VL4 - 10.10.24 Introduction

Question 1

Examples of definitions of weeds

Answer 1

Cause more damage than benefit where they grow

Any plant or vegetation that interferes with goals and needs of humans

A plant considered undesirable in particular situation, growing where it conflicts with human preferences, needs or goals

useless, undesirable and often very unsighly plant of wild growth usually found in land which has been cultivated or in areas developed by man for specific purposes other than cultivation

weeds usually only occur in sites that have been or will be altered in some way by humans and the nature and intensity of the intervention can vary greatly

Question 2

Factors that enable a species to become a weed

Answer 2

Has no special environmental requirements for germination

Has discontinuous germination and great longevity of seed

Shows rapid seedling growth

Spends only a short time in the vegetative condition vefore flowering

Maintains seed production as long as growing conditions permit

Is self-compatible, but not necessarily self-pollinated or apomictic

If cross-pollinated, can be pollinated by a non-specialized flower visitor or by wind

Produces numerous seeds in favorable environment

Can produce some seed in a very wide range of environments

has special adaptations for short- and long-distance dispersal

If a perennial, has vigorous vegetative reproduction

If a perennial, is brittle at the lower nodes of rhizomes or rootstocks

If a perennial, can regenerate from severed protions of the rootstock

Can compete by special means, for example rosette formation, high competition or exocrine production

Question 3

Annual weeds

Answer 3

See page 6 for life cycle

Weeds that grow, reproduce and die in one year or less

Occur in large numbers

Ability to reproduce in crops which are planted annually

Normally reproduce only by seed and they are heavy seed producers

Frequently possess the ability to remain dormant for up to several years

Annuals can be classified as
- summer annuals grow actively during summer, produce seeds and die by end of summer or early fall
- winter annuals may germinate before winter but produce very little growth until the temperature starts to rise towards the end of winter or early spring

Question 4

Biennial weeds

Answer 4

Require more than one year (but not more than two) to complete their growth and reproduction

Are sometimes confused with winter annuals

Are typically rather large plants when mature and have thick, fleshy roots

Are often found in pastures, special crops

-> Annuals and biennials are often mentioned on one single group

Question 5

Perennial weeds

Answer 5

Simple perennials reproduce alomost entirely by seed, e.g. dandelion

Creeping perennials have above-ground or underground vegetative structures which can readily propagate new plants without the necessity of seed, although most of them also have seed.
Vegetative reproductive structures include rhizomes, stolons, tubers, rootstocks, bulbs, bulblets and corms

Question 6

Classification of Weeds - habitat

Answer 6

Cropland
Rageland
Forests
Aquatic
Environmental weeds

Question 7

Classification of weeds - Morphology / number of cotyledons

Answer 7

Monocotyledons
Dicotyledons

Question 8

Classification of weeds - morphology

Answer 8

Grass (monocotyledon)
Broadleaved (dicotyledon)
Sedge (cyperaceae)
Fern or fern ally

Question 9

Classification of weeds - Photosynthetic Pathway classification

Answer 9

Temperature optimum of C3 plant is 10 - 25 °C

Temperature optimum of C4 plants is 30 - 45 °C

Examples of C3:
Atriplex patula L.
Avena fatua L.
Chenopodium album L.
Galeopsis tetrahit L.
Galinsoga ciliata L.
Polygonum aviculare L.
Sinapsis arvensis L.
Solanum nigrum L.

Examples of C4:
Amaranthus retroflexus L.
Cyperus esculentus L. (neophyt)
Digitaria sanguinalis (L.) Scop
Echinochloa crus-galli (L.) Beauv.
Setaria viridis (L.) Beauv.

Question 10

Classification of weeds

Answer 10

Life cycle
Habitat
Number of cotyledons
Morphology
Season of germination
Photosynthetic Pathway Classification

Question 11

Indicator species - Horsetail (Equisetum arvense)

Answer 11

Improper drainage of the (sub)soil

Question 12

Indicator species - Canada thistle (Cirsium arvense L.)

Answer 12

High iron content in the soil
Low calcium content in the soil
Poor in organic matter (low humus content)
Low availability of phosphate in the soil

Question 13

Indicator species for high plant nutrient content in the soil

Answer 13

Galium aparine
Veronica persica
Chenopodium album
Rumex obtusifolius