Gary Y. Gao, Joseph F. Boggs, Pamela J. Bennett, Jane C. Martin, James A. Chatfield, Joseph W. Rimelspach, Randall H. Zondag, John R. Street, William E. Pound, Erik A. Draper, and Amy K. Stone
Weed control in lawn, nursery, and landscape settings is a major challenge every year. This report is a compilation of the 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, in 1999.
Crabgrass is present every season and was more so this year in lawns that were damaged by drought during the fall of 1998. Crabgrass seeds germinate when the temperature in the upper inch of soil reaches 50°F to 55°F for at least five consecutive nights under moist conditions. Exposure to sunlight is also critical to seed germination. This is why thin lawns are more susceptible to crabgrass infestation. The best method of crabgrass control is by applying preemergent herbicides. The application deadlines for preemergent controls are normally March 1 to April 1 for southern Ohio. For northern Ohio, dates are April 1 to May 1, and for central Ohio, they are March 15 to April 15.
During the week of April 29, crabgrass germinated in the Ohio State University turf plots in Columbus, Ohio. Once crabgrass had germinated, Dimension (dithiopyr) was recommended. Good crabgrass control was achieved when Dimension was applied prior to the three- to five-leaf to one-tiller stage. Siduron (e.g., Tupersan) was the only safe preemergent material recommended for crabgrass control in areas newly seeded this spring.
Once crabgrass passed the two- to three-tiller stage, Acclaim or Acclaim Extra (fenoxaprop-ethyl) was recommended as the postemergent product for later stages. Acclaim or Acclaim Extra can be mixed with a preemergent product as well. Drive (quinclorac) was suggested as another good postemergent control with rapid kill. It works on mature crabgrass and can be mixed with a preemergent control material. Drive can also be mixed with phenoxy herbicides (e.g., 2,4-D) for broadleaf weed control while Acclaim and Acclaim Extra can not. Drive does a good job under adverse conditions, such as dry soil.
There are several important facts about post-emergence crabgrass control. Drive, a post-emergence crabgrass herbicide, must be used with a surfactant to be effective. Methylated seed-oil surfactants should be used with Drive. When used with a surfactant at a rate of 1% volume to volume, it can be very effective. Dimension also should be used with a surfactant. A surfactant is not necessary when using Acclaim. Drive, when mixed with any of the broadleaf herbicides, could cause discoloration. However, turfgrass does recover. Mixing these herbicides does not affect their efficacy.
The development and maintenance of a dense, healthy stand of grass is the best way to reduce the incidence of broadleaf weed problems. It is important to identify the weed(s) that you are attempting to control, since not all weed species are controlled by using one specific herbicide. The most readily available chemicals to homeowners for selective, post-emergence control of broadleaf weeds include 2,4-D, 2,4-DP, MCPP, and dicamba. These chemicals can be found in various combinations with each other. Combination products are recommended for difficult-to-control weeds or when a variety of weed species is present in the lawn. Examples of very effective product combinations are Cool Power (dicamba + MCPA + triclopyr,) and Super Trimec (2,4-D + 2,4-DP + dicamba.) Both of these products are ester formulations. All of these chemicals are safe for use on Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue lawns if the label directions are followed. MCPP is the safest of the listed herbicides to use on bentgrass lawns.
Spring herbicide applications should be made from mid-April through early June, and fall applications should be made during the months of September and October. Herbicide formulation plays a major role in determining the success or failure of broadleaf weed control in the spring. Weeds tend to absorb and translocate ester formulations more readily than amines under the cooler, more erratic weather conditions of early spring. Amines are more effective later in the spring when air and soil temperatures are warmer. In general, both amine and ester formulations may exhibit poor weed control before late March. Ester formulations may provide good-to-excellent weed control in the first three weeks in April and be superior to amine formulations. However, the effectiveness of amine formulations may equal that of esters from about late April and beyond.
Postemergent herbicides should not be applied if rain is expected within 24 hours of application; nor should the grass be mowed or watered within 24 hours of application. Please note that drift from herbicide applications can damage or kill non-target plants and that dicamba should not be applied within the dripline of trees or shrubs. Dicamba can be root absorbed by these plants, possibly resulting in damage.
Gallery, Factor, Princep, Surflan, Treflan, Pennant, Devrinol, and Goal are a few examples of preemergent herbicides. They were recommended to be applied to soils of nursery and landscapes in mid April. These products prevent weed seeds from germinating, but most have little, if any, post-emergence control. After cool season weeds such as mustard, hairy bittercress, chickweed, ground ivy, and speedwell emerged, mechanical or postemergent control were recommended.
Dodder (Cuscata spp.) is a common plant parasite that infests various kinds of wild and cultivated plants. This wiry, yellowish-orange annual plant looks like a bunch of tangled-up yellow fishing line. The color comes from the fact that dodder lacks chlorophyll and functions as a parasitic plant. Dodder weakens plants by taking nutrients from the host as it intertwines. In addition, dodder acts as 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.
Several preemergent herbicides are labeled, but applications must be made in the spring, and control has been reported as only "fair." 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 picking it off the plants or removing the plants it has infested.
Lontrel herbicide was released to the turf and limited ornamental market. It had also been known as Stinger, a post-emergent broadleaf weed control herbicide. Ornamentals listed on the label include flowering dogwood, fir, pine, spruce, some oaks and maples, arborvitae, juniper, some boxwoods, and azaleas. It is most useful in controlling weeds such as thistle, clover, galinsoga, curly dock, vetch, ragweed, and many others. This product does not control grasses.
Lontrel Turf and Ornamental can be used in a backpack sprayer, as well as a large commercial sprayer. Lontrel may be sprayed over the top of some crops, mostly evergreens. If soil is too dry to apply preemergent herbicides and you do not want to cultivate, Lontrel may be one product to assist in controlling-fall germinating broadleaf weeds in your field operations. It is not registered for use on container plants.
Application rates vary from 0.25 lb./acre to 1.33 lb./acre. Read the label before purchasing the product, and conduct your own trial before using it in a regular program.
Herbicide injury symptoms can mimic many symptoms caused by poor cultural practices, environmental stresses, fungal diseases, insect damage, nutrient deficiencies, soil pH imbalances, and viral diseases. There is a wide variety of herbicides, with very different modes of action.
Some of the herbicide families include amino acid synthesis inhibitors, cell membrane disruptors, growth regulators, lipid synthesis inhibitors, photosynthetic inhibitors, and seedling growth inhibitors. Correctly diagnosing herbicide damage takes many years of working knowledge in the field. Some laboratories will test soil samples for herbicide residues, but the procedure can be expensive. For some of the newer herbicides, a lack of information in general may preclude meaningful interpretation of test results.