Gary Y. Gao, Joseph F. Boggs, Pamela J. Bennett, Jane C. Martin, James A. Chatfield, Mary Ann Rose, Joseph W. Rimelspach, Randall H. Zondag, John R. Street, and William E. Pound
Weeds such as crabgrass, roughstalk bluegrass, yellow nutsedge, dandelions, Canada thistle, poison ivy, ground ivy, common purslane, galinsoga, and pokeberry were reported to cause major problems in Ohio landscapes and nurseries. This report is a compilation of the noteworthy weed problems and their controls discussed during Buckeye Yard and Garden Line (BYGL) conferences that occurred weekly, from April to October, in 1998.
Because of warmer than normal temperatures in March, many lawn-care professionals called Ohio State University turf specialists concerning the cutoff dates for applying preemergent herbicides to control crabgrass. The approximate dates for this application are estimated to be March 1 to April 1 for southern Ohio, March 15 to April 15 for cen-tral Ohio, and April 1 to May 1 for northern Ohio. During the second week of April, the OSU Extension turf specialists indicated that those dates were right on the mark after taking soil temperature readings in Columbus.
The first crabgrass seedlings of spring 1998 were spotted on April 17 at Ohio State's Turf Research facility in Columbus. At that time, the crabgrass seedlings were in the single-leaf stage and were only found in bare spots and areas of limited turfgrass cover. Once germination begins, it generally continues over the following 10-12 weeks. Annual grass weed control products such as pendimethalin, Team, Dimension, and Barricade will generally provide 100 or more days of residual control, assuming the treatments were properly applied and timed.
Crabgrass reached the three- to five-leaf to first-tiller stage in central Ohio in the second week of June. Two products are recommended for postemergent control by professional applicators. Dimension (dithiopyr) can be applied for a short period and is effective until the first-tiller stage. MSMA can be used for one- to three-tillered crabgrass. Acclaim and Acclaim Extra (fenoxaprop-ethyl) provide control as late as the two- to three-tiller stage. Soil moisture must be adequate for rapid growth of both crabgrass and turf. A word of caution with Acclaim; the turf can be discolored and/or stunted if the applicator overapplies the product and if soil moisture is low.
Roughstalk bluegrass, a light, apple-green colored grass, is generally found in damp and shady areas. It has a tendency to mat down, has a musty odor, and is stoloniferous. Roughstalk bluegrass went dormant and turned brown with high temperatures in early July of 1998. Even with adequate irrigation, this species has a tendency to go dormant during hot periods but resumes growth with the return of lower temperatures. In 1998 there were many reports of brown areas in home lawns and golf courses that were, in fact, Poa trivialis.
Yellow nutsedge "stuck out like a sore thumb" in many lawns in 1998. Nutsedge is easy to identify; the stems are erect, triangular in shape, and yellow-green in color. Blades are about one-half inch in width and have a thick mid-vein and waxy coating. Nutsedge produces many nut-like tubers and rhizomes, which, in turn, produce new plants.
Unlike other lawn weeds, this weed is a member of the sedge family and requires the use of specific herbicides for satisfactory control. Nutsedge should be controlled when it is at the three- to eight-leaf stage and actively growing. Two professional products are available for use. Bentazon (i.e., Basa-gran) requires thorough leaf coverage; delay mowing for three to five days after application. Add a spreader-sticker for improved efficacy. A repeat application may be needed 10 to 14 days later. Halosulfuron (i.e., Manage) can be applied at the three- to eight-leaf stage; use a surfactant as directed. Total kill occurs in three to five weeks.
Dandelions were in full bloom in southern Ohio by the second week of April. Most homeowners are usually anxious to apply herbicides to dandelions when they see them. However, for effective control, applications of postemergence chemicals should wait until dandelions reach the early puffball stage. Recommended chemicals include those containing 2,4-D, dicamba, or MCPP, or a three-way combination. These herbicides also provide good control of chickweed.
Canada thistle, a prolific seed producer, was visible in landscapes across Ohio in April. It propagates 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. But timing is everything and on a practical basis, this is difficult to accomplish. Herbicides can save a lot of labor. A 2% solution of glyphosate (e.g., Roundup) is effective, but usually more than one application is necessary. In landscape beds, glyphosate needs to be applied selectively with a wick applicator or some other method of wiping it on, using at least a 30% solution. Bentazon (Basagran) does a fair job on Canada thistle, while dichlobenil (Casoron) provides control in some woody ornamentals.
Poison ivy was in full bloom in Columbus during the second week of May. The clusters of delicate, cream-colored flowers are attractive. However, it pays to be able to identify this plant and avoid it. Poison ivy has a characteristic compound leaf consisting of three leaflets, two- to four-inches long, and dull or glossy green with pointed tips. The leaves are arranged alternately on the stems. In contrast, Virginia creeper, a nonpoisonous vine often mistaken for poison ivy, has five leaflets radiating from one point of attachment.
Three methods were recommended to eradicate poison ivy in ornamental beds. They include hand (gloved) pulling or grubbing when the soil is moist; severing the vine and then treating the regrowth with a herbicide; or applying a herbicide to individual leaflets. Glyphosate can be applied to new shoots that emerge from the base of old plants. Repeat applications to treat regrowth may be necessary.
Ground ivy was reported to "grow like mad" in home lawns in early August. Ground ivy is also called gill-over-the-ground and creeping Charlie. This perennial member of the mint family is a weed problem in turf and ornamentals. It has a blue flower and a distinctive odor when the leaves are crushed. One of the better identification features is the scalloped edge of the round leaves. Acting as a vine, it moves across grass areas, rooting from the nodes as it travels. Application of herbicides containing 2,4-D, dicamba, or MCPP, or a combination of these materials, will provide good control, but do not apply these materials when temperatures are above 85°F.
Purslane is a summer annual with opposite leaves. Each pair of leaves is rotated around the stem 90 degrees from the previous pair. Leaves are wedge-shaped and taper toward the base, and are thick, fleshy, and glabrous. Stems are prostrate and reddish. Mechanical removal of the weed is the best option.
Galinsoga was a common weed in vegetable gardens this year. Its other common names 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. Galinsoga 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 Composite family, which has many flowers grouped together so that they appear to be a large single flower. Galinsoga 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.
Gardeners, landscapers, and nature buffs found pokeberry or common pokeweed growing in rich, low-ground pastures, along roadsides and borders of fields, and as an occasional weed in landscapes. This large perennial can grow as high as nine feet from its thick, fleshy taproot, with green or reddish branching stems. Leaves are alternate on the stem, oblong in shape with entire margins, and lower leaves can be a foot in length. Flowers form on branched racemes at or near the ends of stems, and the fruit is a dark purple, many-seeded berry with red juice. Fruit ripens in August.
Pokeberry is a poisonous plant; all parts are considered poisonous. The raw berries are attractive to children, but are highly toxic and potentially fatal. This is a plant gardeners and landscapers should eliminate from properties, if found, to avoid unfortunate incidents.
BYGL readers were reminded that Roundup Pro is not the same as Roundup. The new Roundup Pro is Roundup with a surfactant that makes the product work faster on targeted plants. Many users are finding that Roundup Pro is causing damage to plants where the Roundup did not. It is suggested that anyone using Roundup Pro should target and apply the product ONLY to the plants to be controlled. The surfactant increases penetration of the active ingredient through any green tissue, including young bark.
Roundup Pro injury to plants resulted in stunting and discoloration. In some plants, where buds are treated, they may never grow out of the injury. Over-the-top applications with this product are not recommended. Prevent drift and only mix suggested levels of the product at label rates. Do not apply this product to the point of run-off.
Greenview's Preen is a pre-emergent granular herbicide used in many garden settings. There are now three granular products for homeowners in this line.
Professional Preen is a fourth product in the line for professional landscapers and nursery operators. Professional Preen (2.5G) contains 2.0% trifluralin + 0.5% isoxaben. This product contains the same active ingredients as Snapshot 2.5G.
Another new granular product is Pre Pair, a granular herbicide that contains 4% napropamide + 2% oxadiazon. Products that have been cancelled and will be available only as long as supplies last include Dacthal and DeMoss.
1. Kuhns, L., T. Harpster, M. Rose, and S. Guiser. 1998. Ohio State University Extension Bulletin 867. Controlling Weeds in Nursery and Landscape Plantings.
2. Pound, W., D. Shetlar, J. Rimelspach, and J. Street. 1998. Ohio State University Extension Bulletin L-187, Management of Turfgrass Pests.
3. North Central Regional Research Publication No. 281. Weeds of the North Central States.
4. Herbicide Damage CD. Mike Dana and others at Purdue University developed a new CD titled "Picture the Damage! Herbicide Damage Symptoms on Ornamentals," which has more than 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.