Wild buckwheat  Scientific name: Fallopia convolvulus  Family: Polygonaceae  Life cycle: Annual  Where found: Cropland  Physical description:  Seed: black, three-angled  Cotyledon: linear to oblong  True leaves arrowhead to heart shaped  Alternate arrangement  Growth habit: Prostrate/climbing  Leaves possess small stiff hairs making it rough to the touch  Interesting facts:  Latin name describes resemblance to bindweed  convolvulus =refers to species associated with Convolvulaceae family (bindweeds), meaning “to intertwine”

Bedstraw aka cleavers, goosegrass  Scientific name: Galium aparine  Family: Rubiaceae  Life cycle: Annual  Where found: Range/Cropland  Physical description:  Seed: ball-shaped with stiff, hooked bristles  Cotyledon: ovate to round, apex indented  True leaves linear with barb at the tip  Whorled arrangement, 4-5 leaves at first nodes, then 6-8  Leaf surface has short stiff hairs that help it cling to other plants  Interesting facts:  Square stems  Latin name describes low, dense growth habit  Galium = milk, aparine = seizer  Rumored to have once been used as a strainer in cheese making

Field pennycress  Scientific name: Thlaspi arvense  Family: Brassicaceae  Life cycle: Annual  Where found: Cropland  Physical description:  Seed: fingerprint pattern  Cotyledon: oval with long petiole  True leaves round to spatulate, then oblong to oval  Forms a basal rosette at first, then alternate when flowering  Early leaves have long petioles; later stem leaves are sessile, clasping around stem  Leaves without hair, in contrast to shepherd’s purse  Growth habit: erect  Interesting facts:  Seed pods are disc-shaped with a distinct notch at tip  Distinct, garlic-like odor when brushed  Latin name describes flat pod  Thlas =to crush or flatten

Shepherd’s Purse  Scientific name: Capsella bursa-pastoris  Family: Brassicaceae  Life cycle: Annual  Where found: Cropland  Physical description: highly variable  Seed: small, sticky when wet  Cotyledon: ovate, apex may be indented  Growth habit: basal rosette; flowering stem alternate  True leaves oval, then elliptic to oblanceolate, most becoming pinnately divided  Stem leaves lanceolate  Early leaves have long petioles; later stem leaves are sessile, clasping around stem  Leaves are sparsely hairy  Interesting facts:  Seed pods heart-shaped, flattened  Latin name describes seed pods  caps =small box  bursa = purse, pastor =shepherd

Canada thistle  Scientific name: Cirsium arvense  Family: Asteraceae  Life cycle: Perennial  Where found: Range, Cropland  Physical description:  Seed: light brown, 3-4mm long, with feathery white plume  Cotyledon: oval to oblong, visible white midvein  True leaves oval to elliptic in shape, with dentate to deeply pinnate margins  Forms a basal rosette at first, then alternate when flowering  Leaves sessile; prickly and spine-tipped with a waxy surface  Purplish-pink flowers less than 2.5cm across  Interesting facts:  Primarily reproduces by extensive creeping rhizomes  the only rhizomatous thistle  Female flowers have a pleasant, vanilla-like aroma  Latin name describes distinct midvein of leaf  Cirsium = swollen vein

Classification of weeds

Weed classification groups  Habitat  Life Cycle  Taxonomic Group  Physiology

Habitat  Terrestrial  Live on land  Crops, rangeland, turf, forests, etc.  Aquatic  Structurally and physiologically modified to live on, near or around water  Aerial  Not rooted in the soil an use other plants for support  Parasitic: Mistletoe, dodder  Epiphytic: Orchids, Spanish moss

Life Cycle  Herbaceous plants  Plants with non-woody aboveground stems  Annuals  Plants that live for one growing season only  Re-establish from seed  Biennials  Plants that require parts of two growing seasons to complete their life cycle  Reproduce from seed  Perennials  Plants that live indefinitely  In addition to seed, some of these plants produce other structures that allow them to overwinter and/or reproduce  Modified stems (stolons, rhizomes,corm, bulb, tuber), leaves (part of a bulb) or roots (tuber)

Life Cycle  Woody plants  Plants with woody aboveground stems that persist from year to year  Trees  Woody perennials with a single main stem or trunk  Shrubs  Woody perennials with more than one principal stem arising from the ground

Taxonomic Group  Dicots  Plants whose seedlings produce two cotyledons (seed leaves)  Typified by:  Net leaf venation  Flower parts in multiples of 4 or 5  Called “broadleaves”  Examples?  Monocots  Plants whose seedlings bear only one cotyledon  Typified by:  Parallel leaf venation  Flower parts in multiples of 3  Called “grasses” or “grass-like plants”

Physiology  Photosynthesis is the process by which plants convert CO 2 to glucose (carbon fixation)  Plants can vary in how they convert CO 2 to glucose (carbon fixation)  C3 plants  First stable product of the Calvin Cycle is a 3 carbon acid  C4 plants  First stable photosynthetic product is a 4 carbon acid  More efficient at photosynthesis under high temperatures  Many weeds exhibit this photosynthetic pathway

How weeds interfere with desirable plants

Interference  Not all interference is negative  Weeds interfere with growth of desirable plants via three mechanisms:  Competition  Allelopathy  Parasitism  Mistletoe, dodder, broomrape, witchweed

Competition  The ability of weeds to compete for light, water and nutrients depends on three main factors:  Timing of weed emergence  The first plant to emerge has a distinct competitive advantage  Why?  Can access resources  Can negatively affect the other plants  Critical weed-free period concept

Competition  Growth form  Growth habit and rate of development  Which are more competitive, broadleaves or grasses?  Stem height, leaf area, branching, leaf angle  Root development  Weed density  Increased weed density = decreased crop yield  Are there exceptions to the rule??

Allelopathy  Allelopathy refers to the chemical inhibition of one species by another  The "inhibitory" chemical is released into the environment where it affects the development and growth of neighboring plants  Allelopathic chemicals can be present in any part of the plant  May inhibit shoot/root growth  May inhibit nutrient uptake  May attack a naturally occurring symbiotic relationship thereby destroying the plant's usable source of a nutrient  Has proven difficult to study  The case of spotted knapweed and catechin  2003 study showed that the plant produces catechin  Found that native grasses were more susceptible to catechin than European grasses  2005 study unable to detect catechin in soils infested with spotted knapweed

How weeds persist

Weed seeds  Large numbers  Weeds can produce thousands of seeds per plant  Small seeded species are usually more prolific Weed speciesWeed seeds/plant Barnyardgrass7,000 Common ragweed15,000 Shepherd’s purse38,500 Common lambsquarter72,000 Redroot pigweed117,000 Russian thistle200,000 Adapted from: Ross, M. A., & C.A. Lembi. Applied weed science. 3 rd Edition

Weed seeds  Can survive and remain viable under adverse conditions  Well-protected by seed coats resistant to breakdown  Resist freezing, drought, fire, animal predation  Inactive seeds cannot be controlled by herbicides  Have adaptations that help with dispersal  Hooks and spines adhere to animals  Floating on water, carried on wind  Are of similar size and shape to crop seeds so they cannot be removed

Seed banks  Weed seeds build up in the soil over time  One study  7 million weed seedlings/ac = 280 million seeds per acre-furrow slice (6”deep)  Weed seed bank dynamics dependent on  Number of seed present  Species composition  Depth of distribution  Seed viability  Seeds can remain viable for years WeedSeed Viability in Years Quackgrass1-6 Wild oat4-7 Foxtail20 Field bindweed20+ Canada thistle21 Common lambsquarter 40 Redroot pigweed40 Adapted from: Ross, M. A., & C.A. Lembi. Applied weed science. 3 rd Edition

Seed banks  Dormancy  Dormancy is a temporary condition where viable seeds fail to germinate even when environmental conditions are adequate  Seed dormancy ensures continued germination for many years  Primary dormancy  Seeds are unable to germinate after they first mature  Secondary dormancy  Induced over a period of time by environmental conditions  Quiescence  A period of inactivity cause by the lack of a necessary factor (e.g., oxygen, water, light)  Afterripening  Transition from dormancy to a more readily germinable state  Stratification (exposure to cooler temperatures for a period of time)  Scarification (breaking of seed coat)  Light-regulated

Vegetative Reproductive Structures  Major food storage organs  Possess numerous buds capable of starting new plants  Rhizomes, tubers, bulbs, stolons and creeping roots  Serve as overwintering mechanisms  Serve as a second means of propagation  Allow plants to grow more quickly than those from seed  Help with survival after disruption  ½ inch piece of Canada thistle can start a new plant

Questions! 1. Dormancy is a temporary condition where viable seeds fail to germinate even when environmental conditions are adequate. True or False? 2. Biennial weeds complete their life cycle in ____________ year(s)? a. Two b. One c. Every other d. More than two 3. Which are more competitive, broadleaf or grass weeds? Why?