There are different types of weeds in Alaska, posing a threat to the other plants in the ecosystem. As these weeds grow faster and thicker compared to the desired plants, they must be removed and controlled. In this article, you will learn about the most common and well-known weeds in Alaska, along with their characteristic features, type, and control measures.
Table of Contents
Alaska Weeds
| Name of Weed | Family |
|---|---|
| Canada Thistle | Asteraceae |
| Chickweed | Caryophyllaceae |
| Bull Thistle | Asteraceae |
| Spotted Knapweed | Asteraceae |
| Orange Hawkweed | Asteraceae |
| Narrowleaf Hawksbeard | Asteraceae |
| Common Tansy | Asteraceae |
| Japanese Knotweed | Polygonaceae |
| Bird Vetch | Fabaceae |
| Scotch Broom | Fabaceae |
| Himalayan balsam | Balsaminaceae |
| Splitlip Hempnettle | Lamiaceae |
| Rampion Bellflower | Campanulaceae |
| Purple Loosestrife | Lythraceae |
| Reed Canarygrass | Poaceae |
Canada thistle
Canada thistle has erect, ridged, branching stems and grows up to five feet tall. Its leaves are curled, oblong, and wavy, with woolly hairs. You can see purple-pink flowers in clusters.
The weed species forms colonies through an extensive vertical and horizontal root system and can cover acres of land! Canada thistle is commonly found in forests, fields, river banks, and along roadsides. It spreads easily by windblown seeds. Once established, it is difficult to eradicate this weed.
Type
Perennial
Family
Asteraceae
Control
Well, it is not easy to control Canada thistle. The most effective method known to reduce its population is to provide herbicide treatments containing glyphosate, clopyralid, or aminopyralid between mid-May and mid-June (the period before flowering). Alternatively, a rotary mower can be set at the highest height to cut Canada thistle mechanically before flowering.
Chickweed
Common chickweed is a weed that forms mats of foliage with tiny white flowers. It is a low-growing, semi-evergreen plant that is capable of affecting different locations in your lawn or garden, including beds, borders, and uncultivated ground. The weed species can grow up to 30 cm and can be identified by its frosty leaves that are arranged uniformly opposite each other, and the white flowers with five petals.
Type
Annual
Family
Caryophyllaceae
Control
Chickweed thrives in lawns that are mowed low to the ground and kept moist. So, if you want to prevent its invasion, raise your mower blade and avoid over-watering the lawn in the autumn. You can also try hand weeding to get rid of this wood species.
Bull thistle
This weed species is an erect plant that arises from a fleshy taproot. Bull thistle can be identified by its urn-shaped, purple ray florets and leaves which are hairy and prickly on the upper side and cottony on the underside. The stems have peculiar, irregular spiny wings and grow up to 5 feet tall with many spreading branches.
Bull thistle can be found on roadsides, disturbed sites, and riparian areas. It spreads extensively and is known to decrease land value, restrict recreational land use, and compete with native vegetation for light, water, and space.
Type
Biennial
Family
Asteraceae
Control
To control bull thistle manually, it has to be dug up using a shovel. Removing the top two inches of the root is generally sufficient to kill the weed, especially after it has produced stems. You have to ensure that you don’t leave behind the cut stems of flowering bull thistle, because they may form viable seeds even after they are cut.
Spotted knapweed
Spotted knapweeds shoot up from a stout taproot and grow up to three feet tall. Deeply lobed grey-green leaves arise from the basal rosettes. Solitary, pink-purple flower heads can be found at the ends of branches.
This weed species is adapted to well-drained soils and spread only by seeds. You can find this weed along roadsides in Alaska. It is responsible for extreme environmental damage and economic loss.
Type
Biennial or short-lived perennial
Family
Asteraceae
Control
It is extremely difficult to control the spotted knapweed invasion. Hoeing, pulling, or digging two to four times per year is generally recommended to remove this weed. To prevent resprouting, it should be cut at least two inches below the root crown.
Orange hawkweed
Also known as devil’s paintbrush, this weed species can be recognized easily by its bright red-orange flowers. The leaves are hairy and lance-shaped and form a basal rosette. The whole plant contains a milky sap or juice. Its root system is fibrous.
The weed is considered to be a noxious weed. It spreads aggressively and outcompetes a lot of native species by forming dense mats.
Type
Perennial
Family
Asteraceae
Control
Digging up the rosette plants is one method to manually control these weeds. However, care should be taken that the roots are not broken and the entire plant is pulled out to prevent regrowth. Another effective treatment is using a herbicide containing 2, 4 D plus dicamba. This should be applied post-emergent to flowering plants, but it is not effective in autumn.
Narrowleaf Hawksbeard
This weed species is a winter annual that grows up to 3 feet tall. Its stems are hairy and grooved and contain a milky juice. It has a slender, deep taproot and grows in waste places, recently disturbed sites, and woodland clearings. While the weed grows on a variety of soils, it often prefers lighter soils. You can find the narrowleaf hawksbeard in any place where there is moisture and sun. The plant regenerates solely by reseeding.
Type
Annual
Family
Asteraceae
Control
Narrowleaf hawksbeard seems to be a problem in direct-seeded systems due to its ability to behave as a winter and summer annual. It can be controlled effectively in the late autumn before the soil freezes up using herbicides like glyphosate, 2,4-D, or 2,4-DB.
Common Tansy
This weed species can be identified by its dark green foliage and bright yellow, round-shaped, flat-topped flowers growing in clusters. Its leaves are fern-like with sharp edges. These plants grow anywhere between 0.4 and 1.5 metres tall, and they grow in clumps.
Common tansy can be found in sunny, disturbed areas like pastures and roadsides. The plants spread extensively via roots, and the seeds can stay viable for almost 25 years.
Type
Perennial
Family
Asteraceae
Control
It is believed that mature stems that remain erect throughout winter help the spread of tansy as the seeds shatter and move over packed snow. To reduce the spread to new areas, it is important to cut the plant immediately after it flowers.
Japanese Knotweed
This weed species can be identified by its reddish-purple shoots and white flowers blooming from pink buds. The weed grows through buildings, piping, cables, and foundations, thereby causing considerable damage to the property.
The Japanese knotweed is in full bloom during late summer and early autumn days. The weed is very difficult to control. Specialist care is required to get rid of these plants.
Type
Perennial
Family
Polygonaceae
Control
It is recommended to seek professional help to control this weed. To prevent it from spreading, you can spray or inject its stems with approved herbicides. Regardless of the treatment, it usually takes three years to treat this weed.
Bird Vetch
Bird vetch is an attractive plant with pretty purple flowers that serve as a food source for many insects and butterflies. However, it also overcrowds the other landscape plants. Its stems are branching and vine-like, with small tendrils.
This weed species thrives in full sun and prefers dry, sandy soils as well as disturbed soil. It can grow up to a minimum of 4 feet tall in a single summer. It reproduces both through seeds and underground rhizomes. It easily spreads along trails, roadsides, and other disturbed areas.
Type
Perennial
Family
Fabaceae
Control
Manual and mechanical options to control bird vetch include pulling and mowing respectively. If these two procedures are done frequently, it is possible to reduce the vigour of bird vetch, however, you cannot totally eradicate it. Mowing and pulling regularly are likely to eliminate or reduce seed production.
Scotch broom
This weed species can be easily identified by its vibrant, tiny yellow flowers in leaf axils. The stems are green and strongly angled and small leaves appear in groups of three. Fruits are pea-like pods, flattened, and brownish-black in colour.
Scotch broom thrives in full sunlight and dry, sandy soils. However, it can survive in a wide range of soil conditions. It is often found along meadows, clearings, and forest edges. Its seeds can remain viable for almost 80 years!
Type
Perennial
Family
Fabaceae
Control
Small scotch broom plants can be removed by hand pulling when the soil is wet. However, for the proper control of this weed, a systemic herbicide needs to be used. These plants tend to produce shoots from cut roots, stems, and stumps, so using a herbicide that kills the entire plant is mandatory.
Himalayan balsam
This weed species grows between 3 and 6 feet tall. It can be identified by its red/purple stems that are hollow and smooth and its tiny purple, pink, or white flowers with five petals. The fruit capsules tend to explode when they are ripe and touched.
Himalayan balsam thrives in lowlands, along beaches, and in riparian zones. It is found extensively in forests, gardens, roadsides, and wetlands. The plant can tolerate different types of soil. It competes with native species and seems to alter the composition and behaviour of pollinating insects.
Type
Annual
Family
Balsaminaceae
Control
Himalayan balsam should be hand pulled before it starts seeding. One effective treatment to control this weed is to spray its foliage with glyphosate. While the glyphosate treatment should be done in the spring before flowering, it is important to ensure that the germinating seedlings have developed sufficiently so that they are covered adequately by the spray.
Splitlip hempnettle
This weed species grows up to 1 metre and can be identified by its pink, purple, or white flowers growing in clusters at the base of leaf stalks. Stems are bristly-haired and branched. Leaves are egg- or lance-shaped with rounded teeth and pointed tips.
This species is hermaphrodite and self-fertile. It adapts well to different types of soil; however, it prefers moist soil. Splitlip hempnettle forms dense stands on riparian areas, meadows, disturbed sites, beaches, and forest edges.
Type
Annual
Family
Lamiaceae
Control
As splitlip hempnettle is an annual plant, hand pulling can be considered; roots can be pulled out easily. However, it should be done frequently. Herbicide treatment can be effective if done at the right time after consulting with specialists. The controlled area has to be monitored properly for several years.
Rampion bellflower
This weed species is a miserable plant and it is very difficult to get rid of once established. It grows up to 40 to 80 cm tall and can be identified by its unique bell-shaped violet or blue flowers. The stems are slightly hairy and branch towards the top. Stems produce milky juice when broken. Rampion bellflower thrives in open areas and under the spruce/birch forest canopy in southcentral Alaska. The weed is very difficult to control in natural and cultivated areas.
Type
Biennial
Family
Campanulaceae
Control
Herbicides containing dicamba or glyphosate are recommended, but none are completely effective. The application should be repeated frequently.
Purple loosestrife
Purple loosestrife is an erect herb that grows up to three to ten feet in height. It can be identified by its purple flowers in long spikes on the tip of the branches. The stem is square and sometimes woody.
This weed species forms dense stands with thick mats of roots, spreading over large areas. It degrades the habitat of many insects, native birds, and other species. The weed also reduces biodiversity by crowding out the native plants. A single plant can bear millions of small seeds that can be easily dispersed by water, wind, and wildlife.
Type
Perennial
Family
Lythraceae
Control
When the area infested by purple loosestrife is small, hand pulling, cutting, and digging are recommended. Removing the flower stalks before germination ensures future plants will not be produced. Approved herbicides can also be used for spot-treating small weed infestations.
Reed canarygrass
This weed species is a cool-season grass that normally invades floodplains and wetlands, but it also survives in dry soils, especially in shady wooded areas. It grows up to a height of 2 to 9 feet. Its branching flower clusters are initially greenish purple and as seeds mature, they turn yellowish brown.
The sod-forming reed canarygrass spreads through rhizomes and runners. Its dense growth is capable of completely eliminating other vegetation in the area. In fact, it can even impede the growth of trees in floodplain forests!
Type
Perennial grass
Family
Poaceae
Control
It is very difficult to control the reed canarygrass invasion. Generally, a formulation of glyphosate is used to kill these weeds in wetlands. It is applied to the foliage of young plants. The treatment should be done in early spring when the grass is green and most other native wetland species remain dormant.
