Category: Learn

This post kicks off a new series that we will be posting via turf tips called, “Weed of the Month”. In each post we’ll discuss a timely weed (one that you’re seeing at that particular time of year) and we will highlight its biology, identification, and control.

February’s weed of the month is Prostrate Knotweed

Biology: Prostrate knotweed (Polygonum aviculare) is an early germinating summer annual broadleaf that is often found in low-oxygen soils, including compacted areas next to sidewalks and previously flooded areas. Germination starts in late February and early March in many Midwest states.

Identification: Prostrate knot weed is the earlier summer annual weed to germinate in Indiana. Look for it first next to driveways and sidewalks. First germination has been in late-February or the first week of March the past three years in Indiana. Initial germinating weeds have a red hypocotyl.

Cultural control: Reduce soil compaction through aerification and improve drainage in areas prone to flooding.

Biological control: None known.

Chemical control: 2,4-D by itself will provide only fair control of prostrate knotweed, but when combined with triclopyr (Turflon Ester Ultra or Triclopyr 4) or dicamba (Banvel, Vanquish), it should provide excellent control in cool-season turf. There are many combination products that contain 2,4-D and dicamba, including Trimec 992 and SpeedZone. Combination products that contain 2,4-D and triclopyr include 4-Speed XT, Chaser, Chaser 2 Amine, Momentum FX2, Turflon II amine, and TZONE.

In warm-season turf, metsulfuron (Manor, Mansion, MSM) or the herbicides listed above will provide effective postemergence control of prostrate knotweed.

Preemergence control of prostrate knotweed can be achieved with late fall (November or December) applications of isoxaben (Gallery, Isoxaben 75WG). Other preemergence herbicides will also work, but are less effective than isoxaben. You can apply isoxaben in late winter, but spraying conditions are not typically favorable at that time of year and it is difficult to predict exactly when prostrate knotweed might germinate although it is usually in early March.

Aaron Patton, Turfgrass Extension Specialist

Biology: Prostrate Spurge (Euphorbia humistrata) is a summer annual broadleaf weed that can be found in dry/sandy and/or nutrient-poor soils along with compacted, weakened or disturbed turfgrass and landscape sites. Look for it first in driveways and sidewalks or in potted plants in a landscape or nursery as temperatures start to get warmer. Prostrate spurge can also be found in cultivated fields, brick walls, and parking lot cracks. It germinates from seed in June and July in Indiana and spreads via low-growing prostrate stems than form a dense mat as they invade the turf canopy. Its ability to establish and grow in multiple soil/climate conditions and highly compacted soils, as well as its ability to withstand low mowing heights, make prostrate spurge a common turfgrass weed throughout the state of Indiana.

Identification: Prostrate spurge is a low-growing summer annual weed in Indiana. The plant is anchored by a central shallow taproot and, as suggested by its common name, it forms a ground-hugging mat with prostrate stems that grow outward throughout the turf canopy. The plant produces these spreading stems along with viable seed very quickly, often within a couple of weeks after germination.

The leaves of prostrate spurge are pale green, hairy, egg-shaped, widest at the apex, and located opposite of each other on the stems which are pinkish in color and distinctly hairy. Prostrate spurge continually flowers from July to September and produces large quantities of viable seed throughout its life cycle. These flowers are small but numerous, originate from the base of leaves located on the upper-stem, and are composed of several male and female flowers within a cluster. It produces a fruit that consists of a 3-lobed, 3-seeded capsule with stiff hairs on its surface.

Prostrate spurge is very difficult to distinguish from other spurge species, particularly spotted spurge (Euphorbia maculata). In fact, some taxonomists consider the two plants to be the same species. An identifying characteristic of both species is a small reddish-brown splotch at the mid-vein/base of the leaves which acts almost as a camouflage; thus, making the weed difficult to distinguish from the desired turf. The primary difference between these two species is that spotted spurge leaves are often darker in color and the nodes do not produce roots when they come into contact with the soil.

Additionally all spurges exude a milky/white sap when damaged that can be toxic to animals if ingested.

Cultural control: None known specifically for prostrate spurge. Proper turf management such as adequate mowing heights, irrigation, and fertilization will help to produce a dense, aggressive turf which is the greatest defense against invading weeds. Prostrate spurge also thrives in compacted soils; thus, soil cultivation (hollow-tine aeration) may aide in management of the weed. Due to its shallow taproot, prostrate spurge can often be hand pulled when populations are small enough; however, it is important to remove weeds as soon as possible due to its ability to produce copious amounts of viable seed very quickly after germination.

Biological control: None known specifically for prostrate spurge.

Chemical control: Control options for prostrate spurge can include both pre- and postemergence herbicides. Preemergence control can be achieved with spring applications of isoxaben (Gallery, Isoxaben) prior to germination in summer. Dinitroaniline herbicides (such as Barricade, Pendulum) can also be applied for prostrate spurge control though the results are often less consistent than applications of isoxaben.Once spurge germinates, control in cool-season turf can be achieved with applications of two- or three-way mixtures of 2,4-D, dicamba, MCPP, or MCPA which are available in multiple product formulations at local retailers. Repeat applications may be necessary due to the germination of new seedlings.

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.

Biology: Quackgrass ( Elymus repens) is a cool-season perennial that vigorously spreads by rhizomes. It is a sod-forming grass that can crowd out desirable grasses and even other weeds. Quackgrass has been shown to be allelopathic, which means it releases chemicals that inhibit the growth of other plants. Large, nearly pure patches of quackgrass are able to form due to the invasive nature, extensive rhizome production and spread, and allelopathy of the species. These patches stand out in a lawn due to the ashy, blue-green color of quackgrass.

Identification: The most distinct identification feature of quackgrass is its clasping auricles. Quackgrass can be distinguished from annual ryegrass (Lolium multiflorum) with the presence of rhizomes (i.e. quackgrass has rhizomes and annual ryegrass does not). Quackgrass has rolled vernation and a short, membranous ligule. Lower sheaths are often hairy while upper sheaths are usually smooth. Leaves are an ashy, blue-green color and can sometimes have a longitudinal twist.

Biology: Roughstalk bluegrass, primarily known by its scientific name (Poa trivialis), is a cool-season perennial grass that can be found throughout the Midwestern United States. Though roughstalk bluegrass can be found in landscapes, roadsides, meadows, and waste areas, it is primarily considered a turfgrass weed. It can successfully germinate in multiple environmental conditions, but it has a preference for moist soils and high levels of shade. This ability to successfully establish in conditions ideal for the growth and development of most turfgrass species, as well as its ability to spread throughout the turfgrass canopy by stolons, make roughstalk bluegrass a common turfgrass weed throughout the state of Indiana.

Identification: Roughstalk bluegrass is a cool-season perennial grass that can be found in both high- or low-maintenance turfgrass throughout the Midwestern United States. Though the plant looks like it has clumping growth patterns, the plant survives from year-to-year through creeping, above-ground stems called stolons, which spread easily throughout the surrounding turfgrass canopy. Seedlings of the plant are generally small and slow to establish compared to other turfgrass varieties. Despite being included in turfgrass seed mixtures for shady areas, roughstalk bluegrass is also a common contaminant of uncertified turfgrass seed mixtures, and will successfully germinate alongside the desired turf species with adequate soil temperature and moisture conditions. Roughstalk bluegrass leaves are folded in the bud with a membranous ligule that can range from absent to very distinct (long) in size (NOTE: when samples are sent to me for identification, it is usually the type with no or very short ligules). The presence of very small, scabrous hairs give the leaf surface and margins a rough feel, thus accounting for the common name ‘roughstalk bluegrass’. The plant has a broad collar and a boat-shaped leaf tip that is characteristic of other bluegrass turf species. The leaves are shiny, and are pale green or yellow-green in color, but they often turn red or maroon during periods of drought or heat stress. Seedheads are produced from mid-May through June in an open panicle similar to that of Kentucky bluegrass. Roughstalk bluegrass can remain green throughout the winter (with some minor leaf-tip burn) and during the summer months it generally goes dormant. Stolons can successfully germinate after many years of prolonged dormancy. It is often confused with other bluegrass species such as annual bluegrass, though it is considerably larger, and Kentucky bluegrass, though it is generally lighter green in color. Annual bluegrass is primarily bunch-type. Kentucky bluegrass has rhizomes (underground creeping stems). Roughstalk bluegrass can also be confused with creeping bentgrass which is also stoloniferous; however, creeping bentgrass is rolled in the bud while roughstalk bluegrass is folded in the bud.

Cultural control: Rough bluegrass likes shady, wet areas. Therefore, reduce irrigation frequency to reduce the spread of this grassy weed. Mowing practices alone will not provide adequate management since roughstalk bluegrass can survive in many of the same environmental conditions and management programs as other desired turfgrass species. The best method of cultural control for roughstalk bluegrass is to avoid contaminating your turf system in the first place by buying certified seed mixtures/blends from a reputable seed company. Carefully read the labels of each seed bag. Unless the seed is advertised as a shade tolerant mixture, make sure roughstalk bluegrass species are not mentioned in the varieties of seed contained within the bag as a ‘weed seed’.

Biological control: None known specifically for roughstalk bluegrass.

Chemical control: Small areas and patches of roughstalk bluegrass can possibly be managed by making repeat applications of non-selective herbicides such as glyphosate and glufosinate; however, complete control is difficult due to the survival of creeping stolons.Spring application timings before the stress of summer will aid in the control of rough bluegrass with these non-selective herbicides. 

For golf courses and sod farms, other products exist that are not labeled for use in lawns. For more information on these products and on weed control, check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

Aaron Patton, Turfgrass Extension Specialist

Leslie Beck, Postdoctoral Research Associate

Biology: Smooth crabgrass (Digitaria ischaemum), is a summer annual grassy weed that is found throughout the Midwestern United states. Closely related to large crabgrass (Digitaria sanguinalis) and southern crabgrass (Digitaria ciliaris), these three species are often considered to be the most problematic weeds in lawns due to their ability to survive extremely low mowing heights, poor quality soils, and dry/hot climates.

Identification: Smooth crabgrass is a summer annual grassy weed that is commonly found in home lawns throughout the US. Smooth crabgrass can tolerate very dry, poor quality soils and is found in multiple cropping systems ranging from agronomics, to landscape, to horticulture, to vegetable gardens, along with both cool and warm season lawns in Indiana. Crabgrass plants are very opportunistic, so look for it to germinate in areas of bare soil like walkways, gardens, newly seeded turf areas, as well as a very open, thin turfgrass canopy.

Germination typically occurs from mid- to late-spring (late March-early May) in Indiana. If germination occurs while the temperatures are still slightly cooler, the plant will remain small for an extended amount of time. As the temperatures warm, more leaves will start to develop and the plant will begin tillering by early- to mid-summer (June). The young leaves of smooth crabgrass will have very little hairs, while large and southern crabgrasses have a dense covering of very fine hairs. All three crabgrass varieties will have a membranous ligule that has a torn or ‘shredded’ appearance.

The development of multiple tillers can contribute to the clumpy appearance of a crabgrass plant, though smooth crabgrass is generally smaller in size than large crabgrass. Once mature, smooth crabgrass produces seedheads in the form of 3-5 spikes that are clustered at the top of long, erect stems. Seedheads mature at the end of summer prior to fall/autumn. As crabgrass dies with the first killing frost, the plant can appear as unsightly brown patches surrounded by green cool-season turf in lawns.

Biology: Tall Fescue (Festuca arundinacea) is perennial grass that can be both desirable as a lawn species when using improved cultivars or undesirable when forage-type (wide-bladed) tall fescue plants a contaminant other primary species in a lawn.

For all of you nerds out there like me, you might be interested in know that there has been much recent debate about the scientific name of tall fescue. While tall fescue has used the above scientific name consistently for over 60 years, it is now being classified by scientists formally as Schedonorus arundinaceus (Schreb.) Dumort. (also = Lolium arundinaceum (Schreb.) S.J. Darbyshire; formerly = Festuca arundinacea Schreb.). I know, very confusing even for me. Remember that there are many grasses called “fescues”. I wrote about this in a previous turf tip that I would encourage you to read (click here).

Identification: Tall fescue is a coarse-textured (wide-bladed), bunch-type grass. Improvements in tall fescue leaf texture have resulted in more fine-bladed varieties/cultivars that have helped to increase the turf quality and use of this drought-tolerant turf in Indiana. We often recommend improved turf-type varieties of tall fescue as the primary species for lawns, but older, wider-bladed, forage-type varieties of tall fescue such as Kentucky 31 (KY-31) still exist, and can be problematic weeds in lawns. This forage-type tall fescue can be easily spotted in lawns in early spring when they green-up faster than Kentucky bluegrass and by its bunch-type growth habit, which results in a clump of turf when present as a weed. Also, forage-type tall fescue can be easily spotted in lawns during drought as tall fescue stays green and actively growing during drought whereas Kentucky bluegrass will often enter a drought-induced summer dormancy.

Tall fescue will often lack a ligule or possibly have a short membranous ligule.

Auricles are usually short and blunt but some can also be classified as short-clasping meaning that the auricle may wrap-around the stem but may not fully clasp or cross one another. You may also see small hairs protruding from the auricle.

The vernation (how the leaf is oriented inside the stem) is rolled on tall fescue and the collar is conspicuous (obvious) and usually wide.

The leaf blade is wide but variable in length with a pointed leaf tip. In some cases you can actually feel little barbs along the leaf margin when you run your fingers from the leaf tip down the leaf blade.One last helpful identification is the prominent veins in tall fescue compared to Kentucky bluegrass (only midrib is clearly visible).

Biology: Wild Garlic (Allium vineale) is a monocotyledonous cool-season perennial that can be found throughout most of the eastern and southern United States. Despite having linear leaves and parallel veins, wild garlic is neither a grass nor a sedge; it is a member of the lily family. Wild garlic is more noticeable in the winter months when the turf is not actively growing or being mown. Plants reproduce from seeds and aerial bulbets from early spring and throughout the summer months. Its ability to tolerate a wide range of soil types, and to survive mowing height typical of lawns make wild garlic a difficult-to-control weed in cool-season turf.

Identification: Wild garlic is a bulbous perennial with grass-like leaves that emerges in turf in the early spring. Leaves are slender, rounded, and hollow. Wild garlic is often mistaken for wild onion; however, wild onion leaves are more flattened and are not hollow. Wild garlic leaves have a distinct garlic-like odor when crushed or mown. Leaves emerge from an underground white bulb with a papery outer coating, which also gives rise to multiple bulbets that are flattened on one side and also covered by a papery-like membrane. Greenish-white ‘flowers’ can be observed atop short flowering stems in late spring through early summer. In the place of flowers, small globe-shaped aerial bulbets are produced that are greenish-white and have long tail-like green leaves. Wild garlic plants may die back in the summer, but leafless stalks bearing viable seed capsules may remain.

 

Cultural control: Proper turf maintenance such as adequate mowing height, fertilization, and irrigation to develop a dense, aggressive turf leading into the winter months may help to manage wild garlic. Hand-pulling wild garlic is generally not an effective method of weed control since hollow stems are easily broken leaving the bulb below the soil to generate new leaves and new bulbets. As a result, bulbs need to be dug-up in order to achieve an adequate level of control.

Biological control: None known for specific use in wild garlic.

Chemical control: In cool-season turf, wild garlic is difficult to control. There are no preemergence herbicide options for wild garlic in cool-season turf; however, there are a few postemergence herbicide options. Applications of 2,4-D alone or in multiple combinations with MCPP and dicamba (Trimec, Triplet, etc.) may achieve fair levels of control. The ester formulations of 2,4-D are more effective against wild garlic than the amine formulations (consult the Purdue Turfgrass Weed Control for Professionals extension publication (link below) for more information regarding the differences between amine and ester 2,4-D formulations). Additionally, mowing the weeded area prior to application may improve herbicide uptake and overall control of wild garlic in cool-season turf.

For more information on weed control, search this blog and check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

Aaron Patton, Turfgrass Extension Specialist
Leslie Beck, Postdoctoral Research Associate

Biology: Collectively, turf managers refer to the Midwest species common blue violet (Viola sororia), wooly blue violet (Viola papilionacea), and confederate violet (Viola sororia f. priceana) all as wild violet. Additionally, yellow violet (Viola pubescens) is also found in Indiana. Wild violets are a persistent, perennial, and difficult-to-control broadleaf plant. It is regarded as a desirable perennial plant by some as well as a weed by others.

Identification: Violets can be identified by their heart shaped leaves which are pointed at their tip and have rounded teeth on their margins. Violets spread by short rhizomes and by seed. Short rhizomes about the size of your “pinky” finger are common to all Indiana wild violet species. Wild violets are typically found in shady areas with moist soil but they can also grow in sunny, droughty areas.

Flower color varies by species. Common blue and wooly blue violets (both have a purple, blue, violet color. Confederate violet has white petals with an inner violet color. Yellow violet has a yellow color.

Following flowering and pollination, fruit capsules form. Seed is dispersed from the capsules by gravity after the capsules dry.

Cultural control: Cultural practices such as proper mowing, fertilization, and irrigation can be manipulated to control some weed species but these practices have little impact on wild violet populations in lawns. Wild violet can be decreased by more frequent mowing but not by fertilization. It is unknown how irrigation, drainage, and soil compaction influence wild violet populations. As such, turf managers rely on herbicides to control wild violet.

If you wish to increase wild violets in your lawn, simply reduce your lawns nitrogen fertilization and maintain moderate to high levels of shade by withholding pruning of trees.

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: Good chemical control of wild violet is typically obtained with triclopyr (Turflon Ester Ultra or Triclopyr 4). Many herbicides are available with triclopyr as the key ingredient (see Commonly Used Broadleaf Herbicide Combinations for Turfgrass, page 62). For best control with triclopyr use more than 0.5 lb ai/A. Turflon Ester Ultra and Triclopyr 4 at 1 pt/A will deliver 0.5 lb ai/A; and at 1 qt/A will deliver 1.0 lb ai/A. Chaser, Chaser 2 amine, Confront, 2-D, and Tailspin will also deliver ≥0.5 lb ai/A.

For more information on weed control, search this blog and archived turf tip postings and check out our Turfgrass Weed Control for Professionals Publication.

Aaron Patton, Turfgrass Extension Specialist