Weed of the Month for April 2013 is Purple Deadnettle

Purple Deadnettle 

Biology: Purple deadnettle (Lamium purpureum) is a common winter annual broadleaf weed found throughout the US. It is closely related to another winter annual broadleaf, henbit (Lamium amplexicaule). Both have vibrant purple flowers that can been seen now in lawns, landscapes, and fields.

Identification: Purple deadnettle is a winter annual meaning that it germinates in the fall, survives the winter as a plant, then flowers, develops seeds, and then dies when temperatures rise in late spring and early summer. Purple deadnettle blooms are mainly visible in April although you can find it blooming earlier and later depending on the area it is growing and the temperatures. Purple deadnettle is a member of the mint family and has a characteristic square stem. Purple deadnettle flowers are light purple in color and are small and tubular in shape.  

Purple deadnettle leaves are triangular in shape with shallow lobes. Typically, the upper leaves are more purple-red in color than the lower leaves.  

Cultural control: Purple deadnettle mainly occurs in turf and soils that are disturbed during the fall when it germinates. Proper mowing (higher mowing heights), proper fertilization (some rather than none to improve turf density), irrigation to prevent summer dormancy during drought, and aerification of compacted areas to improve turf health are all cultural practices that can be used to reduce purple deadnettle. If you only have a few purple deadnettle plants, you can usually pull them by hand.

Biological control: Some organic herbicides are available. Among the postemergence organic herbicides, the most common are pelargonic acid (Scythe) and acetic acid (5 percent or greater solutions). Other products that contain medium-length fatty acids and clove oil (eugenol) show some promise; however, these organic postemergence herbicides are nonselective and can injure actively growing desirable plants in the lawn and landscape, so their use should be limited to directed spot treatments. The bottom line is that most organic postemergence herbicides have limited use in turf and are better suited to weed control in parking lots, fence rows, and other bare ground applications. Many new organic products contain the active ingredient iron HEDTA (FeHEDTA). Multiple applications of this product are required for control. FeHEDTA containing products injure turf less (can actually make turf darker green), but their efficacy for weed control is yet to be well documented.

Chemical control: Purple deadnettle can be controlled using preemergence or postemergence products, but I will mainly discuss postemergence control as preemergence control is more limited to bermudagrass and zoysiagrass lawns.

The more common approach to controlling purple deadnettle in cool-season turf is to use postemergence herbicides after it has already emerged. Most postemergence herbicides including those containing 2,4-D, dicamba, fluroxypyr, and others will control purple deadnettle. As plants get bigger, herbicides will be less effective at controlling this weed. Additionally, since it is a winter annual, it will naturally die in the summer so late spring herbicide applications aren’t necessarily warranted. You can tell that purple deadnettle is beginning to die from summer heat stress when the leaves start to turn yellow in color.

For more information on weed control, search this blog (search box in upper left corner of page) and archived turf tip postings and check out our Turfgrass Weed Control for Professionals Publication.

Aaron Patton, Turfgrass Extension Specialist

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Weather and Turf Diseases

From a temperature perspective, weather patterns in the Midwest have returned to normal this spring.  I recall the 80 F days in March 2012, and all of the concerns about scheduling fungicide sprays.  Hopefully most turf managers have resisted the temptation (regardless of who or what is doing the tempting) to apply fungicides for early season dollar spot control this year.  Fungicides will be effective only if the pathogen is active, and Sclerotinia homoeocarpa becomes active when mild weather prevails—not yet, but we’re getting close!

I also think it is too early for a summer patch spray.  The decision rule suggests that applications targeted towards summer patch should be initiated when soil temperature (2” depth) is 65 F or greater for several days.  There is so much “fudge factor” there.  Little or no hard science went into developing the rule—it’s all empirical.  Keep in mind that the pathogen comes out of dormancy more like a dimmer switch than an “on-off” switch, so it will take a while to ramp up to speed.  We intend to conduct some summer patch trials this summer, so I hope to have something useful to report next year.   

I suspect that symptoms of yellow patch (aka, cool season brown patch) are apparent on bent/poa greens and surrounds.  The heavy rains during the week of April 12 will have aggravated the situation.  Last April, we established a fungicide trial in an area where a yellow patch outbreak was severe—as bad as I have seen it in 15 years or so.  The fungicides included Prostar, Heritage (representing QOI products), Banner Maxx (representing DMI products), Cleary 3336, a chlorothalonil, and an untreated check.  The plots were monitored closely for 4 weeks.  In terms of symptom reduction, there were no differences among treatments, including the unsprayed check.  However, as daily temperatures increased, and the superintendent applied supplemental N, symptoms in ALL plots disappeared within a week.  By June 1, there was no recognizable damage, cosmetic or otherwise, to the turf.

Rick Latin
Turfgrass Pathologist

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Black Cutworms Making Their Annual Migration North

Black Cutworms have started showing up in light traps around Indiana. This means they will soon laying eggs, if they haven’t already.  Superintendents should be on the lookout for evidence of feeding damage on greens and tees. Also, remember that a soap flush of vulnerable, short-cut areas will often reveal the presence of black cutworms before damage is evident. One gallon of soapy water solutions consisting of 15 ml of lemon scented liquid dish detergent (Lemon Joyâ) poured over a 0.25 m area at several locations on each green or tee will quickly disclose these larvae which may be very small at this point in the season. Black cutworms are easy to control and there are a number of products that will do an excellent job, but remember to treat the target areas and at least a 15 ft. perimeter. Higher cut areas are not usually damaged, but they do serve as a potential reservoir of cutworms when they are located around more sensitive low-cut areas.

Some recommended active ingredients include:

Lambda – cyhalothrin
Stienernema carpocapsae (insect parasitic nematode)
Bacillus thuringeinsis (kurstaki strain)

As always, follow label directions for proper rates and do not irrigate for at least 24 hours after making a liquid application.

Doug Richmond
Turfgrass Entomologist

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Annual Ryegrass Showing Up in Lawns

I have had several emails and weed samples submitted recently of an unknown grass. In each case, the sample was annual ryegrass (Lolium multiflorum).

Annual ryegrass is a common ingredient in low quality seed mixtures. It appears in the spring time in lawns seeded the previous year either from some annual ryegrass in the seed mixture or from some seed in the soil. Annual ryegrass is a winter annual and it should die later this summer when it gets hot. Before dying, it produces a seedhead and its seed can mature quickly and drop to the soil where it can germinate the following fall. No control is recommended as it is an annual grass.

To reduce the likelihood of this weed being problematic in the future choose a seed mixture that does not contain annual ryegrass, Italian ryegrass or intermediate ryegrass and one that has no weed seed. If you have this problematic weed each spring, make sure to mow the grass before it can produce a seedhead to help reduce the likelihood that it will return.

For more information on differentiating annual ryegrass from winter wheat, a similar looking weed that also shows up this time of year in lawns seeded last fall, see this turf tip posted last year: Grassy Weeds in Turf Planted Last Fall.

Dr. Aaron Patton, Turfgrass Extension Specialist

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How to Mow Now That it has Stopped Raining

Tips for Mowing Wet Turf
  1. Sharpen your blades if you have not yet this spring.
  2. Mow in the afternoon when the leaf blades are dry if possible to reduce clumping of the grass blades. However, it is fine to mow wet turf or mow during light rain.
  3. Set the mower higher (especially if your grass is taller than it normally is when you mow).
  4. If possible, use a side-discharge mower rather than a mulching mower as mulching mowers are prone to clogging.
  5. Double cut the area if there were a lot of clippings or if the area was uneven after cutting.
  6. If there are too many clippings (they sit on top of the turf after mowing), consider bagging the clippings and using them as mulch or compost.
  7. If you are creating “muddy” tire tracks with your riding lawn mower, consider using a walk behind push mower to mow these wet areas. It is worth the extra effort to push mower an area in order to avoid making ruts in the soil and permanently damaging the turf.
    Be careful not to turn too sharply when mowing wet areas. Use a push mower to mow until the area dries.

    Muddy wheel tracks and permanent turf damage caused by mowing a wet area with a ridding lawn mower. to avoid this, use a push mower to mow until the soil dries some.
  8. Lastly, make sure to clean underneath the mower deck after mowing when wet.
For more information on managing flooded turf areas, see this previous Turf Tip: Flooding on Turf

In the spring you may not be able to mow often enough to abide by the one-third rule. An occasional mowing that removes more than one-third of the leaf blade may be necessary during time periods with frequently rainfall and little to no long-term damage in turf health should result. However, your long term maintenance program should include mowing as often as needed to never remove more than one-third of the leaf blade in a single mowing.

Removing more than one-third of the leaf blade. This was my lawn when I mowed it Saturday after a week of rain.

Dr. Aaron Patton, Turfgrass Extension Specialist

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When Should I Apply My Preemergence Herbicide for Crabgrass Control?

Despite proper cultural practices, crabgrass may still remain problematic in certain turf areas. The best approach to controlling crabgrass is to use a preemergence herbicide such as dithiopyr (Dimension), pendimethalin (Pendulum), prodiamine (Barricade), prodiamine + quinclorac (Cavalcade PQ), sulfentrazone + prodiamine (Echelon), and others. These herbicides inhibit cell division and prevent crabgrass seeds from properly emerging. Since these herbicides work on germinating seeds, you must apply them prior to germination — with the exception of dithiopyr, which controls crabgrass after germination until it reaches one tiller.

These preemergence herbicides must be applied and watered in (through rainfall or irrigation) prior to crabgrass germination to be effective. Two growing degree models are available to help you time your preemergence application.

The first GDD model is for application timing. The link below helps you determine what stage you should be in of your applications. These stages are designed for turf professionals. Homeowners should target the early or optimum timings.At the website for this model you will see the map with areas of the state colored into five different stages. Here is a key to what these stages mean.
  • Done = this means that you should be done making your preemergence herbicide application for crabgrass. If you are at this stage but you haven't finished applying your spring preemergence herbicide, you should consider using dithiopyr (Dimension).
  • Late = this means that crabgrass might be germinating now. You should finish your applications or consider switching to a preemergence herbicide containing dithiopyr.
  • Optimum = optimum timing for a preemergence herbicide for crabgrass control.
  • Early = denotes the start of preemergence herbicide applications for most lawn care companies. It is not too early to apply though as preemergence herbicides do not breakdown in the soil until late spring when soils warm and microbial activity increases.
  • Under = denotes that it is very early in the growing season. While this may be called "under", research shows that these very early spring preemergence herbicide applications provide good crabgrass control.

See the application timing GDD model here: http://www.gddtracker.net/?model=7&offset=0&zip=47905

The second growing degree model estimates crabgrass germination. Research suggests that 200 GDD need to accumulate with a base of 50 °F before crabgrass germinates (source: Dr. Ron Calhoun). See this model here: http://www.gddtracker.net/?model=10&offset=0&zip=47905. More details on how to predict crabgrass germination, including other theories and approaches, can be found at last year's blog posting: When Will Crabgrass Germinate?
For more information on controlling crabgrass, see these two Purdue publications.
  1. Control of Crabgrass in Homelawns (AY-10-W)
  2. Turf Weed Control for Professionals (AY-336)
Special thanks to the Midwest Regional Turf Foundation for their financial support of this GDD Tracker website for use by all Indiana turf professionals.

Dr. Aaron Patton, Turfgrass Extension Specialist

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Still Time for Spring Seeding

Seeding in spring is difficult and unsuccessful if not done correctly. However, there are many in Indiana who didn’t seed last fall but still need to seed this spring to help fill in thin areas from last summer’s drought. The following circumstances that warrant a spring seeding:
  • Thin turf due to winter damage
  • Poor turf density due to poor recovery from previous year’s problems, i.e., grub damage, drought damage, etc. This is the case in 2013 due to heat and drought in 2012.
  • Construction of a new building.
If a spring seeding is necessary, it is best done as early as possible. Ideally, early spring seeding should actually take place in winter before the ground thaws. Although it is not necessary to seed before the ground thaws it may make seeding more easy as soils are often soft and moist in the spring which may make it more difficult to seed certain areas, especially with heavier equipment.

Seed planted now will germinate in mid to late April as temperatures warm. Although any cool-season grass can be seeded in the spring, spring seedings are more successful with tall fescue and perennial ryegrass than with Kentucky bluegrass due to the faster germination rate and better seedling vigor of perennial ryegrass and tall fescue compared to Kentucky bluegrass (Fig. 1). If Kentucky bluegrass is seeded in the spring consider using a mixture of tall fescue: Kentucky bluegrass (90:10, weight: weight) or a mixture of Kentucky bluegrass:perennial ryegrass (such as 80:20, weight: weight)(Table 1). Seeding Kentucky bluegrass alone will result in marginal bluegrass establishment due to the slow germination and vigor of the seedlings and increased competition from crabgrass. 

Germination of perennial ryegrass (left, PR) will be followed by tall fescue (center, TF) and then Kentucky bluegrass (right, KBG).

Table 1. Recommended seeding rates for lawns in Indiana.

rate lbs/1,000 ft2
Days to
Kentucky bluegrass
1.0 to 2.0
Kentucky bluegrass + perennial ryegrass
3.0 to 6.0
Tall fescue
8.0 to 10.0
6 to 10
Tall fescue + Kentucky bluegrass
5.0 to 7.0
6 to 21

Fertilizing seedings properly is important. New turfgrass seedlings have poorly developed root systems and thus they cannot effectively take up the nutrients from the soil. Therefore, it is important to fertilize after seeding to encourage establishment. To help the turf establish, apply a "starter fertilizer" at seeding to enhance seedling root development. Starter fertilizer is high in phosphorus which is listed as the second number in the analysis on the fertilizer bag. For instance, a 16-22-8 fertilizer contains 22% P2O5. Apply the fertilizer according to the label directions would should supply at least 1.0 lb. P2O5 /1000 ft2. This application will likely include nitrogen (first number in the fertilizer analysis), which will also help the turf develop an extensive fibrous root system that is better able to take up nutrients and obtain water.

Weed control in spring seedings is tricky. See this prior post for more information on this.

Dr. Aaron Patton, Turfgrass Extension Specialist

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A Tale of Two Years

We are finally through a cold March and into what appears to be a normal April. The graph below compares January, February, and March in 2012 and 2013 to our 30 year normal weather averages for those months.

The temperature outlook for the next three months has us with slightly above average temperatures.

The rainfall outlook for the next three months has us with slightly above average rainfall.

Lastly, following last years drought, we had some good winter precipitation and we are no longer under drought.

Dr. Aaron Patton, Turfgrass Extension Specialist

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Weather and Turf Disease –Early Spring 2013

Nobody needs to be reminded that March 2013 has been colder than the last several years.  The good thing is that wintry conditions prevent wasted fungicide applications.  Keep watching the summer patch soil temperature monitor.  Remember that there are several elements to the decision rule.  The cardinal temperature seems to be around 65F—in soil at 2” depth.  Also understand that the pathogen does not emerge from dormancy like an “on/off” light switch.  It is more like a dimmer switch, which reinforces the notion of waiting until the natural warming period prevails, rather than hastily making an application in response to an unnatural spike in soil temperature.

I doubt that anyone has had the opportunity to apply early season sprays for dollar spot control.  Results from our research over the past 3 seasons indicate that fungicide sprays would surely be wasted if applied over the past 4 weeks.

Combination Fungicide Products – 2013

There is a trend among basic manufacturers to combine active ingredients to improve efficacy and broaden the spectrum of activity of treatments for turf disease control.   Below is a list of fungicide combinations that may serve as a resource for identifying the active ingredients in new fungicide products.

Product Name
Active ingredients
Equivalent products
azoxystobin + propiconazole
Heritage + Banner 
azoxystrobin + difenconazole
Heritage + difenconazole
propriconazole + chlorothalonil
Banner + Daconil
propiconazole + ctl + fludioxanil
Banner + Dac + Medallion
azoxystrobin + chlorothalonil
Heritage + Daconil

trifloxystrobin + triadimefon
Compass + Bayleton
triticonazole + chlorothalonil
Triton + Daconil
trifloxystrobin + iprodione
Compass + 26GT

pyraclostrobin + boscalid
Insignia + Emerald
boscaild +  chlorothalonil
Emerald + Daconil
Pillar G
triticonazole + pyraclostrobin
Trinity + Insignia

Iprodione + thiophanate-methyl
26GT + Cleary 3336
iprodione + thiophanate-methyl
26GT + Cleary 3336

fluopicolide + propamocarb
Fluopicolide + Banol

Disarm M
fluoxastrobin + myclobutanil
Disarm + Eagle
Disarm C
fluoxastrobin + chlorothalonil
Disarm + Daconil

chlorothalonil + acibenzolar
Daconil + acibenzolar

mancozeb +  copper hydroxide
Fore + copper hydroxide

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