Scentless Chamomile

Scentless chamomile Tripleurospermum perforatum (Merat) M. Lainz, is a noxious weed in Saskatchewan. Other names for the weed are wild daisy, scentless mayweed, false chamomile, Kandahar daisy or barnyard daisy. Plants can be summer annuals, winter annuals or short-lived perennials. The weed is often found in moist, disturbed areas such as roadsides, farmyards, sloughs, cropland, pastures, utility rights-of-way, shelterbelts, drainage ditches and waste areas. Scentless chamomile can cause yield losses in cereal, pulse, forage and oilseed crops.

Identification

Scentless chamomile, Tripleurospermum perforatum (Merat) M. Lainz, is a noxious weed in Saskatchewan. Other names for the weed are wild daisy, scentless mayweed, false chamomile, Kandahar daisy or barnyard daisy. During wet years, the weed has spread rapidly throughout the black and gray soil zones of Saskatchewan.

Flowers (a) are conspicuous, 2 to 4 cm in diameter, and appear from June to October. The outer white ray florets and the central yellow disk florets give the flower a daisy-like appearance.

Leaves (i) are finely dissected and smooth. The plant is erect with ascending branches and does not have a distinct odour. Mature plants range in height from 15 cm to 1 metre. The roots are dense and fibrous.

Achenes (seeds) are about 2 mm long and are dark brown or black, with three distinct light-brown ribs (d). Reproduction is by seed.

Seedlings (c) have pointed, oval-shaped cotyledons (3 to 6 mm long) which are not divided. The first set of true leaves is coarsely divided.

Plants can be summer annuals, winter annuals or short-lived perennials. The winter annuals germinate in the fall, and overwinter as hardy rosettes (b). The plant then bolts and flowers the following year.

This weed may be confused with:

Wild chamomile - Chamomilla recutita (L.) Rauschert
Pineappleweed - Matricada matricarioldes (Less.) Porter
Ox-eye daisy - Chrysanthemum leucanthemum L.

To distinguish scentless chamomile from wild chamomile and pineappleweed, the mature flowers can be used.

The flowers on pineappleweed lack the outer white ray florets. The yellow centre of the mature wild chamomile flower is conical, not rounded as in scentless chamomile. The immature flowers of wild chamomile are not distinctly conical, but very similar to scentless chamomile. Crushed pineappleweed or wild chamomile flowers produce a pineapple-like odour while crushed scentless chamomile flowers are nearly odourless.

The leaves can be used to distinguish scentless chamomile from ox-eye daisy.

Ox-eye daisy leaves are broad, linear and coarsely toothed while scentless chamomile leaves are finely divided.

Habitats

Scentless chamomile is often associated with disturbed habitats where there is little competition from established vegetation. The weed is adapted to moist areas, and in Saskatchewan is found primarily on the Black, Dark Grey and Grey soils. The weed is rare on the Brown and Dark Brown soils, possibly because of the drier conditions. Moist conditions in recent years have allowed the weed to become more widely established in these areas.

To determine the specific habitats associated with scentless chamomile, farmers were surveyed by mail and asked to report where the weed commonly grows. Additional information was gathered by interviewing farmers and by intensively surveying 36 quarter sections of land.

Reported scentless chamomile habitats

Differences between the survey results and the information gathered in the farmer interviews suggest that the habitats in which the weed grows may be related to how long the weed has been in an area. The survey covered a large area, and included many places that have had the weed for only a few years. The most common habitats were roadsides and farmyards. The farmer interviews, however, were conducted in the Dubuc-Esterhazy­-Stockholm area where the weed has occurred since 1905. In this area, the weed is relatively abundant and has had time to exploit most of the available habitats. The weed is more commonly found on agricultural land, such as the low spots in a field and around slough margins.

Roadsides - In areas infested with scentless chamomile, it is common to see the weed growing along the side of the road. It is often introduced to this habitat by weed seeds falling from transported grain and forage, and by seeding newly constructed roadsides with contaminated grass seed. Once established, weed seeds are spread further by road maintenance equipment (i.e. mowers, graders, etc.). Moist soil conditions in the road ditch and on the roadside are ideal for the growth of this weed. Since roadsides are a primary pathway for the spread of invasive weeds, they can be used to monitor the spread of scentless chamomile.

Farmyards and town sites - The handling of weed-infested grain, machinery and forage often results in the introduction of scentless chamomile. The weed is frequently found in places that are disturbed by machinery and livestock. Areas used for storing grain and forage are especially prone to infestation. Vacant town lots, grain elevator sites, and neglected gardens and yards can also be infested.

Fences, lanes and power lines - Nearby farming activities disturb the natural vegetation and favour the growth of scentless chamomile. The weed is often not controlled since tillage and spraying equipment are hard to use in these places. The weed is therefore left to proliferate.

Low areas that are sometimes cropped - In some years it is too wet to cultivate the low places in a field. If these areas are not cultivated or sown to a crop, scentless chamomile grows extremely well in the moist soil. Periodic disturbance by cultivation or flooding prevents the establishment of perennial grass, so the weed grows with little or no competition.

Cropped land - Scentless chamomile can cause serious economic losses in most crops. Flax and lentil do not compete well, and are especially prone to infestation. Scentless chamomile generally appears first in moist low areas or along field edges, and then spreads by seed or transplantation onto the adjacent farmland. Plants growing close to cropland should be treated as a threat since the weed produces large quantities of seed.

Near permanent wetlands - Slough margins, riverbanks and drainage ditches make ideal habitat for scentless chamomile. The moist conditions are favourable and seeds can spread in moving water. Periodic disturbance by flooding or cultivation inhibits the growth of grass and allows the weed to grow with little competition.

Waste areas - Piles of rock, brush, junk or manure often contain uncontrolled weeds such as scentless chamomile. The best way to prevent the weed from establishing in these places is to eliminate the waste area. Rock piles however do create protected habitat for biocultural agents to survive, flourish and repopulate cropland areas.

Pastures and rangeland - Although well-established stands of grass will generally prevent the growth of scentless chamomile, the weed can be a problem in some cases. Wet areas, where flooding or livestock trampling has disrupted natural vegetation, are ideal sites for scentless chamomile.

Shelterbelts - Scentless chamomile grows close to the shelterbelt where cultivation is not possible because of the tree roots. This area is often very wet in the spring since the shelterbelt stops drifting snow. The moist soil and uncropped ground make an ideal habitat for scentless chamomile.

Hayland and forge crops - The weed can be a problem because of the lack of available control methods. Areas that have high moisture content and poor crop cover are often the first places to be invaded by the weed. The weed may then spread throughout the entire field.

Other habitats - Scentless chamomile grows on recently disturbed areas such as utility rights-of-way (underground cables and pipelines). The weed was also reported on saline areas, airstrips, gravel piles, alfalfa pelleting sites and mine tailings.

Summary

Scentless chamomile prefers moist, disturbed areas where there is little competition from other vegetation. It appears the weed is first introduced into areas such as roadsides and farmyards by seeds in weed-infested agricultural equipment and crops. If the weed is not controlled and becomes established, it produces large numbers of seeds that spread the weed to other habitats such as nearby farmland. The most agriculturally significant habitats are the low areas in fields and slough margins.

Distribution

Scentless chamomile is native to northern and central Europe. The weed was introduced to Canada either as an ornamental or as a grain contaminant. Scentless chamomile has spread rapidly and can now be found in all 10 provinces and the Northwest Territories.

Early documented records of scentless chamomile indicate that the weed was present in Saskatchewan as early as 1910. The majority of the sites in Saskatchewan are on the Black, Dark Grey and Grey soils. The wetter sites in these soil zones are suitable for the growth of scentless chamomile. The drier conditions on the Brown and Dark Brown soils appear to be less suitable, but several moist years have allowed the weed to advance into those areas.

To obtain a more detailed picture of the weed's distribution, a questionnaire was sent to farmers living on the Black and Grey soils in 1988.

At that time, scentless chamomile was reported throughout the surveyed area, but heavy infestations of the weed occurred in the St. Walburg, Hafford, Shellbrook, Nipawin, Wynyard, Balgonie and Esterhazy areas.

To approximate the spread of scentless chamomile, farmers who reported having the weed were asked the year that it was first seen growing on their land. The first reported sighting in the province was at Esterhazy in 1905, but the weed remained relatively rare until 1940 (Figure 1).

Figure 1. Scentless chamomile on the Black, Dark Grey and Grey soil zones of Saskatchewan. Each dot represents a township in which there was at least one reported occurrence of scentless chamomile.

The weed became more abundant in the 1950s and 1960s. During the 1970s and 1980s, scentless chamomile spread rapidly. The sudden increase in the weed's population could have been caused by above-average moisture conditions that occurred in the early 1970s. Increasing mobility of machinery, grain and forage may have also contributed to the spread of the weed. As the weed's population increases, it spreads more rapidly since more seeds are produced.

Farmers reporting the weed were asked to report the percentage of their quarter-sections which have scentless chamomile growing on them (Table1).

Although 43 % of the farmers have the weed on less than 20 % of their quarter-sections, a significant number (14 %) have the weed on over 80 % of their land.

Table 1: Distribution of Scentless chamomile on infested farms in 1988.

The weed continues to spread. In certain areas of the province the weed is abundant, while elsewhere it is still rather rare. This is reflected in the results of a survey of roadside infestations of scentless chamomile conducted in 1999 and updated in 2002 by Dr. Gary Bowes, Coordinator, Integrated Noxious Weed Management Program. The survey found that the weed was not found on road rights-of-way in 97 rural municipalities but was present in 200 rural municipalities (Figure 2). Municipalities reporting no roadside infestations of scentless chamomile appear green. Various shades of red are used to depict municipalities' rates of road rights-of-way harbouring the weed.

Figure 2: Survey of Scentless Chamomile density on roadsides 2001-2003

The Integrated Noxious Weeds Management program was funded by the Canada-Saskatchewan Agri-Food Innovation Fund (1999-2001) and The Technology Adoption and Demonstration (TAD) Fund (2002) and then as The Noxious Weed Program funded by the Canadian Adaptation and Rural Development Fund in Saskatchewan (CARDS) and Agriculture Development Fund (ADF) (2003-2005) to raise awareness of scentless chamomile and develop integrated control strategies for it and other noxious weeds.

Summary

Scentless chamomile has spread rapidly in Saskatchewan and by appearances, continues to spread. The weed is concentrated in the black soil zones and areas around Shaunovan. To prevent further problems with this weed, steps must be taken to restrict the spread of scentless chamomile.

Crop Yield Losses

Scentless chamomile may grow as a summer annual, germinating and flowering in the same year, or as a winter annual, germinating late one year and flowering in the next. There is also a short-lived perennial form.

Scentless chamomile that survives control attempts will compete with the crop. To quantify yield losses, two studies were conducted at sites in the Black soil zone. In one study, spring and winter wheat yield reductions caused by summer and winter annual scentless chamomile were evaluated on experimental plots. In the other study, spring wheat yield reduction was examined in farmers' fields.

Spring wheat

Summer annual scentless chamomile caused serious spring wheat yield losses in the experimental plots in a cool, wet year (Figure 1). Losses were much lower during a moist year. In a hot, dry year, spring wheat yields were not reduced at scentless chamomile densities up to 25 plants per square metre.

Winter annual scentless chamomile was able to substantially reduce spring wheat yield under moderately moist conditions (Figure 2). Small but significant losses were also found in a hot, dry year. The winter annual has a competitive advantage over spring wheat because it is established when the crop germinates.

In farmers' fields, spring wheat yield was reduced more during a moderately moist than a hot, dry year for a given density of scentless chamomile (Figure 3). Individual plants were larger, and therefore more competitive, during the moderately moist year. Under favorable weather conditions, 5 to 10 plants per square metre can grow rapidly and be competitive.

Winter wheat

Winter wheat was more competitive than spring wheat in the experimental plots. Summer annual scentless chamomile was able to reduce yield only in cool, wet conditions. Winter annuals caused some reduction of winter wheat yield in both moist and hot dry years but, compared to their effect in spring wheat, losses were low (Figure 4).

Summary

The yield losses described here, some of them severe, occurred in two competitive crops. Winter wheat was more competitive than spring wheat and should be considered as an alternate crop to control scentless chamomile and reduce economic loss. Winter annual scentless chamomile plants were more competitive than summer annual plants. Further work is required to determine the effect of scentless chamomile on yields of less competitive crops, such as lentil, dry pea and flax. It is likely, however, that yield losses in such crops will be high.

Weed Management

Why scentless chamomile is a problem

Scentless chamomile has many characteristics that make it a difficult weed to control.

1. Many of the commonly used herbicides will not control this weed at crop tolerant rates.
2. The plant may be a summer annual, winter annual or short-lived perennial. Weed control practices that control the summer annuals often do not kill the winter annuals.
3. Scentless chamomile is a very prolific seed producer. A single plant can produce over a half million seeds. The seeds are easily dispersed by machinery, flowing water and drifting snow. Under the right conditions, seed can lie dormant in the soil for a decade or more.
4. The plant's dense, fibrous root system traps soil and moisture, enabling the weed to survive for some time after being uprooted. When the soil is moist, tillage often only transplants the weed.

Although scentless chamomile is a pleasant looking plant, it is a noxious weed and should be treated as such. This means that the weed must be controlled both inside and outside the field. Since no single control method can be used in all habitats, a number of management strategies are needed.

Prevent scentless chamomile spread

The first step in controlling the weed is to prevent introducing it to new areas. Since scentless chamomile spreads primarily by seed, controlling the weed depends on identifying and eliminating the weed's seed sources.

The transport of weed-infested crops and forage often introduces the weed to roadsides. Once the weed is established on road shoulders, maintenance equipment (i.e. mowers, graders, etc.) spread seed further along the road. Road maintenance equipment should be thoroughly cleaned after contacting the weed. To prevent both long- and short-distance spread, tarp grain trucks, clean farm machinery after use in weed-infested fields and eliminate the use of weed-infested livestock feeds.

A clean source of seed is essential. Grain elevators are often not equipped to adequately clean seed. Forage seed, which is the same size as scentless chamomile, is very difficult to clean, and should be purchased with caution. Properly cleaned seed may initially cost more, but money is saved in lower weed-control expenses.

Keep the weed in a confined area by harvesting and tilling weed-infested areas separately. This prevents the weed from spreading. Remember to clean the machinery after working each infested area.

Care must be taken to control scentless chamomile growing along slough and field margins. These areas are not always tilled and are a main source of scentless chamomile seed. Plants can also be picked up by tillage equipment and transplanted into the field. Swathers frequently cut weeds growing on the field edge and deposit them inside the field. Harvesting then scatters the seeds further.

Scentless chamomile often grows in high traffic areas of farmyards, such as implement parking areas and around grain storage facilities. Plants and seeds are easily picked up by vehicles and machinery and carried into fields. Mow and hand-weed to reduce seed production.

Tillage

On summer fallow, tillage during suitable weather conditions can be used to control scentless chamomile. Shallow tillage with disc or cultivator followed by harrowing is needed to uproot the plant and remove the soil from around the plant's roots.

Till on hot, dry days rather than on moist, cool days so the plant's root system dries out as soon as possible. Tillage during moist, cool days will not adequately separate soil from scentless chamomile's fibrous roots. Poorly timed tillage can transport the weed to new locations in a field. Even under ideal weather conditions, some areas may have to be worked several times in order to achieve good control (Table 1). To prevent seed-set, always try to control the plant before it flowers.

Table 1: Tillage and the control of scentless chamomile.

Late fall and early spring tillage may effectively control young winter annual rosettes. Any surviving rosettes and spring-germinating plants may be killed by tillage during seedbed preparation.

When using any form of tillage, soil erosion is always a concern. Shallow, intensive or late-fall tillage all promote soil erosion. Soil loss will be less if the weed is confined to small areas and only those areas are worked. If the weed occurs throughout an entire field, intensive tillage can be used with discretion.

Mowing and swathing

Mowing or swathing the weed can also be used. Be sure to cut the weed before it flowers since viable seeds can form in flowers, even after cutting. The plants may produce new shoots and flower again, making it necessary to re-cut the plants. Cutting is not always effective, since the plant will flower again below the cutting height of a swather or mower.

If the weed is cut while in flower, eliminate as many seeds as possible by baling the weed. Clean all equipment after use. The bales can then be burned in a controlled manner. The movement of bales containing scentless chamomile should be kept to a minimum to reduce the spread of seeds. Scentless chamomile is not suitable for livestock feed since it is low in nutrients and feed quality.

Hand-weeding

In areas that cannot be tilled or mowed, it is often necessary to control these weeds by hand. Either pull the weeds or cut them with a grass whip. Collect the weeds in garbage bags and then burn them in a controlled area where wind and water will not spread the weed's seed. Any weeds missed by tillage can also be pulled by hand. Although time consuming, hand-weeding is an effective way to control small patches and prevent spreading.

Competition

Fields with serious infestations of scentless chamomile should be sown to a competitive crop such as barley. Winter wheat competes well with winter and summer annuals, especially during dry years. Flax and lentil compete poorly, and should be avoided on land infested with scentless chamomile.

Low areas that are too wet to work in some years are ideal habitats for this weed. If possible, work these areas later on in the year and sow them to oats or some other crop with a short growing season.

It may be beneficial to sow infrequently tilled low areas to a perennial grass. Solid stands of perennial grass are very competitive, except in wet environments. Wasteland and recently disturbed soils should also be sown to grass to reduce the amount of weeds growing in these areas. Try to maintain a good cover of grass around farmyards, especially in areas where machinery is parked and grain is stored. Mowed lawn areas around farmyards or in towns not only look better, but also control weeds.

Herbicides

For current recommendations on herbicides, refer to the annual publication, Guide to Crop Protection, produced by Saskatchewan Ministry of Agriculture.

Summary

Care must be taken to prevent the spread of scentless chamomile. Tillage provides control, but can only be used in some habitats during suitable weather conditions and must be used sparingly to prevent soil erosion. Herbicides, mowing and hand-weeding can be used to supplement tillage. Perennial grasses compete well with scentless chamomile, except under wet conditions. Since scentless chamomile reproduces by seed, controlling the weed depends upon eliminating its seed sources.

Seed Production and Germination

Seed production

Seed production in solid stands of scentless chamomile can exceed one million seeds per square metre (Table 1). Smaller but still significant amounts of seed are produced from stands of scentless chamomile growing in other non-cropland habitats such as field and slough margins, fence lines and roadways. In an annual crop such as wheat, infestations produce less seed.

Table 1. Examples of scentless chamomile seed production in different habitats.

Seed dispersal

Since the weed is commonly found growing along the margins of fields and sloughs, experiments were conducted to determine the extent of seed spread into fields. At the edge of a field, 100,000 viable seeds per square metre were found in the soil. In the cultivated field 18 metres from the edge, the average number of viable seeds was still 1,000 seeds per square metre. This reflects the importance of controlling weeds growing along the margins of fields and sloughs.

Crop seed contamination

Scentless chamomile seed contamination in grain was studied by collecting grain samples from 23 farmers (Table 2). The high number of seeds in some samples suggests that contaminated grain is a significant factor in the spread of this weed.

Table 2. Scentless chamomile seed contamination of various grain and oilseed crops.

Seed germination

Scentless chamomile seeds are able to germinate under a wide range of temperature and moisture conditions. The ideal average daily temperature for seed germination is 17.5 C, but a large percentage of seed will germinate under average daily temperatures as low as 2.5 C to as high as 40 C. This allows the seeds to germinate throughout the growing season. The seeds absorb water quickly and have a high rate of germination when moisture content is at or above 10% of soil capacity. Even when the soil is saturated with water or flooded, seeds germinate readily (Table 3). This facilitates colonization of habitats which are prone to flooding.

Table 3. Seed germination under various conditions.

Light has a major influence on seed germination. Darkness suppresses the germination of new seed, suggesting the seeds are adapted to germinating on the soil surface where they are exposed to sunlight (Table 3). Once the seeds are buried in the soil, they can remain viable for at least 15 years. With time, scentless chamomile seeds lose their requirement for light to germinate and will germinate in the dark (Table 4).

Table 4. Germination of scentless chamomile seed after being buried in soil.

*Fresh seed was collected and placed in soil in pots that were placed outside. Seed was collected from the pots each month and germinated in the dark at 25 C (16 hr.) and 5 C (8 hr.).

In the field, scentless chamomile seeds can germinate and establish after a period of cool, damp weather during any part of the growing season. The soil surface must remain moist for two or three days so the seed has enough time to absorb moisture, germinate and establish. Since shading helps to maintain soil surface moisture, germination occurs best under a vegetation canopy, rather than on a barren summer fallow field. Most seedlings establish in the spring or fall.

Summary

Scentless chamomile produces large numbers of seeds, which enable the weed to spread rapidly. Plants growing close to cultivated land should be considered as a threat. Scentless chamomile seeds are able to germinate under a wide range of temperature and moisture conditions. Most seedlings are established in the spring and fall. Buried seed can lie dormant in the soil for several years.