Dr. Pete's Turf Tips
Peter H. Dernoeden, Ph. D.
April started with an unusual snow storm, followed by incessant high winds and average air temperatures mostly 5-10oF below average. Longer days with some sun promoted enough growing degree days to stimulate weeds to grow and become noticeable. Most weeds in evidence are winter annuals; primarily the usual’s such as annual bluegrass, henbit, horseweed, chickweeds, hairy bittercress, etc. A few perennials such as dandelion and sweet vernalgrass have begun flowering. On April 22, I noted a few crabgrass seedlings had emerged in hot spots (e.g., next to driveways and sunny bare areas). Crabgrass will be emerging much later than usual, but a major flush should occur around mid-May.
Both Star of Bethlehem and wild garlic are members of the Lily family and survive as perennials via underground bulbs. Wild garlic leaves appear in October and remain evident all winter and spring. Conversely, Star of Bethlehem leaves don’t appear until early spring (usually March or April). Leaves of both species disappear during summer, and as such, plants are not objectionable for long periods nor do they generally become invasive enough to out-compete turf.
Star of Bethlehem bulbs are sold for use in ornamental beds and rock gardens and this usage is the original source/escape of this plant into turf. Star of Bethlehem mostly is found in solitary clumps, but where soil has been tilled, bulbs are re-distributed and hence clumps may be present in abundance. Leaves are grass-like, but notably fleshy and have a whitish, grooved mid-rib like Crocusand Liriope. Flowers are bright white (rarely bluish), waxy and appear in spring from late April to early June. Pollen bearing anthers are yellow in the center of five radiating petals. Mature plants produce dense leafy clumps and 20 or more white, thumb-size onion-like underground bulbs. Like Crocus, leaves die and plants disappear during summer only to reappear early next spring.
All parts of the Star of Bethlehem plant are poisonous if consumed. The remarkable aspect of its lifecycle is that viable seed production is rare, and thus it is primarily spread via bulbs by tillage. Given its poisonous nature it is unlikely that bulbs are spread by burrowing animals, such as squirrels or chipmunks. How it manages to pop up in lawns and golf roughs is a mystery, which suggests that a few viable seeds are produced.
Wild garlic (WG) is most conspicuous in winter and spring and is especially problematic in winter dormant warm-season grasses. Wild onion is very similar, but less common in turf. WG also is a common weed in ornamental beds. WG usually develops in greater populations in sunny versus shaded sites and wet versus dry soil situations. WG produces smooth, waxy, slender, hollow and cylindrical (i.e., rounded) leaves. Leaves are blue-green in color and have a “garlic or onion” odor, especially when crushed or mowed. Leaves emerge from underground bulbs during cool moist periods in early autumn (usually October). Leaves remain dark-green throughout winter, but senesce and disappear following the advent of warmer temperatures in early summer. Underground bulbs are white, and have the appearance and odor of onion and garlic.
WG is most objectionable in warm-season grasses. WG gets a competitive growing advantage since plants emerge in the autumn to coincide with warm-season grasses turning brown and entering winter dormancy. It is the contrast between brown-dormant turf and the long, blue- green leaves that makes WG an aesthetic problem in dormant warm-season grasses. WG also commonly invades cool-season grasses, but these grasses retain enough green color in winter to mask its presence. During spring, however, WG leaves out-grow the turf canopy and often present an aesthetic problem in cool-season grasses.
Flowers (usually purple, but sometimes greenish-white, in color) and aerial plants with bulblets are formed in globe-shaped pods (i.e., umbels). Flowers and umbels are produced on top of stems that are 1 to 3 feet in height. Stems appear in May and June and only in unmowed sites. Seed as well as aerial plants consisting of long, green leaves with a purple colored bulb at the base are dispersed by wind when the paper-like globes open. Hence, it is only in unmowed sites from which seed and aerial plants (i.e., small bulbs with leaves) are produced and dispersed. Underground bulbs also are dispersed by tilling.
I am unaware of any studies that have investigated control of these weeds; hence, herbicide recommendations are largely conjecture. We do know that both weeds keep coming back each year, even where herbicide use is attempted. Control is hampered for several reasons including: little leaf area is present to obtain good herbicide contact and uptake; plants only can be targeted between autumn (WG) and spring (WG and Star of Bethlehem) when air temperatures are cooler rendering herbicides less effective; and it is difficult to get herbicidal levels translocated to bulbs, especially in cooler weather. Low volatile ester forms of 2,4-D, dicamba, triclopyr, fluoxypyr and others mixed with carfentrazone (i.e., Quicksilver) are the preferred herbicides. An application of the aforementioned herbicide (s) normally causes twisting and etiolated leaf growth and more rapid senescence. Other herbicides are available for use in warm-season grasses.