Peter H. Dernoeden, Ph. D
In May there continues to be many dreary overcast days and rainy weekends. The generally lousy weather of past springs has had a huge, negative economic impact. It has cut revenues for public golf courses; plagued efforts to keep up with mowing and avoid scalping, and for sod growers it has cost them lots of scrapped sod trying to get a few pallets to send down the road.
Some weeds that produce yellow flowers have added some brightness to a mostly dreary spring. Some are invasive and others are not. Among those broadleaf weeds showing yellow flowers now include cinquefoil, Indian mock strawberry, yellow hawkweed, common catsear, and buttercup. All are perennials, but only catsear is non-invasive.
Identifying the Varying Species of Cinquefoil
There are several species of cinquefoil, and all are similar in appearance. Cinquefoil is low growing and perennial.
Plants die-back in winter, and new leaves and shoots appear in spring. Leaves are glossy with five, dark-green, radiating (i.e., palmate) and toothed leaflets.
Stems are brown to purplish and are conspicuously hairy. Some cinquefoil’s spread by above ground stems called stolons, which root at nodes. Other species have shorter above ground stems that may be hairy and purplish in color, but do not root. Just under the soil surface, you may find slender, dark-brown wiry stems called rhizomes. It is either the presence of stolons and/or rhizomes that allows plants to pack together in dense mats and compete with turf.
Flowers of cinquefoil resemble Indian mock strawberry, but the species are easily differentiated based on leaflet number.
Cinquefoil produces dense mats of plants with bright yellow flowers with 5 petals, and has 5 radiating, notched leaflets and brown or purple trailing stems.
Indian Mock-Strawberry and its Unique Appearance
Indian mock-strawberry is recognized by its three, dark-green leaflets, yellow flowers and strawberry-like fruit. Rosettes of trifoliate leaves (i.e., 3 leaflets) of Indian mock strawberry are rounded and have rounded teeth on margins. Plants produce long, trailing stems that have a purple color, which may or may not form roots.
Flowers appear in spring and form on long stems and have 5 rounded and yellow petals.
The fruit are red, round, spongy and strawberry-like. Plants remain green throughout summer and winter. Wild strawberry is very similar in appearance, but produces white flowers and is uncommon in our region.
Examining the Anatomy of Yellow Hawkweed
Yellow hawkweed is a perennial and forms rosettes of hairy leaves that spread by both above ground and below ground stems called stolons and rhizomes; respectively. Stolons and rhizomes form dense mats of rosettes that can push turf out of the stand. Older leaves become elongated and oblong, and taper at the base. Leaves are very hairy and exude a milky substance when cut.
Rosettes are prostrate and in the absence of mowing they produce tall seedheads. Seedhead stems are leafless, 10 to 24 inches or higher, produce clusters of 2 or more bright, yellow flowers, and exude a milky substance when cut.
Flowers are similar in appearance to those of dandelion, but smaller and do not develop into globe-like, puff-balls of grayish-white seeds.
Seedheads are evident only in areas that have not been mowed recently.
Common Catsear posing as a Dandelion Imposter
Common catsear (aka false dandelion) is similar in appearance to yellow hawkweed, but is more diminutive, less invasive and found in infrequently mowed, low maintenance turf areas.
Catsear above ground parts senesce and die shortly after seedheads are produced. Leaves are arranged in basal rosettes, with deeply notched teeth or lobes similar to dandelion. Leaves are conspicuously hairy, and like dandelion and hawkweed, ooze a milky substance when broken or crushed.
Flowers are borne on tall (≥ 10”) and almost leaf-less stems. Yellow, radiating flower heads are very similar to dandelion (and yellow hawkweed), but much smaller and may be bright yellow or have an “orange-yellow” tint. Once mature, flowers develop into a dense globe-like, puff-ball of grayish-white seeds.
Like dandelion, seeds are produced on long stalks with a parachute of hairs that become airborne under windy conditions, which rapidly and efficiently redistribute the weed.
The Beauty of Bulbous Buttercup
Bulbous buttercup does not become evident until mid-spring, but suddenly produces a burst of great numbers of yellow flowers.
Young hairy leaves with 3 lobes emerge from underground bulbs (i.e., corms) and form tufts. Corms are onion-like, white and papery and 0.25 to 0.5 inch in diameter. Corms do not have an onion odor. The 3-parted, rounded leaves are borne on long stalks (petioles) and have deep notches or clefts. Two smaller, 3-lobed leaves with teeth or notches form below larger leaves.
In spring (May usually), bright yellow flowers are produced on top of erect stems. Flowers consist of 5 bright, shiny and yellow petals.
Following flowering, leaves senesce with the advent of higher summer temperatures and eventually plants die-back to the corms. Plants survive as corms and seed. There are 2 other buttercup species, which do not produce corms and lack a bulb-like base, but otherwise produce the same shiny yellow flowers and 3-lobed leaves.
Unusual Yellowing due to Overcast and Heavy Rain During Spring
Seemingly endless overcast and rainy weather continues to cause unusual plant responses. I have seen an unusually early yellowing and senescence of annual bluegrass in dormant bermudagrass fairways; despite no heat or drought. In an April 2019 seeded tall fescue sod field, I observed unusual yellowing (chlorosis) of young plants in straight lines.
Weird stuff, but I surmise that the yellowing of tall fescue is due to tractor tires creating depressions in a wet field when seeded. Heavy rains have caused water to inundate young plants in the tire-created depressions. The excessive wetness, combined with inordinate overcast weather, has caused flooded plants to turn yellow due to lack of sufficient soil oxygen and sunshine.
