Weed Identification: Using Plant Structures as a Key

Weed Identification: Using Plant Structures as a Key free pdf ebook was written by Paul A. Baumann on April 20, 1999 consist of 18 page(s). The pdf file is provided by www.cnr.uidaho.edu and available on pdfpedia since April 09, 2012.

b-6079 3-99 weed identification: using plant structures as a key paul a. baumann professor and extension weed..stems are often branched. leaf veination is netlike or has a..early fall, produce vegetative growth, flower and produce seed in mid-...

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Weed Identification: Using Plant Structures as a Key pdf




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Weed Identification: Using Plant Structures as a Key - page 1
B-6079 3-99 Weed Identification: Using Plant Structures as a Key Paul A. Baumann Professor and Extension Weed Specialist, The Texas A&M University System.
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Weed Identification: Using Plant Structures as a Key - page 2
This handbook is intended for use as a companion piece to better understand the plant part terminology used in less complicated identification guides. 1 Introduction W eed identification is necessary to the success of any weed control program. Frequently, simple plant keys or “picture book” identification guides are used to identify weeds. However, some plant taxonomy keys can be quite complex and require an advanced understanding of plant structure and taxonomic terminology. While more difficult to use, a detailed key or guide allows for the precise identification of weeds.
Weed Identification: Using Plant Structures as a Key - page 3
Classification W eeds can be classified into one of three different categories: broadleaves, grasses or sedges. Broadleaf weeds often are referred to as dicots; the seedlings produce two cotyledons (seed leaves) that are evident as the plant emerges through the soil surface. Broadleaf plants generally have wider leaves than grass plants and the stems are often branched. Leaf veination is netlike or has a branched appearance. Grasses and sedges are monocots; their seedlings produce only one cotyledon (sometimes referred to as the coleoptile in grasses). Grasses have bladed leaves that are parallel veined and this veination extends onto the sheath. In cross- section, the stems in grasses are usually round or somewhat flattened. The stems of sedges, in cross-section, are usually triangular. A second, relatively simple method of weed classification is by the categories of annuals, biennials or perennials. Annual plants live for one growing season and are often referred to as either summer annuals or winter annuals. Summer annuals germinate from seed in the spring, produce vegetative growth, set flower and produce fruit mid- to late summer, and die back in the fall. Winter annuals germinate in the late summer to early fall, produce vegetative growth, flower and produce seed in mid- to late spring, and die off in the summer. 2
Weed Identification: Using Plant Structures as a Key - page 4
Biennials are plants that live for two years; seeds germinate in the spring, summer or fall of the first year and the plants overwinter usually as a rosette of leaves. During winter, the shoot tips are exposed to cold temperatures for a period of time. This vernalization promotes normal development of flowering and seed production during the summer of the second year. The plants then die in the fall. Perennials are plants that produce vegetative structures that allow them to live for three or more years. These plants are classified as simple or creeping perennials. Simple perennials spread primarily by seed; they cannot spread vegetatively from underground roots. Creeping perennials, on the other hand, can reproduce by creeping roots and also through seed production. The creeping roots found above ground are called stolons, the below-ground roots are called rhizomes. Rhizomes are most common in perennial grasses. In broadleafs or sedges, these underground root structures are referred to as tubers. 3
Weed Identification: Using Plant Structures as a Key - page 5
Plant Parts leaf blade ligule leaf collar auricle sheath node T he first step in identifying grass weeds is to become familiar with some key grass parts: the leaf blade, the collar, the ligule and the sheath. The ligule may or may not be present on some grass seedlings. The sheath is an extension of the leaf blade that terminates at the node. The areas between the nodes are referred to as internodes. Some grass plants may have extensions of the sheath called auricles. A sedge, however, generally does not have a ligule or an auricle. 4
Weed Identification: Using Plant Structures as a Key - page 6
The cross-sections of grasses may be either round or oval (flattened), compared to a sedge, which exhibits a triangular shape. split overlapping united The sheath of a grass surrounding the stem is generally one of three types: split, overlapping, or united. 5
Weed Identification: Using Plant Structures as a Key - page 7
absent hairy membranous The ligule on a grass plant is a structure on the inside of the collar. It can be either membranous or hairy, or it may not be present at all. smooth lingule margin toothed lingule margin The ligule may exhibit either a smooth margin or a toothed margin. auricles present auricles absent Auricles, appendages found at the junction of the leaf blade and leaf sheath, may or may not be present. 6
Weed Identification: Using Plant Structures as a Key - page 8
hairy sheath margin hairy sheath hairy collar margin hairy collar hairy leaf margin hairy leaf blade Pubescence or leaf hair is often a key to identifying specific grasses and weeds. Pubescence can appear in several different areas on a grass plant: • only on the sheath margin, • over the entire outside of the sheath surface, • on the leaf collar margin, • as a ring-like appearance surrounding the whole collar, • on the leaf blade margins or leaf edges, or • only on the blade surface, with hair absent over the other parts of the plant. Leaves or other plant surfaces without any pubescence whatsoever are often referred to as glabrous. 7
Weed Identification: Using Plant Structures as a Key - page 9
true leaf terminal bud leaf blade alternate leaf arrangement leaf veins petiole stem cotyledon roots A representation of a broadleaf plant with a few key descriptive parts labeled is shown above. 8
Weed Identification: Using Plant Structures as a Key - page 10
linear oblong lanceolate spatulate oval round ovate kidney butterfly Broadleaf weed cotyledons are a key identification feature. However, if cotyledons have fallen off the plant or are in poor condition, they may not be helpful in broadleaf weed identification. Various cotyledon shapes are illustrated above. 9
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