Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityMay, 1997
Preemergence herbicides for container-nursery ornamentals.
Keywords: nursery, container production, herbicides, new products, weed control
T he use of preemergence herbicides is widespread in container production because the alternative, hand-weeding, is extremely labor-intensive. Container media provide an ideal habitat for weeds, thus it is necessary for the container grower to adhere closely to scheduled herbicide applications.
In Ohioâs growing season, three to four applications per growing season may be required for adequate weed control, depending on the nature of the chemical, the rate used, and the date of potting. It is important to rotate several products throughout the year; this will help eliminate the buildup of one or more weed species that may be resistant to a single chemical.
When applying herbicides to over-wintered containers, be sure pots are weed-free before applying preemergence herbicides in the spring, else the effort is wasted. For newly potted, the first herbicide application is made shortly after potting - the sooner the better. Some chemicals may require a waiting period of several weeks before applying; some only require that the potting medium be firmly settled around roots prior to application. This is especially critical for potted
bare-root liners.
One or two more herbicide applications may be made throughout the course of the growing season, and a final application should be made as close to covering houses as allowed by the label. This final application will control germination of winter annuals in the polyhouses. No preemergence products are labeled for use once the houses are covered. Each herbicide
application provides about 2 months of weed control, depending on the product used. A typical application schedule might be something like this: April, June, August, October. Growers who have failed to have much success with chemical weed control in containers generally find that they havenât applied it frequently enough.
The container grower is usually faced with a large inventory of plant species, many of which may not be found on herbicide labels. Some products (e.g., Gallery, Snapshot, Surflan) will allow users to try a product on plants not found on the label. Growers assume all risks in this case. Some products expressly prohibit their use on plants not listed on the label.
Granular formulations seem to be the product of choice for container growers because of their convenience, although sprayable formulations work just as well. The exception are plants that have whorls of leaves that capture the herbicide granules, - a good example is yucca. Donât use granular products on these because the granuled trapped in the whorls will burn the foliage. All of the granular products should be applied to dry foliage and followed with ¸ä irrigation immediately afterwards.
A number of granular products are available that are combinations of grass and broadleaf herbicides. Choose these whenever possible because most will control a broader spectrum of weeds than single-component herbicides. However, there tend to be more label restrictions on combination products because fewer species are tolerant of broadleaf herbicides contained in them. For example, Goal (Oxyfluorfen), contained in several of these products, will seriously injure herbaceous ornamentals and bulbs. Suggested products appear below.
Granular combination products - for use in many woody ornamentals, but labeled for very few herbaceous plants unless noted otherwise. Avoid applying products that contain Goal to plants that are producing a new flush of growth.
- Ornamental Herbicide 2 - OH-2 (Goal + Pendulum).
- Excellent herbicide, used on
containers for years.
- Regal O-O Herbicide (Goal + Ronstar).
- New within the last few years.
- RegalStar (Ronstar + Factor + nitroform fertilizer).
- A new product that also contains
some fertilizer. This looks like it will be a good combination and will be in 1997 university trials. No
need to change your fertility program because at labelled rates, a negligeable amount (about 1/2 gram for a
2 gallon) of slow-release nitrogen is supplied.
- Rout (Goal + Surflan).
- Excellent herbicide, used on containers for years.
- Snapshot TG (Gallery + Treflan).
- Labeled for some herbaceous perennials and groundcovers, however the labels allows for grower
trials. Many Ohio growers have found this to be a good product to use on a wide array of herbaceous
perennials. Remember that you take a risk when using it on plants not appearing on the label, so
experiment with small groups initially. Contains volatile Treflan, so this product loses herbicide efficacy
very rapidly if not followed with irrigation immediately.
- XL. (Surflan + Balan).
- A combination of two grass herbicides that will provide less broadleaf control than other products
in this list. The label includes herbaceous perennials, annuals and groundcovers. The only combination
product labeled for annuals.
Other granular products. - Many of the following herbicides have quite lengthy species labels
including both herbaceous and woody plants. Most of these provide strong grass control
and weaker broad leaf control, with some exceptions.
- Devrinol 5G.
- Primary strength: grassy weed control. Also good on chickweed. Best used for cool-season weed
control.
- Pennant 5G. (2-4 lb aia ? ).
- Primary strength: grassy weed and nutsedge control.
- RegalKade G (.75 - 1.5 aia ?).
- A new product that contains granular Prodiamine which has been available in the sprayable
products Factor and Barricade. Primary strength: grassy weed control.
- Ronstar.
- Few herbaceous plants on the label. Primary strength: broad leaf weed control.
- Treflan.
- Many annual flowers (landscape annuals) on the label, probably more than any other. Primary
strength: grassy weed control.
Sprayable formulations for container plants. For growers that prefer to use sprayable
herbicide formulations for containers, the following chemicals are available. When possible, tank
mix a broadleaf and a grass herbicide.
- Factor.
- Primary strength: grassy weed control.
- Gallery.
- Primary strength: broad-leaf weed control.
- Goal.
- Conifers only. Donât use at budbreak or on soft new growth. Kills small weeds by contact action.
Primary strength: broad-leaf weed control.
- Pendulum.
- Primary strength: grassy weed control.
- Pennant.
- Rinse spray residue off of leaves. Primary strength: grassy weed and nutsedge control.
- Ronstar.
- Do not apply at budbreak and for four weeks afterwards. Primary strength: broad-leaf weed control.
Limited label for over-the-top application, and directed-spray applications is not practical in containers.
Kills small broadleaf weeds by contact action.
- Surflan.
- Primary strength: grassy weed control.
