Gary Y. Gao
Barbara Bloetscher
Joseph F. Boggs
Pamela J. Bennett
Jane C. Martin
Joseph W. Rimelspach
Randall H. Zondag
John R. Street
Erik A. Draper
Amy K. Stone
Weed control in lawn, nursery, and landscape settings is a major challenge every year. This report is a compilation of noteworthy weed problems and their controls discussed during the Buckeye Yard and Garden Line (BYGL) phone conferences that occurred weekly on Tuesdays, from April to October 2000.
Crabgrass seeds germinate when the temperature in the upper inch of soil reaches 50ºF - 55ºF for at least five consecutive nights under moist conditions. Exposure to sunlight is also critical for seed germination, and this makes thin lawns more susceptible to crabgrass take-over. The application date recommendations in 2000 were March 1 to April 1 for southern Ohio; March 15 to April 15 for central Ohio; and April 1 to May 1 for northern Ohio.
During the week of May 25, crabgrass had begun to tiller in Columbus. Products such as Dimension, which has pre and post control, or Acclaim Extra and Drive, which have good early post control, were recommended. Both Acclaim Extra and Drive are foliar absorbed, so care must be taken to apply on a dry, windless day, when crabgrass is actively growing, and no rainfall is expected for 6 to 12 hours. While Acclaim Extra contains a surfactant, Drive must have a surfactant added. Best efficacy has been obtained with methlylated seed oil or crop oil concentrate. Always follow label directions.
During the week of June 8, crabgrass reached the two- to three-tiller stage in many areas of Ohio. At that point, crabgrass was much more difficult to control. Drive was recommended since it has excellent early post (one to two tiller) and late post (five-plus tiller) control, but is less effective at this time. Although Acclaim may kill the crabgrass at the two- to four-tiller stage, it cannot be combined with a phenoxy broadleaf weed killer to control broadleaf weeds and may cause phytotoxicity in lawns if turfgrass is stressed.
A sample of roughstalk bluegrass was sent to the Ohio State University Plant Pest Diagnostic Clinic in July as its prostrate, fast-growing habits became more obvious in Kentucky bluegrass lawns. Roughstalk bluegrass is a darker, greasy looking blue-green and can be distinguished from Kentucky bluegrass by the long, lax stems that root at lower nodes. Preferring shady, moist areas, it will quickly grow over other grasses and may ultimately move into sunnier areas. In the summer, when the soil surface dries, roughstalk bluegrass wilts and turns brown. These brown areas routinely alarm homeowners and lawn care professionals, who think "the lawn is dying." Controlling this grassy weed is difficult as only non-selective, systemic herbicides work, which obviously kills desirable turf as well.
Yellow nutsedge began to exhibit its three-sided stem in flower beds and lawns during the third week of June. Halosulfuron (e.g., Manage) was recommended for the selective, postemergent control of this perennial weed. If Manage is not available, bentazon (e.g., Basagran) can also limit this weed in turf.
Dandelions were in "puffball" stage in southwestern Ohio and in full bloom in central Ohio during the week of April 20. It was the perfect time to treat for dandelions in southern Ohio. Recommended chemicals were those containing 2,4-D, or dicamba, or MCPP, or a three-way combination. Examples of effective product combinations are: Cool Power (dicamba plus MCPP plus triclopyr) and Super Trimec (2,4-D plus 2,4-DP plus dicamba). Both of these products are ester formulations. All of these chemicals listed are safe for use on Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue lawns, if label directions are followed. MCPP is the safest of the listed herbicides to use on bentgrass lawns.
Canada thistle was reported to be a serious problem in myrtle and blue rug juniper beds. Canada thistle (Cirsium arvense) is an aggressive, creeping, perennial weed. One plant can colonize an area 3 to 6 feet in diameter in one or two years. Canada thistle develops from seed or vegetative buds on rhizomes. Rhizomes may extend 15 feet or more and may grow 6 to 15 feet deep. Small root pieces, 0.25" long by 0.125" in diameter, have enough stored energy to develop new plants.Also, these small roots can survive at least 100 days without nutrient replenishment from photosynthesis.
Canada thistle is one of the most difficult weeds to control. Multiple applications of labeled herbicides in combination with cultural and/or mechanical control provide more effective control. One recommendation for control was to use wick applicators to target control. It is possible to use rubber gloves, with a thick cotton glove on top of the rubber glove. Wet the cotton-gloved hand in a bucket of Roundup solution, squeezing the hand lightly upon removing it from the mix. Then grasp the weed at the base and slide it through the glove, up to its top. This effectively puts the Roundup mix on the weeds and avoids getting it on desirable plants.
Basagran T & O is labeled for over-the-top sprays of junipers, but not myrtle. This material burns back the thistle and doesn't translocate much, so repeated sprays are necessary. If it could be spot sprayed on the myrtle, and if a certain amount of injury is allowable, that could work in this situation.
By far the best product for Canada thistle control is Lontrel (clopyralid). Junipers are on the label, however; for landscape use, apply it as a directed spray. Here again, perhaps the thistles could be spot sprayed, and some possible injury to myrtle tolerated.
There was a bumper crop of galinsoga in vegetable gardens in 2000. The common names of galinsoga include gallant soldier, quickweed, or water weed.
Galinsoga has become an important and serious weed affecting many low-growing vegetables such as cole crops, salad crops, onions, peppers, and many vine crops. It is an erect, multi-branched annual growing to a height of two feet. The upper parts of the plant have slender, slightly hairy stems. Galinsoga is a member of the Compositae family and has several small flower heads at the end of each branch. Each flower head has four or five white ray flowers surrounding numerous yellow disk flowers.
Pre-emergent herbicides applied to the vegetable garden earlier in the spring would have provided effective control, but mechanical removal was the only option after seeds had germinated.
As usual, poison ivy was reported to be quite a problem this year. It has a characteristic compound leaf consisting of three dull or glossy green leaflets with pointed tips. The 2"- to 4"-long leaves are arranged alternately on the stems. In contrast, Virginia creeper, a nonpoisonous vine often mistaken for poison ivy, has five leaflets.
Three methods were recommended to eradicate poison ivy in ornamental beds. They included hand (gloved) pulling or grubbing when the soil is moist; severing the vine and then treating the regrowth with a herbicide; or applying an herbicide to individual leaflets. Care should be taken to remove the entire root because the plant can re-sprout from sections of root left in the ground.
Avoid skin contact by wearing gloves while you work and washing clothing and gloves immediately after. The washing machine should be rinsed thoroughly afterward to eliminate the possibility of contaminating other clothing.
Vines growing on trees can be difficult to pull out of the ground because their roots may be entangled with the tree roots. Sever the vine at the base and carefully pull it off the tree. Glyphosate (e.g., Roundup or Ortho's Kleeraway Grass and Weed Killer), a nonselective, translocated herbicide, can be applied to the new shoots that will soon emerge from the base of the old plant.
This herbicide is most effective if applied to actively growing foliage two weeks before or after full bloom, in early summer. Repeat applications to treat regrowth may be necessary. Other herbicide brands or formulations may be found at your local garden center. Be sure to read the label to ensure that poison ivy is listed on the label, then follow the manufacturer's directions.
Numerous phone calls concerned mushrooms in lawns and gardens. Fairy rings produced the diagnostic circle of mushrooms in lawns associated with a darker green ring of turf. These mushrooms arise from a ring of mycelium breaking down organic material in the thatch or soil. This moldy white mass of matted material may extend 8" deep into the soil or more, and may become so dense that the soil becomes hydrophobic and will not absorb water, causing the turf to die. Occasionally the fungi will release a chemical that will prevent the turf from recovering, so that the soil must be replaced.
This ring will continue to expand several inches per year. The ring can be masked by applying a balanced fertilizer and watering the lawn, but if long-term management is needed and the turf is continually wilting, core aerate extensively, and pump water 12" to 24" deep into the soil at one foot intervals just inside the ring of dead grass. When the turf wilts again, repeat the water pumping process.
Stinkhorns and other unusually shaped fungi often alarm homeowners due to their color, shape, and odor; however, they, too, are helping the environment by breaking down organic substances in the soil. Stinkhorns originate from a white sack in the ground that produces a spongy, pointed, pink or creamy orange "stem." They look something like a miniature rocket. Their odor is quite pungent and unpleasant, especially as the liquid dark olive to black spore mass is produced at the tip. Again, these can be left alone or removed by mowing or digging out.
A quick note to applicators who are not getting the degree of control expected from pesticides: You might check the pH and hardness of the water used to mix sprays. High pH water sources can reduce the effectiveness of pesticides. There are products on the market that will help buffer water to prevent this problem.
Every year an interesting incident happens that reminds us of the importance of reading pesticide labels. This year's example: There were several phone calls from concerned homeowners whose lawns died following an application of a "weed and feed" product. It contained atrazine, an herbicide commonly used in field corn for grass control. The product was correctly labeled for turfgrass use as a weed-and-feed product. However, the label indicated "for use on warm-season grasses (e.g., centipede, zoysia, and carpet grass) in the Southern United States," not the Midwest! In fact, the label specifically stated that the product should not be applied to Kentucky bluegrass, bentgrass, fescue, or ryegrass lawns.
Well, what happened? The product had been improperly bar coded and shipped to Ohio. Simply reading the label would have been a lawn-saver in this case. Although not common, this product mix-up has happened before in Ohio. It once again demonstrates the extreme need for both garden center employees and customers to read the label before recommending or using any chemical.
1. Kuhns, L. and M. A. Rose. 1998. Ohio State University Extension Bulletin 867. Controlling Weeds in Nursery and Landscape Plantings.
2. Boehm, M. J., W. E. Pound, J. W. Rimelspach, D. J. Shetlar, J. R. Street. 2000. Ohio State University Extension Bulletin L-187. Management of Turfgrass Pests.