Weeds such as crabgrass, rough bluegrass, wild violets, field horsetail, ragweed, dandelions, and poison ivy were reported to cause major problems to Ohio landscapes and nurseries. Mosses, mushrooms, and puffballs were also prevalent. In addition, there were several important changes in herbicide labels and a few new herbicide formulations. The article is a compilation of weed control notes from 1996.
Weeds presented serious problems to Ohio landscapes and nurseries in 1996. Weeds thrived in response to the cool and wet spring. Wet spring conditions may have led to difficulties in applying herbicides in a timely fashion and may have reduced the persistence of chemical controls in the landscape and nursery.
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 1996.
During the week of May 9, 1996, we reported that wet cool weather impeded control of broadleaf weeds in lawns and that repeat herbicide applications would be needed to bring weeds under control. Lawn areas that were stressed last season, such as areas along driveways, sidewalks, and curbs, were filling in nicely with a variety of weeds, and control was not achieved until later in the season.
In nurseries, we reported during the week of June 27, 1996, that serious failure of pre-emergent weed control materials in northeast Ohio had occurred. Since weeds had germinated, nursery managers were given three options:
In landscapes, there was a crabgrass explosion in June. Warmth and moisture in May to early June produced a bumper crop of crabgrass in ornamental beds in 1996. Post-emergent grass herbicides such as Fusilade (fluazifop-P-butyl) or Vantage (sethoxydim) were recommended to help clean up the problem. The advantage of these herbicides over non-selective herbicides like Roundup (glyphosate) is that they may be used over the tops of many ornamentals.
During the week of April 4, 1996, we suggested that there was still time to apply pre-emergent crabgrass controls across the state of Ohio. (Refer to the current OSU Extension Bulletin L-187 for labeled materials for crabgrass control.) The generally recommended treatment deadline for Ohio is: southern - April 7; central - April l6; and northern - May 1. However, since spring temperatures remained below normal across most of Ohio, the timing of pre-emergent controls for crabgrass in 1996 was modified as follows:
Southern Ohio - April 18/April 20-25
Central Ohio - April 20/April 25-30
Northern Ohio - May 1/May 8-10
During the week of April 4, 1996, it was reported that although lawns were beginning to green-up, rough bluegrass was already intensely green and giving lawns a "patchy" appearance. This cool season grass grows best from about early April until June. It prefers cool, moist conditions and is sometimes seeded into moist, shaded areas where it performs reasonably well. In full sun, rough bluegrass performs poorly. However, its early season surge coupled with a prostrate, vigorous, creeping growth habit often allows it to establish distinct patches within stands of preferred grasses.
Control of perennial rough bluegrass is difficult. A non-selective, post-emergent herbicide (e.g., Roundup or Finale) is required and multiple applications are needed. Applications should be started in late spring while the rough bluegrass is still vigorously growing. The application target area should extend 1-2 feet beyond the patches in order to kill advancing rough bluegrass stolons.
Wild violets were reported to degrade home lawns during the week of May 2, 1996. Wild violets are one of the most difficult weeds to control in the lawn. This perennial weed can persist in lawns indefinitely because of branching rootstocks and, in some species, stolons. Many species are well adapted to moderate shade conditions, but some will also establish and persist in sunny areas.
In June 1995, a wild violet control evaluation was conducted at Ohio State University. Herbicides evaluated in this study included 2,4-D, MCPP, 2,4-DP, dicamba, triclopyr, and clopyralid. Data collected seven weeks after treatment showed the phenoxy herbicides (2,4-D, MCPP, and 2,4-DP) and dicamba only provided 18.3% - 30.0% control following a single application. The best control of wild violet was achieved from two treatments containing tricloyr. The triclopyr + clopyralid and triclopyr treatments resulted in 73.3% - 81.7% control, respectively.
Homeowners wishing to control violets have a few options. First, wild violets can be eliminated from a lawn with repeated hand pulling or digging. Secondly, homeowners may use phenoxy herbicides; this will require numerous repeat applications over an extended period of time. The best option for homeowners is to hire a commercial lawn care firm to apply herbicides containing triclopyr. This product is available in DowElanco's Turflon Ester and Confront. Best control is achieved using triclopyr in liquid spray applications applied to runoff. Proper timing of application is between late April and mid-June or early September to mid-October.
Field horsetail, a very troublesome weed, was discussed during the week of June 6, 1996. It is also called "scrub weed" and is a botanically interesting, but difficult to control weed, with an affinity for wet places. Because horsetail has an odd habit of accumulating silicon in cell walls, early settlers found the weed useful for scrubbing pots and pans. This primitive, spore-bearing plant also has been found in ancient fossils. But, all of this is small consolation to the nurserymen who are trying to eradicate this weed. Farmers don't like it either, because the plant is toxic to livestock.
Roundup (glyphosate) is sometimes recommended for control of this weed, but it hasn't been very effective. Repeated applications may help. Control has been achieved with applications of Casoron (dichlobenil), a soil-applied herbicide that is taken up by roots. However, a disadvantage with this chemical is its volatility in warm seasons. Its use is recommended for late fall and winter applications, as a soil surface or as incorporated treatments, or as a spring incorporated treatment. Incorporation can be achieved by shallow cultivation or irrigation. Six pounds of the active ingredient dichlobenil per acre will provide effective control of horsetail. For example, if you are using a 4G product (4% granule), this would translate into 150 pounds of product per acre, or 3.5 pounds per 1,000 square feet. Dichlobenil will move in the soil and down slopes, so it is important to keep this in mind when using this chemical. Many wet areas where the weed thrives may not be appropriate sites for using dichlobenil, particularly if they drain into an irrigation pond!
During the week of April 25, 1996, we reported that dandelions were blooming heavily in southern and central Ohio lawns. However, it was recommended that herbicide applications should be delayed until the dandelions reach the early puff-ball stage - the optimum stage for their control. An early herbicide application would result in later developing weeds such as plantain and oxalis being missed, requiring a second herbicide application. Usually, applications made in May (early for Southern, mid for Central, and late for Northern) will maximize the efficiency of broadleaf weed control measures.
During the week of June 20, 1996, poison ivy was reported showing up in ornamental shrub and perennial borders, probably seeded through bird droppings. When growing among desirable plants, poison ivy is a challenge to control.
Three methods were recommended:
Potassium salts of fatty acids (e.g., Sharpshooter) work well on seedling poison ivy, but older plants will only be suppressed with top kill, leaving roots to regenerate. Glyphosate (i.e., Roundup) is most effective when applied two weeks on either side of full bloom, in early summer. Ortho makes a couple of homeowner formulations, including triclopyr (i.e., Ortho Brush-B-Gon Poison Ivy Killer) and glyphosate (i.e., Kleeraway Grass & Weed Killer).
During the week of September 12, 1996, we received a few calls concerning plants that cause "hay fever." A lot of people blame goldenrod for their cold-like, miserable feelings. However, the real culprit is ragweed, known to cause widespread allergies in humans.
Morphologically, ragweed looks very different from goldenrod. The leaves of common ragweed are mostly alternate, nearly smooth, and deeply cut into a number of lobes. The leaves of goldenrod are tongue-shaped or oblong, without deep lobes. The flowers of ragweed are of two kinds. Male pollen-producing flowers are in small, inverted clusters at tips of branches. The seed-producing flowers are fewer, and borne at the base of the leaves and in forks of upper branches. The flowers of goldenrod are small and yellow, borne in large panicles with one-sided, recurving branches.
Moss was reported during the week of May 16, 1996. It was favored by the wet conditions this spring. Homeowners may incorrectly believe that the moss is killing the grass when in fact, moss grows where environmental conditions challenge turf growth and establishment. Generally, moss thrives in areas that have poor drainage, poor light quality, inadequate air circulation, low fertility, low or high pH, compacted soil, or a combination of these conditions. Although there are several materials labeled for moss control, they are considered a temporary solution. Moss can be successfully managed by correcting conditions which challenge turf establishment and growth. Nutrient deficits and low/high pH can be revealed and thus corrected by using a soil test. Soil compaction can be alleviated by core aeration; poor light quality and inadequate air circulation can be corrected by thinning or removing trees and shrubs.
During the week of May 16, we reported that conditions were "ripe" for the development of mushrooms and puffballs in Ohio lawns. They vary in shapes, sizes, and growth habits and are caused by fungi living on organic matter in the soil. To control mushrooms or puffballs, the organic food source they live on must be removed; this is a task generally impossible to accomplish. Proper fertilization and aeration can help. No fungicides are labeled for controlling these microbes.
Scythe (Pelargonic acid) is a new post-emergence herbicide from Mycogen with a landscape, non-crop, golf course (edging), turf (site prep only), and greenhouse label. Its active ingredient is pelargonic acid. It is a contact herbicide and has a fatty acid chemistry, but is much stronger than Sharpshooter, another fatty acid herbicide. Like Sharpshooter, it can be legally used (carefully!) in greenhouses under benches while the crop is in place.
Scythe is a good contact herbicide in its own right, and when mixed with the translocated herbicide Roundup, improves rainfastness and penetration of that chemical into the leaf. This combination provides very rapid burndown of annual weeds, as well as some control of perennials. However, there is evidence that combining the contact herbicide with Roundup decreases roundup translocation, long-term, and provides less control of difficult perennial weeds than Roundup alone.
Monsanto's Roundup Herbicide for industrial, turf, and ornamental use is being replaced by Roundup PRO. Roundup PRO, like Roundup, is a 41% solution of the active ingredient, glyphosate, but contains an improved surfactant. The new surfactant in Roundup PRO improves foliar penetration and absorption of the herbicide. It has been a fairly common practice to use additional surfactant with Roundup to improve its effectiveness; this should no longer be necessary with Roundup PRO.
By the same token, where we may have been able to use Roundup with greater flexibility in the past, the new Roundup PRO should be used with even more respect around desirable plants! Advertised advantages of the new product include superior rainfastness and faster burn-down. In addition, the EPA signal word has been downgraded from "Warning" to the lowest and safer category, "Caution."