Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityFebruary, 1997
Those Awful Weeds!
Keywords: container production, field production, herbicides, landscape maintenance, nursery, weed control
I travel around the state giving pesticide applicator recertification talks about weed control. After about a year and a half of doing this, I finally realized I was getting the same questions over and over again! I can tell you that most of these questions really stumped me the first dozen times or so that I heard them, but I learn fast, and Iām proud today to offer some solutions to OHIOāS WORST, WICKED, AND DESPICABLE WEEDS! Most of these solutions are postemergence herbicides, useful for existing weed problems.
Poison Ivy. Poison Ivy is a woody vine that is generally loathed by all and very difficult to control. Roundup Pro does a good job on this weed late in the season (late August, early September) when all perennial plants are actively translocating substances downwards to the roots. Several applications will be necessary. For early-season control, Garlon works better. Garlon, however, is not labeled for direct use in ornamental plantings but may be used in non-crop areas around buildings and wooded or brushy areas near the nursery. Garlon is very useful for the control of many brushy weed species. It is also effective in killing off crown vetch that has escaped.
Field Horsetail. It came as a complete surprise to me that this primitive, spore-bearing plant is a weed problem in Ohio. I have seen it growing wild only once, as a student at Miami University. Apparently many people know this weed all too well! It is usually found in wet, coarse soils. The reproductive shoots of this plant are jointed and unbranched, about 3/8ä in diameter. The non-fruiting shoots are much finer and Īfernyā in appearance, with branches in whorls around the main stem. Casoron is the best control option, but may only be used in certain woody ornamentals during the cool season. Otherwise, Roundup is sometimes used, but is not particularly effective. Casoron should not be used in wet sites where the water drains into other areas, since this chemical may travel and cause injury to non-target plants.
Yellow Nutsedge. Yellow nutsedge can be controlled prior to emergence in the spring with Pennant. Basagran T & O does a good job of controlling the weed post-emergence, but at least two applications will be necessary. Manage is a turf herbicide which recently has had some ornamentals added to its label. Manage does a good job on the nutsedge in turf, and may become an important chemical for ornamental use if the label continues to be expanded. Manage is also labeled for control of field horsetail, but I have not yet observed its use on this weed.
Canada Thistle. Stinger is probably the most effective chemical for thistle control, but its use is limited to conifers and non-crop areas around the nursery. Casoron can be used to control the weed in many woody ornamentals in the cool season. Basagran T & O controls a variety of broad-leaf weeds and can be used as an over-the-top spray in the following three ground covers: English ivy, pachysandra, and liriope. However most ornamentals, particularly conifers, can be injured by Basagran, thus with the exception of the three groundcovers it must be used as a carefully directed spray. Since Basagran is primarily a contact herbicide, Canada thistle is more likely to be suppressed by it than killed.
Probably most landscapers confronted with Canada thistle will find that none of the above scenarios conform to their situation. Whatās left? A selective, wipe-on application of Roundup Pro is the remaining option. Only a small amount of concentrated Roundup Pro (30 to 50% solution) need be wiped on the foliage using a sponge- or wick-applicator. Be careful the applicator doesnāt drip!
Bindweed. Bindweed is bad news because it wraps itself tightly around desirable plants. Just imagine making a selective application of Roundup - not likely! Try pulling this perennial weed, and it sprouts from root pieces left in the ground. Casoron used in the cool season is probably the best chemical option, but as noted above, Casoron is labeled only for selected woody ornamentals.
Grassy weeds in beds. Today we have several products that provide excellent control of grassy weeds in ornamentals. Even better, these products are safe for use over-the-tops of many ornamental plants. Fusilade, Vantage (formerly Poast), Prism, and Acclaim are all translocated post-emergence herbicides. All are good on annual grasses; the first three are effective on some perennial grasses, but usually more than one application will be necessary for perennial control.
Bittercress in containers and other winter weeds. Bittercress is a small, white-flowered weed that has a mechanism to shoot seeds from container to container. This weed can take over container houses in the fall, winter, and spring. A number of preemergence herbicides have this weed on their label: Ronstar, Gallery, OH-2, Devrinol, Snapshot, Surflan, and Pendulum. According to Larry Kuhns, 1997 Short Course Speaker & Penn State University Specialist, Ronstar is the best. However, the secret to controlling this and other winter weeds is more than just finding a good preemergence chemical. First clean up the container houses, - once well-established in the gravel of a polyhouse, itās nigh impossible to keep bittercress out of the containers. Use Surflan to provide preemergence weed control for the floors of the house. Where gravel has sunk into the muck and provides a nice place for weeds to grow, replace the gravel, or use weed control mats or plastic as house-floor coverings. Finally, a fall application of preemergence herbicide should be made to weed-free containers. Make this application as close as you are allowed by the label to house covering. No preemergence herbicides are labeled for use after covering. Generally there must be some period of time, or several sets of irrigation between herbicide application and house covering.
Weed control in greenhouses. This problem was touched on in the previous paragraph. While I recommend Surflan for preemergence control in polyhouse floors, I know of no preemergence chemical currently labeled for use in greenhouses. A distinction between open-type houses (polyhouses) and greenhouses is clearly made on the Surflan label, and the product is labeled only for the open-type. However, several postemergence products may be used in greenhouses. According to the label, Roundup Pro may be used in the greenhouse when desirable vegetation is not present and fans are turned off. Scythe, a contact herbicide, is the only chemical I know of that may be used as a directed spray under benches when the crop is in place. Even more interesting: it may be used as a directed spray to the base of woody container plants. However, any remaining green stems or leaves will be injured by Scythe.
Finally, thereās a few weeds that I am frequently asked about, but unfortunately lack chemical options to control them in ornamentals, - wild onion or garlic, violets, and star-of-Bethlehem, a small bulb. However, there are some turf herbicides that provide control. If you choose to use these chemicals, they canāt be used directly on ornamental plants, and must be used with care near them. Wild onion may be controlled with 2,4-D. Violets may be controlled by Garlon (Turflon is the same chemical as Garlon) or Confront. Star-of-Bethlehem can be controlled with Banvel. All of these chemicals must be carefully applied to prevent drift from reaching foliage of any desirable ornamentals. Although they are more effective, avoid using ester formulations of 2,4-D and Garlon near ornamentals because the potential for injury is greatest with this formulation. Banvel (dicamba) is also soil active; avoid using the product where the roots of ornamentals grow. Banvel is one of the most commonly used lawn chemicals, but nonetheless it has the potential to injure ornamentals growing in turf.
A word about the 1997 OSU Nursery Short Course. Two-thousand, seven-hundred, and twenty-nine people attended this yearās Short Course, and this figure does not even include the C.E.N.T.S. exhibitors that received complimentary passes. Iād like to salute members of this industry for their commitment to continued education, which is obvious from the level of participation in this yearās Short Course! Iād also like to thank the Extension-Nursery-Landscape-Turf Team and the O.N.L.A for helping make the program run smoothly.
