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

Dealing with weeds

 

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

Dealing with weeds

Why take action against weeds?

Weeds compete with crops for sunlight, water and nutrients, and can encourage fungal diseases by reducing airflow. Too-frequent cultivation to remove weeds can leave the soil more prone to erosion. Each tilling or deep hoeing stirs air into the soil and speeds combustion of organic matter. Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, its productivity will max out and the weeds will use the remaining nutrients.

Remove weeds at their most vulnerable stage, or at the last minute before the seedpods explode —ignore weeds doing little damage.

Types of Weeds

  •   Annuals and perennials;
  • Stationary perennials (docks) and invasive perennials (Bermuda grass);
  • Cool-weather and warm-weather types;
  •  Quick-maturing and slow-maturing types;
  •   “Big Bang” types (pigweed) versus “Dribblers” (galinsoga).
Burdock is a large perennial weed with a huge root. Photo Bridget Aleshire

Sustainable Weed Management

1.      Prevent weeds from germinating

  •  Grow vigorous crops adapted to the locality,
  •  Switch between spring and summer crops in rotation,
  •  Mulch or tarp to bury short-lived weed seeds
  • Plant promptly after cultivation, so weeds don’t get the head start,
  • Transplant rather than direct sowing, giving your crop a head start on the weeds,
  • Use close spacings, leaving less space for weeds,
  • Use drip irrigation rather than sprinklers, discouraging weed germination between the rows,
  •  Plant cover crops, including no-till systems,
  • Reduce tillage whenever you can, for example, by relay planting, where the new crop is planted while the previous crop is still in place, and prevent new weed seeds coming up to the surface.
Remove weeds before they set seed. Thistle seeds blow a long way on the wind.
Photo Wren Vile

2.      Reduce weed seeding

  • Practice timely cultivation, mowing, flaming, grazing by cattle, chickens, ducks, geese. As Margaret Roach says: “No matter what weed you are facing, if it’s flowering or setting seed now, be sure to behead it: mow it down, harvest the blooms for bouquets, or otherwise prevent a successful sexual reproduction cycle.”
  • Reduce weed seed banks to 5% of original levels by preventing weeds from seeding for 5 consecutive years.
  •  Use post-emergence organic weed killers: corn gluten, vinegar, flaming
Dandelions are another perennial weed with seeds that blow and spread easily. Photo Wren Vile

3.      Reduce weed seed viability

  •  Reckon that most weed emergence happens within two years of the seeds being shed.
  •  Encourage seed-eating birds, insects, worms, mice
  •  Small, short-lived seeds of weeds with no dormancy period, such as galinsoga, will almost all die within a year or two if they are buried a few inches. Till and mulch to bury short-lived weed seeds.
  •  Longer-lived seeds (pigweed, lambsquarters, velvetleaf) if buried, may remain viable and dormant for years – Leave such weed seeds on the soil surface, rather than tilling them in! Delaying tillage if weeds have already seeded generally reduces the number of seeds added to the long-term seed bank. Seeds lying on or near the soil surface are more likely to deteriorate or become food for seed predators than buried seeds,
  •  If they do not get eaten, dry out or rot, seeds on top of the soil are more likely to germinate than buried seeds, and you can take prompt action.
  • Use stale seed-beds – prepare bed a couple of weeks before planting, water as if you had planted. The day before planting your crop, hoe the surface shallowly to kill new weeds,
  •  Solarize weedy soil in hot weather to kill weed seeds – mow the weeds, cover the soil tightly with clear plastic, weighted down or dug in round the edges. Bryan O’Hara in No-Till Intensive Vegetable Culture has popularized this technique, which makes a great use for used hoophouse plastic film. Solarizing can produce temperatures of 125˚F (50˚C) whereas temperatures under tarps (see section on perennial weeds) will be more like 110˚F (43˚C). You may need only 1-3 sunny days to kill crop residues with solarization. Cover crops and weeds may take longer to die. The heat will not go deep into the soil in that short time, and so more of the soil life will survive than with tarping.
Solarizing with clear plastic. Photo Pam Dawling

4.      Reduce the strength of perennial weed roots and rhizomes

  • Understand apical dominance: when a rhizome grows a green shoot, chemicals from that shoot prevent other nearby nodes on the same rhizome from sending up shoots.
  •  Act in a timely way – On long rhizomes, after a certain length, the dominance effect is too weak and another node can grow a shoot.
  •  Reduce the strength of perennial weed roots and rhizomes by frequent tilling or digging out.
  • Beware tilling invasive “traveling” perennial weeds once and thinking you’re done – When rhizomes are cut into pieces during tillage, the apical dominance is lost and each piece can grow a shoot of its own.
  •  Consider tarping: after tarping the plot for two summer weeks, 3-4 weeks in spring and fall, and two months or more in winter, dig out or pull up all the weed roots still alive.
  •  Next comes a counter-intuitive move (from Jesse Frost ): sow or transplant an intensive valuable crop in the areas with the worst perennial weed pressure. Of course this will motivate you to deal effectively with the weeds!
  • Pull out the pieces to dry on the surface – the depleted pieces of root or rhizome may die
  •  Or cultivate again when the new shoots have reduced the plant’s reserves (in the roots), but before they have grown enough to send energy back to the roots – it’s more effective than going almost daily after every sprig. Removing the shoots whenever the weeds reach the three- to four-leaf stage can be most effective.
  •  Late summer and fall turn out to be the best time for getting the upper hand over a wide range of common weeds, including Japanese knotweed, ragweed, Ailanthus, bindweed, curly dock and more. See Some weeds are best tackled late summer and fall Margaret Roach in A Way to Garden

Biointensive Integrated Pest Management

The weed strategies above follow the four steps of IPM: prevention, avoidance, monitoring and suppression.

1.      Prevention: Focus on restoring and enhancing natural balance and resilience to create healthy plants and soil, better able to withstand attacks. Maintain soil fertility, good drainage and soil structure; plant resistant, pest-tolerant, regionally adapted varieties; grow strong plants; practice good sanitation,

Hoe the small weeds in this bed of young lettuce soon, and the closing canopy of the lettuce will shade out most weeds after that. Photo Bridget Aleshire

2.      Avoidance: The next stage includes actions to reduce the chances of a weeds taking over. These actions are also known as physical controls. Physically remove weeds. Use good crop rotations, remove weed habitat, deter weeds. Provide habitat for weed seed predators.

3.      Monitoring:  regularly inspect your crops, find out when conditions are right for an outbreak of particular weeds. Be prepared. Identify your weeds and choose good strategies for each type. Decide when it is time to act. How to identify your weeds – online guides

4.      Suppression: When the prevention and avoidance strategies have been exhausted, control measures can be used to reduce damage of crops, while minimizing environmental risks. There are four types of sustainable bio-intensive control measures to choose from, starting with the least damaging to the wider environment:

  • a)      Biological control involves working to boost populations of existing resident weed seed predators. (For a few serious weed pests, like prickly pear, host-specific insect enemies are introduced)
  • b)      Microbial controls (bioherbicides) are plant-pathogenic fungi, bacteria, and viruses to kill weeds. Not common.
  • c)      Botanical control uses plant-based products for pest control. Examples include orange, clove and peppermint oils, and phytotoxic plant residues, such as root exudates from winter rye cover crops, and hay from sorghum, which inhibit germination of small seeds.
  • d)      Biorational controls (aka inorganic, mineral, controls) make use of manufactured products such as herbicidal soaps or strong vinegar.
Hoe weeds while they are small and you can be rid of those with short-lived seeds in a few years. Galinsoga and Outredgeous lettuce. Photo Pam Dawling

Critical weed-free period

One important factor is to observe the critical period of weed control for each crop. This is the period when crops are most affected by competition, whether from weeds, sister seedlings or those of an intercrop. Seedlings suffer more than transplants from being out-shaded. Transplants are soon past their critical weed-free period, perhaps half of it before you even set them out. As well as the critical period, take note of the severity of drop in yield for the particular crop. A lot of the information below comes from The Living Soil Handbook by Jesse Frost, which I had the pleasure of reviewing recently.

  • Small salad crops like arugula, spinach and baby lettuce mix, really need to be weed-free throughout their growth. Apart from the risk of being smothered and producing poorly, there is the risk of including bits of recognizable weeds in your salads.
  • Bulb onions also benefit from being weed-free throughout growth. Like other narrow-leaved plants, they are poor competitors. Carrots also are very poor competitors – for most of us, the over-abundance of carrot seedlings in the row are as much of a threat as the weeds. Parsnips are similar, with the added challenge that they are slow to emerge.
  • Peas do best with no competition, although, because they grow vertically, they can do OK with a companion crop such as spinach (or weeds!) a short distance away.
    Hilling potatoes before the weeds get too big will deal with the weeds as well as giving the potatoes more growing space. Photo Wren Vile

    Potatoes, weeds and standing water. Until the soil drains, the potatoes cannot be hilled, and the weeds here are already large. The yield will be reduced by weeds competing with the potatoes.  Photo Bridget Aleshire
  • Potatoes need 1-8 weeks after emergence free from weeds, although small weeds are not a problem and the process of hilling potatoes (needed to provide growing space) effectively deals with weeds.
  • Beets need 2-3 weeks after emergence weed-free from direct-sowing. My experience is that beets are their own worst enemy, and the clusters of seedlings that emerge from each seed-ball should be singled as soon as possible. Yields can easily drop 1-5% with small-average weeds. Turnips also need to be competition-free for the first few weeks after emergence.
  • Broccoli, cabbage, cauliflower, collards, kale and most Asian greens need 2-3 weeks after transplanting free of weeds.
  • Sweet potatoes need 2-6 weeks free of competition after planting. Because it gets hard to wade in and pull weeds later, we try to keep them weed-free.
Garlic beds under a stormy sky. Keep alliums free of weeds.
Photo Wren Vile
  • Garlic needs 3-7 weeks from emergence free of weeds. If you plant in the fall, start counting in early spring when weeds start to grow again. Like most alliums, the narrow vertical leaves make it a weak competitor.
  • Basil, cucumbers, squash, zucchini, lettuce and many other crops need four weeks from transplanting free of weeds. Be careful not to damage squash roots when removing weeds.
  •  Tomatoes need 5-6 weeks after transplanting free from competition, although they are fairly strong competitors later, and we routinely transplant our hoophouse tomatoes down the center of a bed of salad greens, progressively harvesting the greens over the next month. We have noticed problems only if we leave other crops too close for too long. Always prioritize the well-being of the new crop!
  • Peppers need 5-10 weeks after transplanting free from competition, although the drop in yield is small (5%)
  •  Fava beans need four weeks from emergence free of weeds
  •  Direct sown kale needs 6 weeks from emergence weed-free.
  • Okra requires 6-8 weeks after sowing weed-free. If you transplant okra as we do, half that period will be over by transplanting date.
  • Beans are a crop that can generally out-compete weeds (losing only 3% yield from competition), but keeping the rows clean until the beans flower (about 6 weeks from sowing) will maximize yields.
  • Corn needs about 7 weeks from seeding free of weeds (until there are 6 leaves).
  • Eggplant calls for 8 weeks from transplanting free of competition.
  •  Leeks, another weakly competitive allium, need 12 weeks post emergence weed-free. If, like us, you transplant leeks at about 10 weeks after sowing, this translates to hoeing the beds of transplanted leeks a couple of weeks of transplanting.

Flameweeding

I won’t say more about this here. Click the link to read previous posts.

Mulches

Mulches are a big asset in weed control. Organic mulches also add biomass to the soil. Remember not to use organic mulches around warm weather crops for their first month, as they need warm soil to grow well, and insulating mulches keep the soil cold.

See our experience with Biodegradable plastic mulch

Read Organic Farming Has A Plastic Problem. One Solution Is Controversial about the controversy surrounding biodegradable plastic in Organic Farming

Cover crops

Summer cover crops smother emerging weeds, prevent weed seed germination, between a spring food crop and a summer or fall one. Winter cover crops smother emerging winter annual weeds. Good cover crops for this purpose: sorghum-sudangrass, pearl millet, winter rye, wheat, barley, oats, buckwheat, brassicas (beware – rotation, bugs), lupins, red clover, subterranean clover, berseem clover, soybeans, cowpeas.

Ida Gold mustard (Sinapis alba) contains a gluscosinolate, ‘sinalbin’, a non-volatile compound that has shown the ability to inhibit weed seed germination. Tillage radish has a similar effect. The cover crop needs to be mowed and tilled in. Solarization after incorporating mustard is known as biofumigation.

Cover crops also improve the soil for crop production.

Iron and Clay southern peas as cover crop in the hoophouse, smothering weeds.
Photo Pam Dawling

Sustainable pest, disease and weed management

I’m off to the Southern Sustainable Agriculture Working Group Conference in a couple of days. I’m presenting Intensive Vegetable Production on a Small Scale. At the link you can view a version of the slide show with lots of bonus material! (It was hard to cut the show down to 75 minutes!) I also had a lot of material on sustainable management of pests, diseases and weeds which I couldn’t even fit in the handout, so I’m posting that here.

A ladybug on a potato leaf, looking for pests to eat Photo Kathryn Simmons
A ladybug on a potato leaf, looking for pests to eat
Photo Kathryn Simmons

Biointensive Integrated Pest Management

The goal of IPM is to deal with problems in a systematic and least toxic way. Biointensive IPM goes further in emphasizing non-toxic methods.

There are four steps of IPM: prevention, avoidance, monitoring and suppression.

Sustainable Animal Pest Management

  1. Prevention: Focus on restoring and enhancing natural balance and resilience to create healthy plants and soil, better able to withstand attacks. Maintain soil fertility, good drainage and soil structure; plant resistant, pest-tolerant, regionally adapted varieties; grow strong plants; practice good sanitation,
  2. Avoidance: The next stage is taking actions to reduce the chances of a specific pest taking over. These actions are also known as physical controls. All these methods reduce problems without adding any new compounds into the soil. Use good crop rotations, remove pest habitat, deter known pests, use rowcovers, ProtekNet, low tunnels, high tunnels. Provide habitat for bats, insectivorous birds, spiders, birds of prey and rodent-eating ground predators (snakes, bobcats). Physically remove pests by hand-picking, spraying with a strong water spray, flaming, vacuuming, or by using a leaf-blower to blow bugs into a collecting scoop; solarize soil in the summer to kill soil-dwelling pests, as well as diseases.
  3. Monitoring (is action needed?) : regularly inspect your crops, find out when conditions are right for an outbreak of a particular pest, set traps and lures (sticky traps and pheromone traps) so you know when pests arrive or hatch out. Identify the pests you catch, keep records each year. Be prepared.
  4. Suppression: When the established action level for a particular pest has been reached, and prevention and avoidance strategies have been exhausted, bio-logical, microbial, botanical and mineral control measures can be used to reduce pest damage of crops to an economically viable level, while minimizing environmental risks. There are four types of sustainable bio-intensive control measures to choose from, starting with the least toxic solution:
    1. Biological control involves either introducing beneficial predators or parasites of the pest species, or working to boost populations of existing resident predators and parasites.
    2. Microbial controls refer to the use of fungi, bacteria, and viruses to kill pests.
    3. Botanical control uses plant-based products for pest control. An example is neem oil,
    4. Inorganic (mineral) controls, also known as biorational disease controls, make use of oils and soaps.

 

A zipper spider on a tomato plant, catching anything that lands on its web. Photo Wren Vile
A zipper spider on a tomato plant, catching anything that lands on its web. Photo Wren Vile

Sustainable Disease Management

Diseases need a susceptible host and the presence of a pathogen and suitable environmental conditions. Plant pathogens can be soil-borne, foliar-borne, seed-borne, or a combination of seed-borne with one of the others.

A. Soil-borne pathogens can live in the soil for decades, so long crop rotations are needed. Club Root is one. Fusarium oxysporum and Verticillium dahliae are two soil-borne fungi. Fusarium survives a long time in soil without a host, and can also be seed-borne.

B. Foliar pathogens need foliage! They die in soil in the absence of host plant debris, so practice good sanitation. Late blight (Phytophthora infestans) is a good example of this type of disease: it does not carry over in the soil, on dead plants, the seeds or the stakes. Cucurbit angular leaf spot (ALS) bacteria (Pseudomonas syringae) overwinter in diseased plant material and on the seed coat

C. Seed-borne pathogens: Lettuce mosaic virus is an example of a disease in which the seed is the main source of the pathogen and if seed infection is controlled, the disease is prevented. Other seed-borne pathogens may start life as a foliar-borne or a soil-borne pathogen. Infected seeds will produce infected plants even in clean soil. Pathogens can infect the seed via several routes: The parent plant can become infected by drawing soil pathogens through its roots up into the seed; Pathogenic spores can float in on the air (Alternaria solani, early blight of tomatoes; Anthracnose fungus that affects nightshades, watermelon and cucumber); Insects that feed on the plant can transfer the disease (striped cucumber beetles vector bacterial wilt, which is caused by Erwinia tracheiphila); Insects that pollinate the plant can bring infected pollen from diseased plants.

Rolling biodegradable plastic mulch to prevent weeds, warm the soil and prevent splash-back which can spread diseases from the soil. Photo by Wren Vile
Rolling biodegradable plastic mulch to prevent weeds, warm the soil and prevent splash-back which can spread diseases from the soil. Photo by Wren Vile
  1. Prevention and Avoidance (cultural controls)

Apply good compost and maintain healthy, biologically active soils; Optimize nutrients and moisture for crop vigor;

Practice good soil management (eg timing of tillage) to preserve maximum diversity of microorganisms; Use rotations to minimize disease and improve the environment for natural enemies of diseases; Time your plantings to avoid peak periods of certain diseases; Practice good sanitation of tools, plants and shoes; Use seed hot water and bleach treatments; Plant locally adapted, resistant varieties; Provide good airflow; Use mulches to reduce splashback from soil to plants; Use drip irrigation to reduce moisture on foliage; Use farmscaping to encourage beneficial insects.

  1. Monitor crops for problems

Make a regular tour of your crops once a week to monitor growth and health. Keep good records. If you see a problem, identify it. Plant Diseases Diagnostic lab can help. The mere presence of a disease does not automatically require spraying. The economic threshold (ET) or action level is the point at which losses from the disease warrant the time and money invested in applying control measures.

  1. When control measures are needed
    1. Physical controls: Removing diseased plant parts, protecting vulnerable plants with rowcovers or sprayed kaolin barriers, mulching to isolate plant foliage from the soil, tool and shoe sanitation, soap washes for foliage, hot water or bleach seed treatments, and soil solarization to kill disease spores are all methods that reduce problems without adding any new substance into the mix.
    2. Biological controls: Beneficial animals and insects are more common in insect pest reduction than in disease control, but the use of milk as a fungicide qualifies as a biological control. Plants in danger of developing powdery mildew can be sprayed weekly with a mix of one volume of milk with four volumes of water. When exposed to sunlight, this is effective against development of fungal diseases.
    3. Microbial controls: Homemade microbial remedies employ liquids (simple watery extracts and fermented teas) made from compost. For a simple compost extract, mix one part mature compost with six parts water. Let it soak one week, then strain and dilute to the color of weak black tea. Fermented compost tea can deal with many maladies. If your strawberries are prone to Botrytis, apply fermented compost tea every two weeks, starting when the berries are still green. See ATTRA or the Soil Foodweb site for how to make fermented compost teas.
    4. Botanical controls: Using plant-based products to reduce disease. Neem oil, as well as being a pesticide, forms a barrier on foliage that prevents some fungal diseases from establishing. It degRolling biodegradable plastic mulchdegrades in UV light in four to eight days and must be reapplied if the disease organisms are still around. Like all broad-spectrum insecticides, neem can kill beneficials as well as pests, so caution is needed if it is used. Garlic can be used against fungal diseases: blend two whole bulbs of garlic in one quart (one liter) of water with a few drops of liquid soap. Strain and refrigerate. For prevention, dilute 1:10 with water before spraying; for control, use full strength. Kelp sprays are also used to generally boost the resistance of plants to pest, disease and weather-related problems. Biofumigation by incorporating Ida Gold and Pacific Gold mustards into the soil
    5. Inorganic controls, also known as biorational disease controls: These include Bicarbonates (baking soda) one teaspoon (5 ml) in one quart (one liter) of water, with a few drops of liquid soap as a spreader-sticker against fungal diseases. Oils and soaps copper and sulfur products, as part of a prevention program (not a cure). Several of these need to be used with caution if the plants and the planet are to survive the treatment.

Sustainable Weed Management

Weeds compete with crops for sunlight, water and nutrients, and can encourage fungal diseases by reducing airflow. Too-frequent cultivation to remove weeds can leave the soil more prone to erosion. Each tilling or deep hoeing stirs air into the soil and speeds combustion of organic matter. Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, its productivity will max out and the weeds will use the remaining nutrients.

Remove weeds at their most vulnerable stage, or at the last minute before the seedpods explode —ignore weeds doing little damage. There are different types: annuals and perennials; stationary perennials (docks) and invasive perennials (Bermuda grass); cool-weather and warm-weather types; quick-maturing and slow-maturing types; “Big Bang” types (pigweed) versus “Dribblers” (galinsoga).

  1. Preventing weeds from germinating
  • grow vigorous crops adapted to the locality,
  • close spacings, leaving less space for weeds,
  • switch between spring and summer crops in rotation,
  • drip irrigation rather than sprinklers,
  • mulch to bury short-lived weed seeds
  • plant promptly after cultivation,
  • transplant rather than direct sowing,
  • Multiple cropping, relay planting
  • Cover crops, including no-till, reduced till
  • Encourage seed-eating birds, insects, worms, mice
  1. Reducing weed seeding
  • Reduce weed seed banks to 5 % of original levels when weeds are not allowed to seed for 5 consecutive years.
  • Timely cultivation, Mowing, Flaming, Grazing by cattle, chickens, ducks, geese
  • Using post-emergence organic weed killers: corn gluten, vinegar, flaming
We use flaming to kill quick germinating weeds in our carrot beds. Photo by Brtitany Lewis
We use flaming to kill quick germinating weeds in our carrot beds. Photo by Brtitany Lewis
  1. Reducing seed viability
  • Most weed emergence happens within two years of the seeds being shed.
  • 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
  • If they do not get eaten, dry out or rot, seeds on top of the soil are more likely to germinate than buried seeds.
  • Small, short-lived seeds of weeds with no dormancy period, such as galinsoga, will almost all die within a year or two if they are buried a few inches. Till and mulch to bury short-lived weed seeds
  • Longer-lived seeds (pigweed, lambsquarters, velvetleaf) if buried, may remain viable and dormant for years
  • Avoid deep tillage if you have long-lived-seed weeds
  • stale bed techniques draw down the seed bank in the soil
  • Solarization
  1. Reducing the strength of perennial weed roots and rhizomes
  • Apical dominance: when a rhizome grows a shoot, chemicals from that shoot prevent other nearby nodes from sending up shoots.
  • On long rhizomes, after a certain length, the dominance effect is too weak and another node can grow a shoot.
  • When rhizomes are cut into pieces during tillage, the apical dominance is lost and each piece can grow a shoot
  • But such shoots may be weak – Cultivate again before the new shoots have grown enough to send energy back to the roots, or pull out the pieces to dry on the surface: the depleted pieces of root or rhizome may die.
  • It’s more effective to wait time until the new top growth has drawn down the plant’s reserves (in the roots) before hoeing or pulling, than to go almost daily after every sprig.
  • Removing top growth whenever the weeds reach the three- to four-leaf stage can be most effective

 

Hoeing corn, planting potatoes, sowing fall broccoli and cabbage

Corn at sunrise. Credit Wren Vile
Corn at sunrise.
Credit Wren Vile

More of our time in the garden this week is taken up by harvesting (a sign of success), leaving less time to stay on top of the weeds. On Thursday (June 19) we sowed our fourth of six sweet corn plantings. We have a system I like that helps us stay on top of sweet corn weeds. Each time we sow sweet corn, we hoe the previous planting, thin the plants to one every 8-12″ in the row, and wheel hoe or till between the rows. We have got two Valley Oak wheel hoes that we really like. The handle height is adjustable and they are available with different width hoes (and other attachments).

Courtesy of Valley Oak
Courtesy of Valley Oak

We also hoe the rows of the corn planting before that, and till between the rows and sow soybeans. Soybeans will grow in partial shade, handle the foot traffic of harvesting, and provide some nitrogen for the soil. When we harvest the corn we pull out any pigweed that has somehow survived our earlier efforts. I learned at a workshop on Sustainable Weed Management, that pigweed puts out its seeds in one big burst at the end, so pulling up enormous pigweed is worthwhile, if it hasn’t yet seeded. (Actually you can see it for yourself, but before the workshop I hadn’t noticed!) Our soil has improved over the years, so it is now possible to uproot the 5ft pigweeds. Sometimes we have to hold the corn plant down with our feet, but we do almost always succeed in getting the weeds out.

Today we at last got our June potatoes in the ground. We had planned for Saturday, but the forecast had rain in it, which would have messed up our chance to do the tractor work to cover and hill them. So we postponed till Monday. Well, no rain happened on Saturday, but a big rain happened early Sunday morning! Grrr! So we postponed till today (Tuesday), and happily were successful. June 16 is our ideal date, giving the potatoes plenty of time to grow before our average first frost date of October 21.

I found some interesting maps at Plantmaps.com. You can zoom in on your land. The site also has last frost, winter-hardiness zone, heat zone, drought monitoring, record highs and lows, ecoregions and native plants, on maps for the whole of the USA, and at least parts of Canada. Twin Oaks is in ecoregion 64b – Trap Rock and Conglomerate Uplands!

Yesterday I sowed our first round of broccoli and cabbage for the fall. I sowed 6 kinds of broccoli (Tendergreen, Fiesta, Diplomat, Green magic, Gypsy and Arcadia) and 6 of cabbage (Faroa, Early Jersey Wakefield, Tribute, Kaitlin, Melissa and Deadon)

A happy cabbage plant. Credit Kathryn Simmons
A happy cabbage plant. Credit Kathryn Simmons

We also sowed more squash (Zephyr and Spineless Perfection Zucchini) and cucumbers (our standard General Lee, or Generally, as we prefer to call it) this week. And released some pedio wasp mummies to kill the Mexican Bean Beetles organically. You can read more about how we do this here.

Now we’re fully caught up on planting, we can attack more of the weeds.