Chapter 2: Plant Biology, Identification, and Management

Annual weed

Completes life cycle from seed in less than one growing seasons

Axil

Angle between leaf stalk and stem

Biennial weed

Completes life cycle in two years

Conifer

Plants that bear seeds in cones

Cotyledons

First leaves of a sprouted seed. They are not true leaves.

Deciduous

Trees that shed leaves seasonally

Defoliation

Loss of leaves, often caused by pesticides

Forb

a broadleaf herb

Hardwood

Broadleaf trees with seasonal leaf loss

Meristem

Growing point with cells capable of division

Perennial weed

Lives more than two years

Phloem

Tissue that transport metabolic compounds in plants from the leaves to points of active growth

Foliar applied herbicides move primarily in the Phloem

Plant Growth Regulator

Chemical that influences plant growth

Respiration

Metabolic process converting nutrients to energy

Rhizome

Horizontal stem that grows underground

Rosette

Low growing circular cluster of leaves

Seedhead

Stalk on which seeds form. Common in grasses and sedges/

Stolon

Aboveground runner or rooting structure

Stomata

pores for gas exchange in plant leaves and stems

Summer Annual Weed

Germinates in spring, grows in summer, dies in fall

Tuber

Underground storage structure.

example: potato

Weed

a plant growing where unwanted

Winter Annual Weed

Germinates in fall overwinters, mature and dies in spring

Germination

Seed developing into a young plant

Volatize

Transition from liquid to gas

Xylem

Vascular tissue that transports water upwards in plants. moves water and nutrients from the roots to leaves

The wood, both sapwood and heartwood are xylem tissue. Soil applied herbicides move upwards in this tissue.

Abiotic plant growth factors

Herbicide and plant growth regulators work best when plants are actively growing. Any conditions that hinder growth will reduce the effectiveness of chosen chemicals. During periods of drought, movement of water, sugar, and other plant material is slowed which in returned will affect applied herbicides.

Weed classification and Biology

Weeds are by far the most common pest on Right-of-ways. Being able to classify helps determine what application to use for treatment.

Identification of plant pests

Correct identification of weeds and a working knowledge of their development are key to effective control.

Grasses

Have a single leaf as they emerge from the seed and are called monocots. Narrow, upright parallel veined leaves and a fibrous root system. Growing point or meristem of a grass plant is protected near or below the soil of the surface.

Broadleaf plants (forbs)

Herbaceous/Woody

- Two cotyledon leaves (dicots)

- broad, net-veined leaves and tap roots, or coarse root system

- can be annual, biennial, or perennial

- exposed growing points at the end of each stem

annuals are easy to control/ they have above ground growing points

Woody plants

Forms secondary tissue from cambium. Includes brush, shrubs, and trees

Brush and shrubs

regarded as woody plants that have several stems and are less than 10ft tall. When trees are present brush and shrubs may be understory.

Trees

Have a single stem (trunk) and are over 10ft tall.

Hardwoods: shed leaves in fall (example maple)

Conifers:: keep their needles year round

Vines

Woody and herbaceous vines are also broadleaves, however vines have persistent woody stems

- climb structures

- netliked veins and a taproot

- vigorous sprouting habit which makes it harder to control

Herbaceous broadleaf plants

- Vascular system, but no woody stems above ground

- can have either annual or perennial life cycle

Growth stages

There are four growth stages of plants.

- seedling

- vegetative

- reproductive

- mature

Seedling

Cotyledons appear followed by the first true leaves

- most susceptible to herbicide

- leaf surface easily penetrated

- small hairs

- roots near surface of soil

- less herbicide required to kill compared to later growth stages

Vegetative

Stems, roots, and foliage grow rapidly

- rapid uptake of water and nutrients

- perennial underground structure forms

- more difficult to control than seedling stage, easier to manage compared to reproductive stage

Reproductive

Flowers, and produces seed, and may set fruit

- limited growth and reduce uptake of water and nutrients

- movement of herbicide slows and are not as effective

Maturity

Final stage that a plant undergoes

- little or no above ground growth

- water, nutrients and foliage applied herbicides move very slowly

- larger leaves are harder to penetrate and roots grown deeper and have more stored food.

Plant life cycles

either annual, biennial, or perennial

- consider the life cycle of plants to properly control the target

Annuals

Completes life cycle from seed in less than one growing seasons

- winter or summer annual

- defoliation best control option choice because growing points for shoots are above ground

- root system does not persists

Winter annual

Germinates in the fall, overwinter, mature, set seed, and die in spring or early summer

- Best control during seedling stage of growth in fall,. late winter or early spring

Summer annuals

Germinates in the spring, grow in the summer, set seed, and die in late summer or fall

- treat during germination or soon after germination in the seedling stage of growth

Biennials

Complete life cycle in 2 years

- first year forms a basal rosette or clump of leaves on the soil surface and completes first two stages. During the second year the biennial flowers, matures, and die

- Control during first year of growth

Pernnials

Reproduce by seed or vegetative

- live more than 2 years and some indefinitely

- some can complete 4 stages in year 1 and then repeat vegetative, reproductive, and mature stages in following years

- these stages can be delayed

best control during seedling stage and during fast growth stage

- translocated herbicide works best

Simple pernnials

Spread by seed, crown buds, but root segments

- large fleshy persistent tap roots

- mechanical cultivation may increase the number of these plants

Creeping perennials

Spread vegetative through stolons and by rhizomes or by seed

- shallower root system

- can extend outside of the right-of-way

Time translocated herbicide for late summer after rapid growth has stooped when plants have begun to store food in their roots can improve control

Bulbous

Some perennial plants reproduce vegetatively from underground bulbs or tubers

- can spread by mechanical control

Deciduous Vs Evergreen trees

Deciduous (hardwood) shed leaves once a year in fall

Evergreen (conifers) keep same or all leaves year-round

woody plants can be controlled at any time of the year

Water

Carries nutrients up to leaves and sugar down to roots. Soil applied herbicides must dissolve in water to be taken up by the roots.

- part of photosynthesis

- when there is a lack of water that limits growth, herbicides are plant growth regulators are less effective

Relative Humidity

at high relative humidity leaves are more succulent, less waxy layers and have a thinner cuticle.

- plants grow more at high relative humidity

- high relative humidity enhances the effectiveness of herbicides and sprays are more likely to penetrate

Temperature

affect all plant activities

- important factor of evaporation

- when temperature increases so does the growth of plants

- when temperature decreases so does the growth of plants

- most growth occur between 50 and 100 degrees F

- herbicides and Plant growth regulators are ineffective during low temperature. Herbicides work quickly in warmer weather because plant is actively growing

- high heat can cause volatilization of chemicals

Light

energy source for photosynthesis. plants growing shade tend to be taller and have larger leaves, Leaves in the sun are thicker and smaller

- little direct effect on application of herbicides but can play a role in photodegradation

Soil type

Important for how herbicides move

- clay adsorbs more than sand and siltly soils

- organic matter adsorbs more relatively than clay because of high microbial activity

- microbial break down shortens herbicide's life

Conducting tissues

Xylem moves water and nutrients from roots to leaves. Phloem transport sugar from leaves to points of active growth. Both tissues are separated by the cambium.

- in grasses and broadleaves they are in vascular bundles

Compaction

promotes surface run off rather than the downward movement of water

Cambium

living tissue responsible for tree growth

- this is the part of the tree to treat during a fresh-cut stump application

Other plant characteristics

Consider the target plant characteristics such as growing points, leaf shape, cuticle, and leaf hairs

Location of growing points

Important for how well certain types of herbicides work

- example a grass plant has its growing point at or below the soil surface so a contact herbicide would fail

Leaf shape

Critical for effectiveness of herbicide. Take in consideration of retention of the chemical spray on leaves

- drooping narrow leaves often have herbicide bounce or runoff

- broadleaf plants have flat or wide leaves that retain herbicide

Cuticle

Outermost layer of a leaf. Forms protective barrier for living plant tissue, has waxy layer on outside called leaf wax

- thin cuticle easily penetrated compared to thicker. Cuticle wax are thinner on young plants

Leaf hairs

Another barrier between spray droplets of herbicide and the leaf surface

- sparsely distributed leaf hairs can promote herbicide effectiveness by holding the chemical close to the leaf for a longer period

Time of year

Some herbicides work better in the spring and early summer while others work best in the late summer and early fall

- late summer and early fall are good times for perennial treatment

- fall is also a good time to spray biennials and winter annuals

Eastern red cedar

- reproduces solely by seed

- host for cedar-apple rust

best control is by removing small trees and cutting is the most effective method

Autumn olive

- deciduous shrub

- seeds spread fast by animals

- nitrogen fixer

- best control before fruiting and use herbicides by thoroughly wetting the leaves`

Chinese privet

- impenetrable thickets

- wide habitat

- displace natives

- basal bark with appropriate herbicide and crop oil can be used any time of year but easiest in dormant season

Kudzu

- aggressive climber

- requires persistent treatment by use of herbicides, burns, mowing, and the usage of livestock

- late summer to early fall for treatment

- burns should be down in the winter or early spring

Multiflora rose

- spread vegetative and seeds

- produce half a million seeds annually

- has two biological agents the rose seed chalcid wasp and rose stem girdler

- basal bark treatment, mowing and cutting small populations, cut stump treatment, and foliar spraying can help control

Common mullein

- easily pulled out of loose soil

- use native grasses to help control and preemergent herbicides

Johnson grass

- Perennial with large purple seed head

- host of sorgnium midge

- can produce cyanide when stressed

- best way to control is through prevention

Musk Thistle

- annual or biennial that is propagated by seeds and have disk-shaped purple flower

- highly competitive weed of Eurasian origins

- dispersed by wind

- controlled with cultural practices, mowing, and herbicide

- Rhinocyllus conius seed feeding weevil is a biological agent

Poison Hemlock

- toxic noxious winter annual or biennial herbaceous broadleaf plant

- very toxic to animals and humans

- reproduce by seed so physical methods that destroy the top growth are effective

- manual/ chemical/ mechanical control are highly effective