Gary Y. Gao
Joseph F. Boggs
Pamela J. Bennett
Jane C. Martin
Mary Ann Rose
Joseph W. Rimelspach
Randall H. Zondag
William E. Pound
Crabgrass, dandelions, Canada thistle, poison ivy, garlic mustard, annual bluegrass, and dodder were reported as some of the weeds to cause problems to Ohio landscapes and nurseries in 1997. This report is a compilation of the noteworthy weed problems discussed during Buckeye Yard and Garden Line (BYGL) conferences that occurred weekly, from April to October in 1997.
There were some concerns about inadequate crabgrass control in 1997 due to the wet weather. Preemergent herbicide effectiveness may have been reduced due to heavy rains in May and June. By the week of July 31, heavy crabgrass infestations were noted.
Dandelions started blooming in some parts of the state during the second week of April, but clientele were reminded that it was still too early to apply post-emergence herbicides which are most effective in the early puffball stage.
Canada thistle emerged in landscapes across Ohio during the second week of May and bloomed in mid- to late-June. This weed is a prolific seed producer. The weed also propagates itself from underground rootstocks and will sprout from any root pieces left after weeding. Theoretically, it can be eradicated by hand-pulling or mowing at least three times a season - June, August, and September.
Problems with poison ivy are reported every year, and 1997 was no exception. Poison ivy is a woody vine that has a distinctive compound leaf consisting of three leaflets, two- to four-inches long, dull or glossy green with pointed tips. The middle leaflet is generally larger than the two laterals. The margins of the leaflets are variable, appearing irregularly toothed, lobed, or smooth. The leaves are arranged alternately on the stems. In contrast, Virginia creeper, a non-poisonous vine often mistaken for poison ivy, has five leaflets radiating from one point of attachment. It may also be mistaken for boxelder seedlings, but boxelder has opposite leaves instead of alternate.
In May, BYGL participants noted that this weed was in bloom in central Ohio. This relative newcomer to Ohio landscapes has aggressively spread throughout much of the Midwest, the eastern United States, and Canada. Garlic mustard is biennial, forming a basal rosette of kidney-shaped leaves in the first year, and flowering stalks, one- to four-feet in height, the following spring. Clusters of unexciting, small, white, four-petal flowers appear April through June. The leaves on the flowering stalks are triangular or heart-shaped and coarsely toothed. When crushed, the leaves have a pervasive smell of garlic. Ecologists and wildflower enthusiasts are concerned about the weed because it forms large stands to the exclusion of native wildflowers. Garlic mustard favors shaded, disturbed sites, but apparently is able to move into undisturbed woodland communities.
There were an unusual number of complaints regarding annual bluegrass in lawns in 1997. This weed is an apple-green colored annual grass that tolerates all mowing heights and grows vigorously in cool, moist weather, often forming extensive patches. It is considered a weed because of the different color and the fact that during hot, dry weather, it dies and leaves turf with unsightly bare areas.
People may be confused by the fact that Kentucky bluegrass and Poa annua produce seedheads around the same time, possibly masking diagnosis. The color of annual bluegrass makes it fairly easy to spot in a bluegrass lawn. One other factor, to make things even more confusing - it has been determined that there are some bio-types of the weed that behave like a perennial. These patches go dormant during hot, dry spells but come back in cooler weather.
Dodder was reported to have parasitized herbaceous perennials in 1997. This unusual weed may infect other wild and other cultivated plants. This wiry, yellowish-orange annual plant has the appearance of a 'bunch of tangled-up yellow fishing line.' Dodder lacks chlorophyll and functions as a parasitic plant, stealing nutrients from the host plant it covers. Dodder may be a vector of some hard-to-transmit diseases.
Although it is categorized as a broadleaf weed, dodder lacks leaves. This, coupled with its growth habit, makes postemergent control all but impossible. Dodder is a prolific bloomer and produces small white flowers borne in clusters. Hand-pulling the plant during the bloom stage will reduce seed production for the next season. To control dodder in the garden, try to pick it off the plants or kill the plants it is infesting.
W. Pound, D. Shetlar, J. Rimelspach, and J. Street. 1997. Ohio State University Extension Bulletin L-187, Control of Turfgrass Pests.
North Central Regional Research Publication No. 281, Weeds of the North Central States.
Herbicide Damage CD. Mike Dana and others at Purdue University have developed a new CD titled Picture The Damage! Herbicide Damage Symptoms on Ornamentals, which has over 500 four-color images of herbicide damage from 12 different herbicides on 21 different ornamental plants. The cost of the CD is $39.95. For information and to order, contact the Agricultural Communication Service, Media Distribution Center, 301 South Second Street, Lafayette, IN 47901-1232. Phone: 317-494-6794; FAX 317-496-1540.