Catoctin Mountain Orchards using black plastic mulch and straw between rows.
We are often trying to manage one weed while producing another for sale. Most growers use a combination of methods in order to increase soil organic matter and avoid the buildup of pest and pathogen populations. These methods can be loosely grouped under the headings: Preplant Soil Preparation, Cultivation and Hand Removal, Chemical / Herbicide, Barrier, and Flame.
Pre-plant Soil Preparation
Pre-plant Soil Preparation can include any of the following: Sequential cover cropping, Fallow ground with burn or plow down, and Solarization. Cover crops are an excellent way to prepare the ground for cut flower production. This is especially true when you are taking ground from pasture or turf and trying to prepare it for production. Among the cover crops commonly used are Cereal Rye, Buckwheat, Rape, and various Legumes. Each has inherent advantages and limitations that a grower needs to factor in prior to planting. For example: while cereal rye is an excellent smother crop that yields between 4,000 lbs. and 8,000 lbs. of dry matter per acre, will tolerate very late season planting, and does an excellent job of scavenging nitrogen, it can suppress the germination of some direct seeded flowers through the secretion of allelopathic chemicals and can be difficult to work into the soil with small equipment. Once cereal rye is worked into the soil it is ideal for most transplants and does an excellent job suppressing the germination of Oxalis, chickweed and purslane. Legumes are an excellent method to build soil nitrogen, increase soil organic matter and smother weed seedlings, but there is the potential to increase nematode, pest and pathogen populations. Buckwheat makes for an excellent fast turnaround, summer cover crop, but it is critical that it be either mowed or killed before any mature seeds are set or it can become a weed.
Fallowing ground, that is leaving it unplanted and regularly killing any germinating or emerging weeds, is an excellent tool to use in reducing tough perennial populations and reducing weed seed banks. Regularly tilling any weeds that emerge or the application of a contact herbicide such as glyphosate, Gramoxone, Scythe, Axxe, Finale, Reward or 20% Acetic Acid (heavy vinegar) will generally reduce tough weeds that are very difficult to control in a cropping situation.
Soil solarization is a good low-input tool that accomplishes many of the same goals as chemical fumigation. By covering the ground with clear plastic after tilling and a good watering in the summer, you can reach temperatures in excess of 120oF at 6-8" deep under the plastic. This combination of clear plastic which allows weed seeds to germinate and high heat to kill the seedlings can significantly reduce weed and pest populations. It is very important to maintain moisture levels under the plastic in order to get the deepest penetration of the heat. Unfortunately, purslane often thrives under solarization. Be sure to use a biological inoculant such as Actinovate AG or RootShield Plus to help in re-establishing a beneficial soil microflora after solarization.
Cultivation for cut flowers is no different than the practices used in vegetable production with the added challenge of a high plant population to work around. Most cut flower growers are small (less than 2 acres) operations making rototillers of various sizes very practical for weed control. Hand weed removal may be the only option when working in tightly planted perennial cut flowers.
Chemical Weed Control
There are a number of pre and post-emergent herbicides labeled for use in cut flowers. See the table at the IPM guidelines website as a starting point in selecting specific herbicides for cut flowers. With the large number of cut flowers that most growers plant, selecting a single pre-emergent material may be impossible, but with careful selection of chemicals, you may be able to get by with just a few.
Wick, brush and roller type applicators allow the use of non-selective herbicides such as glyphosate (Roundup, plus many other names) in planted areas with minimal damage to desirables. Versions of these "wick' applicators can be found at many farm equipment suppliers and many can be readily built on the farm. Wick applicators can use systemic or contact materials. Use herbicides such as glyphosate and Finale to control emergent perennial broadleaf and grass weeds. Contact / burn down materials like Scythe, Axxe, Reward, and 20% Acetic Acid (commercial processing grade vinegar) are excellent for cleaning up young weeds or "burning back" tougher weeds. Established perennials, woody plants and strong annuals are likely to come back when using just contact materials. However, regular 'burning back' of these weeds tops can eventually reduce weed populations.
Some specific herbicide suggestions for really tough weeds: Every farm seems to have its' own specific combination of weeds that the owner / operator believes to be worse than those found in any other piece of ground anywhere. However, some weeds fit into a category of those that are just simply hard to kill.
A commonly used material like glyphosate has a very high number of dilution options based on the weed to be killed. Roundup Original (41% glyphosate) can be used at dilutions from. 5% to 50% based on the problem at hand. Young, tender seedlings are controlled at very light concentrations while freshly cut woody stumps require 50% dilutions to prevent regrowth. Often, really tough weeds like poison ivy, Rosa multiflora, and thistle(s) require multiple applications in a single season for full control.
Many of the pre-emergent herbicides available for use in cut flowers are formulated as granules since they were primarily designed for use in landscape and nursery situations. This allows the applicator to more easily apply granules under plants as compared with liquid sprays. With pre-emergent materials, it is always necessary to water the chemical into the soil for the material to work. Typically about an inch of water is sufficient for this purpose.
Barriers such as colored plastic mulch are probably the most common method of cut flower weed control today. Most growers still use the standard black plastic film, but biodegradable mulches have recently become good alternatives. Plastic mulch's are a petroleum-based product and can be a disposal problem. The combination of plastic or biodegradable mulch in the planting row and straw in between will make for an easier harvest when things get muddy as well as reduce erosion from the row middles during heavy rains.
Flame Weeding is only useful in cut flowers in fallowed areas. Growers seeking a non-chemical method of maintaining a clean fallow field may find flame weeding practical. Singeing seedlings with a quick burn will usually finish them off. If you do experiment with flame weeding, be sure to go after plants as young as possible, don't try to burn the plant to the ground as a simple wash over the tender plant with flame is sufficient to damage tender plant cells and be especially careful of setting fires in dry weather.
Developing a strategy for weed control in cut flowers is extremely important as the two best methods to reduce stem length and overall quality are to under-water or allow too much competition from weeds.
The comments herein on the use of chemicals are intended to assist growers in decision making and specific herbicide selection. Applicators are responsible for each materials label requirements, pesticide record keeping and pesticide safety practices. Pesticide labels provide substantial quantities of important information including rate, application methods and suggestions, tank mixing instructions, weed sensitivity and specific crop tolerances. Read any pesticide label thoroughly before use.
Prepared by Steve Bogash, former extension educator.