Prevention

Curly dock fruits have a papery 3-winged structure that surrounds the 2 mm long triangular achene. The structure helps fruits to float, thus disseminating seeds within the farm. 

Minimize field movement of weed seeds through irrigation/rainwater

Many weed seeds, due to their low density, are capable of floating on water until surface tension is broken including pigweeds, barnyardgrass, horseweed, foxtail, and lambsquarters. Some weed species’ seeds, such as curly dock, have specific structures that allow seeds to be carried long distances by running water. Farmers who rely on surface water for irrigation could be increasing weed problems when using weed seed-infested irrigation water. Seed movement with drainage water can also contribute to the spread of weeds, as can the movement of water and weed seeds in the field when heavy rains run along furrows between crop rows or across fields.

Ensure weed-free inputs to prevent weed seeds from entering the field

Prevention is the foundation of weed management. Preventative weed management means stopping weeds from entering a field, or once present, stopping the spread within a field and between fields. Eliminating seed production should be the goal of any weed management program for a troublesome species. NO SEEDS. NO WEEDS.

A good weed management program will help manage weeds because the plants are controlled before they complete their life cycles and produce seeds. To achieve a good foundational IWM program, see our section on best management practices.

While weeds in the field in this photo are well-controlled to prevent yield loss, the ditch is managed to encourage the growth of native species that support pollinators at Harborview Farms, MD. 

Manage field borders and ditches with different tactics than in the field

Uncropped areas, such as ditch banks and field margins, are typically not managed intensively and can be colonized by weeds. The weeds in these areas can be a source of weed infestation; wind, water, and wildlife are all ways seeds in these areas can be carried into a field. Surveys have shown that while ecological and environmental processes can move weeds for miles, most of the seed is deposited within only a few hundreds of feet from the source. While managing these areas may be difficult due to time constraints and additional costs, long-term benefits need to be considered.

Ensure weed-free inputs: bales or hay

Baling is a common practice, whether it is baling forages for hay or baling the remaining crop residue for animal feed. Baling will also gather any weed seeds present at haying time. Over 19,000 wild oat seeds have been found in a single straw bale. Baling equipment can also spread weed seeds to different fields. Furthermore, weed seeds in hay bales can be spread through the manure after livestock consume the hay.

Weed-free grain eliminates weed seed dissemination as well as commanding better prices at the elevator.

Storage and transportation of grain or forages

When harvesting a weed contaminated field, consider separating weed seeds from the grain through mechanical cleaning or other means before storing the grain. When grain or forage bales are transported outside the farm, there is an increased chance for weed seeds to drop off or out of vehicles and be distributed across fields and to non-cultivated areas such as roadsides.

Weed seeds and plant parts can be spread via field traffic. Field bindweed vines and rhizome fragments are dragged with a cultivator.

Tillage and cultivation equipment

Tillage and cultivation equipment can spread weed seeds and move asexual propagules from perennial species, such as stolons and rhizomes. For example, a chisel plow was found to spread bermudagrass almost 20 feet from the original patch. Although it is easily overlooked, dirt and mud on equipment could contain weed seeds. If not cleaned, weed seeds can be spread from field to field and farm to farm. Cleaning equipment is especially important after use in fields that contain difficult-to-control weeds as well as herbicide-resistant weeds. Make sure to thoroughly clean equipment before moving it to a new field to stop the spread of seeds. Additionally, if contractors are hired to perform tillage or other tasks, make sure their equipment is cleaned before use.

Risk of moving seeds with plant material requires that the weeds have reached reproductive stage and viable seeds are present. However, anytime mud or soil is moved from field to field, weed seeds can be transported, regardless of the time of the year.

Planting green into a cover crop before it is terminated.

Planters

Planters, drills, air seeders, and other tools used for planting typically have many parts, such as disk openers, row cleaners, parallel arms, gauge wheels, closing wheels, and trash wheels. When it comes time for planting day, it is tempting to not stop to clean off/out planting equipment, particularly when moving from one field to another. However, it is better to prevent weed introductions into new fields than to need to manage newly-introduced weeds. One simple preventative measure is to consider the role of planting equipment in introducing new weeds to fields and moving weeds among fields.

Special care should be taken when using no-till planters, since they have more parts than a conventional planter on which weed seeds, stolons, and rhizomes could easily get stuck. Such propagules can then easily hitch a ride to new parts of a field and new fields on a farm. Taking a few minutes to remove these weed contaminants from planting machinery can prevent future headaches.

Large machinery tires could carry large amounts of weed seeds when muddy.

Equipment tires

Tires, fenders, and wheel wells from trucks, trailers, tractors, combines, and other large equipment can hold large amounts of mud. The mud could contain weed seeds that will travel within fields or to other fields. Cleaning tires and other places where dirt and mud buildup before leaving each field is important to prevent weed spread.

Ensure weed-free inputs: manure

Manure is an important soil amendment, providing nutrients and organic matter. But, manure may contain viable weed seed that can be spread unto fields. A survey of dairy manure in New York found an average of 75,000 viable weed seeds per ton (Mt. Pleasant and Schlather, 1994). A Nebraska survey studied the top ten challenges to using manure in cropping systems and found that 48% of growers are concerned about weed seeds coming from manure.Thoroughly composting manure can greatly reduce viable weed seed.

Plant residues and weed seeds can accumulate on flat surfaces and can be transported within and between fields.

Mowers as weed seed carriers

Mowers are frequently used in fields after weeds have set seed. Mowing pastures, corn stalks, and ditch banks late in the year are common examples. Consequently weed seeds and weed reproductive structures can be carried by the mower and spread within a field and from one field to another. Mowers are one of the easiest pieces of equipment to clean. A leaf blower or air compressor can be used to clean a mower.

Ensure weed-free inputs: seeds

Farmers can decrease or prevent the entry of new weeds by purchasing and using selecting weed-free crop seeds. Crop seed has the potential to be contaminated with weed seeds. This includes grain crop seed, cover crop seed, and conservation seed mixes. In some cases, herbicide-resistant weed seeds have even been transported over several states in this way.

Cleaned combine ready to be stored to wait for the upcoming harvest season.

Combines

Combines are a very efficient way that weeds, including herbicide-resistant weeds, are introduced to new fields. There are numerous examples of troublesome weed seeds being brought to a farm when a used combine was purchased. Factors that make combines a spreader of weed seeds: 1) they come in to contact weeds within a field to be harvested and after producing viable seed; 2) there are many small spaces within a combine where weed seeds can hide; and 3) combines are time-consuming to clean. The movement of a few seeds of a troublesome species into a new field can cause a serious and costly infestation within a couple of seasons.

Palmer amaranth infestation in a cotton field which has expanded along the harvester path and between crop rows where heavy rainfall spread the seeds of the initial infestation.

Prevent weeds from spreading: prevent seed set

Weeds that escape season-long management need to be prevented from producing seeds. This can be achieved through mechanical and cultural tactics, such as hand weeding and tillage. If seeds return to the soil seedbank, then a continual weed infestation occurs. Plants that have produced viable seeds (within 2 to 3 weeks of flowering) need to be removed from the field.

Bale hay from weed free fields or cut hay before weeds have produced seeds.

Ensure weed-free inputs: bale or hay

Baling is a common practice, whether it is baling forages for hay or baling the remaining crop residue for animal feed. Baling will also gather any weed seeds present at haying time. Over 19,000 wild oat seeds have been found in a single straw bale. Baling equipment can also spread weed seeds to different fields. Furthermore, weed seeds in hay bales can be spread through the manure after livestock consume the hay.

Waterfowl and weed seed dispersal

Waterfowl have been documented to spread agronomically important weeds, including Palmer amaranth and waterhemp. Scientists have concluded that weed seeds can remain viable after passage through the digestive tract of mallard ducks and that Palmer amaranth, waterhemp, common lambsquarters, giant foxtail, and smartweed have the potential to be dispersed over long distances.

Tillage and cultivating equipment, planters and mowers can spread weed seeds and vegetative propagules across fields.

Tillage, planters, mowers and cultivation equipment

Tillage, planters, mowers and cultivation equipment can spread weed seeds and move asexual propagules from perennial species, such as stolons and rhizomes. For example, a chisel plow was found to spread bermudagrass almost 20 feet from the original patch. Although it is easily overlooked, dirt and mud on equipment could contain weed seeds. If not cleaned, weed seeds can be spread from field to field and farm to farm. Cleaning equipment is especially important after use in fields that contain difficult-to-control weeds as well as herbicide-resistant weeds. Make sure to thoroughly clean equipment before moving it to a new field to stop the spread of seeds. Additionally, if contractors are hired to perform tillage or other tasks, make sure their equipment is cleaned before use.

Risk of moving seeds with plant material requires that the weeds have reached reproductive stage and viable seeds are present. However, anytime mud or soil is moved from field to field, weed seeds can be transported, regardless of the time of year.

Weed-free grain eliminates weed seed dissemination as well as commanding better prices at the elevator.

Storage and transportation of grain or forages

When harvesting a weed contaminated field, consider separating weed seeds from the grain through mechanical cleaning or other means before storing the grain. When grain or forage bales are transported outside the farm, there is an increased chance for weed seeds to drop off or out of vehicles and be distributed across fields and to non-cultivated areas such as roadsides.

Cleaned combine ready to be stored to wait for the upcoming harvest season.

Combines

Combines are a very efficient way that weeds, including herbicide-resistant weeds, are introduced to new fields. There are numerous examples of troublesome weed seeds being brought to a farm when a used combine was purchased. Factors that make combines a spreader of weed seeds: 1) they come in to contact weeds within a field to be harvested and after producing viable seed; 2) there are many small spaces within a combine where weed seeds can hide; and 3) combines are time-consuming to clean. The movement of a few seeds of a troublesome species into a new field can cause a serious and costly infestation within a couple of seasons.

Plant residues and weed seeds can accumulate on flat surfaces and can be transported within and between fields.

Mowers as weed seed carriers

Mowers are frequently used in fields after weeds have set seed. Mowing pastures, corn stalks, and ditch banks late in the year are common examples. Consequently weed seeds and weed reproductive structures can be carried by the mower and spread within a field and from one field to another. Mowers are one of the easiest pieces of equipment to clean. A leaf blower or air compressor can be used to clean a mower.

If a mixer is used to feed livestock in the field, be sure that it contains weed-free components to prevent weed seed contamination.

Use weed-free feed for your livestock

Since livestock manure is used as a soil amendment, it is important that the feed consumed by livestock is not a source of troublesome weed species. Scouting and keeping grain and forage fields free of weed seeds is important. It is important to purchase off-farm inputs that are free of weed seeds to prevent the spread of weeds through animals and into fields. And prevent the mixer from contaminating weed-free fields.

Common cocklebur is an example of a weed species with structures that can get tangled in the fur of livestock or wildlife and can be moved from field to field.

Prevent weed seeds/fruit arriving with livestock

Some weed species have special structures which help livestock transport seeds in their fur. Common cocklebur and burdock are two species with burs adapted to cling unto fur.

Weeds seeds can spread when grazing animals eat infested forage or feed and then the manure containing the seeds is spread throughout a field.

Preventing new livestock from spreading weed seeds

Livestock ingest many weed seeds when grazing pastures or consuming hay, silage, or grain products. One study investigated the percentage of viable weed seeds that was recovered after passing through cattle, horses, hogs, and chicken. It found that 24% of weed seeds were still viable after passing through hogs, while 23% of weed seeds remained viable after passing through cattle, and 3% for chickens. When buying new livestock, it is sound practice to isolate the animals in a paddock until their digestive system has been cleared. It typically takes 10 to 12 days, depending on the kind of weed seeds eaten, for livestock to pass any weed seeds that they might have previously consumed.

Managing on farm manure will help to avoid unknown resources, thus preventing weed seed dissemination.

Avoid weed seed contaminated manure

Manure is known as an important soil amendment as well as providing nutrients amongst other benefits. But, it could be an important weed seed carrier if not properly managed. A Tulare County, [3] CA report shows that almost 22,000 viable weed seeds were collected per ton of manure. Ideally manure should be weed-free before spreading in the field, but there is not a simple way to test if manure is weed free or to buy certified manure. In the same study, composting the manure decreased viable seeds to less than 2,000 per ton of composted manure. Other study done at Nebraska, shows that an important factor to help decrease the amount of viable weed seeds is moisture, being a 35% optimum for kill, and weeds such as pigweeds, morningglories, cocklebur, foxtail, velvetleafs, and shattercane were killed when managed at 35% moisture when compared to dry compost.

Ensure weed-free inputs: seeds

Farmers can decrease or prevent the entry of new weeds by purchasing and using selecting weed-free crop seeds. Crop seed has the potential to be contaminated with weed seeds. This includes grain crop seed, cover crop seed, and conservation seed mixes. In some cases, herbicide-resistant weed seeds have even been transported over several states in this way.

While weeds in the field in this photo are well-controlled to prevent yield loss, the ditch is managed to encourage the growth of native species that support pollinators at Harborview Farms, MD. 

Manage field borders and ditches with different tactics than in the field

Uncropped areas, such as ditch banks and field margins, are typically not managed intensively and can be colonized by weeds. The weeds in these areas can be a source of weed infestation; wind, water, and wildlife are all ways seeds in these areas can be carried into a field. Surveys have shown that while ecological and environmental processes can move weeds for miles, most of the seed is deposited within only a few hundreds of feet from the source. While managing these areas may be difficult due to time constraints and additional costs, long-term benefits need to be considered.

Cotton gin trash contains leaf fragments, lint, immature cotton seeds, and weed seeds.  Cotton gin trash, is often used as a livestock feed or soil amendment.

Prevent weed seed movement through contaminated crop by­products

a) Cotton gin trash is the crop waste from the ginning process. It contains leaf fragments, lint, stems, immature cotton seeds, and weed seeds.

Cotton gin trash and cottonseed hulls are usually used as soil amendments, bedding material for dairy cattle, or to feed livestock. A 2009 survey in Arkansas showed that gin trash contained seeds from several troublesome weed species including Palmer amaranth, redroot pigweed, johnsongrass, morningglory species, and a large number of grasses.

Palmer amaranth infestation in a cotton field which has expanded along the harvester path and between crop rows where heavy rainfall spread the seeds of the initial infestation.

Prevent weeds from spreading: prevent seed set

Weeds that escape season-long management need to be prevented from producing seeds. This can be achieved through mechanical and cultural tactics, such as hand weeding and tillage. If seeds return to the soil seedbank, then a continual weed infestation occurs. Plants that have produced viable seeds (within 2 to 3 weeks of flowering) need to be removed from the field.