AgronomyAgronomy

Weed Plants Weed Plants and Seedsand Seeds

What is a Weed?What is a Weed?Plant that is out of Plant that is out of placeplace

Plant not intentionally Plant not intentionally growngrown

Plant that decreases Plant that decreases aesthetic valueaesthetic value

Why are Weeds Why are Weeds Troublesome?Troublesome?

Reduce Crop YieldReduce Crop YieldSteal light, water, Steal light, water,

nutrients, space, and nutrients, space, and timetime

Can produce toxic Can produce toxic substances (Allelopathic)substances (Allelopathic)

Why are Weeds Why are Weeds Troublesome Troublesome

cont’d?cont’d?Hosts for plant diseasesHosts for plant diseasesShelter for insects and Shelter for insects and

diseasesdiseasesReduce crop quality/tasteReduce crop quality/tasteMultiply rapidlyMultiply rapidly

Why are Weeds Why are Weeds Troublesome Troublesome

cont’d?cont’d?Clog equipmentClog equipmentDecrease future Decrease future stands and longevitystands and longevity

Add to frustration Add to frustration and safety concernsand safety concerns

Groups of WeedsGroups of Weeds AnnualsAnnuals

– Summer Summer (germinates in (germinates in May and June)May and June)

– Winter Winter (germinate in (germinate in late summer or late summer or fall)fall)

BiennialsBiennials PerennialsPerennials

1 year1 year

1-2 years1-2 years > 2 years> 2 years

Groups of Weeds Groups of Weeds cont’d.cont’d.

Grassy WeedsGrassy Weeds–Simple leaves, Simple leaves, monocotsmonocots

Broadleaf WeedsBroadleaf Weeds–Complex leaves, dicotsComplex leaves, dicots

Groups of Weeds Groups of Weeds cont’d.cont’d.

Early SeasonEarly Season

Late SeasonLate Season

Monocots VS. Monocots VS. DicotsDicots

Simple Simple leavesleaves

One seed One seed cotyledoncotyledon

Complex Complex leavesleaves

Two seed Two seed cotyledonscotyledons

How To Manage How To Manage WeedsWeeds

Field ScoutingField ScoutingProper Identification Proper Identification and Recording of and Recording of WeedsWeeds

Economic ThresholdEconomic Threshold

Economic Economic ThresholdThreshold

The amount of weeds The amount of weeds in a given area that is in a given area that is needed to justify needed to justify taking action to taking action to reduce their impact reduce their impact

Weed ControlWeed Control

Good Weed control Good Weed control requires an requires an integrated approach integrated approach systemsystem

Cultural ControlsCultural Controls

Forces the plant Forces the plant being grown to be being grown to be more competitive more competitive against the weedagainst the weed

Cultural Control Cultural Control cont’d.cont’d.

Seed Seed PreparationPreparation

Planting datePlanting date FertilizationFertilization Crop RotationCrop Rotation Row SpacingRow Spacing Seeding RateSeeding Rate Seed VarietySeed Variety

Mechanical Mechanical ControlControl

Physical action Physical action completed to reduce completed to reduce the rate of weed the rate of weed growth and spreadinggrowth and spreading

Mechanical Mechanical Control cont’d.Control cont’d.

PlowingPlowing DiskingDisking Field Field

CultivatingCultivating

Chemical ControlChemical Control

The use of chemical The use of chemical pesticides pesticides (Herbicides) to (Herbicides) to control weedscontrol weeds

Chemical Control Chemical Control Issues?Issues?

Safety and Safety and HandlingHandling

Cost of Cost of Chemical and Chemical and EquipmentEquipment

Crop and Crop and Chemical Chemical RotationRotation

Environmental Environmental HazardsHazards

Carryover and Carryover and Residual EffectResidual Effect

Herbicide Herbicide ResistanceResistance

Reduced and Reduced and Conservation Conservation TillageTillage

Chemical Chemical HerbicidesHerbicides

Pre-EmergentPre-Emergent– Applied before the crop or Applied before the crop or

weed plant emerges weed plant emerges through the soilthrough the soil

– Must be timed perfectlyMust be timed perfectly

Chemical Chemical HerbicidesHerbicides

Post-EmergentPost-Emergent– Applied after the crop or Applied after the crop or

weed plant emerges weed plant emerges through the soilthrough the soil

– Timing not as criticalTiming not as critical

Noxious WeedsNoxious Weeds

A noxious weed is a A noxious weed is a plant defined by law as plant defined by law as being troublesome, being troublesome, undesirable, and undesirable, and difficult to controldifficult to control

List of Noxious List of Noxious Weeds in PAWeeds in PA

There are currently There are currently 13 noxious weed 13 noxious weed species on PA’s listspecies on PA’s list

Herbicide Herbicide CharacteristicsCharacteristics

Contact HerbicidesContact Herbicides

–A chemical that kills A chemical that kills on contact of any on contact of any plant tissueplant tissue

Herbicide Herbicide CharacteristicsCharacteristics

Systemic HerbicidesSystemic Herbicides

–A chemical that is A chemical that is absorbed or absorbed or translocated in a planttranslocated in a plant

Selective VS. Selective VS. NonselectiveNonselective

Selective HerbicidesSelective Herbicides

– Selective herbicides kill Selective herbicides kill weeds without significant weeds without significant damage to desirable plantsdamage to desirable plants

Selective VS. Selective VS. NonselectiveNonselective

Nonselective Nonselective HerbicidesHerbicides–Nonselective herbicides Nonselective herbicides kill kill ALLALL plants present plants present when appliedwhen applied

Herbicide Herbicide ResistanceResistance

Herbicide resistant Herbicide resistant plants are uninjured plants are uninjured or unaffected by or unaffected by certain chemical certain chemical applicationsapplications

Herbicide Herbicide ResistanceResistance

Resistant plants are Resistant plants are becoming more commonbecoming more common

Begins with a few tolerant Begins with a few tolerant plants that survive plants that survive

These plants then These plants then reproduce and spreadreproduce and spread

Herbicide Herbicide Resistance Resistance PreventionPrevention

Minimize tillage of the soilMinimize tillage of the soilRotate cropsRotate cropsUse various chemicalsUse various chemicalsThe perfect herbicide The perfect herbicide

does not exist!!!does not exist!!!

CarryoverCarryover

Chemical carryover or Chemical carryover or residue may affect residue may affect future crops in the future crops in the rotationrotation

Occurs due to excessive Occurs due to excessive applicationsapplications

Managing Organic Managing Organic WeedsWeeds Organic Farming is the growth of Organic Farming is the growth of

crops without the use of crops without the use of chemicals and synthetic chemicals and synthetic fertilizersfertilizers

How can an organic farm How can an organic farm manage weeds without manage weeds without pesticides and synthetic pesticides and synthetic fertilizers?fertilizers?

Waging war with Waging war with weeds weeds Weeds compete with Weeds compete with

crops for moisture and crops for moisture and plant nutrients.plant nutrients.

Gardeners pull or hoe Gardeners pull or hoe weeds.weeds.

Farmers use tillage and Farmers use tillage and cultivation.cultivation.

Conventional farmers use Conventional farmers use chemical treatments.chemical treatments. ARS photo by Scott Bauer.

Farmers are in a fight Farmers are in a fight with nature …with nature …

Nature wants a diversity of plant Nature wants a diversity of plant growth.growth.

Farmers want to limit nature to Farmers want to limit nature to grow just one crop.grow just one crop.

Conventional tillage and fertilization Conventional tillage and fertilization increases crop production and also increases crop production and also encourages weeds.encourages weeds.

The battle heats up!The battle heats up!

The organic approach is The organic approach is different …different …

The organic farmer tries to work The organic farmer tries to work with nature.with nature.

An organic grower tries to An organic grower tries to "manage" the crop ecosystem to "manage" the crop ecosystem to help the crop thrive while help the crop thrive while suppressing weeds.suppressing weeds.

This requires observing and This requires observing and understanding nature.understanding nature.

A weed is a “plant out of A weed is a “plant out of place.”place.”

Annual weedsAnnual weeds Grow one seasonGrow one season Reproduce from Reproduce from

many seedsmany seeds Thrive under Thrive under

same conditions same conditions as annual crops.as annual crops.

Perennial weeds:Perennial weeds: Grow for several Grow for several

seasonsseasons Reproduce from Reproduce from

roots, stolons, roots, stolons, bulbs, tubers, bulbs, tubers, rhizomes or fewer rhizomes or fewer seedsseeds

Do best in areas Do best in areas with less with less cultivationcultivation

Defining succession:Defining succession: Natural diversity will result in either Natural diversity will result in either

forest or prairie.forest or prairie. First step: annual weedsFirst step: annual weeds Second step: perennialsSecond step: perennials Third step: brush and young trees in Third step: brush and young trees in

forest regions or perennial grasses forest regions or perennial grasses in prairie regionsin prairie regions

During succession plants compete During succession plants compete for moisture, nutrients and light.for moisture, nutrients and light.

Organic farmers grow crops and Organic farmers grow crops and create conditions in which weeds create conditions in which weeds cannot compete.cannot compete.

Using cover crops …Using cover crops … Cover crops hold down weed growth Cover crops hold down weed growth

and add organic matter to the soil.and add organic matter to the soil. Allelopathic cover crops produce a Allelopathic cover crops produce a

chemical in the soil that inhibits the chemical in the soil that inhibits the growth of other plants. growth of other plants.

Rye is allelopathic, winter hardy,Rye is allelopathic, winter hardy,and grows almost anywhere.and grows almost anywhere.

Rye crop residues leachRye crop residues leachallelopathic chemicals intoallelopathic chemicals intothe soil and prevent thethe soil and prevent thegermination of small-germination of small-seeded weeds.seeded weeds. ARS photo by Scott Bauer

Shows rye cover crop.

More on allelopathic More on allelopathic effects:effects:

Some large-seeded food crops can Some large-seeded food crops can tolerate the allelopathic effects tolerate the allelopathic effects (corn, cucumbers, peas, (corn, cucumbers, peas, snapbeans).snapbeans).

Smaller-seeded crops had less Smaller-seeded crops had less tolerance (cabbage and lettuce).tolerance (cabbage and lettuce).

More crops with allelopathic effects: More crops with allelopathic effects: sunflowers, sorghum and rapeseed.sunflowers, sorghum and rapeseed.

Mulches and cover Mulches and cover crops:crops: Cover crops can be Cover crops can be

used to physically used to physically smother weeds by smother weeds by growing faster and out-growing faster and out-competing the weeds. competing the weeds.

Mulches can be black Mulches can be black plastic, or plant plastic, or plant material such as wheat material such as wheat straw.straw.

ARS photo by Scott Bauershows wheat straw mulch.

More weapons: crop More weapons: crop rotation and rotation and intercroppingintercropping Crop rotation changes the growing Crop rotation changes the growing

conditions each year, breaking the conditions each year, breaking the weed cycle.weed cycle.

A good rotation for weed control will A good rotation for weed control will include clean-cultivated annual crops, include clean-cultivated annual crops, tightly spaced grain crops, and mowed tightly spaced grain crops, and mowed or grazed perennial sod crops.or grazed perennial sod crops.

Add a short-season crop to smother Add a short-season crop to smother weeds, if needed.weeds, if needed.

Intercropping is another Intercropping is another alternative …alternative …

Growing two or more crops Growing two or more crops together to give weeds more together to give weeds more competitioncompetition

Often established by planting a Often established by planting a row crop into a standing grain row crop into a standing grain cropcrop

Example: interplant soybeans into Example: interplant soybeans into standing green wheatstanding green wheat

Ideal organic farming Ideal organic farming minimizes tillage …minimizes tillage …

Tillage leaves soil exposed, allowing Tillage leaves soil exposed, allowing annual weeds to sprout and grow.annual weeds to sprout and grow.

Can lead to soil erosionCan lead to soil erosion Speeds decomposition and Speeds decomposition and

increases runoffincreases runoff Can damage soil structureCan damage soil structure Adds equipment, fuel and labor Adds equipment, fuel and labor

costs.costs.

Ways tillage can be Ways tillage can be used:used: Preplant tillage clears away annual Preplant tillage clears away annual

weeds and reduces perennial weeds.weeds and reduces perennial weeds. Blind cultivation works the soil to kill Blind cultivation works the soil to kill

weeds with minimum damage to weeds with minimum damage to seedling crops.seedling crops.

Between-row cultivation cleans out Between-row cultivation cleans out more weeds emerging as crop begins more weeds emerging as crop begins to grow.to grow.

More weapons in the war More weapons in the war on weeds:on weeds:

Flame weeding works on Flame weeding works on broadleaf weeds.broadleaf weeds.

Hand weeding and topping Hand weeding and topping require hand labor.require hand labor.

Weeder geese are good for Weeder geese are good for grassy weeds.grassy weeds.