Control

This factsheet will review preventative measures and list registered herbicides for planning a weed control program in tree nurseries. Information about herbicide selectivity, soil versus foliar activity and steps for planning a weed control program with herbicides is also included.

Grassy leaves

Wild Oat

Avena fatua

Life Cycle

An annual grass that reproduces by seed.

Distribution

Wild Oat occur in almost all cultivated fields in Alberta but are less severe in the south-east of the province.

Germination

Wild Oat germinate throughout the growing season. The main flush occurs in the spring with a secondary flush in the fall. The germination period varies as much as three weeks, depending on weather conditions. Under warm and moist conditions, the main flush can occur over a short period of time and before crop emergence. Under prolonged cool weather, germination may continue until after the crop emerges.

The optimum soil temperature for the germination of wild Oat is between 16 and 22 degrees Celsius. Germination is slow at 4 degrees Celsius and very slow at 33 degrees Celsius. Most germination occurs at depths of 2 to 5 cm if soil moisture is adequate. However, if the surface layer is dry, germination can occur at depths up to 20 cm.

The wild oat seed will not germinate while exposed to light; it must be buried. Seed can be buried naturally by wind drifted soil, soil washed by water or through its unusual self-burial process. When wild oat seed is moistened, the awn unwinds. As the seed dries out the awn twists again. Alternate wetting and drying enables the wild oat to bury itself, thereby satisfying one condition for germination.

Emergence and Growth

Most wild Oat germinate and emerge in early to mid-spring. Cool, moist conditions promote maximum emergence, so crops that are seeded early are usually the most heavily infested. Fall or early spring applications of nitrogen fertilizer stimulate germination. Growth of roots and shoot of wild Oat is slow for the first two weeks, but increases quickly from then on. Most wild Oat tiller within a month of emergence.

Flowers

Wild Oat usually start to flower in early July and may continue to flower for up to six weeks. Seeds at the tip of the main axis of the panicle may ripen and fall to the ground before the seeds at the base are filled. Seeds shatter as they mature and are shed by mid-August, generally before the crop is harvested.

Reproduction

Seed

Mature seeds of wild Oat are usually dormant when they shatter. Dormancy is broken by warm, dry conditions after the seeds ripen. If moisture is available when dormancy is broken, the seeds will germinate; otherwise they become dormant again.

The annual rates of seed germination are:

  • The spring following seeding - up to 80 per cent.
  • The second spring following seeding - up to 97 per cent.
  • The remaining 3 per cent may have what is termed deep-seated dormancy and can germinate for up to 12 years.
Vegetative

Though not a major method of reproduction, wild Oat are capable of vegetative regeneration. Wild oat plants can be transplanted and regrown if cultivation is incorrectly or incompletely carried out, and field and weather conditions are good for plant growth. Even severely injured (mutilated, sectional or segmented) wild oat plants are capable of vegetative propagation.

Competition

Competition is greatly influenced by the relative emergence dates of wild Oat and the crop. If wild Oat emerge before the crop, yield losses are greater than when the crop emerges first. Density and rates of growth of the weed and the crop alone influence competition. Increased growth rates and densities of wild Oat increase crop yield losses. The following table shows the estimated yield losses caused by various densities of wild Oat in four crops. The actual losses may vary from year to year depending on climatic conditions.

Wild Oat per ft2
percentage yield loss wild Oat and crop emerged at the same time
Time of emergence* factor (+/-)
 
Barley
Wheat
Canola
Flax
 
0.5
5
8
7
14
0.5
1
8
11
10
20
1
2
11
16
15
28
1
3
13
19
18
34
2
5
17
25
24
44
2
8
21
32
30
56
2.5
10
24
35
33
62
2.5
15
29
43
41
75
3
20
34
50
47
88
3
*The time of emergence information was developed experimentally for barley and wheat only. However, it may also be accurate for canola and flax. Add or subtract the appropriate number for every day wild Oat emerge before or after the crop. For example, if wild Oat at 2 plants per square foot emerge 3 days before barley, the yield loss changes from 11 to 14 per cent.

Management Strategy (Line of Defense)

  • Prevent seed production.
  • Encourage germination of existing seed reserves.

Control Mechanisms

Preventing seed set of wild Oat in annual crops is very difficult unless the crop is taken off early for greenfeed or silage. Therefore, a combination of cultural and chemical control methods are needed to attack a wild oat problem.

Tillage

Summer fallow - Summer fallow increases the number of seeds that break dormancy. A new stand of wild Oat will emerge after each tillage operation. Summer fallow can be grazed to control wild Oat. Seed fall crops in the same year as the fallow to provide competition against wild Oat that germinate in the spring.

Pre-seeding tillage - Till as early as possible after spring thaw. This warms and aerates the soil and stimulates early germination of wild Oat. Early tillage of heavy, wet soils is particularly important.

Tillage prior to seeding should be done before weeds reach the three-leaf stage. This minimizes the moisture and nutrients they use. Tillage should be to a depth of 2.5 to 5 cm during warm, dry weather so the wild Oat cannot re-establish.

Post-seeding tillage - Post-seeding tillage is valuable because wild Oat that emerge before the crop are more competitive than those that emerge with or after the crop. Till before crop emergence to prevent any crop damage. A shallow cultivation with a rod-weeder or harrows will eliminate wild oat seedlings.

Fall tillage - Fall tillage is useful if wild oat seeds have been exposed to two or three weeks of warm, dry weather. A shallow tillage will lightly cover wild oat seeds and promote early germination in the spring. A cultivator is more suitable than a discer or harrow. If fall weather is cool and moist, avoid tillage so that dormant wild oat seeds remain on the surface exposed to the elements.

Mowing

When an infestation of wild Oat is moderate to heavy, and the crop is of low density, mowing is an effective preventive measure. Wild Oat should be mowed at the shot-blade stage. Early mowing can result in wild oat regrowth and seeds can still be produced.

Mowed wild Oat can be used for greenfeed or, if some of the seeds have set, for silage. The fermentation process will destroy wild oat seed viability.

Rotation

Fall-seeded crops emerge early the next spring and can smother the emerging wild Oat. Fall rye is generally more vigorous and competitive than winter wheat.

Land seeded to perennial forage for three or more years can provide good control for heavy infestations of wild Oat. However, some wild oat seeds can survive under sod and germinate when the sod is broken.

A green-feed crop such as Oat can be seeded early to enable a competitive advantage over the wild Oat. To prevent weed seed production, cut the crop before the panicles of wild Oat start to emerge from the sheath. Silage effectively destroys any seeds produced.

Use annual crops in the rotation, especially the more competitive crops so that yield losses are minimized and the wild Oat are suppressed. In descending order, barley, canola and wheat are the most competitive small grains.

Delayed seeding

Delay seeding to allow time for wild oat seedlings to be destroyed by tillage before or at seeding. Seed an early maturing crop such as barley. Yields may be reduced if seeding is delayed by more than 10 to 14 days.

Fertilization

Nitrogen fertilizers broadcast in the early spring can stimulate wild oat emergence. This can enable more complete control prior to seeding. Phosphorous fertilizer drilled in with the seed promotes more vigorous crop growth that helps to smother wild oat plants and reduce wild oat seed production.

  Seed yield (bu/ac)
Phosphorous fertilizer placement Barley Wild Oat
Control - no fertilizer 33 12
Drilled with barley 62 5

Multi-technique approach

Like most other weeds, successful control of wild Oat will require a combination of tillage, crop rotation and chemical control. Each situation has to be evaluated and the appropriate control method(s) taken.

Broad-leaved weeds

Cleavers

Galium aparine

Life Cycle

An annual that reproduces by seed. Cleavers was once considered a summer annual, but now there's evidence that it can overwinter and grow as a winter annual.

Emergence

The main flush of seedlings is in midspring with fewer seeds germinating throughout the summer.

Flowers

Cleavers flowers from June through August and seed is produced from August to freeze-up.

Reproduction

A single cleavers plant can produce 3,500 seeds. They are difficult to separate from canola seed owing to their similar shape and size. Cleavers seed becomes dormant in dry soil and can remain viable for one to three years. Seeds remain viable when eaten by animals. In fact, seed germination increases when seeds are recovered from animal droppings.

Planting contaminated canola seed has become the main source for spreading cleavers. Cleavers seed is a similar shape and size to canola, making it hard to mechanically separate cleavers seed from canola seed.

Because of this similarity, seed stock can be contaminated easily. According to the Canada Seeds Act, cleavers is a class 2, primary noxious weed seed. There is a zero tolerance limit for cleavers and cleavers seeds in all grades of pedigreed seed (foundation, registered or certified) for cereals, forage crops and oilseeds.

It is easily spread by harvesting equipment and in contaminated animal manure. The bristly seeds cling to the hair and wool of animals and people's clothing.

Competition

Cleavers can be very competitive because it clings to crop plants when growing towards light. The trailing plants can become tangled in moving parts of harvest equipment. Seed quality suffers when canola seed is infested with cleavers seed. Established forages compete well with cleavers.

Cleavers competes with crops for light, moisture and nutrients. Heavy infestations will cause yield reductions. In canola, one experiment showed a 20 per cent yield loss when cleavers were present at densities of 100 plants per square metre.

Management Strategy

Prevent seed production, especially in canola fields, and sow clean seed.

Plant certified seed. All grades of pedigreed seed (foundation, registered and certified) for cereals, forage crops and oilseeds, by their designations, must be free of cleavers seed. Planting with high quality seed produces more vigorous seedlings, which are better able to compete with weeds. Avoid contamination during transportation. Tarp trucks loaded with grain or screenings, even for short distances.

Clean tillage and harvesting equipment, paying particular attention to custom combine operations.

Compost contaminated manure. Cleavers infested manure should be composted for several months, so that the heating and decomposition process can destroy the seeds. Control cleavers in fencelines, road allowances, sloughs and other non crop areas. Mowing, grazing and spot spraying with a herbicide are all increasingly important sanitation methods, especially with reduced tillage.

Control Mechanisms

Tillage

Summer fallow - The number of cleavers seed can be reduced by summer fallowing. Till weed flushes to shallow depths to prevent seed production. Plants can re-root in moist soil, so tillage is most effective under warm dry conditions.

Pre-seeding tillage - An early shallow tillage encourages germination of cleavers seeds. A second tillage, immediately before or at seeding destroys these seedlings. Seeding may be delayed, however. If delayed seeding is not possible, sow the crop early so that it gains a competitive advantage over cleavers.

Post-seeding tillage - If pre-seeding tillage is performed then post-seeding tillage should not be necessary. Crops that are seeded early may not benefit from post-seeding tillage because crop growth may be too advanced before weed emergence is complete.

Fall tillage - Fall tillage will encourage cleavers seeds to germinate and the seedlings will be killed by frost.

Rotation

Rotations that include summer fallow, cereals, and annual and perennial forages should help minimize cleavers populations. Winter annual cereals are especially effective. Do not grow canola on land infested with cleavers because cleaning cleavers seed from the crop is very difficult.

In heavy cleavers infested fields, crops such as barley and wheat will compete more vigorously with cleavers than oilseeds and pulses. Rotating cereals with canola is an important line of defence. Managing cleavers during a cereal rotation will have carry over effects that will help keep subsequent canola crops clean.

In rotations to eliminate cleavers, avoid crops with no herbicide options, i.e. clover, lentils and canola (With the exception of Pursuit-Smart canola for which Pursuit is a registered herbicide option). In fields with heavy cleavers infestations, planting perennial forages will help to reduce the populations to a manageable level.

Seeding

Spring seeding of land infested with cleavers should be either very early or delayed until after weed seedlings emerge.

Mowing

Because of the prostrate growth form of cleavers, mowing is not effective. Chemical Control Spray early (1-2 whorls). If cleavers are past the 2-3 whorl stage, they will not be controlled consistently. A range of herbicides are available to effectively treat cleavers. The majority are for treatment during cereal rotations. Use the Pesticide Selector Chart to choose a registered herbicide for your crop.

Herbicides registered for cleavers

Crops Herbicides Staging Weed Control/Suppression (Prices 1996 sugg. retail
Crop Weed
Wheat
spring wheat
winter wheat
durum
Barley
Oats
         

Target

Winter Wheat

2-4 leaf (barley)
2-5 leaf (durum,oats and
spring wheat)
Spring: before crop is more than
30 cm tall
1-2 whorl
1-2 whorl

C

C

C

$6.50/acre
Banvel+MCPA or
24-D Amine
(high Banvel rate only, wheat only)
2-5 leaf Before 3 whorl C $5.39/acre

Dyvel

Winter wheat

2-5 leaf
Spring:15-25 cm tall before
shot blade
2-3 whorl

S

S

$4.43/acre

Dyvel DS

Winter wheat

3-5 leaf (wheat)
2-3 leaf (barley)
3-4 leaf (oats)
Spring: before crop
is 30 cm tall

2-3 whorl

2-3 whorl

2-3 whorl

S

S

S

S

$4.39/acre
Mecoprop/Compitox 3 leaf to early flag leaf 2-4 whorl C $14.72 - 18.73/acre
Refine Extra
Refine Extra+MCPA
or 2, 4-D Amine
2 leaf to flag leaf
full 3 leaf to expanded shot blade
1-3 whorl
1-3 whorl

S

S

$4.95/acre
Canola Edge Apply at the recommended
rates and timings as it pertains to soil texture and organic matter
  S $11.66 - 20.34/acre
Triazine Tolerant
Canola
Bladex Liquid(TTC) 1-4 leaf 1-2 whorl C $12.19/acre
Pursuit-Smart
Canola
Pursuit 1-4 leaf Up to 4 whorl C $18.25/acre
Field Peas Basagran After 3 pairs of leaves (or 2-5 nodes)   C $19.00 - 25.00/acre
Edge Apply at the recommended rates and timings as it pertains to soil texture and organic matter.   S $11.66 - 20.34/acre
Pursuit Up to and including 6 node Up to 4 whorl C $18.25/acre
Flax Basagran Soon after 5cm   C $19.00 - 25.00/acre

* C: Control
S: Suppression

Diagnostic Guide

Seeds
Flower  
Stems
Plant


Seedling


Mature

Narrow-Leaved Hawk's Beard

Crepis tectorum

Life Cycle

An annual or winter annual that reproduces by seeds.

Emergence

Main flushes emerge from mid-May to mid-June and from early August to mid-September. The first flush develops as annuals and the second develops as winter annuals. Sporadic emergence occurs at other times.

Flowers

Annuals flower from early July through August. Winter annuals flower the year after emergence between mid-June and mid-July.

Reproduction

Seeds of winter annuals are set from mid-July to mid-August. Seeds from annuals mature from early August through fall. Seeds exhibit little or no dormancy, losing their ability to germinate after about five years.

Competition

Narrow-leaved hawk's-beard is a serious weed of perennial forages. The winter annual form competes with established forages; the annual form competes with seedling forages, special crops, cereals and oilseeds. The most serious infestations of this weed occur in weak crop stands.

Management Strategy

Prevent seed production and encourage strong crop stands.

Control Mechanisms

Tillage

Summer fallow - Summer fallow reduces populations of narrow-leaved hawk's-beard. However, plants can easily re-root after tillage, especially in wet conditions. Consequently, tillage should be done during hot, dry weather. Perform tillage after the main flushes of annuals appear and in the fall to destroy rosettes of winter annual.

Pre-seeding tillage - Early, thorough spring tillage destroys weeds that have overwintered. Annual crops can then be seeded. Do not seed perennial crops until the first flush of seedlings has been destroyed by cultivation.

Fall tillage - Cultivate thoroughly after weed emergence is complete in the fall, usually around mid-September. If possible, conditions should be dry so that the rosettes do not re-root.

Rotation

Maintain strong stands of perennial crops for three to four years to discourage weed growth. If perennial crops become infested with narrow-leaved hawk's-beard, work the stand under and summer fallow until the following year.

Annual crops in the rotation should be well-fertilized and seeded slightly heavier than normal to encourage competition against spring weeds.

Summer fallow can be an effective control for narrow-leaved hawk's-beard. Perform a shallow tillage after emergence of weeds in the spring and fall and as required during the season.

Seeding

Seed annual crops at a heavier than normal rate after the spring flush of narrow-leaved hawk's-beard. Seed perennial crops after weeds have been destroyed by tillage in the spring. Seed fall crops after the fall flush of weed seedlings has been tilled.

Mowing

Mow narrow-leaved hawk's-beard in perennial crops prior to weed seed production. This is especially important in the year that perennial crops are established.

Contact

Email: chris.neeser@gov.ab.ca

Alberta Pest Surveillance System: 310-APSS (2777)

For more contact options, see the Ag-Info Centre