UPDATE: INVASIVE PLANTS OF INCREASING CONCERN

Antonio DiTommasoDepartment of Crop and Soil SciencesCornell University (ad97@cornell.edu)

WHY WORRY? Invasive plants estimated to cost the U.S. economy $40

billion/year; $26.4 billion due to cropland weeds

Second leading cause of species endangerment and recent extinctions

Climate change will result in different weed flora

Negatively impact human health

Damage human enterprises and ecosystems

Expanding air travel, more ports of entry

Improved access to foreign ecosystems

Decreased diversification in production systems

HOW ARE NON-INDIGENOUS INVASIVE PESTS INTRODUCED?

Accidental versus Deliberate – proportion varies among taxonomic groups

Few invasive microorganisms deliberately introduced

Majority of invasive insects or marine invertebrates likely accidentally introduced

Most invasive vertebrates especially fish, mammals, and birds have been deliberately introduced

Most invasive plants have been deliberately introduced (horticultural industry)

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Local control and management only

Pest Increase Over Time & Control Potential

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Public awareness typically begins

Introduction

Time

Detection

(1) (3) (4)(2)

PLANT INVADERS TO WATCH FOR!

Mile-a-minute (Polygonum perforliatum)

Japanese knotweed (Polygonum cuspidatum)

Spotted knapweed (Centauria stoebe ssp. micranthos)

Pale and black swallow-worts; (Vincetoxicum rossicum & V. nigrum)

Wild parsnip (Pastinaca sativa)

Common reed (Phragmites australis)

Japanese stiltgrass (Microstegium viminieum)

Spotted Knapweed (Centauria stoebe ssp. micranthos)• European plant introduced in the late

19th century to Pacific Northwest, possibly through contaminated clover and alfalfa seed.

• Found in fields, pastures, roadsides, waste spaces and other open areas.

• Also known as Centaurea maculosa, Centaurea biebersteinii.

• Herbaceous biennial or short-lived perennial.

• Not shade tolerant.

• First-year rosette has hairy, grayish, and pinnately lobed leaves up to 6 inches long.

• Mature plants stand 1-3 feet. Leaves of mature plant are alternate, pinnately lobed on lower stem and lance-shaped on upper stem. Stems are ribbed and hairy.

• Develops a long taproot.

Description

• Blooms from mid to late summer.

• Flowers are pink to purple and thistle-like, with stiff, black tipped involucre bracts. Flowers grow singly or in clusters.

• Seeds are achenes, with short bristly pappus at base. Wind dispersed.

• An individual plant can produce up to 2,000 seeds, which may persist in the seed bank for over 8 years.

Reproduction

Brown (Centaurea jacea) and black (Centaurea nigra) knapweed are also present in NY. The leaves of these knapweeds are entire or with only shallow lobes and the involucre bracts have long fringes.

Brown knapweed Black knapweed

Similar Species

Meadow (Centaurea pratensis) knapweed is also present in NY. A hybrid of black and brown knapweeds. Foliage coarse and tough. Blooms in midsummer to fall. Grows from woody root crown and up to 3.5 ft tall. Lower leaves are long-stalked, upper leaves have no stalk. Stems are many-branched and tipped by a solitary flower head up to one inch wide. Flower heads are pink to reddish purple, oval or almost globe-shaped. A key identifying feature is the fringed bracts on the flower head. However, because meadow knapweed is a hybrid, it traits can vary. Also be referred to as C. nigrescens, C. x moncktonii, C. debeauxii ssp. thuillieri, and C. jacea x nigra.

Similar Species

• Low palatability of mature plants to cattle can lead to overgrazing of other plant species in pastures, lowering community diversity and reducing land value.

• Dense stands of dead, dried knapweed stems can impede access to forage.

• Displacement of native species and decreased diversity in natural areas. But late season nectar source for bees.

• Increased soil erosion, particularly if spotted knapweed displaces native and naturalized grasses.

• Spotted knapweed produces the allelochemicals (±)-catechin and cnicin, although the extent to which they affect native plants is uncertain.

Impacts

• Thirteen specialist insects have been released in North America. • Eight feed on flowers, five on roots. • Several released in NY.• Success has been limited, possibly due to complex phylogeny of

knapweed species.

ManagementMechanical Chemical

Biological

• Does not persist under annual cultivation.

• Mowing at flowering can reduce seed production.

• Increase grazing stocking rates. Fertlize/lime fields

• Young plants and spring growth may be vulnerable to browsing by some livestock, particularly sheep.

• Herbicides can be useful in controlling new invasions.

• Clopyralid, dicamba, picloram, and 2,4-D effective at controlling spotted knapweed in rangeland.

• Scope of infestation and persistence in seed bank may make large scale herbicide use impractical.

Wild Parsnip (Pastinaca sativa)• Wild form of the cultivated parsnip.

Native to Europe.

• Common along roadsides, railroads, field edges, and in waste areas and other disturbed sites. Can invade natural areas.

• Much more widespread in NY than map suggests.

• Short lived monocarpic perennial.

• During first year forms a rosette and thick, yellow-white taproot that can reach up to 1.5 m in depth.

• Mature plant generally 2-5 feet tall.

• Stem branching, grooved, sparsely haired, and hollow.

• Leaves alternate, pinnately compound, toothed and clasping. Stem and basal leaves similar.

Description

• Flowers from late spring to early summer. Some individuals may flower later in the season.

• Flowers are small, 5-petaled, yellow, and borne in large (3-8 inch) compound umbels.

• Fruit is dry, flattened, winged, schizocarp that splits into two seeds.

• Dispersal is primarily by wind.

Reproduction

Similar Species - Golden Alexanders (Zizia aurea)

Impacts• Wild parsnip sap contains furanocoumarins, which cause

phytophotodermatitis when skin is exposed both the sap and UV radiation. Symptoms include inflammation, redness, burning and blistering.

• Livestock that consume wild parsnip are vulnerable to phytophotodermatitis.

• May displace native plants like Canada goldenrod (Solidago canadensis) in old fields and meadows.

ManagementMechanical

• Individual plants can be controlled by cutting the stem beneath the basal leaves or by hand pulling.

• Seeds do not survive long in seed bank, so methods that reduce seed production may be most effective.

• Timing of mowing is essential. Mow when flower stalks begin to form to minimize seed production.

• In natural areas, succession may be effective control.

• Whether mowing or hand weeding, proper PPE is essential.

Chemical

• Herbicides most effective on first year rosettes.

Thank You!

https://weedecology.css.cornell.edu/