Weed Prevention
The Noxious Weed Seed Free Forage Program   Weed Prevention Student Paper    

Weed Prevention Measures and Methods
By: Shane Clark  2/29/00      Weed Prevention Links     Revegetation    

Weed spreading via Vehicles: A vehicle driven through a weed infested area can become a weed spreader.  Seeds can lodge in the vehicle’s tires, undercarriage, and countless other nooks and crannies.  These seeds can travel for miles before becoming jarred loose and infesting a new area.  To prevent this, try driving exclusively on well-established roads, trail, and avoid driving through weed infested areas.  If you do have to drive through weeds, thoroughly wash and spray the undercarriage, tires, and body with water as soon as possible. (1)

Spreading through animals: When an animal eats food that is contaminated with weed seeds, the seeds can still grow and survive in the digestive system and be released days later.  Pack animals (or other animals that are going to be moved for some distance) can spread weeds in this manner if they have eaten contaminated food before being moved. This type of spreading can be avoided by feeding the animal certified weed free food for four days before riding or moving it to a new weed free area.  Brush and clean their coats and hooves thoroughly before the trip and carry only weed free feed on the trip. (1) Also, use weed free hay or straw for the bedding in the trailer. (4)

Human prevention efforts: People can also directly spread noxious weeds by picking them for their often attractive flowers.  Do not pick wild flowers that may be noxious weeds!  We can all do our part in weed prevention if we can recognize noxious weeds and know what to do when we find them.  If you find a clump of weeds that lack flowers and seeds, simply yank them from the ground and leave them there.  However, if the weeds do have flowers and seeds, put them in a plastic bag and burn or dispose of them in a landfill.  If you stumble upon an infestation, contact the owner or land managing agency so they can take measures to control the infestation and spread of the weed. (1)

Weed prevention through proper maintenance and care of fields, lawns, etc: To help maintain weed free crops, lawns, or pastures, keep them well irrigated, fertilized, and not overgrazed. Strong, healthy grass, alfalfa, and other kinds of plants are more likely to stop weed development. (2) Weeds spread like wildfire in thin, stringy grass.
The best lawn weed prevention is a thick, healthy, and well-cultivated turf.  Poor fertilizing, mowing, irrigation, watering, drainage, insect or disease outbreaks, and bad soil compaction can all lead to a thin, unhealthy turf.  Using correct mowing height, fertilization and irrigation methods, soil drainage, and other cultural methods will develop a dense, healthy turf that will naturally ward off weeds.  Sanitation is another method to prevent spreading weeds. Sanitation involves the practice of not planting or removing certain plants from a specific area (like the lawn).  Violets can invade the lawn if planted on the edge of the flower bed. Simply try planting the violets away from the flower bed’s edge to avoid this infestation.  Keeping lawnmower blades and other lawn management equipment clean is another sanitation prevention measure.  If the lawn or field must be seeded or reseeded, only buy high quality seeds so there is a less chance of also planting some weed seeds.  Certified weed free seed will ensure that the seeds are of very high quality. (3)
 Never buy the cheaper uncleaned native seed straight from the harvester, because there’s a good chance it will also contain weed seed.  Collecting and planting local native seed right from the land is also a very effective method.  It retains local genetics and will spread no new weeds.  Finally, make sure that it is absolutely necessary to seed or reseed.  Perhaps only in graded or other damaged areas of the land it is necessary to reseed.  If the land and native plants can still survive without reseeding, it is advisable not to even attempt it.
Contractors who plant seeds for you can spread noxious weeds to your land if you’re not careful.  Emphatically indicate that you only want certified weed free seed.  Be sure to inspect all the seed bags and double check you’re getting what you ordered.  Check to see if the contractor applied the right amount of seed per acre that he had specified. (4)
Make sure not to overgraze pastures because permanent damage to the grass can occur and weeds will then easily spread.  Move the animals around to different pastures periodically to prevent this.
Probably the most important step of prevention is early detection.  Weeds are far easier to control in the early stages of development. If the weeds do get a strong foothold, they will grow extremely deep roots that make it very hard to control and remove. (2)

Preemergence herbicidal weed control: This is a weed control and prevention method that is used for annual grasses and annual broadleaf weeds.  There are several different herbicides that are specific to different weeds.  Make sure to correctly identify the weed, and then purchase the correct herbicide.  The herbicide is applied a few weeks before seed germination.  For summer annuals apply in the spring, and for winter annuals apply in the fall.  The exact time for herbicide application varies from place to place and climate to climate.  Check with your county extension agent for your area. For maximum effectiveness many steps can be taken to ensure the herbicide reaches the soil where the weed seed is.  Thoroughly rake the lawn to remove any trash, leaves, and dead grass that could block the herbicide from reaching the soil. Mowing also greatly maximizes the amount of herbicide that reaches the soil.  When applying the herbicide, apply at half rate with double coverage in both directions (apply half of the indicated amount, but go over the lawn twice, once in each direction).  This is more effective than full rate in one direction.  When using a granular herbicide, never apply when the turf is wet.  Irrigate the lawn thoroughly after application, so that the water will carry the herbicide down into the soil.  If not watered, the herbicide will remain on the surface and be degraded by sunlight. (3)

Weed spreading through Mulching (for example: grass cuttings, straw, chippings, etc.): Mulching eroded and bare areas, sandy roads, and new construction sites is unavoidable but is very likely to spread weeds.  Weeds can be spread in a construction site if the specifications and contracting work for mulching and seeding are poorly done.  Good specifications must be written and all materials that a contractor uses must be thoroughly checked.  Another way to prevent using weed contaminated mulch is to hire a contractor to cut and bale weed free native grass on public land.  This eliminates the chance of introducing new weeds and increase the area’s native grass population.  When chipping brush, always do it in-house or by contractor with native plants grown on public land.  Never accept free chippings from a local tree-trimmer or gardener because it may contain weed seeds.  Straw can also bring in noxious weeds if caution isn’t taken.  Rice straw generally is safer than oat, barely, and wheat straw.  Oat, barely, and wheat straw are prone to be contaminated with yellow star thistle.  If you must buy those types of straws, buy it locally and ask the supplier if the ranch from where the straw was taken is infested with yellow star thistle or other noxious weeds.  Finally, make sure to monitor sites where seed, straw, mulch, etc. has been applied for weeds.  If weeds do sprout up, destroy them before they can seed.  If a contractor applied the mulch or other material to the site, be sure the contract specifications require the contractor to keep the site weed free for a certain period of time. (4)

Weed Prevention in the Garden: The best weed control in gardens is to prevent weeds from even getting a foothold.  Prior to planting, make sure all the seeds and the garden soil are all weed free.  If weeds do emerge in the garden, it becomes backbreaking work to remove and destroy the weeds.  The type of vegetables planted in the garden can be the best weed prevention of all.  Vegetables that grow fast and are effective at shading (suppressing) weeds is the best way to naturally prevent weeds.  Shading is most effective when the vegetable rapidly germinates and sprouts before the weeds.  To speed up the germinating process, plant certified weed free vegetable seeds at the proper depth (for that particular variety of vegetable) and adequately water and fertilize the soil. Common vegetables that can serve as these so called “smother” crops include the following: pumpkins, squash, beans, southern peas, cucumbers, sweet corn, melons, Irish potatoes, sweet potatoes, and tomatoes.  If proper cultural methods of prevention are taken, these smother crops can prevent weeds from germinating in future garden generations.  Plant the smother crops in the fall and kill them off in the spring before the desired garden vegetables are planted.  Rye, ryegrass, and other straw residues from the smother crops can prevent early germination of some weeds by up to 75% or more.  Do not use this method if small seeded vegetables such as lettuce are going to be grown because their germination will be reduced.  Also, rotate where the smother crops and vegetables are being planted in the garden.  If the same crops are grown in the same area every year, then the amount of weeds will increase.
 Mulches can be used to prevent weed germination and growth in gardens.  Organic mulches consist of plant matter and naturally decompose in the soil.  Those that are commonly used in gardens include manure, bark chips, ground corncob, sawdust, leaves, straw, etc.  Do not use straw that contains weed seeds as mulch.  If the straw does contain weed seeds, water the straw until the seeds germinate and then air-dry repeatedly until the seedlings are killed.  When applying the mulch in the garden soil, spread the mulch evenly three to four inches deep around the base of the vegetable.  To water and fertilize the vegetables, simply rake back the organic mulch and then return it after watering.  Inorganic mulches are mulches that do not decompose and most be removed from the soil.  Plastics are the most common inorganic mulches.  Black plastic is better than clear plastic because it blocks sunlight that weed seeds need to germinate.  The soil must be well fertilized and watered before the plastic is applied.  Weed fabrics can also be used as an effective weed suppression mulch and can last for twenty years when buried in soil.  Organic mulches are mainly used in the latter part of the spring when the soil is warmer.  If organic mulch is applied to cold soil, the soil warms more slowly and the vegetable growth rate is slower.  Inorganic mulches are much more effective in the early spring when the soil is cooler, because they can raise the soil temperature up 6o to 8o F.  (5)

1) Noxious Weeds a Growing Concern. U.S. Department of the Interior and Bureau of Land Management.

2) Russell Johnson. Prevention of Noxious Weeds. [Online] available:
http://www.arapcsuext.org/agri/prevent.htm. Copyright 1999.

3) Roch Gaussoin and Alex Martin. Turfgrass Weed Prevention and Management.  [Online] Available: http://ianrwww.unl.edu/pubs/weeds/g1045.HTM#WEED%20CONTROL.

4)  Bureau of Land Management, California. Weed Prevention and Management Guidelines for Public Lands. [Online] Available:

5) David W. Monks and Larry Bass. Weed Control in Vegetable Gardens.  [Online] Available: http://www.ces.ncsu.edu/hil/hil-8101.html

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