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Chapter 3

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

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Chapter 3

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  1. Chapter 3

  2. 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

  3. Methods of Weed Control • Preventive • Cultural • Mechanical or physical • Biological • Chemical • Integrated weed-control systems (combinations of the above)

  4. Preventive Weed Control • Prevent the introduction • plant clean seed-seed laws help w/ noxious weeds • feed clean feed, cautiously move animals from field to field • clean equipment – harvest and tillage • Prevent the establishment • Prevent the spread • Today it is too late for some species--they are already here and established

  5. Planting Weed-free Seed Okla. Survey (Terry Semmel’s Thesis) Pg 40 69% of drill box samples were farmer grown and saved. 40% had not been cleaned. 94% did not run a germination test. 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.

  6. Control weeds in Fence Rows

  7. Cultural Weed Control • Basically it is just practicing good production practices--this would even apply to pastures and turf. • fertility and soil pH adjustment practices • row spacing and plant density • dates of planting • variety or cultivar selection • crop rotations

  8. Mechanical Weed Control • Hand pulling • Hoeing • Mowing • Water management • Smothering • Artificial temperature • Burning • Machine tillage

  9. Hand Pulling • Used by gardeners on small areas • Controls annuals and biennials • Poor control of deep rooted perennials • Have any of you tried to control bermudagrass by pulling it up? How about field bindweed?

  10. Hoeing • Very effective, but obviously labor intensive. • Still used today in Oklahoma and especially in high value crops all over the U.S. • Weeds have never developed resistance to the hoe. • Growth and competition of perennial weeds is reduced by frequent hoeing.

  11. Mowing • Generally limited to pastures, roadsides, and lawns • Must be very timely • If done too late, the flowers may mature & make seed • Weeds have adapted to frequent mowing • In lawns, weeds may quickly develop a prostrate growth form • Some weeds can produce seed between mowings

  12. Water Management • Managed flooding can deprive weeds of necessary oxygen. • 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 • In Oklahoma we do not have the water resources or grow the crops that would benefit from this method of weed control

  13. Artificial Temperatures • Used by horticulturalists to raise soil temperature and kill seeds

  14. Burning & Flaming • Burning • Most economical and effect method of controlling Eastern Red Cedar in pastures • Provides limited control of annual weed seed when wheat stubble is burned--depends on where the seed are. • Flaming is practiced to a very limited extent.

  15. Machine tillage • Seedbed preparation--primary tillage • Weed Control--secondary tillage • “Main” value is weed control; however, this tillage is also performed to improve H2O penetration, dust mulches, reducing wind erosion, etc. • Generally, the only “measured” response to tillage is in higher yields due to weed control • Numerous types of equipment used for “primary” and “secondary” tillage--See the pictures in the book.

  16. Moldboard PlowPrimary tillage

  17. Offset DiskPrimary tillage

  18. Tandem DiskPrimary tillage

  19. Field CultivatorPrimary tillage

  20. Row CultivatorSecondary tillage – Weed Control

  21. Advantages & Disadvantages of Using Tillage for Weed Control • Advantages • Relatively inexpensive • Effective against herbicide resistant weeds • Disadvantages • Soil erosion • Effectiveness – weeds within drill rows • Time consuming • Equipment costs • Soil condition limitations • Crop injury

  22. Conservation TillageChapter 4 • No-till • Reduced tillage, Conservation Tillage, etc. • Ridge tillage • Limited tillage • Stubble-mulch • Stale seedbed

  23. Conservation TillageBenefits • Reduced tillage leads to reduced erosion • Reduced economic inputs • More environmentally friendly

  24. Conservation TillageFactors Involved with Delay of Adoption • Tradition of tilling the soil • Anticipated crop yield reduction • Lack of good residue planters • Disease and insect problems • Slower soil warming • Inconsistent and incomplete weed control • Shifting weed populations

  25. Why isn’t no-till wheat production more wide spread in Oklahoma? Past Limitations of No-till Drills Lack of Cheat Control Herbicide Adequate NT Drills are available. Several herbicides control cheat.

  26. Biological Weed Control • The utilization of natural enemies to control “specific” weed species. • Insects-most common • Diseases-fungi • Herbivors-fish, animals, geese, etc.

  27. Types of Biological Control • Classical--the release of a control organism to reproduce and sustain itself. • 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.

  28. Selection of Biological Organisms • Must attack only the weed • Remember-what is a weed? • Must be adapted to the climate of use • Do not introduce organisms that will attack desirable hosts (crops) • Use of disease organisms or insects may restrict the use of other necessary crop protection chemicals---insecticides and/or fungicides

  29. Conflict of Biological Control • What is a weed? • Would you want to release a biological control organism that would control bermudagrass? • Where is the financial return for biological control??? • Who will then develop biological control?

  30. Biological Control has been a Success • Control of prickly pear cactus--insects • Control of Klamath weed--insects • Control of aquatic weeds--herbivore fish, the grass carp or white amur • Control of pasture weeds or brush by grazing animals • Weeder geese • Control of musk thistle by weevils • Brush and broadleaf weed control by goats

  31. Grass carp or white amur--an aquatic herbivore

  32. Biological Control of The Musk Thistle • 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. • The introduction of the musk thistle head weevil has successfully decreased the severity of infestations in the northeastern counties.

  33. 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.

  34. 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.

  35. 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.

  36. 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.

  37. Chemical Weed Control • Herbicides--any chemical substance or cultured biological organism used to kill or suppress plant growth. • Like the text, we will consider a herbicide a chemical substance and mycoherbicide as a cultured biological microorganism (biological control). • Herbicides---specific pesticide used for controlling weeds. • Selectivity is a major key

  38. Annual U.S. Herbicide Market • Soybeans $900,000,000 • Corn $750,000,000 • Small grains $170,000,000 • Cotton $120,000,000 • Others $90,000,000

  39. Advantages of Herbicides • Higher crop yields than with cultivator alone • Reduce labor and time to control weeds • Reduced or no-tillage systems are feasible • Need for hand weeding is reduced • Reasonably economical

  40. Disadvantages of Herbicides • Risk of crop injury • Unusual environmental conditions • Improperly used--application timing or rate • Direct danger to humans • Environmental degradation • Contamination of surface or ground water • Injury to non-target plants • Contamination of our food

  41. Herbicide Classification • Chemical similarity--Herbicide Families • Mode of Action • Herbicide movement in plants or soil • Selectivity or lack of selectivity • Formulations • Application methods or time of application

  42. Chemical Similarities • Herbicide families - Chemically similar pesticides • dinitroaniline • triazines • phenoxy • etc.

  43. Mode of Action • How the herbicide kills the plant • Root growth inhibitor • Photosynthesis inhibitor • ALS or AHAS inhibitor • etc.

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