-emergence programs provide better crabgrass control than a single application and we are seeing history repeat itself in our 2018 crabgrass trials. Split application programs are providing excellent crabgrass control, and two most common pre-emergence herbicides (dithiopyr and prodiamine) are providing the same amount of crabgrass control at both locations. Keep in mind that in our research trials we subject herbicides to intense weed pressure, but the herbicides are applied uniformly under ideal conditions (immediate post-application irrigation, clipping return, non-compact soils) so we can make comparisons amongst treatments. Real world conditions may not be so ideal.

Excellent crabgrass control from a pre-emergence herbicide applied in early April and re-applied mid-June. Notice crabgrass pressure in the non-treated areas around the plot.

Less crabgrass control from a single application of a pre-emergence herbicide in April. In total for the season, the same amount of product was applied to both plots pictured.

 

Moving forward

Apply post-emergence herbicides if possible. Weed suppression that limits seed production is especially worthwhile on and around high-value sites (e.g., putting greens, athletic fields). Pylex (topramezone) is an excellent option for goosegrass control and crabgrass suppression in cool-season turfgrass. In my experience, applications at 1.0 to 1.5 fl oz/A will control multi-tiller plants (only 0.25 oz/A is permitted in creeping bentgrass). Tank-mixtures of Pylex and SpeedZone also provided excellent goosegrass control in our 2018 research. This tank-mixture will be evaluated more in 2019 as an option in Kentucky bluegrass, perennial ryegrass, and tall fescue. Quinclorac products (Drive XLR8, Solitare, generics) that can be applied at up to 0.75 lbs quinclorac/A are more effective than Pylex on crabgrass in cool-season turfgrass (lower rates can be used in creeping bentgrass) but will not control goosegrass. Tank-mixtures of Drive XLR8 and Pylex are safe to Kentucky bluegrass, tall fescue, and perennial ryegrass in my experience. Acclaim Extra (fenoxaprop) is another good option that will provide multi-tiller crabgrass and goosegrass control at higher rates. See product labels for more information on turfgrass tolerance, tank-mixtures, and weed control efficacy. Be sure to read the label carefully for information on adjuvants. Not including an adjuvant, or using the wrong one will severely reduce the efficacy of many post-emergence herbicides. For even more information, an excellent guide for weed ID and herbicide selection can be found here at the Purdue University Bookstore. I highly recommend this comprehensive guide.

More importantly, use fertilization and cultural practices to encourage recovery of the cool-season turfgrass once temperatures are more favorable and cool-season grasses regain the competitive advantage (hopefully around labor day). A strong stand of turfgrass will be more competitive against winter annual weeds and crabgrass in 2019. Even in cases of severe crabgrass or goosegrass infestation, a total kill of the existing turfgrass stand is usually not necessary if there is a good base of desirable turfgrass lurking beneath the crabgrass. Use selective herbicides, seed, cultural practices, fertilizer, and September weather to your advantage.

Spring Weed Control Update

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Weed Control Update

It feels like winter is hanging on and it looks a bit more Siberia-like than it did at this time in 2017. I’m writing this while watching the telecast of the Arnold Palmer Invitational in sunny Florida (where the greens are rolling PURE) and another snowstorm is taking aim at the Northeast. Interestingly, when comparing the 2018 GDD accumulation to 2017, things aren’t too different. We have accumulated about 300 GDD (using a base of 32 F) to date compared to 340 GDD at this time in 2017 in central New Jersey. However, things do look different when using a GDD model with a base of 50 F. We have accumulated 26 GDD50 to date in 2018 compared to 58 GDD50 at this time in 2017. Soil temperatures (3 inch depth) hit 50 F for a couple days in February, but have been hovering between 35 and 40 F ever since. So what does that mean for weed control?

 

Annual Bluegrass Seedhead Suppression

Using the based 32F GDD model (which in my opinion is more appropriate for this region the the base 50F model) we are within the optimum application window for spring ethephon (Proxy) applications. If you haven’t already applied and are making spring-only applications, later this week or early next week would be a good time to apply if the snow melts. If you made an application in the December, January, or February, you have a lot more flexibility on the spring application timing and can probably wait until near the end of the optimum GDD window. For more information on GDDs and annual bluegrass seedhead suppression see this previous blog post

 

http://turfblog.rutgers.edu/?p=989

 

Our 2016-2017 seedhead suppression research (in collaboration with Dr. Zane Raudenbush at OSU-ATI) demonstrated that Proxy applied in December and twice in the spring provided better annual bluegrass seedhead suppression than two spring applications. Interestingly, a single Proxy application in December with no spring applications was very effective in both New Jersey and Ohio. We are currently repeating this research. I’ve been asked if Proxy applications in January or February instead of December would be effective. Dr. Shawn Askew’s research in the Mid-Atlantic region demonstrates that January or February applications are extremely effective, but this application timing has not been evaluated in the Northeast or Midwest where annual bluegrass tends to be more dormant in January and February than in the Mid-Atlantic. This concept is something we plan to explore in more detail next winter.

 

Crabgrass Control

The forsythia bush is an effective phenological indicator of crabgrass germination. When forsythia reaches full bloom, it is an indicator that the opportunity to apply crabgrass pre-emergent materials is about to pass. If you are using dithiopyr (Dimension) you can wait until shortly after crabgrass emergence to apply.

You may remember last year that in Central and Southern New Jersey, forsythia bloom began in early March and these early blooms were killed by a snowstorm. Forsythia full bloom occurred in early April 2017 (and crabgrass germinated in mid April), which was a bit earlier than normal. This year with more seasonal temperatures, buds are visible but we are still several warm days away from forsythia full bloom. We are also well below the 3-day 55 F soil temperature threshold that is another good indicator of crabgrass germination. The 5-day rolling soil temperature average has been below 38 F for the last week.

Forsythia buds in Central NJ on March 18.

 

The Bottom Line 

With this seemingly long winter you may be stir crazy or trying to find something to do besides clean up tree debris. In regards to weed management, be patient and make applications when the plants are ready. The soil is slowly warming and the sun intensity is increasing as we trudge towards spring. In the meantime, make sure your sprayer is calibrated and get the dust off your golf clubs. Spring is coming – allegedly.