Container nursery growers are at a disadvantage compared to some other cropping systems when it comes to weed control because, at least in container production, our only tools are preemergence herbicides, hand-weeding, and mulch. About 25% of growers spend over 100 hours per month on weed control, and with labor becoming more expensive and harder to find, it is becoming more important for growers to improve efficiency in any way possible. Weed control is also expensive. Estimates have shown that growers spend an average of $5,000 or more per acre on weed control, but this just includes chemical costs and labor. What is not included in these estimates is the opportunity cost that is lost when labor is diverted from profit generating/production related tasks (loading trucks, potting, propagation, etc.) to a corrective or profit reducing task like hand-weeding. While weed control is challenging, there are growers in many different parts of the country that have consistently clean nurseries. In each case, these growers are following similar practices that have been shown to work both in research and in the real world. In this article I will describe the five common things I have seen in the most consistently clean nurseries I have visited.

1. They scout daily and hand- weed frequently to reduce weed pressure.

The goal of improving a weed control program should be to reduce hand-weeding labor, but we want to reduce the total time spent weeding, not the frequency. Research out of North Carolina State has shown that weeding every two weeks reduces labor costs by an average of 36% (and some much more) compared with weeding only every eight weeks, or just before herbicides are reapplied (Barker and Neal., 2016). I have visited several nurseries that have adopted this approach, or a similar approach, and have seen tremendous improvements including cutting labor costs for weeding almost in half (or more) and reducing the total number of herbicide applications they need. How does this work? First, most nursery weeds spread exclusively through seeds, and they do not have time to produce seed in two weeks. This reduces the overall weed pressure throughout the rest of the season. This allows subsequent herbicide applications to be more effective because the “seed bank” or weed pressure is low. Secondly, it is time consuming to look for and pull very small weeds. If you keep a two-week schedule, crews can skip over very small weeds and only focus on weeding plants that may go to seed within the next two weeks. For more information including how to implement this in your nursery, see “Frequent Hand Weeding Saves Money” (bit.ly/hand-weeding-NCSU).

2. Sanitation is their most effective tool.

Proper sanitation is discussed in many different Integrated Pest Management (IPM) guides. In terms of weed management, the main principles to follow include:

• Hand weed frequently.
• Do not recycle potting media. Many growers do this to reduce costs, but savings on soil deliveries can be quickly lost by heavy weed pressure. I have seen very strange (and hard to control) weeds that aren’t normally in containers, such as dollarweed (Hydrocotyle spp.), yellow nutsedge (Cyperus esculentus) and horsetail (Equisetum spp.) show up in pots with recycled soil. If someone is determined to recycle soil, solarization or steam sterilization is one way to reduce pest pressure. If that is not an option or not feasible, at least avoid using recycled soil on herbicide sensitive plants like herbaceous perennials because you will not want to limit your preemergence herbicide options. Using recycled soil only for certain crops like trees in larger containers or in pot-in-pot systems could allow the use of directed postemergence herbicide applications.
• Use preemergence herbicides in non-crop areas (walkways, aisles, ditches, etc.). Weeds in non-crop areas will inevitably move into the crop if they are not controlled. Non-selective herbicides such as glyphosate (or possibly glufosinate if glyphosate resistant weeds are present) can be used to control most weeds. While these postemergence herbicides are relatively low-cost, the applicator is not. Tank-mixing a preemergence herbicide in with your post application can significantly improve control and reduce the total herbicide bill by reducing the number of applications that are needed throughout the year.
• Clean pots before reusing them. Pressurized water, heated water or steam can be used to reduce weed seed presence and/or viability.



• Moving liners and other plants in the greenhouse off the ground. Tables are expensive and not feasible in all cases, but simply moving plants in the greenhouse up on benches can help prevent weed growth in the crop. This also allows the use of postemergence herbicides or Marengo (indaziflam, a preemergence herbicide) to be used on the floor underneath the benches. Other preemergence herbicide options are available if there are no crops in the house when treatments have to be applied.
• Start with weed-free liners and keep liners weed free prior to potting.
• Stabilize plants whenever possible. Blown over pots can create several issues – first, the herbicide barrier in the top portion of the soil is broken, so weeds have greater opportunity to take over after a pot has been blown over. Probably a bigger issue is that the spilled soil is an ideal place for weed seeds to germinate.

3. They use non-chemical controls.

Certain ornamental species are notoriously sensitive to preemergence herbicide applications (e.g. hydrangea, herbaceous perennials, succulents, tropicals, etc.). These untreated areas can quickly become “hot spots,” or areas where weed growth is concentrated and spreads to other parts of the nursery. Mulch like rice hulls, pine bark nuggets, wood chips, and many others are going to cost much more than preemergence herbicides, but they cost much less than hand-weeding. If the mulch is applied properly (about 1 to 2 inches depending on the situation), a single application of mulch will usually outperform a single herbicide application. Another way I have seen some growers reduce weed pressure is by subdressing fertilizer. While it is usually easier to topdress or incorporate fertilizer, subdressing is a method of “layering the fertilizer” at potting in a single layer several inches below the media surface. When fertilizers are subdressed or layered, the pot is filled halfway at potting, fertilizer is applied in a single layer, and then the rest of the potting soil is added along with the liner. This results in a 2- to 4-inch (or greater) layer of potting soil that contains no fertilizer, and so no nutrients are available to weeds germinating on the soil surface. In research at the University of Florida, growth and seed production of common container weed species has been reduced by 40% to over 90% by subdressing with no negative impacts to several different ornamental species. The benefit diminishes later on in the production cycle when a topdress application is needed to finish off the crop, but subdressing can still provide a benefit early on in the production cycle when plants are most sensitive to weed competition.

4. They select herbicides based on their specific nursery and rotate.

There are over 20 different preemergence herbicide products labeled for over-the-top use in container plant production, but in reality we only have just a few different modes of action (MOA) including Weed Science Society of America’s herbicide MOA groups 3, 14, 15, 21, and 29. With most herbicides, growers are limited to around two applications per year, but in most cases an application is needed every 8 to 10 weeks during the growing season to keep weeds under control. This means that multiple herbicides are going be needed. Another thing to keep in mind is that all herbicides have weak areas, and if you only use one product or just one (or two) MOA, you will quickly figure out the weed(s) that your current herbicide is weak on. To get the best weed control, you need to rotate through different MOA throughout the year, timing the herbicides when they work best for your specific weed spectrum each season. Avoiding back-to-back applications of the same herbicide can also improve crop safety. A list of common preemergence herbicides including their MOA and general weeds they control are included in Table 1. Weed efficacy guides, such as the “2017 Southeastern U.S. Pest Management Guide for Nursery Crops” (bit.ly/SE-pest-control-guide) can be used as a reference for which herbicides are most effective on different weeds, and on which crops these herbicides can be applied. An herbicide rotation should be based on the specific conditions at a particular nursery. I have published a lot of examples of rotations that would work great for some growers but would yield horrible results for others because of differences in ornamentals and weed species. When developing your own rotation, the first priority is making sure the herbicide is labeled for use on the ornamental, or you have determined it is safe by testing it on a small group of plants. The next priority is selecting an herbicide that is highly effective on the most troublesome weed during a particular time of year. As several herbicides are likely effective, the next step would be to select the best option that controls both the worst weed and then the other most common two or three species that are problematic at the same time. For the next application, an herbicide with similar efficacy but a different MOA could be chosen. This process is repeated throughout the year until you have your program developed. Implement that program, take notes, and reevaluate and make changes as needed. Some of the most successful nurseries may utilize four or five (or more) different preemergence herbicide products, using each to take advantage of the products’ strengths such as crop safety or efficacy of key weed species during different times of year.

5. They make weed prevention an overall priority.

The most consistently clean nurseries all make weed management one of their top priorities. They understand and have seen how much money can be saved by preventing weed issues compared with correcting weed issues. Weed populations (and the associated costs) do not increase linearly, they increase exponentially. In nursery weed control, it is definitely true that a dime spent on prevention is worth a dollar of the cure. With labor being more expensive and harder to find, weed control programs are one area where minor changes can make a big difference.

Chris Marble is associate professor at the University of Florida’s Mid-Florida Research and Education Center, marblesc@ufl.edu.

On Sunday, July 11, Joe Neal, professor of weed science and extension specialist at North Carolina State University, spoke to a crowd of growers at Cultivate'21 who are all facing the same problem: weeds. At his educational session, "Strategies to reduce weed control costs in container nurseries," Neal covered some of the most-common problem weeds and how growers can develop a plan to stop them.

Bittercress is the most-common cool-season weed and spurge is the most-common warm-season weed, Neal said. Spurge is particularly nefarious, requiring only five days to germinate.

Neal asked and answered the big weed control question during his talk: despite effective herbicides, why do weeds continue to emerge? In many cases, the answer is that growers are not rotating effectively.

Neal said that whoever’s in charge of herbicide application at your nursery needs to be adhering to the label. If you apply any herbicide more frequently than it’s meant to be applied, its efficacy will drop and your weeds will develop resistance. That’s how a once-stellar herbicide becomes useless. Commonly used herbicide Broadstar can have 2 applications per year. Barricade and Gemini: also 2 applications per year. Freehand and Tower: 2 applications per year. Snapshot and Gallery: 3 applications per year. Marengo: 2 applications per year.

“None of them say ‘6,’” Neal says.

The NC State Extension website has plenty of charts and sheets that growers can use to develop their own rotation plan, depending on which crops they grow. Check them out at his website: weeds.ces.ncsu.edu/weeds-herbicides.

Neal also discussed the importance of uniformity in herbicide distribution. A typical application has a 250% variation, he said. That means some plants are getting the correct dose but some may be getting two-and-a-half times more or less than the recommended dose. If you have a variable application rate, you’ll end up with variable weed control, he said.

Calibration of your spreader is a crucial step to improving uniformity. Consistent walking and handle speeds are important to achieving uniform distribution. Neal suggests using a metronome to ensure consistent walking speed. Neal said many growers balk at this and say applicators should just use their smartphone.

“How many of you out there handling pesticides would want to get your phone out and handle it? Don’t ask your employees to do that,” Neal said.

Smartphones are typically difficult to operate with gloves on, and PPE should definitely be used while applying herbicides. Neal suggests buying them a $15 metronome and clipping it to the spreader.

Neal also discussed how the path you take with a spreader affects herbicide distribution. Swath width and directional spreading are areas to address. For instance, if your beds are 10 feet wide with a 12-foot swath width, and you use the left, right and center rudder positions, you will have areas that have heavy herbicide coverage and areas with light coverage. Heavy herbicide coverage could injure crops sensitive to that particular product, and areas with light coverage will be more susceptible to weed infestations.

Neal found that this could be remedied by keeping your beds 6-8 feet wide and using only the center rudder position. Also, applicators should refill when the hopper gets to about 25% full.

Walking pattern also makes a difference. Instead of walking down one row and up the next, use the single direction, parallel pass method. Calibrate for half the dose, then walk the same path in opposite directions. In tests, Neal found that method resulted in a much more uniform herbicide distribution.

Another topic Neal covered in his Cultivate talk was the importance of weeding frequently vs. “when it’s weedy.”

If growers get proactive with their hand-weeding and remove weeds before they set seed, they can reduce labor costs. Neal discussed an experiment that chronicled the difference between hand-weeding a 250-container nursery every two weeks versus hand-weeding on an eight-week interval.

Neal said he often hears complaints from growers at this point, citing a lack of employees or not enough time to hand-weed every two weeks. However, he said that several nurseries of various sizes have implemented this process, and each have reported significant cost savings.

The more frequent hand-weeding, unsurprisingly led to a 50-80% reduction in weeds (depending on the site). However, it also averaged a 39% reduction in labor costs, due to the lower number of hours spent weeding.

When using the more frequent hand-weeding method, the largest labor savings will be obtained in crops or sites with high weed populations, long-term crops that will be in production at least 16 weeks, and during weather that is conducive to high weed growth.

The challenge with a higher-frequency hand-weeding program is labor management. If you happen to get busy with something else at the nursery and miss a cycle, Neal says it becomes very difficult to catch up. He suggests keeping the nursery clean through effective herbicide use and sanitation around the containers.

Bayer is proud to once again sponsor the weed management special issue of Nursery Management. Last year’s first-of-its-kind issue provided valuable insights into the ongoing and ever-changing challenges growers face. Carefully examining those important trends — and the new ones in this edition — help us focus on what matters: bringing innovative ornamentals solutions and expertise to support your growing business

As an ornamental grower, what you do isn’t just special — it’s uniquely beautiful. Every day, you cultivate and grow the flowers and plants that transform the environments where we live, work and play. At Bayer, we want to help you continue to grow your operation and find success by providing expert advice in addition to a balanced and innovative product portfolio with demonstrated and proven results.

We recently brought innovation to the industry through an expanded use labeling of Marengo®, a selective, preemergence herbicide that provides up to eight months of control on broadleaf weeds, grasses and annual sedges and is labeled for use on more plants than ever before to control more weeds. Marengo is now labeled for use inside greenhouses while plants are present, and it can be used on 178 additional plants and controls 15 additional weeds. It’s also now approved for over-the-top application on 12 added plants in nursery settings, giving growers even more flexibility than before. There has never been a better time to try Marengo.

We know that watching the bottom line and managing labor costs is always top of mind, and in 2021, labor challenges have been front and center for many. No other herbicide lasts as long in production settings (up to eight months with Marengo and up to five months with Marengo® G). And since no product lasts longer than Marengo, it can help reduce labor costs by eliminating the need for repeat applications, ultimately making it one of the most cost-effective program options for weed management.

ALWAYS READ AND FOLLOW LABEL INSTRUCTIONS

Bayer Environmental Science, a Division of Bayer CropScience LP, 5000 CentreGreen Way, Suite 400, Cary, NC 27513. For additional product information, call toll-free 1-800-331-2867. environmentalscience.bayer.us. Not all products are registered in all states. Bayer, the Bayer Cross, Altus, Broadform and Marengo are registered trademarks of Bayer. © 2021 Bayer CropScience LP.