Weeds


Every year at the UConn Home & Garden Education there are a few topic of interest that we get a lot of calls about. Several years ago we fielded a lot of calls about the drought situation in Connecticut that occupied many people’s thoughts in 2016. In fact, that encompassed two years as we started to feel the effects of it in 2015. On the tail end of the drought, and perhaps in part because of it, many parts of the state were visited with an infestation of gypsy moth caterpillars. When we have a wet spring the fungus Entomophaga maimaiga, a natural control of the gypsy moth caterpillar, can flourish. The fungus overwinters as spores in leaf litter and in the soil. It then reactivates in the spring when there is sufficient rainfall. Although we were receiving an adequate amount of rain by 2017 it happened to occur a bit late for the fungus to be fully effective against the voraciously feeding caterpillars. So the summers of 2016 and 2017 were dedicated to answering many questions about the gypsy moth caterpillars and the damage that they wreaked.

As those two events have wound down a new concern arose for many of our clients. Thanks in part to press releases and an interview that aired on NBC CT in June the giant hogweed, Heracleum mantegazzianum, (below images) jumped to the front of the queue. The Connecticut Invasive Plant Working Group (CIPWG) issued a warning about this invasive species which was first spotted in Connecticut in 2001. Most of the populations of giant hogweed are under control and none of the reported sightings in 2018 were positive.

There are many look-a-like plants and it is those species that we are asked to identify. Starting in early-June calls and emails began to come in to identify large herbaceous perennials that were striking fear into Connecticut residents. This is in part due to the pretty noxious nature of the giant hogweed sap. Within 24-48 hours after skin has been in contact with the sap painful blisters may appear in individuals that are sensitive to it. Three things need to be present for the reaction known as phytophotodermatitis to occur. First, direct contact between the skin and the sap. Second, the skin must be moist as from perspiration, for example. Third, the contaminated area must be exposed to sunlight. If you are working in an area that contains giant hogweed it is easy to imagine that all of the criteria could be easily met.

Before attempting to remove giant hogweed from an area the first step should be positively identifying it. As I mentioned earlier, there have not been any confirmed sightings in Connecticut yet this year. It may be that the suspected plant is one of the following instead.

The first plant that is most commonly mistaken for giant hogweed is fellow member of the Heracleum genus: cow parsnip, Heracleum maximum, (images below). Unlike giant hogweed which was introduced to the United States 100 years ago from the Caucasus region of Central Asia, cow parsnip is native to North America. A tall herbaceous perennial that can reach up to 10 feet in the shade, nowhere near the 18 feet possible height of the giant hogweed, cow parsnip bears its flowers in in the flat-topped or rounded umbels that are characteristic of other members of the carrot family, Apiacea. Both species have compound deeply-lobed, toothed leaves but the cow parsnip lacks the red veining and leaf stalks common to giant hogweed. Cow parsnip also contains chemicals that cause phytophotodermatitis.

The next most common look-a-like is angelica, (below images). A first cousin once-removed, it shares its family, Apiaceae, with the giant hogweed and cow parsnip but is in the genus Angelica. Angelica grows 3-9 feet tall and also has large umbel flower heads. The compound leaves of angelica are what distinguish it from giant hogweed as they are bipinnate, meaning that they are compound leaves in which the leaflets are also compound (think honey locust leaves). Often used as a medicinal herb, angelica is the least toxic of the hogweed look-a-likes although it may still cause a skin reaction.

Queen Anne’s lace, Daucus carota, (below images) takes compound leaves one step further to tripinnate, having pinnately compound leaves that are bipinnate. The more levels of pinnation, the more delicate the overall effect. The airy-looking leaves of D. carota are what give it the ‘lace’ part of its name and are similar to its subspecies, the domestic carrot. Queen Anne’s lace has an umbellate flower head atop a much slimmer stem than giant hogweed, cow parsnip, or angelica. The sap from the leaves and stems can cause a phytophotodermatitis reaction although the flowers are used to make jelly similar to the yarrow jelly from our June 26th blog post.

The native Lactuca species includes wild lettuce (Lactuca Canadensis),

prickly lettuce (L. serriola), hairy lettuce (L. hirsute), and the blue lettuces (l. biennis, L. floridana, L. pulchella, L. villosa).

These tall plants start out from a basal rosette of leaves and can grow to 7 feet tall with large alternating broad leaves.  They have pale blue insignificant flowers compared to the dense clustered heads of the previous plants.

Finally, giant ragweed, Ambrosia trifida, has also made a plant identification appearance.  This 6-foot tall annual herb is a noxious weed that has become invasive in other parts of the world as it out competes native species in much the same way that the giant hogweed has here.

As plants and seeds have spread across the globe through human, animal, mechanical, or water means many species have landed in non-native locations and taken root there. If you are a fan of podcasts, check out the Infinite Monkey Cage’s Invasion episode where scientists and comedians take a look at the problems caused by alien (plant) invasions.

Susan Pelton, UConn Home & Garden Education Center

All images by CIPWG and UConn

 

 

mullein.greenway.jallen  Photo: J. Allen, UConn

 

Common mullein (Verbascum thapsus) is, well, common around here.  Right now it’s in its glory, with spikes of yellow flowers standing tall along roadsides and in other open areas.  I really thought this was a native plant, and when I spotted them along this paved trail in central Connecticut and decided to snap a few pics and do a blog on it this week, the idea was to share info on an interesting but often overlooked native.  As usual, I started reading up on it prior to writing and discovered that it’s not native to North America at all. This plants’ native range includes Europe, northern Africa and Asia.  It was introduced in North America very early in the 18th century and by the early 1800s it was widespread and reported as far west as Michigan in 1839 and California in 1876.  Today it is found in all 50 states and much of Canada.

A couple of states, Colorado and Hawaii, list it as a noxious weed. In most cases, common mullein is not considered an important agricultural weed.  This is because it does not compete well with other plants for establishment and is also not tolerant of tilling.  Seed germination occurs on pretty much bare soil, so disturbed areas are ideal sites for colonization.  Speaking of the seeds, they are impressive!!  One notable characteristic having to do with the seeds is the number of them produced by a single plant: 100,000-240,000 of them in a single season (number varies by reference)!  Not only are seeds produced in massive quantities, they can also remain viable and dormant in the soil for over 100 years.  This means that where this plant grows, a huge seed bank can rapidly accumulate.

First year rosette by John Cardina, The Ohio State University, Bugwood.org

Common mullein is a biennial plant that produces a large rosette of low-growing leaves in the first year and a single tall flower spike in the second year. Rosette leaves can be up to a foot long and are quite fuzzy.  Leaves on the lower part of the flower stalk are attached (no petiole), alternate and decrease in size towards the top.  Flowers are yellow, stalkless, one inch across, and have five fused petals.  Each flower only blooms for one day.  Flowers are produced on the stalk from June through August, or in some areas, September.  Seed capsules are fuzzy and split open at maturity to release as many as 700 or more seeds each.  Most of the seeds fall to the ground within a short distance of the parent plant but some are dispersed by animals, soil movement, etc. Very few animals are known to feed on the seeds, even birds, because they are so tiny.

mullein.flower.jallen  Flower close-up with Syrphid fly. J. Allen, UConn

This plant is a mixed blessing when it comes to the insects that it attracts. Some of them are pests that will also feed on plants in the garden or on the farm.  These include tarnished plant bug and spider mites. Others, though, like the Syrphid fly shown in the photo, are beneficial.  The larvae of the Syrphid fly are predators and will feed on aphids and other tiny, soft-bodied insects.

The reason this plant was introduced into the United States, and probably other areas of the world, is because it has well-documented medicinal uses. Disclaimer: This blog does not advocate the use of plants for these purposes unless a doctor is consulted. Because common mullein was introduced to the U.S. so early, it’s not known whether it was mostly shared with European settlers by Native Americans or the other way around.  A very early record of medicinal use was from Dioscorides about 2000 years ago for treatment of pulmonary diseases, especially coughs. Chemicals in the plant (and tea made from it) include expectorant saponins and emollient mucilage.  Any tea or extract made for the plant needs to be filtered well to remove the hairs that can cause irritation.  Leaves have also been smoked for pulmonary problems.

Some groups have also used a poultice from common mullein for treatment of skin conditions including sores, rashes, warts, hemorrhoids and more. Oil from the flowers has a history of use for many external issues, too.

Other interesting uses for the plant include piscicides (fish killing compounds), shoe insulation, candle wicks, and torches (made from the flower stalk by dipping into suet or wax). Piscicides have been widely used through history for fishing (the toxic chemicals in this case are from the seeds).  The flowers can be used as a source of natural yellow or green dye.

While not planted much in gardens, seeds are reported to be available from a few vendors. Because of the persistence of the seeds, it can be hard to get rid of when needed.  The best method is hand pulling but herbicides can also be used.  This will require some persistence due to the longevity of the seeds left behind.

To finish up, I’ll share some of the other, sometimes fun, common names of this plant: great mullein (commonly used in Europe), cowboy toilet paper (western U.S.), flannel mullein, velvet dock, woolly mullein, and in the 19th century U.S. Indian rag weed, hare’s beard, ice-leaf, blanket mullein, poor man’s blanket, shepherd’s club, feltwort, and Moses’ blanket.

J. Allen

 

japanese-knotweed-1

Japanese Knotweed is a beautiful plant when in full, white flower stage. Too bad it is such a thug and invasive. It also makes a nice hedge, but quickly overtakes the properties if used as a boundary plant. Colonies can be seen just about everywhere along roadsides, in meadows and yards as it spreads so freely.

japanese-knotweed-5

Japanese knotweed is also known as Japanese bamboo, American and Mexican Bamboo due to its hollow stems with nodes on them. The plant is known by three different Latin names of Fallopia japonica and Polygonum cuspidatum Siebold & Zucc.  And Reynoutria japonica Houtt, but it all the same plant. No matter what you call it, it is aggressive, invasive and extremely hard to kill once established.

The plant was brought to the United States during the 1890’s from Asia as a solution to erosion. It will grow in just about any situation from full sun to complete shade, rich or lean soils, and dry or soggy soils. It tends to make a colony of plants, out-competing any and all other plants resulting in a monoculture. Since it evolved on another continent, it has no native predators, insect or animal that eats it enough to control its spread.

japanese-knotweed-4

It reproduces vegetatively. If digging it out, any tiny piece of root left in the ground will quickly send up a shoot to get reestablished.  Control measures are difficult. Heavy machinery can dig out large infestations and monitor for a new sprouts to pull or treat with herbicides. Herbicides which contain Glyphosate or Triclopyr are the most successful and should be used before the plants flower or sprayed on cut stems. It has been reported that monthly mowing for five years will finally eradicate a large area.

 

-Carol Quish

 

Masses of white flowers are a common and beautiful sight along Connecticut’s roadways and in fields this time of year (late May through June). While there are (of course) many shrubs and trees bearing white flowers, one of the most predominant is multiflora rose (Rosa multiflora).   This rose is native to Japan, Korea and parts of China and has become invasive throughout eastern North America.  While it is invasive and is a real problem, we’re sort of stuck with it overall so go ahead and enjoy the gorgeous blooms.MultifloraRoseBush.JAllen  Photo: J. Allen, UConn

Multiflora rose was first introduced into the U.S. as early as 1866 for use as a rootstock for ornamental roses. In the 1930s, the U.S. Soil Conservation Service began to recommend it for erosion control and as a ‘living fence’ for livestock.  In the 1960s plants were even distributed to landowners for free to encourage planting as cover for wildlife including birds and rabbits and as a food source for songbirds.  Thanks to the songbirds, many seeds have been distributed to new sites because they do like to eat the nutritious rose hips (fruit).   The plant is now considered a noxious or invasive weed in many states including in Connecticut “…prohibited from importation, movement, sale, purchase, transplanting, cultivation and distribution under CT General Statutes §22a-381d”.

MultifloraRoseflowers.J Photo: J. Allen, UConn

It’s pretty easy to recognize multiflora rose when it’s in flower but also once the bloom period is over. Flowers are borne in clusters of mostly white but sometimes slightly pink flowers that are ½ to 1” across and have five petals.  Leaves, too, are distinctive.   They are alternate and compound, having 5-11 oval leaflets with toothed margins.  The base or petiole of the leaf is fringed.  Even the thorns are unique to this species.  They are large, curved backwards and have an oval base.  If a thorn is removed, it will leave a visible oval scar on the stem.  They’re pretty serious thorns and are reported to be capable of puncturing tires and leaving a painful gash in skin.  Overall, this plant can reach a height of about 15’ with long, arching stems.  It can also be a climber and at times you will see it spreading up against other vegetation or structures.  For some great info and photos of the thorns, fringed petals (stipules), and more check out this web page: http://na.fs.fed.us/spfo/invasiveplants/factsheets/pdf/multiflora-rose.pdf

MultifloraRosespreading.J.AllenMultiflora rose spreading through a natural area and up another tree in the background. Photo: J. Allen, UConn.

Reproduction is by seeds (prolific at 500,000 to a million seeds per large bush per year), suckers and by rooting at the end of stems that arch over and touch the ground. Widespread dispersal is via birds that eat the fruit and expel the seeds.  It’s reported that seeds which have passed through a bird’s digestive system germinate more readily.  Invasiveness is enhanced by not only the huge potential for seed production but also by the fact that the seeds can remain viable in the soil for up to 20 years.

Like other roses, the hips and other plant parts (leaves and flowers) are edible. The hips are high in Vitamin C, carotene and essential fatty acids.  It’s recommended to harvest after the first frost when berries are softened and sweet.  They can be eaten raw but do contain some hairs between the flesh and the seed that can cause irritation.   Leaves, flowers and hips can be used to make tea.  To make rose hip tea, mash the fruits and steep in hot water.  Leaves are best when young as the hairs on the undersides can become stiffer and less palatable later in the season.

Some of the broader impacts of this plant, like other invasives, include displacement/replacement of native plants and the resulting impacts on habitat and food supply for native wildlife. Pasture lands are adversely affected when these thorny plants encroach and reduce forage area for livestock.  Even forestry operations are affected because of the impenetrable, thorny thickets that form, reducing access and making work difficult.  Multiflora rose can thrive in a wide range of habitats from open sunny sites to woodland edges.  It can survive on a range of soil types but is not found in extremely dry or wet sites.

Control methods used include physical or manual removal including mowing, digging, and prescribed fire. Chemical herbicides can be used as either a cut stem (fall) or foliar application.  Biological controls are not yet available.  A virus that causes rose rosette disease limits growth in some areas but that also affects ornamental roses.  An insect, the European rose chalcid, is being studied for potential use.

By J. Allen