Chapter 3

Integrate Chapters 1 and 2 with 3 To develop a weed control plan you must know

Why control/management is needed The competitive nature of the weed Noxious weed seed producer

How you must control it Life Cycle of the weed – annual vs. perennial

Eradication is the ideal goal of weed control, but is rarely achieved (very rarely achieved on a large scale).

All seedlings must be killed Long lived seed in the soil is the main reason for failure

All vegetative propagules must be killed Hard work but this is can be accomplished

Methods of Weed Control

A. Preventive

B. Cultural

C. Mechanical or physical

D. Biological

E. Chemical

F. Integrated weed-control systems (combinations of the above)

Preventive Weed Control

1. Prevent the introductiona) plant clean seed-seed laws help w/ noxious

weedsb) feed clean feed, cautiously move animals from

field to fieldc) clean equipment – harvest and tillage

2. Prevent the establishment3. Prevent the spread4. Today it is too late for some species--they are

already here and established

1) Okla. Survey (Terry Semmel’s Thesis) Pg 40

d. 69% of drill box samples were farmer grown and saved.

e. 40% had not been cleaned.

f. 94% did not run a germination test.

g. Farmer saved and not cleaned planted an average of 17 weed seeds per pound of wheat. 62.5 lb/a seeding rate = 1,060 weed seeds per acre.

Planting Weed-free Seed

Control weeds in

Fence Rows

Cultural Weed Control

1. Basically it is just practicing good production practices--this would even apply to pastures and turf.

a) fertility and soil pH adjustment practices

b) row spacing and plant density

c) dates of planting

d) variety or cultivar selection

e) crop rotations

Mechanical Weed Control

1. Hand pulling

2. Hoeing

3. Mowing

4. Water management

5. Smothering

6. Artificial temperature

7. Burning

8. Machine tillage

Hand Pulling

a) Used by gardeners on small areas

b) Controls annuals and biennials

c) Poor control of deep rooted perennials1) Have any of you tried to control

bermudagrass by pulling it up? How about field bindweed?

Hoeing

a) Very effective, but obviously labor intensive.

b) Still used today in Oklahoma and especially in high value crops all over the U.S.

c) Weeds have never developed resistance to the hoe.

d) Growth and competition of perennial weeds is reduced by frequent hoeing.

Mowing

a) Generally limited to pastures, roadsides, and lawns

b) Must be very timely1) If done too late, the flowers may mature & make

seed

c) Weeds have adapted to frequent mowing1) In lawns, weeds may quickly develop a prostrate

growth form

2) Some weeds can produce seed between mowings

Water Management

a) Managed flooding can deprive weeds of necessary oxygen.

1) Flooding of rice fields is done, in part, to control weeds. If done in a timely manner the weeds drown and the rice grows rapidly

b) In Oklahoma we do not have the water resources or grow the crops that would benefit from this method of weed control

Artificial Temperatures

a) Used by horticulturalists to raise soil temperature and kill seeds

Burning & Flaming

a) Burning1) Most economical and effect method of

controlling Eastern Red Cedar in pastures

2) Provides limited control of annual weed seed when wheat stubble is burned--depends on where the seed are.

b) Flaming is practiced to a very limited extent.

Machine tillagea) Seedbed preparation--primary tillageb) Weed Control--secondary tillage

1) “Main” value is weed control; however, this tillage is also performed to improve H2O penetration, dust mulches, reducing wind erosion, etc.

2) Generally, the only “measured” response to tillage is in higher yields due to weed control

3) Numerous types of equipment used for “primary” and “secondary” tillage--See the pictures in the book.

Moldboard PlowPrimary tillage

Offset DiskPrimary tillage

Tandem DiskPrimary tillage

Field Cultivator

Primary tillage

Row CultivatorSecondary tillage – Weed Control

Advantages & Disadvantages of Using Tillage for Weed Control

1) Advantagesa. Relatively inexpensiveb. Effective against herbicide resistant

weeds

2) Disadvantagesa. Soil erosionb. Effectiveness – weeds within drill rowsc. Time consumingd. Equipment costse. Soil condition limitationsf. Crop injury

Conservation TillageChapter 4

1) No-till

2) Reduced tillage, Conservation Tillage, etc.

3) Ridge tillage

4) Limited tillage

5) Stubble-mulch

6) Stale seedbed

Conservation TillageBenefits

a. Reduced tillage leads to reduced erosion

b. Reduced economic inputs

c. More environmentally friendly

Conservation TillageFactors Involved with Delay of Adoption

a. Tradition of tilling the soil

b. Anticipated crop yield reduction

c. Lack of good residue planters

d. Disease and insect problems

e. Slower soil warming

f. Inconsistent and incomplete weed control

g. Shifting weed populations

Why isn’t no-till wheat production more wide spread in Oklahoma?

1. Past Limitations of No-till Drills

2. Lack of Cheat Control Herbicide

Adequate NT Drills are available.

Several herbicides control cheat.

Biological Weed Control

1. The utilization of natural enemies to control “specific” weed species.

a) Insects-most common

b) Diseases-fungi

c) Herbivors-fish, animals, geese, etc.

Types of Biological Control

a) Classical--the release of a control organism to reproduce and sustain itself.

b) Mycoherbicide--biological herbicide. Organisms (usually fungi) are grown and put into formulations that can be applied as sprays to weeds. Organisms cannot survive from year to year.

Selection of Biological Organisms

a) Must attack only the weed1) Remember-what is a weed?

b) Must be adapted to the climate of use

c) Do not introduce organisms that will attack desirable hosts (crops)

d) Use of disease organisms or insects may restrict the use of other necessary crop protection chemicals---insecticides and/or fungicides

Conflict of Biological Control

a) What is a weed?1) Would you want to release a biological

control organism that would control bermudagrass?

b) Where is the financial return for biological control???

1) Who will then develop biological control?

Biological Control has been a Success

a) Control of prickly pear cactus--insectsb) Control of Klamath weed--insectsc) Control of aquatic weeds--herbivore fish,

the grass carp or white amurd) Control of pasture weeds or brush by

grazing animalse) Weeder geesef) Control of musk thistle by weevilsg) Brush and broadleaf weed control by goats

Grass carp or white amur--an aquatic herbivore

1) Since initiation of weevil collecting with Missouri personnel in 1991, more than 150,000 weevils have been collected and released by Oklahoma Cooperative Extension Service personnel.

2) The introduction of the musk thistle head weevil has successfully decreased the severity of infestations in the northeastern counties.

Biological Control of The Musk Thistle

Biology of the Musk Thistle Head Weevil

3). The musk thistle head weevil overwinters as an adult. In early spring, they feed on rosettes, mate and females lay eggs on the emerging seed heads.

Biology of the Musk Thistle Head Weevil

4). The eggs (cases) are laid on the bracts of developing flowers. Each female can lay up to approximately 100 eggs.

Biology of the Musk Thistle Head Weevil

5). Eggs hatch in 6 to 8 days and the larvae feed on immature seed for 25 to 30 days.

Biology of the Musk Thistle Head Weevil

6). In July, adults emerge to seek an overwintering site. A second generation has been observed in some locations.

Chemical Weed Control1. Herbicides--any chemical substance

or cultured biological organism used to kill or suppress plant growth.

2. Like the text, we will consider a herbicide a chemical substance and mycoherbicide as a cultured biological microorganism (biological control).

3. Herbicides---specific pesticide used for controlling weeds.

4. Selectivity is a major key

Annual U.S. Herbicide Market

a) Soybeans $900,000,000

b) Corn $750,000,000

c) Small grains $170,000,000

d) Cotton $120,000,000

e) Others $90,000,000

Advantages of Herbicides

a) Higher crop yields than with cultivator alone

b) Reduce labor and time to control weeds

c) Reduced or no-tillage systems are feasible

d) Need for hand weeding is reducede) Reasonably economical

Disadvantages of Herbicides

1. Risk of crop injurya) Unusual environmental conditionsb) Improperly used--application timing or

rate

2. Direct danger to humans3. Environmental degradation

a) Contamination of surface or ground water

4. Injury to non-target plants5. Contamination of our food

Herbicide Classification

a) Chemical similarity--Herbicide Familiesb) Mode of Actionc) Herbicide movement in plants or soild) Selectivity or lack of selectivitye) Formulationsf) Application methods or time of application

Chemical Similarities

a) Herbicide families - Chemically similar pesticides

1) dinitroaniline

2) triazines

3) phenoxy

4) etc.

Mode of Action

b) How the herbicide kills the plant1) Root growth inhibitor

2) Photosynthesis inhibitor

3) ALS or AHAS inhibitor

4) etc.

Herbicide Movement

1) Soila. Does it leach?

b. Does it have soil activity?

c. Is it applied to the soil?

2) Planta. Does it move in the plant?

b. Is it applied to the plant directly?

Selectivity

1) Selectivity--the killing or controlling of one or more plant species without injury to the crop.

a. Some herbicides are selective

b. Some herbicides are nonselective

Formulations

1) We will discuss this when we get to Chapter 10

Application

1) Sometimes referred to as “methods of application” or “time of application”

2) Two major categoriesa. Applied directly to the soil---soil active

b. Applied directly to the plant---foliar active

3) “Generally” based on the “crop” growth

Timing of Application

a. Preplant---applied to soil or plant foliage before planting

b. Preplant Incorporated---applied to soil and mixed in

c. Preemergence---applied to the soil after planting, but before crop emergence

d. Postemergence---applied after the crop has emerged. Numerous variations.

Preplant

Preplant Incorporated

Rotor Tillers Incorporate the Herbicide the Full Depth of Cut

Offset & Tandom Disks Incorporate the Herbicide ½ the Depth of Cut

Preplant Incorporated

An Activating Rainfall is Neededwith all Soil Applied Products

Post-directed

Hooded Sprayer