Weed of the month: Docks in June

Dock weeds flowering and seeding in early June.
Photo Pam Dawling

 This is the second of my once-a-month series of posts focusing on weeds. One weed that is making itself very evident on our farm in late May and early June is the dock. We have both the broadleaf dock, Rumex obtusifolius L. and the narrow-leaved or curly dock, Rumex crispus L. Docks are in the buckwheat family.

Docks are tap-rooted perennial weeds, requiring different approaches to last month’s weed, the fast-seeding annual galinsoga.

Cover of Manage Weeds on Your Farm
SARE

See the excellent information on docks in the book, Manage Weeds on Your Farm: A Guide to Ecological Strategies, By Charles Mohler, Antonio DiTommaso and John Teasdale. Click the link to read my review. It’s a book worth having on your shelf and it’s also available online from SARE  It explains how to tackle various types of weeds in an ecological way and then profiles many individual weeds. With good clear photos of weeds at various stages of their lifecycle. Here you can find out what dock seedlings look like, and go and hoe them out before they get too big.

Another resource on ecological weed management is the ATTRA publication Sustainable Weed Management for Small and Medium-Scale Farms

When dock seeds germinate they first develop a rosette of leaves close to the ground. The rosette grows quite large (leaves can be 12″ by 6″ with broad-leafed docks, 12″ x 2.5″ for narrow-leafed docks), at which point most of us cannot simply pull the dock out as the tap root will be sturdy and long. You will need a digging fork or a shovel to get the root out. As with other tap-rooted perennial weeds, if the root breaks, the part remaining in the soil can regrow. The short, vertical underground stem that attaches to the roots regrows readily. In spring, new plants can also grow from fragments of the true root.

Broad-leafed docks have branching taproots, while the narrow-leafed docks have a single root, with almost no branches. If left to their own devices, the leaves become speckled with red  and the plant puts up a tall stem with clusters of inconspicuous reddish flowers. The flowers mature into winged fruits surrounding three-sided glossy reddish seeds.

Dock as a rosette. Photo University of Maryland Extension

Docks can become established in uncultivated but fertile areas, especially along edges of pastures or areas with long-term cover crops. frequent mowing before docks get a chance to grow large can help other plants to out-compete the docks. The key is to provide enough nitrogen for your crops but not more, or the docks will suck it all up! Vigorous crops can out-compete docks for light (part of why docks do well on edges where they have no competition).

If docks get too big and have flowering heads or even seed heads, it is best to dig them out and take them away. This is a good time of year for that, before the seeds mature and scatter. If I dig just one or two docks, I put them on the driveway to dry out and get road-killed by vehicles rolling over them. If we take advantage of a day with lots of help, especially after rain when the soil is easier to dig, we take wheelbarrows and make a team sport of it, digging all the docks from one area. We have a special place under trees that we call the End of the World, where we pile noxious weeds. The shade discourages them from regrowing, as does the sheer weight of the weeds we pile up.

On a larger scale, if a whole field has become infested with dock, say a pasture that you want to convert to growing annual crops, then stronger measures are called for. Disk or plow the field in midsummer (now!), and repeat the cultivations whenever the weather is suitable for drying out fresh root pieces that will get brought to the surface. I would not normally advocate repeated tillage and leaving soil bare, but annual crops are no match for established perennial weeds.

Narrowleaf or curly dock with a stem of still-green flowers. Photo University of Kentucky Dept of Plant and Soil Sciences

If you are using a rototiller, be sure to work down to a depth of four inches. If you till shallowly, you might just severe the neck from the root, allowing the dock to regrow. Run your machinery slowly and get maximum chewing-up action. When you see new shoots with 2” leaves growing, repeat the tilling. This is the stage at which the regenerated plant has extracted lots of nutrients from the root piece and has not yet paid much back. Don’t wait longer!

Winter cover crops can do a lot to suppress new dock seedlings as well as regrowths. The growth rate of docks is slow-and-steady, the opposite of galinsoga! Tackle docks before they disperse their seeds. Once shed, dock seeds are initially dormant for some months. Germination occurs at 50°F–95°F (10°C–35°C) with 68°F–77°F (20°C–25°C) optimal for fastest germination. Cooler nights and warmer days help speed germination, as does light exposure, unless filtered through overhead trees, which decreases germination. Flushes of seedlings tend to germinate in spring and fall.

Seeds of broadleaf dock can remain viable for 40 years, and those of narrowleaf dock can live in the soil as long as 80 years! But the rate of seed mortality each year is quite high. Manage Weeds on Your Farm quotes one experiment in Ontario, when less than 15% of curly dock seeds and 1% of broadleaf dock seeds survived more than one year.

Large dock weeds in early June
Photo Pam Dawling

Docks that survive the winter as rosettes make new growth in spring (February to March) and flower in April and May. Seeds mature a mere 6-18 days after flowers open. If you see flowering docks, don’t delay!

Both dock species are relatively short-lived perennials, nearly all dying within 4 years. By that time, they may have produced over 240,000 seeds.

Dock leaves are edible by people and pigs, but not cattle, horses or poultry. They may be cooked like spinach and many people find them very tasty.

Weed of the Month for May: Galinsoga

People in early spring weeding spinach that has been hooped and covered overwinter.
Photo Wren Vile

This is the first of my new monthly series of posts. All about weeds.

Sustainable (or Ecological) Weed Management: A Holistic Approach to Organic Weed Management

In the early days of organic farming, maximum use was made of frequent cultivation to kill weeds. Now we know that too-frequent cultivation risks causing soil erosion, and that each tilling or deep hoeing stirs air into the soil and leads to a burning-up of organic matter. The practice of sustainable weed management is about effectiveness – including removing weeds at their most vulnerable stage, or at the last minute before the seed pods explode – and ignoring weeds while they are doing little damage. Work smarter, not harder!

Start with restoring and maintaining balance in the ecosystem. Develop strategies for preventing weeds and for controlling the ones that pop up anyway. An obvious point is to avoid adding new kinds of weeds to any part of your fields. Remove the hitch-hikers from your socks out on the driveway, not when you notice them as you squat to transplant onions! We use our driveway as a convenient place to “roadkill” particularly bad weeds by letting them die in the sun. Beware of Trojan plant swaps!

Weeding in early June. Photo Lori Katz

Weeds are not a monolithic enemy, but a diverse cast of characters. Applying biological principles is not an attitude of war, but more like ju-jitsu, using the weaknesses of the weeds to contribute to their downfall. Develop an understanding of weeds and the different types: annual/perennial; stationary perennials/invasive perennials; cool weather/warm weather; quick-maturing/slow-maturing; and what Chuck Mohler referred to as “Big Bang” versus “Dribblers”. In this monthly blogpost series, we’ll meet various types of weeds, and develop a broader understanding of how and when to tackle each kind.

One factor to consider is how vulnerable the crop is to damage from that weed at that time. Weeds that germinate at the same time as a vegetable crop usually do not really affect the crop’s growth until they become large enough to begin competing for moisture and nutrients. These early weeds have the greatest potential for reducing crop yields if allowed to grow unchecked. We need to cultivate or otherwise control weeds before this 2- to 3-week grace period is over.

Weedy sweet corn. ideally, we would have cultivated two weeks and four weeks after sowing. Photo Bridget Aleshire

The critical period for weed control for the crop is the interval from the end of the initial grace period until the end of the minimum weed-free period, which is approximately the first third to one half of the crop’s life. For vigorous crops like tomato, squash and transplanted brassicas this is four to six weeks; less vigorous crops like onion or carrot need weed-free conditions for eight weeks or more. During that period it is essential to control weeds to prevent loss of yield.

Weeds that emerge later have less effect, and ones that emerge quite late in the crop cycle no longer affect the yield of that crop, although there are long-term reasons for removing weeds to improve future crops.

Know Your Weeds

Lettuce with weeds, easily hoed. Photo Bridget Aleshire

Learn to identify the major weeds on your farm, and any minor ones that suggest trouble later. Observe and research. Start a Weed Log with a page for each weed. Add information about your quarry’s likes and dislikes, habits and possible weak spots. Find out how long the seeds can remain viable under various conditions, and whether there are any dormancy requirements. Note down when it emerges, how soon it forms viable seed (if an annual), when the roots are easiest and hardest to remove from the soil (if a perennial), what time of year it predominates, which plots and which crops have the worst trouble with this weed. Monitor regularly throughout the year, each year. Look back over your records and see if anything you did or didn’t do seems to have made the problem worse or better.

Next think about any vulnerable points in the weed’s growth habit, life cycle, or responses to crops or weather that could provide opportunities for prevention or control. List some promising management options. Try them, record your results, decide what to continue or what to try next.

Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, the corn productivity will max out and the weeds will use the remaining nutrients. Some crops, like carrots and onions never cast much shade at any point of their growth, so that sun-loving weeds like purslane are more likely to thrive there, but not be a problem for crops which rapidly form canopies that shade the ground.

Galinsoga – a fast growing, fast-seeding weed of cultivated soil.
Photo Wren Vile

Galinsoga

This month’s Weed Character is galinsoga, a “Seed Dribbler”, that matures seed while still quite small plants, sheds some, makes some more, and can carry on for a long seed-shedding season.

Encouraging information is that a constant percentage of the seeds that are still left from one year’s shedding dies each year. This varies widely among species – for lambsquarters it’s 31% per year in cultivated soil (only 8% in uncultivated soil). The number of seeds declines rapidly at first, but a few seeds persist for a long time.

While seeds survive better deeper in the soil, they don’t germinate better down there. Larger seeds can germinate at deeper levels than small seeds. If you are trying to bury seeds deep, use inversion tillage, don’t rely on rotavating, as seeds somehow manage to stay near the surface with rotary tilling. Chuck Mohler, author of the excellent book Manage Weeds on Your Farm, has tested this out with colored plastic beads.

We have two kinds of galinsoga: narrow-leaved and hairy. Both behave the same way. They thrive in highly fertile, freshly tilled soil, just the same as you hope your vegetable seeds will. Mostly we think about how to get rid of galinsoga (prompt hoeing or other cultivation before it flowers), or stop it germinating in the first place (mulches). Its flowers attract beneficial insects such as hoverflies, and it can be eaten by humans and livestock. Young leaves can be used in a soup or in mixed dishes. It doesn’t have a strong flavor. The plants contain flavonoids and phenolic compounds, and it has been found to have antioxidant and anti-inflammatory properties. Extracts from hairy galinsoga can coagulate blood. It is an alternate host for certain nematodes and over twenty insect pests. Hairy galinsoga is thought to have originated in Central and South America, and has become naturalized in North America and other temperate and tropical regions.

Galinsoga is a summer annual that belongs to the sunflower family (Asteraceae) and can invade vegetable gardens with dense infestations that crowd out crop plants. The secrets of galinsoga’s success are that its seeds germinate immediately they reach the soil (no dormancy period), it grows very fast, shading out other plants, it sets seed in as few as 30–40 days after emergence, and continues shedding seed as long as it is growing. It also has the knack of re-rooting if pulled and laid on the surface of the bed, if there is any moisture in the soil. Large plants seem able to transfer the water in their cells to their roots, helping re-rooting happen. Seed that is shed early in the year is capable of growing a mature plant very quickly. There can be multiple generations in one warm season. Fortunately, the seeds are short-lived, and have to be in the top 0.25″ (6mm) of the soil to germinate.

Hoe weeds while they are small and you’ll be rid of those with short-lived seeds in a few years. Galinsoga and Outredgeous lettuce.
Photo Pam Dawling

Galinsoga Identification

Hairy galinsoga (Galinsoga quadriradiata), has profuse hairs on stems and leaves. Narrow-leaved galinsoga ( Galinsoga parvifolia), is very similar, except it is not hairy and it has narrower leaves. Leaves are oval with serrated margins and distinct petioles. They are arranged opposite each other on the stems. The flowers have densely packed yellow disc florets and five tiny white ray florets, each with three scalloped teeth at the end. Seeds of hairy galinsoga germinate between 54°F-86°F (12°C-30°C) with an optimum temperature requirement of 68°F-75°F (20°C-24°C). Most of the seed germination occurs from May to June, after the last frost. It flowers abundantly from about late-May until late fall here in central Virginia. Fallen seeds can germinate immediately due to the absence of dormancy requirement. Take advantage of this phenomenon to eradicate hairy galinsoga from an infested field in three to four years by careful management.

Controls for Galinsoga

Prevention of Weed Germination

Hoeing or mechanical cultivation is effective if carried out repeatedly during the early stages of growth (before flowering). Mulches, such as thick (6-mil) black plastic, or straw, hay, leaves, woodchips over cardboard or newspaper, are effective to control galinsoga in small gardens if applied immediately after planting the crop and before the galinsoga germinates.  Tarping is the equivalent solution for larger areas.

Reduction of Weed Seeding

Grazing, or the mechanical equivalent, mowing, will take care of galinsoga in places you are not currently growing a crop. This weed is not usually found in lawns. It has no resistance to frost. Livestock will happily graze it.

Reduction of Viability of Seeds

Most weed emergence happens within two years of the seeds being shed. Not all seeds that are produced will ever get to germinate (I was very pleased to learn that seeds have many ways of not succeeding!) You can help reduce their chances, by mowing crops immediately after harvest, (to prevent more weed seed formation); then wait before tilling to allow time for seed predators to eat weed seeds that already produced. Seeds lying on or near the soil surface are more likely to deteriorate or become food for seed predators than buried seeds, so delaying tillage generally reduces the number of seeds added to the long-term seed bank. (Short-term, they may germinate!)

If they do not get eaten, dry out or rot, seeds on top of the soil are more likely to germinate than are most buried seeds, and small, short-lived seeds of weeds which have no dormancy period, such as galinsoga, will almost all die within a year or two if they are buried a few inches.

Putting it Together

Strategies include

  1. Inversion tillage such as moldboard plowing (seeds will die off deep in the soil within a year or so.)
  2. Mulching – the seeds will not germinate or be able to grow through the mulch, and will be dead by next year. Be sure to rotate the mulched crops around the farm, so that the benefits are not confined to one section;
  3. Grazing with small livestock, or harvesting galinsoga for human consumption, or mowing: especially mow as soon as the food crops are finished, if you cannot till right away.
  4. Tarping (mow first);
  5. No-till cover crops, with summer crops transplanted into the dying mulch;
  6. Stale seed bed techniques, including flaming;
  7. Plant flowers that attract beneficial insects, particularly seed-eating insects, and birds.
Front cover of manage Weeds on your Farm

Resources on Weeds

Gathered Info on Weeds

Spiny amaranth – a weed to exterminate by careful pulling.
Photo Pam Dawling

Following on from my recent seasonal posts on How to succeed with transplanting crops and Direct sown vegetable crops, I reckon people are now thinking about weeds.

Below is material excerpted from the Sustainable Weed Management chapter in my book Sustainable Market Farming, which was also published in Growing for Market as New Ways to Think About Weeds, back in 2011.

Do you need a justification for having some weeds visible among your crops? Do you crave a system to help you get a grip on your to-do list, so you’re not overwhelmed? Sustainable (or Ecological) Weed Management does all this! In the earlier days of organic farming, maximum use was made of frequent cultivation to kill weeds. Now we know that too-frequent cultivation can cause soil erosion, and that each tilling or deep hoeing stirs air into the soil and speeds combustion of organic matter. The practice of sustainable weed management is about effectiveness – including removing weeds at their most vulnerable stage, or at the last minute before the seed pods explode – and ignoring weeds while they are doing little damage. Work smarter, not harder!

Strawberries need a lot of weeding if grown on bare soil.
Photo Twin Oaks Community (Renee)

A Holistic Approach to Organic Weed Management

As always, strive to restore and maintain balance in the ecosystem. Develop strategies for preventing weeds and for controlling the ones that pop up anyway. An obvious way to prevent weeds is to avoid adding new kinds to any part of your fields. Remove the hitch-hikers from your socks out on the driveway, not when you notice them as you squat to transplant onions! We use our driveway as a convenient place to “roadkill” particularly bad weeds by letting them die in the sun. Beware of Trojan plant swaps (nice plants in soil concealing nasty weed seeds)!

Weeds are not a monolithic enemy, but a diverse cast of characters. Applying biological principles is not an attitude of war, but more like ju-jitsu, using the weaknesses of the weeds to contribute to their downfall. This chapter aims to develop our understanding of weeds and the different types: annuals and perennials; stationary perennials and invasive perennials; cool weather and warm weather types; quick-maturing and slow-maturing types; and what Chuck Mohler (Manage Weeds on Your Farm: A Guide to Ecological Strategies) refers to as “Big Bang” types versus “Dribblers”.

One factor to consider is how vulnerable the crop is to damage from that weed at that time. Weeds that germinate at the same time as a vegetable crop usually do not really affect the crop’s growth until they become large enough to compete for moisture and nutrients. If allowed to grow unchecked, however, these early weeds have the greatest potential for reducing crop yields. We need to cultivate or otherwise control weeds before this 2-3 week grace period is over.

The critical period for weed control for the crop is the interval from the end of the initial grace period until the end of the minimum weed-free period, which is approximately the first third to one half of the crop’s life. In other words, the most important time to weed a crop is from 2 weeks after sowing until the crop is half-way to being finished. For vigorous crops like tomato, squash and transplanted brassicas this is four to six weeks; less vigorous crops like onion or carrot need weed-free conditions for eight weeks or more. During that time it is essential to control weeds to prevent loss of yield.

A carpet of weeds, but the crop is easily seen! A good time to hoe!
Photo Bridget Aleshire

Weeds that emerge later have less effect, and ones that emerge quite late in the crop cycle no longer affect the yield of that crop, although their seeds give a reason for removing them to improve future crops.

Know Your Weeds

Learn to identify the major weeds on your farm, and any minor ones that suggest trouble later. Observe and research. Start a Weed Log with a page for each weed. Add information about your quarry’s likes and dislikes, habits and possible weak spots. Find out how long the seeds can remain viable under various conditions, and whether there are any dormancy requirements. Note when it emerges, how soon it forms viable seed (if an annual), when the roots are easiest and hardest to remove from the soil (if a perennial), what time of year it predominates, which plots and which crops have the worst trouble with this weed. Monitor regularly throughout the year, each year. Look back over your records and see if anything you did or didn’t do seems to have made the problem worse or better.

Next think about any vulnerable points in the weed’s growth habit, life cycle, or responses to crops or weather that could provide opportunities for prevention or control. List some promising management options. Try them, record your results, decide what to continue or what to try next.

Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, the corn productivity will max out and the weeds will use the remaining nutrients. Sun-loving weeds like purslane are more likely to thrive among crops (like carrots and onions) which never cast much shade at any point of their growth. They won’t be a problem for crops that rapidly form canopies that shade the ground.

Galinsoga – a fast growing, fast-seeding weed of cultivated soil.
Photo Wren Vile

A few weeds, such as giant ragweed, emerge only during a 3-week interval, while others, such as pigweed and velvetleaf, can germinate during a two-month period, if temperatures are warm enough. Galinsoga seeds are short-lived and germinate only near the soil surface, but velvetleaf seeds can lie dormant for years deep in the subsoil, and germinate whenever they get brought close to the surface. Clearly, different strategies work best with different weeds.

Red Root Pigweed is a “Big Bang” weed – the plant grows for a long time, and then all its seeds ripen at once, as the plant starts dying. Most seeds come from a few large plants – pigweed-monsters that mature late in summer can shed 400,000 seeds! Pulling the largest 10% of the weeds can reduce seed production by 90% or better. We used to ignore pigweed growing in our sweetcorn, once it escaped two cultivations, believing anything that big must already have done damage. Now we pull while harvesting. Some pigweeds are as tall as the corn, but most don’t have mature seed heads. Since starting this a few years ago, we have noticed a considerable drop-off in the number of pigweeds we have to deal with. This is different from the “Seed Dribblers” like galinsoga, which mature seed while still quite small plants, shed some, make some more, and can carry on for a long seed-shedding season.

Silver Queen sweet corn with wilting pulled pigweed amaranth. Corn is a C4 crop, amarnath (pigweed) a C4 weed. Photo Kathryn Simmons

Another useful piece of information is that a constant percentage of the seeds left from one year’s shedding dies each year. For lambsquarters in cultivated soil it’s 31% per year (only 8% in uncultivated soil). The number of seeds declines rapidly at first, but a few seeds persist for a long time. The percentage varies widely among species.

While seeds survive better deeper in the soil, they don’t germinate better down there. Larger seeds can germinate at deeper levels than small seeds. If you are trying to bury seeds deep, use inversion tillage; don’t rely on rototilling, as seeds somehow manage to stay near the surface with rotary tilling. Chuck Mohler has verified this with colored beads.

Most of the weeds in cultivated soils are annuals, but some of the worst ones are perennials, either stationary (tap-rooted) perennials like docks and dandelions, or wandering/invasive perennials with tubers, rhizomes or bulbs (Bermuda grass, quackgrass). Stationary perennials in their first year act like biennials – leaves, roots, but no flowers or seeds. In annually tilled areas, they get killed in year one and don’t often establish. Wandering perennials are a more difficult problem, and understanding apical dominance is important in tackling them – see Reducing the Strength of Perennial Weed Roots and Rhizomes in the book’s chapter.

Burdock is a large perennial weed with a huge root. Photo Bridget Aleshire

The chapter also includes information on Prevention of Weed Germination, Reduction of Weed Seeding, Reduction of Viability of Seeds, Reducing the Strength of Perennial Weed Roots and Rhizomes, and Two Examples (galinsoga and nut sedge).

Knowing and understanding the particular weeds that are giving you the worst problems enables you to design an approach that includes removing weeds at the most important point in their life-cycle, before they do their worst damage. While focusing on that you can relax and ignore weeds that are not doing much harm.

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I have written here on my website about weeds previously. See my blog posts

Resources on Sustainable Weed Management