How to Remove Dandelions From Your Yard
How to Remove Dandelions From Your Yard
- 1 How to Remove Dandelions From Your Yard
- 2 When to Remove Dandelions
- 3 166 Wilson Road, Middle Swan
- 4 Perth, Western Australia
- 5 08 9250 4575
- 6 Call: (08) 9250 4575
- 7 Organic Weed Control
- 8 Snail and Slug Control
- 9 Preventing and Managing Infestations
- 10 Low Impact Approaches
- 11 Snail and Slug Control Pesticides
- 12 Regulatory Updates on Snail and Slug Control Pesticides
- 13 Integrated Weed Management
- 14 Monitoring
- 15 Weed Management Before Planting
- 16 Weed Management After Planting
- 17 Layby
- 18 Preharvest
Joerg Hauke/Getty Images
- Total Time: 60 mins
- Skill Level: Beginner
- Estimated Cost: $0 to 20
Dandelions, with their little yellow flowers and fluffy seed puffs, can be a nuisance to gardeners when they pop up where they’re not wanted. Above ground their seeds ride the wind currents to propagate the species. And below ground the weed sends down a taproot up to 10 inches long that can be difficult to remove in its entirety. Gardeners typically approach dandelion removal in two ways: pulling the plant or spraying it with herbicide.
When to Remove Dandelions
Dandelions are broadleaf, herbaceous perennials that die back in the winter, though the plant’s roots live on underground. In the early fall, nutrients are transferred from the leaves to the roots, making this the best time to use herbicide. Chemicals applied during this time will be absorbed by the leaves and passed on to the roots along with the nutrients.
You can harvest and eat dandelion greens in the spring. The leaves can be boiled or used raw in a salad. This superfood is rich in vitamin A, vitamin C, and iron. Moreover, the flower can be used in wine or boiled and stir-fried. And the roots can be dried and steeped for a tea. For the best taste, harvest dandelion greens and dig up their roots before the plant goes to seed.
When pulling dandelions to eat, avoid harvesting near roads where road salt or other toxins might be present. Likewise, don’t harvest from a lawn where herbicides and other chemicals have been used. Always thoroughly wash the dandelions before consuming.
166 Wilson Road, Middle Swan
Perth, Western Australia
08 9250 4575
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Organic Weed Control
WEEDS — WHAT TO DO ABOUT THEM?
Every autumn and winter, the ground at our place seems to spring to life. While we struggle to keep things alive in summer, and the earth is brown and dry — come the first rains the landscape suddenly changes, and before we know it we are surrounded by lush, green growth.
The trouble is, that lush green growth is weeds.
Wintergrass, oxalis, cape weed, flat weed, fumaria, onion grass — they’re all here — and more varieties I don’t even know the names of!
I’m guessing if you’re reading this — you have weed problems too!
As an organic gardener, there are things to do to control weeds. You don’t have to resort to using Glysophate. This herbicide, touted as being safe and biodegradeable really doesn’t have such a good name if you take the time to look into research around the world. Why take the chance? Let’s look at what else you can do to keep weeds under control. Methods of Organic Weed Control include:
Weeds will always emerge strongly in a barren piece of land; and particularly disturbed ground which has been dug over, or new soil put down and left. This is because the surface is lovely and friable, meaning seeds which blow in the wind can easily germinate and get good root penetration. In hard, compacted areas where there is regular traffic, weeds don’t tend to grow so readily. So outcompete weeds by growing something else. Look for spreading, quick growing groundcovers. There are a huge range available. Native plants, flowering plants, rockery plants, succulents, and also herbs and edibles. If it is an area which you are wanting to plant into — but not just yet — consider a green manure crop or a flowering annual; something that can grow quickly but will be short lived or ‘disposable’. There is a saying — nature abhors a vacuum. So quite simply — don’t leave any vacuums!
They say one year’s seed = seven years’ weed. Whether or not this is true, it certainly feels like it is! Tackle weeds when they are small. Remove them quickly before they spread too much. Either hand weed, or hoe them into the ground. If the area is far too big — then at the very least whippersnip them before they flower and set seed. Weeds will try to push out more seeds when you do this — so you may need to do it two or three times, a week or so apart. Each time you do however, the plant’s vitality is greatly depleted. Each subsequent lot of seeds the weed is trying to produce will become smaller as the plant uses up vital life force.
This method is reliable and easy to do even in large areas, but you do need patience as it will take several weeks – 4 — 6 in summer, 8 – 10 in winter.
Slash or mow weeds, and remove rocks and large debris from the area. Damp area down slightly – moisture helps the ‘cooking’. Throwing a handful of blood and bone over the weeds before you lay down the plastic also helps cook weeds as they sweat.
Use a sheet of plastic (you can use any plastic, but we’ve found especially in winter, black plastic works best as it attracts more heat). Lay it out over the weedy area and weigh down the edges with rocks, bricks or a little pile of dirt here and there. Starved of sunlight, and without air circulation they can’t grow, and will cook. This method also prevents pollination and seeds spreading, but if seeds are already present then they may survive to germinate next season.
Particularly in summer, temperature under the plastic gets high enough to kill weed seeds and some soil borne pathogens (eg. Root knot nematode). The flipside is that beneficial
organisms can also be harmed, so when you are ready to remove the plastic and plant, don’t forget to top up organic material in the soil to help re-establish soil microbial life
Wintergrass and many other lush green grass provides free food for chooks, ducks and rabbits. If you can, allow your fowl out to forage in weedy areas — they will not only eat the weeds, but help scratch up the soil too.
Did you know many types of weeds are edible? ‘Wild harvesting’ your weeds is in fact a bit of a trend right now! There are books, magazine and internet articles which cover this topic in detail. Make sure there are clear photographs, as positive plant ID is important.
Make weed tea. This is a fantastic way to recycle the nutrients the weeds have been stealing from your soil. It’s easy to do, and makes a great liquid feed for your garden. We have covered how to make weed tea in another fact sheet — click here for instructions on making weed tea.
Mulching over weeds works well to smother them, but you do need to make sure you mulch thickly enough. Using a layer of cardboard or newspaper (about 10 sheets per layer) will help prevent weeds emerging through. Lay this directly on top of the weeds, then put down a nice thick layer of mulch on top. This is an instant garden makeover, and is great if you need to transform an area quickly. Same rules apply as mulching in summer — keep mulch away from stems of garden plants to avoid rotting. Weed seeds can and will blow onto the surface of mulch and germinate — however if you have layed a nice deep mulch layer they are very easy to pick out as the mulch is lighter than soil, and the roots don’t tend to ‘grip’ as well.
See more information on our range of mulches and their use here.
Using heat you don’t ‘cook’ or burn the weeds, but intensive heat applied to weeds causes water in the leaves to heat up and burst the cells as it expands. The cellular structure of the plant is destroyed and the weed dies. In some cases, if the weed has a strong root system, it may eventually re-grow, but this is no different to what happens with using herbicides.
Some councils now use a contractor that has special steam weeder mounted on a truck. This is a forward thinking way to reduce pesticide use, and should be applauded.
You can achieve the same thing at home.
For weeds in paved areas, simply boil your kettle and take it outside. Pour the very hot water slowly and deliberately along the cracks where weeds area growing. Doing this once a week as maintenance should be all you need.
For larger areas, it is worth buying a flame weeder. There are several types available.
Some hardware stores sell a small model which uses butane canisters (the same things you use in those small portable camping stoves). I have not had experience using one of these, but there is no reason why they wouldn’t work effectively.
We have a larger weed burner at home, (pictured here) which attaches to a normal gas bottle with a hose. The brand is a «Weed Dragon». Made in the USA, they are available online in a number of models.
Obviously, a weed burner can’t be used in summer due to the risk of fire, but summer’s not the time when weeds are at their worst. In winter, our weed burner is the most useful thing! I like to use it early when dew is around, or else in between light showers, just to be safe. It is quick and easy and highly effective. It is no more effort to use a weed burner than it would be to use a spray bottle. Definitely I think it’s worth the investment. Click here to see Weed Dragon’s website. They have an Australian distributor here (contact them to purchase)
7. Organic Sprays
Yes, there are a number of organic (even Certified Organic) weed treatments available. Some of these are based on pine oil, and others on vinegar and salt. Always read the label to make sure the product is suitable for your needs.
Here’s a recipe to make your own simple weed spray. (I admit I haven’t tried it — your feedback would be welcome!)
Home Made Weed Killer
Add one cup of common table salt to 1 Litre of white vinegar. Stir or shake to dissolve salt.
After it has dissolved, brush or spray directly on the weed you want to kill. Make sure you don’t get it on your favourite plants.
Note: Using any product with high amounts of dissolved salts will, in time adversely effect your soil’s microbiology. (This includes commercial herbicides and many inorganic fertilisers.) Use sparingly.
Snail and Slug Control
Garden snails and slugs are particularly bothersome garden pests. Prevent them from going after your vegetable patch and ornamental plants with low impact approaches to reduce their habitat and control their numbers. Weigh the trade-offs of using chemical baits before starting a treatment plan.
Preventing and Managing Infestations
Snails and slugs feed on a wide variety of living plants and decaying vegetation. As they eat, they create irregular holes with smooth edges in leaves, vegetables, flowers and succulent plants. They also like to chew on the fruit, foliage and young bark of some trees, particularly citrus. Once a food source is found, these pests will often return to feed at night or on cloudy days. Look for the silvery trails they leave behind to confirm their presence.
Remove Snail and Slug Habitat
During the day snails and slugs hide out under boards, in dense ground covers, in weedy places and in low, leafy branches—anywhere cool and moist is potentially a favorite hangout.
- Focus on areas near vegetable beds and vulnerable plants.
- Thin out infested areas so that sunlight can reach ground level and air can circulate to dry the space. If weeds are a problem, use repellent mulch, such as rough-cut cedar chips.
- Young snails stay close to the place where they hatched for months, providing a clue for where snails are laying eggs.
- Reducing sites for them to shelter will allow fewer snails and slugs to survive and you can easily search them out for removal in the remaining sites.
Protect vulnerable plants and surround areas harboring pests to discourage their movement into other parts of the garden.
- Put floating row covers over vulnerable plants until they grow large enough to withstand predation.
- Wrap copper foil around planting boxes or tree trunks to keep snails out and off of your prized plants. When a snail touches copper metal, it receives an electric shock.
- Heap dry ashes, diatomaceous earth or other abrasive materials in a band 1 inch high and 3 inches wide to protect plants. These barriers are effective, but do not work when wet.
- Some plants are resistant to damage, including: geraniums, California poppies, lavender and sage. Many woody plants and grasses are not appealing to these pests and will have very limited damage.
- Using drip irrigation will reduce the humidity and moisture that these pests thrive on. Make your yard less slug friendly while conserving water.
Read on for information on low-impact methods for snail and slug control. Also included is a comparison of active ingredients commonly used in snail and slug molluscicides.
Interested in finding out more about specific snail and slug pesticide products? The Pest Smart app is now available in the iTunes Store. Conveniently access pesticide data on your iPhone and iPad while on the job, in the store, and at home.
- Search by product name or registration number.
- Search by pest to find pesticide products that target common household and garden pests like ants, fleas, cockroaches, lawn weeds and aphids.
- Quickly verify the eligibility of a pesticide product for use in the LEED v4-certified Integrated Pest Management (IPM) program.
- Compare products and find least-toxic alternatives to streamline decision-making.
- Link to PRI’s Pest Management Bulletins to learn about low-impact methods of pest control that minimize pesticide use and exposure.
Low Impact Approaches
- When suffering heavy damage, look for slugs and snails daily. Pay special attention to the places they like to hide. When populations decline significantly, a thorough weekly handpicking will help keep their numbers down.
- Encourage them to come out of hiding by watering an infested area in the late afternoon. Take a moonlit stroll with a flashlight or get up early in the morning to catch them in your garden.
- Wear rubber gloves if needed, pick them up, and place them in a sealed plastic bag destined for the trash. Or dump them into soapy water before adding them to the compost pile as fertilizer; crushing these pests is also fast and effective.
- Beer will draw in any slugs and snails within a few feet of a trap. Replenish every few days to keep levels high enough for drowning, install a raised top to reduce evaporation and make sure traps have deep vertical sides to prevent escape.
- Slugs and snails are also attracted to inverted melon rinds, citrus peels and potato slices. Check your traps daily and remove any pests found.
Support Natural Enemies
Slugs and snails have many natural enemies: ground beetles, toads, turtles, birds, snakes, rodents and pathogens. Their predation will compliment other control strategies.
- Ducks and geese in particular love to snack on snails and slugs. When penned in infested areas they will quickly reduce populations. Be careful, birds also eat seedlings and tender plants.
- For the control of snails in citrus orchards, the decollate snail provides effective biological control in Southern California. They are only available for release in certain counties due to their potential impact on endangered mollusk species. Be aware that they also feed on seedlings, plants and flowers.
Snail and Slug Control Pesticides
Types of Snail and Slug Control Pesticides
There are many products available that target slugs and snails, including bait, granule, and dust formulations. When using these chemical products, take precautions to minimize human, pet, and environmental exposure. The information below will help you understand the risks associated with the active ingredients in these products.
Potential Consequences of Using Snail and Slug Control Pesticides
Recognize that when you use slug and snail pesticides, you should be ready to deal with these potential consequences:
- Methiocarb is a restricted use material that must be applied by a licensed professional. It is also highly toxic to pets, who may become very ill or die from non-target poisoning.
- Baits containing the active ingredient metaldehyde are very toxic to cats and dogs. Dogs are particularly attracted to its pelleted form and may be poisoned from eating the bait.
- Some metaldehyde products are formulated with carbaryl to increase the spectrum of pests controlled. Carbaryl is toxic to pets, wildlife and beneficial insects, including honey bees.
- Baits are toxic to all snails and slugs, including predatory decollate snails and native species.
Precautions to Take When Using Snail and Slug Control Pesticides
If you determine that pesticides are necessary, take these precautionary steps to reduce the potential for adverse effects:
- Isolate your treatment area to prevent non-target poisoning.
- Don’t use methiocarb or metaldehyde baits where children or pets may be present.
- Avoid getting any bait on plants, especially vegetables.
- Use baits sparingly. Overuse can lead to the creation of resistant snail and slug populations or pests that ignore the bait you set out.
Lower Impact Pesticide Snail and Slug Treatments
|Bordeaux Mixture||A mixture of copper sulfate and lime, it poses a moderate acute oral toxicity risk. Toxic to fish, invertebrates, and aquatic organisms. Brush a Bordeaux mixture onto tree trunks to repel snails; one treatment should last a year.||Dust, Spray|
|Boric Acid||Boric acid and other borates occur naturally in the diet and have relatively low acute toxicity . They are not absorbed through the skin; however, ingestion of small amounts of boric acid every day over several months has been shown to reduce sperm counts in laboratory animals. Borates are toxic to plants.||Bait pellets, Granules, Dust|
|Diatomaceous Earth||Causes lung irritation when inhaled. Long-term exposure to diatomaceous earth dust is associated with lung cancer in occupational settings.||Dust|
|Iron Phosphate||Low acute toxicity to humans, pets and wildlife. Pets that eat bait may get an upset stomach.||Bait pellets, Granules|
Pesticide Snail and Slug Treatments With Significant Adverse Effects
|Carbaryl||Toxic to the nervous system of pets, people, and bees. Classified as a likely carcinogen by the EPA. Carbaryl is often added to metaldehyde bait to increase its toxicity . Highly toxic to bees and other beneficial insects.||Bait Pellets|
|Metaldehyde||Moderate acute oral toxicity for humans. Metaldehyde is toxic to dogs, cats and birds. Pelleted baits can cause non-target poisoning in pets and wildlife.||Bait Pellets, Granules, Dust, Spray|
|Methiocarb||High acute oral toxicity and moderate acute inhalation toxicity. Highly toxic to birds, bees and other beneficial insects. Methiocarb is also highly toxic to aquatic species.||Bait Pellets, Granules, Powder|
|Spinosad||Spinosad is often added to iron phosphate bait to increase the number of pests controlled. It poses a low acute toxicity risk to humans and is not likely to cause cancer or other long-term harm. Long-term studies have not been conducted. Moderately toxic to fish, aquatic invertebrates and beneficial insects.||Bait pellets|
Regulatory Updates on Snail and Slug Control Pesticides
On June 22, 2007 the EPA issued an Amended Reregistration Eligibility Decision document revising the label requirements for metaldehyde products, including new risk mitigation measures. Application of metaldehyde is prohibited unless children and domestic animals can be excluded from the treated area from the start of the application until applied material is no longer visible.
Integrated Weed Management
An integrated weed management program is essential for onion and garlic production because of the unique challenges posed by their planting densities and susceptibility to weed competition. These crops are slow-growing and shallow-rooted, planted at high densities, and susceptible to severe yield loss from weed competition. Their narrow, upright leaves do not compete well with weeds, and their long growing season allows for successive flushes of weeds. Weed control is often challenging in these crops because few herbicides are registered, mechanical cultivation is often limited in high-density plantings, and handweeding can be costly. A good integrated weed management plan can increase the ease and effectiveness of these management tactics.
Planting densities for onion and garlic pose unique challenges to weed management. These crops are sown at high plant densities and are not thinned to produce the greatest possible yield per acre. Onions are planted with 4 to 10 seed lines on beds that are 40 to 80 inches wide (furrow to furrow), or 36 inches wide in the intermountain area. Garlic is typically planted with 2 to 4 seed lines on 40-inch beds. These planting configurations limit cultivation to the furrow and narrow row middles on the bed top.
Emphasis must be placed on techniques that reduce weed pressure before planting, such as the use of the stale seedbed method, weed-free seed, or soil solarization. Any method that reduces the amount of weed seed in the soil will reduce weeding costs during crop production. Another good way to prevent weed problems is to control existing weeds before they go to seed.
Monitor the fields and keep records (PDF) of the weed species present in each field during the growing season. Pay special attention to weeds likely to be present at planting time. Not only are these records valuable in choosing the most suitable fields for growing onions and garlic, they also help track the occurrence of hard-to-control weeds.
Plant onion and garlic in the most weed-free fields available, and avoid fields with high amounts of difficult-to-control perennial weeds such as nutsedge, field bindweed, bermudagrass, johnsongrass, clovers, and Canada thistle. If weedy fields must be used, control weeds during fallow periods using stale seedbeds and herbicide application or shallow tillage. Fumigation with metam potassium or metam sodium can also be used to reduce the weed seed bank.
Nonchemical control options are primarily limited to the preplant period in onion and garlic production. For most weed control methods, timing is important because small weed seedlings are easier to kill than larger weeds.
Weed Management Before Planting
Nonchemical control options are primarily limited to the preplant period in onion and garlic production. For most weed control methods, timing is important because small weed seedlings are easier to kill than larger weeds.
Crop Rotation With Cover Crops
Cover crops are rarely used in onion and garlic production. However, they can provide a variety of benefits to the crop when used in crop rotations, especially if they are grown in the fall prior to planting Alliums.
Timing is the key to whether cover crops promote or inhibit weed growth. If cover crops become established quickly, they will suppress weeds. Adequate seeding rate of the cover crop is also an important factor in providing rapid ground cover and suppressing weeds. Vigorous cover crops that provide complete ground cover in the first 30 days of the cover crop cycle are very competitive with weeds and greatly limit weed growth. Competitive species include cereal rye (Secale cereale), white mustard (Sinapis alba), and Indian mustard (Brassica juncea). Avoid slow-growing winter cover crops, including legumes and many cereal-legume mixes, which allow substantial weed growth and set seed early in the growth cycle of the cover crop. Cover crop residues must have adequate time (at least 3 to 4 weeks) to break down in the soil before planting onion and garlic, which require shallow, precise seeding depth with good seed-to-soil contact.
Cover crop residues can increase pressure from certain diseases and insect pests. For example, cover crops can increase seedcorn maggot numbers. If a cover crop is used, incorporate the cover crop three to four weeks before planting onion or garlic to avoid tilling in green residues that attract this pest.
Cover crops also have the potential to increase weed pressure for the following reasons.
- Annual weeds frequently establish themselves at the time of the cover crop.
- Depending upon the species, weeds can grow in the cover crop and set seed unnoticed.
- Weeds often decompose before the end of the cover crop cycle, making their detection difficult. In such cases, the cover crops act as nurse crops to weeds, making substantial contribution to the weed seed bank.
It is important to monitor your cover crops, particularly in the first 40 days following seeding, to make sure that they are not creating a weed problem for subsequent plantings of onion and garlic.
Solarization effectively controls seedlings (but not mature plants) of bermudagrass, johnsongrass, and field bindweed, and is more effective on annual weeds than perennial weeds. It partially controls yellow nutsedge, but does not control purple nutsedge. Annual weeds with a harder seed coat such as little mallow and velvetleaf are often hard to kill with solarization.
Plan to solarize soil according to planting time: plastic must remain in place for a minimum of 4 weeks, and the best results occur when the crop is planted immediately after removing the plastic. For some crops, growers burn holes into the plastic mulch and transplant directly into them; however, this practice may be of limited value for high-density plantings of onion and garlic.
Because solarization requires a summer fallow, it works best with a fall-planted crop. In the desert and Central Valley, the plastic should be in place during June through August, and can remain in place until planting begins in the fall.
Solarization may not be practical in areas with short growing seasons, or in coastal areas, where it does not heat the soil as deep. In coastal areas, apply plastic in fall when there is less chance of fog (i.e. August and September). Cultivate solarized soil less than 3 inches deep to avoid bringing viable weed seeds to the surface, where they germinate.
For more details on how to effectively solarize soil, see Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377.
Flaming can be used to kill or suppress the flush of weeds anytime between seeding the crop and its emergence. This technique is particularly effective on crops that have slow seed germination like onion, where nonprimed seed is used. Timing is critical: flaming must occur just prior to the emergence of the onion plants, when a good number of weeds are emerged. Flaming is more effective on small (i.e., less than two true leaves) broadleaves than on grass weed species.
Propane-fueled flamers are the most common type of flamer used for this method. Other equipment without an open flame includes hot water or steam applicators and infrared devices. Flamers can be handheld or mounted on a handcart or tractor. Mechanized flamers have multiple burners, while small devices typically have a single flame source.
Typically, flaming can be done at 3 to 5 miles per hour through fields, although this depends on the heat output of the unit being used. Briefly touch the basal stem area with the tip of the flame to disrupt the cells; do not flame weeds to the point where they char and burn. Best results occur under windless conditions, as winds can prevent the heat from reaching the target. Early morning or evening are the best times to observe the flame for adjustment.
Determine the correct working pace or travel speed by checking weeds after flaming a test area. Weeds are being killed if gently pressing their leaves between your thumb and index finger creates a water-soaked appearance, indicating that cell membranes have ruptured. Plants may wilt, change color, or appear unaffected soon after flaming. Even if no change in the weeds is evident immediately, proper flaming causes plants to yellow and die within several days.
Fire is a serious hazard when flaming weeds. Only an experienced operator with demonstrated skill and good judgment should be allowed to flame weeds. Wet conditions during the rainy season or after a thorough irrigation are often good times to flame. Work in the early morning or late evening when winds are lower and any open flame is more visible. Proper flaming should not create smoldering vegetation or air pollution other than fuel burning emissions.
Use good judgment to identify hazardous situations in which flaming should not be conducted due to the risk of starting a fire. Do not use flame weeders in dry areas or during the dry season. Be especially cautious around mulch and leaf litter. Keep fire suppression equipment (e.g., a fire extinguisher, shovel, water) handy in case of an accident.
To prevent the increase of weed seed in the soil, cultivate weeds before they set seed in cover or rotation crops. After incorporation of the cover crop (if a cover crop is used), clean cultivate the field before planting onions or garlic.
Deep plowing is a tillage technique that buries weed seed or propagules of perennial plants below the depth at which they can germinate. The viability of buried weed seed declines over time. A relatively long interval (3–5 years) is preferred between deep plowing and subsequent deep plowing, to avoid bringing up large numbers of viable weed seed back to the soil surface. In fields heavily infested with nutsedge, plow fields with a specialized moldboard plow that fully inverts the soil, to bury tubers 10 to 12 inches. This can reduce up to 95 to 98% of nutsedge in the field.
This method can provide substantial weed control. It involves controlling the final flush of weeds before planting, followed by minimal soil disturbance to reduce subsequent weed flushes. To do this, prepare a seedbed and preirrigate it to germinate weed seeds. Cultivate as shallow as possible to kill emerged seedlings and prevent bringing up weed seed from deeper soil layers. Other options for killing the flush of weeds include flaming and foliar herbicides. The crop can then be planted on these beds soon afterward. If an herbicide is used, be sure to follow label directions on plantback restrictions.
The time of year and the irrigation system used may also affect the efficacy of this technique. Irrigate and cultivate as close as possible to planting time to ensure that soil temperature and climatic conditions are similar to the crop germination period, and to maximize weed control. If the interval between irrigation-cultivation and planting is too long, the weed spectrum (seasonal variation in weed species) may change due to changes in season or weather. Using shallow tillage 14 days after irrigation can reduce up to 50% of weeds in the subsequent crop.
Herbicides, combined with good cultural practices, control most weed pests of onion and garlic. There are specific herbicides that are applied before planting or after planting.
Herbicide selection depends upon the weed species that are expected to occur. Plantback restrictions need to be considered when selecting herbicides—herbicide residues in soil can limit the growth of sensitive rotational crops. Herbicide labels are the best source of information on plantback restrictions.
Preplant treatments are used in fields with persistent perennial weed problems. Metam sodium will destroy most weeds present. Paraquat and glyphosate can be used before the crop is planted to control emerged weeds. Glyphosate has been particularly helpful in controlling perennial weeds the season before planting.
Organically Acceptable Methods
Use the above-mentioned nonherbicidal methods in an organically certified crop. The stale seedbed method and cultivation are especially important preplant weed management tactics in organic onions and garlic.
Weed Management After Planting
Cultivation is one of the most effective postplant cultural weed control practices. Because of the high-density plantings of onions and garlic where most of the bed top is occupied with the seedlings, cultivation is often limited to a narrow band on the bed and the shoulders of the bed and furrows. Not all planting configurations of onions allow for bedtop cultivation, but the middle of the bed can be cultivated in garlic production.
The goal of cultivation is to remove weed seedlings as close to the seed row as possible without disturbing the crop. Precision guidance systems for cultivation (e.g. EcoDan®) can help improve the accuracy of cultivation operations. More precise cultivation allows for reducing the width of the uncultivated band, thereby removing a higher percentage of the weeds. Uncontrolled weeds in the seed line can be removed by postemergence herbicides or by handweeding.
Handweeding, although effective, is costly. Handweeding is particularly difficult in onion due to close plant spacing and the placement of multiple seed lines in a single bed. Handweed carefully to avoid damaging or killing onion plants, especially those that are young. Preventive measures, precision cultivation, and herbicides can also make handweeding less time-consuming and more effective.
Flaming can be used to kill the flush of weeds any time between seeding the crop and its emergence. This technique is particularly effective on crops that have slow seed germination. However, its use in onions is limited if the onions germinate too quickly. This is particularly true in fields where primed seed is used.
Foliar-applied herbicides may be used after crop emergence to control established weeds. Layby herbicides are applied to clean-cultivated soil, typically at the 4- to 5- leaf stage of crop development, to keep the crop weed-free until harvest. Most fields require one or more postplant preemergence applications and one layby application. Split applications are most common for controlling weeds throughout the season, and to prevent unacceptable crop injury from herbicides.
Herbicide application sequences in onion and garlic typically involve applying preemergence herbicides to control or slow the growth of weeds germinating shortly after planting, and applying postemergence herbicides during the 1- to 5-leaf stage to control any weeds that escape preemergence treatments. Layby herbicides can help prevent weed flushes after cultivation or weeds that tend to germinate later in the growing season.
Preemergence herbicides typically require activation through irrigation. In both onion and garlic, DCPA, bensulide, ethofumesate, and pendimethalin can be used preemergence. However, preemergence use of pendimethalin is only registered for some areas and crops as directed by special labeling (see the Herbicide Treatment Table for more information regarding use at 75% radical emergence and the loop stage). In garlic, the above-mentioned materials can be used, as well as flumioxazin and oxyfluorfen. Pendimethalin controls many annual grasses and broadleaf weeds, and provides optimal weed control through sprinkler irrigation. In the southern San Joaquin Valley, a common practice is to combine application of flumioxazin or oxyflourfen with pendimethalin to control weeds after planting garlic.
DCPA may be applied to bulb onions before or at seeding or transplanting, before weeds emerge. DCPA suppresses weeds and delays their growth, giving the crop time to mature. Later, when postemergence herbicides can be used, weeds are small and easier to control, whereas the crop has become large enough to withstand the herbicide application.
In both onion and garlic, occasionally postplant applications of glyphosate or paraquat are used to control germinated weeds before the crop emerges. The timing of this application is critical, because any emerged crop plants will be killed if contacted by these herbicides. If applied at more than 1% crop emergence, glyphosate may reduce the stand.
Several herbicides, including grass-selective herbicides, are available for postemergence use in both onion and garlic. Clethodim controls annual bluegrass, whereas other herbicides do not. See the Herbicide Treatment Table for more information.
Oxyfluorfen and bromoxynil can only be used on young onions (see the Herbicide Treatment Table for additional information). Oxyfluorfen is complimentary to bromoxynil in onion; together they control a wider spectrum of weeds than either do alone. They are usually used in sequence about 1 week apart depending on the crop growth rate and weeds present, and the order in which they are applied may vary according to experience. They can also be tank-mixed, or the sequence strategy can be combined with the tank mix method. If tank mixing these two chemicals, use a sufficient spray volume per acre and closely follow the label to avoid crop injury. Oxyfluorfen is commonly used when the crop has 1.5 fully developed true leaves, followed by an application of both oxyfluorfen and bromoxynil at the 2- and 3-leaf stages.
Ethofumesate can provide control of a variety of broadleaf and grass weeds. Dimethenamid controls yellow nutsedge if applied before nutsedge emerges.
Organically Acceptable Methods
After planting, use cultivation, flaming, and handweeding in an organically certified crop.
Cultivation will remove weeds from the furrow and sides of the bed. In the intermountain region, cultivate weeds between the 4- to 6- leaf stage. When drying out the field out for cultivation, avoid causing water stress to the crop. Take care to avoid injury to the root system on outside seed lines while cultivating.
Cultivation during the layby period can sometimes stimulate new flushes of weed species such as pigweed.
DCPA and pendimethalin are registered for use during the layby period in onion. Pendimethalin is available for layby use in garlic. These herbicides may be applied over the top of the crop and activated with irrigation. They do not control emerged weeds, and are used after cultivation of furrows. Some carryover can occur under certain conditions, creating a plantback problem. Consult the herbicide label before application.
Organically Acceptable Methods
During the layby period, use cultivation and handweeding in an organically certified crop.
Late-season weeds can be a problem in onion and garlic fields in the Central Valley, so it may be necessary to impose preharvest weed management efforts. Problematic weeds during this period include nightshade, nutsedge, and field bindweed. Weed growth during this time can increase the relative humidity within the field, increasing the risk of bulb rot. Harvest efficiency can also be hindered as weeds become entangled in the topping and harvest equipment, particularly with field bindweed.
If tall annual weeds (like nightshade) occur in patches in the field, using hand knives to sever the shoot from the roots can be effective. Controlled weeds should be layed in the furrow bottoms or removed from the field so they do not interfere with topping and harvest equipment.
When the weed infestation is widespread across the field, it is more efficient to apply glyphosate as a preharvest aid application. This is effective at drying down weeds like nightshade, nutsedge, and field bindweed, and allows for improved harvest of the crop. Application of glyphosate as a preharvest aid is available for onion and garlic grown for processing under a Special Local Needs [Section 24(c)] registration (see the Herbicide Treatment Table for more information).
UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453