It is one of the great ironies of agriculture that as you struggle to successfully grow your crop of choice all kinds of other plants in your field seem to have no problem at all thriving, to the point at which they threaten the very existence of the plant you are trying to grow. In general all these other plants are known as weeds. By its very definition a weed is simply a plant growing somewhere it is not wanted. In general weeds are plants that grow wild, spread aggressively, and interfere with the growth of a cultivated plant.
The effects of climate change aren’t going to make the battle against weeds any easier. Research is showing that the increasing carbon dioxide level in the atmosphere and rising temperatures we are experiencing due to climate change are working against us when it comes to weed control. As the temperature increases and frost-free dates are pushed back, the growing season for weeds is extended. Temperature changes also increase the risk of invasive weeds moving up from the south. At the same time, rising levels of carbon dioxide in the atmosphere appear to make some weeds grow faster and enhance their reproduction.
People have been at war with weeds ever since they first began to farm, over ten thousand years ago, and during this time have developed many strategies for controlling them—from simply pulling them up by hand to using heavy machinery to blast them with highly toxic synthetic chemicals. When weeds are out of control in a hop yard, they compete with the hops for water as well as nutrients from the soil. When the hops are still small, weeds also compete with them for sunlight. Weeds are a particular problem in hop yards because they provide a cover for harmful insects and also create a shaded, humid environment around the base of the hop plant, which is conducive to the development and spread of fungal diseases such as downy mildew, as well as other disease pathogens. Controlling weeds in the hop yard is difficult because the perennial hop plants are permanent fixtures. Once the hops are in the ground the soil in the hop yard cannot be turned entirely over to kill weeds or sow a weed-suppressing cover crop. This is one reason it is important to take major steps to control weeds before the hop rhizomes are planted. That being said, no matter what extremes you go to before the hop yard is planted you are still going to be dealing with weeds, and there are a variety of methods of control.
Prevention
As always, prevention is the first step, and some of the advance planning you will do in your hop yard will be geared around future weed control—as described in previous chapters. Planting cover crops to choke out existing weeds in your hop yard site before planting rhizomes is a great way to get started, as discussed in Chapter 4. But in their efforts to spread their species far and wide, weeds have ways of finding their way into your field, and in many cases there is little you can do about it. Weed seeds fly in on the wind as well as in the stomachs of birds and other types of wildlife. If your hop yard is healthy habitat you will have plenty of critters moving in or passing through, and they will bring weed seeds with them. There’s not much you can do about any of that.
Too many weeds in the hop yard not only compete with the hops for nutrients and water, they provide an environment conducive to the development of disease pathogens and insects.
You can, though, take measures to prevent seeds traveling into the hop yard on the clothes and shoes of human visitors or on farm equipment. The same ad hoc biosecurity measures recommended for preventing the spread of disease (see Chapter 8) apply: bring in only clean plants, wash equipment, and change clothes as necessary.
You should also be aware, though, that weed seeds can be brought in with irrigation if you are using surface water as a source. And they can also flow into the hop yard with runoff from surrounding fields during heavy rain. So it’s not enough to simply prevent and control weeds inside the hop yard; you must also prevent and control them around the borders of your yard and around your water source.
CONTROLLING WEEDS WITHOUT HERBICIDES
In general the best weed management plan for a hop yard involves heavy mulching around the bines in the spring to block weeds from growing up in and around the hop, keeping ground cover in the aisles of the yard mowed to avoid plants going to seed, whacking back any weeds that break through the mulch barrier, and manually removing any weeds that infiltrate the crown.
But the better you understand weeds, the better you’ll be able to control them. Basically there are two categories of weed—broadleaf weeds and grassy weeds. Broadleaf weeds, such as ragweeds, have flat leaves that grow horizontally. Grassy weeds, such as crabgrass, have bladelike leaves that grow vertically. It is important to differentiate between the two because not only do they grow differently, the strategies you will use to control them will differ as well.
It is also key to understand whether a weed is perennial, biennial, or annual. A perennial is a plant that lives for multiple years, a biennial plant has a two-year life cycle, and an annual plant completes its life cycle in one year. There are two types of annuals—summer annuals and winter annuals. A plant that is a summer annual emerges from the soil in the spring, grows and produces seed in the summer, and is killed by frost in the fall. Summer annuals include lamb’s-quarter, purslane, and pig-weed. Winter annuals germinate in late summer or fall, stay alive through the winter, and flower and produce seed in the spring. Winter annuals include shepherd’s purse and chickweed.
When weeds do arrive they are virtually impossible to eliminate, but they must be kept under control. What type of control works best depends on how the weed reproduces itself. Annuals and biennials (and also, in some cases, perennials) reproduce by flowering and going to seed. To control the spread of seed from existing weeds, the trick is to stop this from happening. Most weeds produce a huge amount of seed, and much of this seed can remain viable for a very long time. Every time a single weed in your hop yard goes to seed your problem gets significantly worse. For example, the best and cheapest way to control broadleaf summer or winter annuals—which have shallow root systems and reproduce themselves through seed production—would be to simply pull them out of the ground before they go to seed. That approach is less feasible when dealing with a patch of a perennial grassy weed that enlarges its territory by expanding its deep underground root system. In such cases, you’ll need to employ other methods.
Reducing weeds in the hop yard can be done by planting cover crops to choke out weeds prior to installing the hop yard and using mulch—such as plastic, landscape cloth, or composted wood chips or bark—around the base of the plants.
It is easy enough to mow the aisles in the hop yard so the plants growing there never have the opportunity to go to seed. In the rows of hops themselves, you can carefully wield a weed whacker between the bines. But for weeds growing close to the base of the hop, a hoe is a better bet so that you don’t risk cutting the bine. When weeds infiltrate the hop crown, and they will, they must be pulled by hand. The bigger your hop yard, the more time-consuming this work becomes; but it is worth it in the long run.
Tilling the soil, whether with a hoe or with tractor-drawn equipment, is a time-honored method of weed control. Because hops are perennial, mechanically tilling your hop rows is not an option, but some growers contemplate tilling between the rows. We don’t recommend this. It is important to remember that, for some weeds, chopping them up and turning what remains under the soil is actually a recipe for the weed’s success. This is especially true for those weeds that have rhizomes, which when cut up and spread throughout the field by the tillage equipment sprout anew.
In the long run it is easier to put in more work up front by heavily mulching the hop plants either with an organic mulch such as wood chips or by using landscape cloth or black plastic. If you are using livestock manure or bedding for mulch, make sure it has been completely composted so that all of the weed seeds contained in the bedding and manure have been killed; otherwise you will be in for a big problem when all those seeds sprout right in the fertile mulch directly surrounding your hop plants. No matter what your mulch is, though, the general principle remains the same. Just like any other plants, weeds need sunlight to grow. If you block out the sunlight, the weed will not grow—in theory. Remember that one of the features that makes a weed a weed is its resilience. Upon pulling aside black plastic row covers in our hop yard, I have been truly frightened by the long, white, snakelike growths of weeds that had been searching tenaciously in the dark for an opening to the sunny world above. The shoots of some weeds can even pierce black plastic or landscape cloth. If weeds do break through the mulch barrier, knock them back with a weed whacker or a hoe.
In many cases weed control just comes down to killing individual plants. This is commonly done by painstakingly pulling them up by the roots by hand—a great option if you don’t have too much ground to cover. But whether just for the fun of it or to speed up the process, people have devised numerous alternative ways to kill weeds without harming the environment. One simple but quite lethal technique is to pour boiling water on the weed. Boiling water kills the vegetation aboveground and scalds the root system, preventing the weed from regenerating. This may not be faster than pulling it and is not practical in a big hop yard. But if you just have a few hop plants growing in your garden or outside the kitchen door it works great. Building on this theme is thermal weeding, which can be done with steam or flame. Although the equipment can be expensive, thermal weeding has distinct advantages in that it is effective on most weeds and is not harmful to the environment. An added benefit is that weeds do not build resistance to thermal weeding as they do to many herbicides.
Options for Herbicide Use
Large commercial hop yards covering hundreds of acres control their weeds with herbicides. The downside to herbicides is that they can be expensive and they can be harmful. A decision to use herbicide must be carefully considered. Like insects, weeds are considered pests, and many commercial farmers address them with an IPM regime that includes spraying toxic herbicides to avoid financial loss. However, when calculating your response to a weed invasion, the sustainable approach involves looking beyond a single year’s finances. There are other factors to consider when deciding whether or not it is necessary to spray a toxic chemical on your farm field, such as immediate and long-term threats to the environment, wildlife, and human health.
Unfortunately, many of these growers turn to glyphosate, commonly known as Roundup, one of the most widely used herbicides in the world. In fact it is so relied on that the company that manufactures it, Monsanto, also produces genetically modified seeds for commercial crops, such as corn and soybeans, that can withstand contact with the herbicide. The impact of these Roundup Ready seeds has prompted a host of concerns, as they monopolize farmland, reduce biodiversity, and threaten the ability of small farmers to protect their crops from GMO invasions. Fortunately, there is no such thing as a Roundup Ready hop plant. But today’s large commercial hop farms do tend to rely heavily on glyphosate and in so doing certainly contribute to the environmental and health risks of frequent and widespread use—and also to the creation of Roundup-resistant “superweeds.”
That said, Roundup is just one of many chemical herbicides used by large commercial growers. And one of the many benefits of going small-scale commercial is that you have more flexibility to make sustainable choices, such as using organic versus chemical herbicides. Either way, it’s good to understand how herbicides work. Some herbicides are applied to the soil and others to the plant itself. Some herbicides are selective (meaning they impact only certain species of weeds), but most are nonselective (meaning they will kill any plant they come in contact with, including your hops). Herbicides are divided into two basic categories—preemergent and postemergent. Preemergent herbicides are applied to the soil before the weed surfaces. Postemergent herbicides are applied to the weed itself once it has started to grow. Certain herbicides kill only the parts of the plant they come into direct contact with. These are called contact herbicides. Others penetrate the surface of the plant and enter its root system. These are called systemic herbicides. Contact herbicides are most effective on annual weeds or perennial weeds that are just surfacing. Systemic herbicides are best for controlling established perennial weeds.
There are several different types of organic herbicides made of substances such as clove oil, cinnamon oil, vinegar, citric acid, lemongrass oil, and soap. Although they are less toxic to the environment, organic herbicides tend to be more expensive. This expense increases because they have no residual effect and must be sprayed more frequently. Organic herbicides work on contact and are most effective against broadleaf weeds, but even then they only kill young weeds that are still small. To make the most of an organic herbicide, it is important to spray it when the weather is warm and there is full sunlight to ensure it is absorbed by the plant.
Familiar Weeds in the Eastern Hop Yard
You are likely to confront a variety of weeds in the hop yard, but here are the most common, with guidelines on how to manage them.
COMMON RAGWEED
Ambrosia artemisiifolia, or common ragweed, is native to North America and notorious among the general public as an allergen and among farmers as an aggressive weed. Many farmers also suffer from severe ragweed allergy made unbearable by the fact that they work in the midst of it. Here on Indian Ladder Farms some of the staff is so allergic that when they drive tractors they tie bandannas over their faces like bad guys in the Wild West.
Ragweed is an aggressive weed that produces over sixty thousand seeds and billions of grains of pollen per plant.
Ragweed is an annual, broadleaf weed with shallow roots that grows to a height of about 4 feet (1.2 meters). Ragweed seeds in the soil germinate from May through early June. The plant flowers in August through early September, producing as many as a billion grains of pollen per plant. This pollen spreads far and wide on the wind, pollinating other ragweed plants and setting off hay fever attacks in humans. (Interestingly, seasonal hay fever is an allergic reaction not triggered by hay, but instead by mold spores and pollen from grasses, trees, and plants such as ragweed.) But for farmers the next step is even worse than the pollen release. Once pollinated, the plant disperses a horrifyingly large number of seeds. One ragweed plant can produce as many as 69,000 seeds. To make matters worse, ragweed seeds can remain viable in the soil for more than thirty-nine years.
Ragweed is trouble in the hop yard because it is an extremely aggressive plant that will compete with the hops for nutrients. A severe ragweed infestation can cause nutrient deficiencies in hops. Ragweed can be suppressed in the hop rows with mulch. Because the plants have a shallow root system, it is pretty easy to pull any ragweed plants that manage to surface through the mulch, and young ragweed plants will not survive chopping with a hoe. Mowing the aisles between rows to cut down ragweed before it goes to seed is important, too; but remember that ragweed plants cut in midsummer will have time to grow new stems and still be able to flower unless cut again.
If the presence of ragweed in the hop yard is overwhelming, and not responding to nonherbicide measures, ragweed can be controlled through the application of most types of preemergent herbicide targeting broadleaf weeds, following up with a post-emergent herbicide application to kill any survivors. Unfortunately, there are not a lot of effective organic options for preemergent herbicides. Avenger is a citrus-based organic postemergent herbicide that is quite effective. Unfortunately, it is not selective so don’t get any on your hops. Ragweed woes have prompted many to consider Roundup, which has historically been used to kill it, but incidents of ragweed developing resistance to Roundup have been documented by the International Survey of Herbicide Resistant Weeds (on farms growing crops such as cotton, corn, and soybeans) all around the country over the past ten years.
Because ragweed crops up where people do, and many people are desperately allergic to it, there has been a little more attention to developing environmentally friendly means of control. This need has been exacerbated by climate change, which is working to ragweed’s advantage. The plant benefits from increased carbon in the atmosphere, which enables it to grow faster and produce even more pollen. In addition, climate change has pushed back the hard frost dates in many regions, prolonging the plant’s pollen production and along with it the ragweed allergy season. Hopefully, outcomes of this research will also benefit farmers who prefer not to use synthetic herbicides.
FIELD BINDWEED
Field bindweed, Convolvulus arvensis, is an interesting weed to combat in the hop yard because the qualities that make it “bad” as a weed are the same qualities that make hops strong and resilient. Field bindweed is a broadleaf, hardy perennial vine that resembles a morning glory. Native to Eurasia, it invaded the United States via Virginia back in 1739, possibly as an ornamental plant. It worked its way across the entire eastern United States by the early 1800s. Today it is considered one of the most problematic weeds facing agriculture located in temperate regions worldwide. Belowground, field bindweed’s main root reaches a depth of 20 feet (6.1 meters). This vertical root then sends out lateral roots; once they reach a distance of 15 to 30 feet (4.6 to 9.1 meters) away from the parent plant they turn downward and become a secondary vertical root, which sends up its own shoots. Like the hop, field bindweed also has underground rhizomes that produce buds and form new plants. Just to make sure it has all its bases covered, each field bindweed plant will also produce and spread over 550 seeds, each of which can remain viable in the soil for up to sixty years and can germinate in conditions ranging from 41 to 104 degrees Fahrenheit (5 to 40 degrees Celsius). Once aboveground, field bindweed grows along the surface until it finds something to climb, usually another plant, which it entwines and eventually envelops. In other words, field bindweed is a tough one to beat.
Field bindweed is a perennial vine that, much like the hop, spreads through an underground system of roots and rhizomes.
Conventional means of mechanical weed control such as hoeing and tilling only make matters worse. Chopping up its belowground system of roots and rhizomes only helps it spread faster; however, continuously removing the surface vegetation through hoeing or mowing does have the effect of forcing the plant to use up its carbohydrates stored belowground. The plant will eventually starve to death if you keep this up.
One of the best ways to control field bindweed, though, is to block its light source. This technique works well in the hop yard since hop rows are often heavily mulched as a matter of practice. When dealing with bindweed, nonorganic mulch such as black plastic, which can completely block the sun, is most effective. But you must be vigilant, as field bindweed searching for light has been known to actually puncture plastic row covers. Certainly the bindweed will emerge out from under the edge of the plastic and backtrack across it in an attempt to climb the hop. It will be need to be cut back with a weed whacker or other implement before it can work its way over to the hop plant.
Bindweed in the hop yard can be a particular problem, especially when the bindweed starts coming up in the middle of the hop crown and hop and bindweed shoots and roots become entangled.
Herbicides such as glyphosate work on field bind-weed, but multiple treatments will be necessary and therefore extremely bad for the environment. Bindweed is a significant problem in our hop yard. Although we have not eliminated it, we have suppressed it by laying down black plastic mulch in the hop rows, keeping the hop aisles mowed, and weed whacking where the mulch layer meets the mowed vegetation in the aisles—where bindweed has a tendency to creep out. Of course it will periodically emerge within the crown, and at this point it has to be pulled by hand. So far we have not had to spray herbicide.
PIGWEED
Like ragweed, pigweed is a fast-growing, native broadleaf annual. Part of the grain-producing Amaranthaceae family, pigweed is actually the common name for a group of weeds that includes redroot pigweed, smooth pigweed, powell amaranth, water-hemp, prostrate pigweed, and tumble pigweed. It is an aggressive plant that thrives in hot weather. Seedlings sprout in great numbers in the late spring and early summer. Pigweed grows up to 3 inches (7.6 centimeters) a day and can reach a height of 7 feet (2.1 meters), easily choking out crops. The plant has the advantage of being edible—the young leaves can be served as a green fresh or steamed—which provides a perk when weeding.
A plant will begin to flower and produce pollen as soon as six weeks after emergence. Each plant produces thousands of flowers, and a single plant can produce between 100,000 and 600,000 seeds. Since it is a nitrogen-loving plant it can be a particular problem for hop growers, who must fertilize their hop yards heavily to reach production goals.
Pigweed grows fast and can reach a height of 7 feet (2.1 meters), competing with hops for sunlight and nutrients.
The best strategy for controlling pigweed is to strike early. Since its seeds are very small they do not pack a lot of nourishment for emerging plants. Because of this, pigweed seedlings need to get aboveground and start photosynthesizing to feed themselves. The large numbers of tiny seedlings that sprout up are so delicate and lightly rooted in the ground you can practically scrape them away with your fingers and they won’t regenerate. However, if you don’t get them when they are little, they grow fast and are harder to kill once established. It is best to control them by pulling or mowing before they flower, as they are quick to adapt to herbicides.
QUACKGRASS
Quackgrass is a perennial grass, and perennial grasses are particularly difficult to control. They are frequently a problem in hop yards, as fields not previously intensely cultivated, such as pastures where such grasses are well established, are often the first choice when it comes to locating hop yards. Quackgrass, native to Europe, has a lot of names, including couch grass, dog grass, quickgrass, quitch, scotch, twitch, and witchgrass. Such an abundance of names usually indicates a widespread problem.
It is an interesting challenge to have in the hop yard because, like the hop, it reproduces itself through rhizomes. An extensive underground system of roots and rhizomes spreads underground, sending up new shoots that can survive on their own if they are broken off from the parent system by mechanical cultivation. Aboveground the grass can grow to a height of between 1 and 4 feet (0.3 to 1.2 meters). The green grass generates nourishment for the underground rhizomes. As the end of the growing season approaches, the rhizomes store up energy so that they are ready to go in the spring.
Controlling quackgrass is a matter of combining tilling and mowing. Digging up the roots and repeating the process again before the rhizomes have time to resprout is one strategy. You can also turn over the soil and expose the roots and rhizomes to the sun in the height of summer, which will kill them. Back up the disruption of the root system with repeated mowing of the grass aboveground, keeping it as short as possible. This treatment reduces quackgrass’s ability to generate and store enough energy to get it through the winter. After using these techniques during the growing season, plant a cover crop in the fall that will compete with the quackgrass for space. After a couple of years of this cycle of control, the quackgrass should be significantly compromised. This of course must be accomplished prior to the installation of the hop yard and the planting of the hops. If quackgrass continues to grow in the hop yard despite your efforts, you can use the above-described technique of root disruption followed by repeated mowing in the row covers while heavily mulching the planted rows to deprive the grass of sunlight.
Quackgrass is a persistent grassy weed that reproduces itself through an underground root and rhizome system. Photograph courtesy of Sid Bosworth, University of Vermont
