n insect? - fulda · 2011. 2. 15. · ment and the bodies of warm-blooded animals. one chemical...

Horticulture2010-2011

Lesson 3Unit F - Integrated Pest Manage

To identify insect pests and select and apphcides:

Competencies to Be Developed

M e

After studying this unit, you should be able to

identify common insect pests and select an effective controlmethod for each.

describe the six ways in which insects are killed by insecticidesand the type of insect against which each is most effective .

list the names and characteristics of the three major groups ofinsecticides (according to their chemical makeup).

compare the six ways in which insecticides are applied.

explain the relationship between the life cycle of insects andtiming of insecticide application.

v illustrations of insect pests

3 live insects

3 recommendations for spraying from local extension service

f

3 insecticides with labels (none should be highly toxic)

3 spraying and dusting equipment

3 safety gear , including elbow-length protective gloves andrespirator

T nsecticides, one of the seven types of pesticides This unit deals with chemical insecticides, notmentioned in the previous unit, are used by the biological insecticides discussed in Unit 16.

11

WW HAT IS N INSECT?pcan effectively and safely control insects, they can An insect is a small animal with three clearly definedbe dangerous and even deadly to human beings body regions and three pairs of legs. The three body

when used improperly . For this reason , it is ex- regions are the head , thorax, and abdomen, figuretremely important that they be handled with care 18-1. The proper identification of insects is an im-and only according to directions on the label. portant step in their control. Only after the insect is

most people at one time or another in the con-trol of flies , mosquitoes, and other insect pests.They are used widely by horticulturists to protect

lants from insect damage . Although insecticides

Unit F - Integrated Pest ManagementLesson 3

LEGS

HEAD

THORAX

ABDOMEN

FIGURE 18-I Parts of an insect. Notice that there arethree definite body regions (head, thorax, and abdomen),with the legs attached to the thorax.

identified can the best method of control be se-lected. Guides to insect identification are availablefrom the U.S. Department of Agriculture.

HOW INSECTICIDES KILLTo be considered good insecticides, chemicals mustkill a specific type of insect while doing little or nodamage to the plant. They must also be as safe aspossible for the handler and environment.

STOMACH POISONS These poisons workagainst insects that actually eat a part of the plant.The chemical is sprayed or dusted on the plant; asthe insect eats the plant, it is poisoned through thestomach. Insects that chew their food, such ascaterpillars, grasshoppers, and beetles, are con-trolled by stomach poisons. Rotenone is consid-ered .to be an effective stomach poison.

CONTACT POISONS These insecticides killinsects when they are hit by or come in contactwith the poison; the insect does not have to con-sume it. Any type of insect can be controlled bycontact poisons, including insects that suck plants,such as aphids and leaf hoppers. Contact poisonskill by upsetting the insect's nervous system orbreathing system. An example of a contact insecti-cide is malathion.

New, highly refined oil sprays are excellentcontact poisons against insect eggs and softbodied

insects, such as aphids, mites, scale, and whiteflies.Oils do not contaminate the environment and aresafe to use.

SYSTEMIC POISONS These chemicals enterthe plant sap and move throughout the entireplant. When insects eat parts of plants or suck juicefrom plants, the chemical is swallowed. Systemicpoisons are effective in the control of insects witheither chewing or sucking mouth parts. They areespecially effective in controlling insects thathide under leaves or underground and that there-fore are not affected by contact sprays. If used onplants that are used as food, the chemical must begiven time to break down within the plant andbecome nonpoisonous before the harvest date forthe crop. These poisons are sprayed on the plantfoliage or mixed with water and applied to theroots. Both methods result in the chemical spread--ing throughout- the entire-plant. One systemic in-secticide is Orthene.

FUMIGANTS Fumigants are actually contactpoisons applied in gaseous form. The gases orfumes kill the insect . after entering its systemthrough breathing pores. The insect must actuallyabsorb the poison for this insecticide to be effec-tive. Fumigants are used to control soil-borne in-sects that damage roots, such as weevils and Junebeetle grubs. One example of a fumigant is methylbromide.

Fumigants are also used in greenhouses. Whenapplied in the greenhouse, the fumigant, consistingof tiny particles of insecticide, settles on the insectand is breathed into its system.

REPELLENTS Repellents generally do not killinsects but, instead, drive them away before theyattack the plant. One example of a repellent is alu-minum foil that when placed around plants, repelsflying insects, figure 18-2.

ATTRACTANTS AND PHEROMONESAttractants and pheromones work in the oppositeway from repellents; they lure insects to theirdeaths. One example is the Japanese beetle baitused in traps to catch the beetle. Another exampleis the sex lure used to trap the gypsy moth. The sexlure used in these traps is made from naturally oc-curring or synthetically produced hormones thatattract the adult insects. The male gypsy moth is ir-resistibly attracted to the sex lure; this attraction isstronger than the normal attraction he has to thefemale moth. Since most of the male moths are


FIGURE 18-2 Aluminum foil strips around cucumberplants protect the plants from flying aphids by reflectingultraviolet rays from the sky, malting the area undesirableto the aphids. (Ed Reiley, Photographer)

caught in the trap, the females remain unfertilizedand lay sterile, unfertilized eggs that do not hatch.The sex lure acts in the same manner on the Japan-ese beetle.

THE CHEMICAL MAKEUPOF INSECTICIDESInsecticides are classified in three major groups ac-cording to their chemical makeup.

INORGANIC COMPOUNDSInorganic compounds are of mineral origin. That is, amineral is used as the basis for the poison. Theyusually work in the form of stomach poisons. Sul-fur is one type of inorganic insecticide and is alsowidely used as a fungicide. Lead arsenate is an in-organic insecticide but is not legal in many areas.

ORGANIC COMPOUNDSOrganic compounds are those derived from plants.They usually work in the form of stomach poisonsor contact poisons. Two examples of organic com-pound poisons are rotenone and pyrethrum, whichare very safe when used according to the directionson the label.

SYNTHETIC ORGANIC COMPOUNDSThese chemicals are of relatively recent origin,many of them having come into use in the lastthirty to thirty-five years. They are very effectiveagainst insects, but many of them are also toxic to

human beings. This large group of insecticides issubdivided into three smaller groups; chlorinatedhydrocarbons, organophosphates, and carbamates.They are not found naturally as are the organiccompounds listed above but are produced in thelaboratory.

CHLORINATED HYDROCARBONS Theseinsecticides contain chemicals that have long resid-ual control, that is, they continue to kill long afterthe initial application. DDT is one of the best-known chemicals in this group. It is no longer soldin the United States, however, because of concernabout the buildup of the poison in the environ-ment and the bodies of warm-blooded animals.One chemical from this group that is still beingused is methoxychlor.

ORGANOP_HOSP__ATES This_group _of insec-_ticides is very effective in controlling insects. It alsocontains some of the chemicals most toxic towarm-blooded animals. Parathion is so toxic thatone-drop of the concentrated chemical in the eyecan kill a human being. They are also absorbedrapidly through the skin. Malathion, anotherchemical in this group, is a relatively safe chemicaland one that can be used to control many insects.

Caution: Read the insecticide label for cautionin use of these chemicals.

Organophosphates breaks down quickly in theenvironment (within fifteen to thirty days) anddo not build up in the bodies of warm-bloodedanimals.

CARBAMATES This group of synthetic or-ganics contains some of the safest insecticides onthe market. Carbamates such as carbaryl (Sevin)are very effective in killing some insects althoughnot effective in killing others. They are slightlytoxic to warm-blooded animals. Carbamates breakdown rapidly (in two to seven days) and leaves noresidue to contaminate the environment. Thesechemicals do not build up in the bodies of warm-blooded animals.

CHEMICAL STERILANTSThe most successful use of sterilants involves theuse of gamma radiation treatments that are usedto sterilize insects so that they cannot produceoffspring. One method is to sterilize male insects

and release them to mate with females. Since theeggs are not fertilized, they will not hatch whendeposited by the female. This is a very effectivemethod in the control of certain insects such as thescrew worm, which infests cattle. This process isalso being tested for use on plant insect pests suchas the gypsy moth.

APPLICATIONOF INSECTICIDES

DUSTSInsecticides are applied with dusters if purchasedas dusts. The chemical is already diluted whenbought; it requires no mixing before application.

Dusts are easy to apply with inexpensive equip-ment-hut-tend-to blow or drift from the_target,_figure 18-3. This drifting can damage other crops orcontaminate the environment.

WETTABLE POWDERSWettable powders (WP) resemble dusts in appear-ance but are concentrated and must be dilutedwith water before application. Read the directionsfor the amount of insecticide to mix per gallon ofwater. Wettable powders tend to settle while in so-lution and must be stirred while being sprayed.Some powders are pressed into granules that re-lease less dust into the air during mixing.

With a water-mixed spray, better coverage ofplants is usually possible and less drift occurs, fig-ure 18-4.

FIGURE 18 -3 Nontoxic dust being applied. Note howthe dust drifts away from the target plants.


FIGURE 18-4 Sprayer being used to spray potatoes.There is very little drift with spray, a water solution.(Ed Reiley, Photographer)

EMULSIFIABLE CONCENTRATESEmulsifiable concentrates (EC) are liquids thatare mixed with water in the same manner as wet-table powders. The concentrate is safer to handlesince there is no powder or dust to blow duringmixing. Emulsifiable concentrates do not settle andseparate from the solution, as wettable powders do,and give the same good coverage of plants. Shelflife of these chemicals is generally longer thandusts or wettable powders if the container is keptclosed and stored in a cool, dark place.

GRANULESGranules are insecticides in the form of small pel-lets. They are spread on the soil surface where theyeither penetrate the soil after the application ofwater or turn into gases that fumigate the insects.Some of the systemic insecticides mentioned in thisunit are sold in the form of granules. They may beapplied to the soil in granulated form and wateredin, after which the chemical is absorbed by theroots of the plants.

PMTS

Baits are poisonous materials that attract insects.The pest eats the bait and is killed by the poison.Slugs, snails, cutworms, grasshoppers, and weevilsare examples of pests that are controlled in thismanner.


FIGURE 18-5 Sprays commonly used by the home-owner. The can on the left is an aerosol. The othersuse manual power to spray or dispense the chemical.

--(Ed-Reiley,-Photographer-) --- -

AEROSOLSAerosol insecticides are contained in pressurizedcans. They are generally used for small insect con-trol jobs around the house or in the greenhouse.The chemical is already diluted and ready for usewhen purchased, figure 18-5. Many aerosols in theform of bombs are available for use in the green-house. The bombs are punctured and the chemicalis slowly released as a fine mist.

SPIKESSpikes of various sizes and shapes containing sys-temic pesticides are available. Small spikes arepushed into the soil in pots and larger ones drivenin around the plants in the landscape. Plant, rootspick up the chemical and it spreads throughout theplant. The pesticide is released over a long periodof time, giving extended protection.

EQUIPMENT

HAND-OPERATEDDUSTERS AND SPRAYERSApplication of insecticides on school grounds or ingreenhouses can be done safely using inexpensivehand-operated sprayers and dusters. An explana-tion of the use of each of these pieces of equipmentwill be given by the instructor.

LARGER DUSTERS, SPRAYERS,AND GRANULAR APPLICATION

Large-scale commercial application of sprays, dustsor granules is accomplished by the use of airplanes,helicopters, tractor sprayers, or trucks with specialgranular spreaders or sprayers. Figure 18-6 illus-trates the use of a large boom orchard sprayer.

Airplanes and helicopters are used to spray anddust large acreage of crops, and crops that cannotbe treated by ground-operated equipment, figure18-7. Commercial applicators apply the specifiedchemical and charge the grower at a cost per acre.This is an economical way to apply insecticideswhen large areas must be covered quickly.

FIGURE 18 -6 A large commercial sprayer applyingpesticide to field-grown rhododendrons. (Courtesy ofChesapeake Nursery)

FIGURE 18-7 Airplanes are used to apply pesticides ona large scale. Many acres can be covered rapidly by thismethod. (Courtesy of U.S. Department of Agriculture)


APPLYING THE PROPER AMOUNT

Whatever method of application is used, it is impor-tant that the proper amount of the chemical is ap-plied to a given area. This requires calibration ofsprayers and dusters. Calibration involves measur-ing the amount of chemical applied during a speci-fied period of time or over a measured area and thenadjusting the applicator or speed of application toobtain the proper amount of chemical required.

Dusts and sprays must be applied so that thereis a total coverage of all leaf surfaces. When dustsare applied to plants, they can be seen settling onthe surface of the plants, thereby making it easy tosee the extent of the coverage. When sprays areused, leaves of the treated plants should be wet justto the point of dripping.

entcot trot ofmsects rec^wres the proper conce if.&tton af the chemicaL be` rnbn sprays Rea the labelfor proper nli ittistnictions

IDENTIFYING INSECTDAMAGE TO PLANTSTo identify the insect causing damage to plants, thedamage itself must be examined. Chewing insectsactually eat away part of the plant. This results inholes in the leaves or missing pieces of bark. Chew-ing insects are controlled by a stomach poison or acontact spray, figure 18-8.

FIGURE 18-8 Damage to leaves by Japanese beetles.These chewing insects are actually eating parts of theleaves. Notice that the tough leaf veins are left uneaten.(Courtesy of U.S. Department of Agriculture)

FIGURE 18-9 Aphids attacking a plant. These insectssuck juices from the plant, thereby greatly reducing plantvigor and yield. Notice the ants also present. Ants tendaphids like farmers tend cows. They collect honeydew(a sweet liquid) from the aphids as food and protect theaphids. (Ed Reiley, Photographer)

Sucking insects suck the juices from the leavesof plants. The injury caused by sucking insects isnot as easily detected as that caused by chewing in-sects. Some signals of damage by sucking insectsinclude twisted plant tips and rolled leaves. Plantsthat are infested by sucking insects may show nosigns of infestation at all, but simply appear to beless healthy. Figure 18-9 shows damage to a plantby a sucking insect, the aphid. Sucking insectsmust be controlled with a contact chemical, a fu-migant, or a systemic.

TIMING ININSECT CONTR IInsects must be killed when they are actively feed-ing or moving about on the plant. When in theresting (pupa stage) or egg stage, very few chemicalscan affect insects; however, the new spray oils givecontrol in the egg stage. It is important to deter-mine what stage of growth the insect is in beforespraying. This is done by examining the insect onthe plant.

Insects go through one of the following basiclife cycles. The stages during which the insects arecontrolled are boxed.


• Complete metamorphosis:

Fe-9-9 larva - pupa -

• Incomplete metamorphosis:

egg nymph adult

adult

If the entire insect population of a plant is in aninactive stage, insecticides, other than oil, mustnot be applied until the eggs hatch or the pupaemerges as an adult. If insects in both active andinactive stages are present, an immediate applica-tion of insecticide should be made, with a secondapplication made in seven to ten days when theeggs have hatched and before the insect has achance to mature and lay more eggs. Figure 18-10illustrates the life cycle of the Japanese beetle.

The integrated pest management system relieson..exact_timing and less use of chemicals-to controlpests.

PLANTS ASINSECT REPELLENTSAccording to organic gardening experts, certainplants may be used to prevent attacks by insects onother plants. Figure 18-11 lists some of those plants,along with the insects they repel.

PLANT REPELS

mint fleabeetles, cabbage butterflies

onions, garlic*, aphidschives, leeks

marigolds root nematodes

nasturtiums aphids, cucumber beetles

sage carrot flies, cabbage pests

horseradish potato bugs, other flying insects

*garlic also inhibits the growth of asparagus.

FIGURE 18-1 1 Plants reputed to repel insects.

THE ORGANIC GARDENERAccording to Webster's Dictionary, organic is de-fined as relating to, produced with, or based on theuse of fertilizer of plant or animal origin withoutemployment of chemically formulated fertilizers orpesticides. These gardens rely on insect repellentsthat do not include chemicals in any form-naturalenemies, plants, extracts of ground insects used as

AUG; SEPT.D.-ON'FOLIAGE •: AND FRUIT

FIGURE 18-10 The adult Japanese beetle is killed with an insecticide applied as a spray only during June, July, August,and September. The rest of its life cycle is spent underground where it does a great deal of damage to grass roots.Insecticides, in the form of soil chemicals, or the introduction of natural enemies, such as "milky spore," are used duringthe larval stage, which is October or in early spring. (Adapted from U.S. Department of Agriculture)


sprays, natural insecticides, crop rotation, sanita-tion, and resistant varieties.

It is a generally accepted fact that the incorpo-ration of organic matter into the soil and the use ofmulches result in better plant growth. This is dueto better moisture retention in the soil and to an in-

creased availability of minor plant food elementsand other plant growth stimulants. This leads tothe production of healthier, faster, growing plantsthat are better able to resist attack by insects anddisease.

Horticulture2010-2011


`and apply herbicides so that weeTo selectwithout damage to the crop being cultivate

environment.

Competencies to Be Developed

-identify a weed problem and select. a herbicide -to control theproblem.define and differentiate between selective and nonselectiveherbicides.describe three ways in which herbicides destroy weeds.

'?- outline in writing how a sprayer is calibrated.

list three possible reasons for failure of a herbicide to workproperly.

properly apply a herbicide.

After studying this unit, you should be able to

LTERIALS LISTt/ weed killers complete with label and recommendations

t/ weed charts for weed identification

t/ sprayer for use in calibration and application of herbicides

d an area of lawn or crop land for use in locating andidentifying weeds and applying herbicides

Aherbicide is a chemical that kills weeds. Her-bicides comprise a large percentage of thetotal pesticides used each year. In the past

twenty years, many new weed killers have been in-troduced on the market, and each year new uses arefound for traditional weed killers. It is estimated thatin the United States, weeds cause damage and loss ofproduction to crops in excess of $4.5 billion each

year. Herbicides are used to kill weeds in crops, onlawns, along roadways, and in many other places.

A weed is considered to be any plant growingwhere it is not wanted. Grass that is growing in alawn is not a weed but is considered a weed if it isgrowing in the garden.

Weed control can be accomplished without theuse of chemicals. In some cases, mulching and


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the cultivation of ctops may be more effective andjust as economical to control weed growth. For ex-ample, it would be very difficult to spray weedkillers in a small garden without damaging otherplants. It is in large acreages of single crops thatselective weed killers can be used to greatest ad-vantage.

There are many different types of chemicalsused as weed killers. A partial list of herbicides andtheir toxicity levels is given in figure 20-1. Noticethat some of these pesticides may be very poiso-nous if swallowed (oral). They are generally not astoxic dermally (on the skin).

MWI Y CA ASS . , " OR DESIGNATIONSOME. COMMTRADE NAME

Very Toxic

COMMON.';N _-

3 sodium arsenite

Moderately Toxic paraquatdiquat

Slightly Toxic 2,4-DMSMAcacodylic acidaspirinlinuronDSMAnorea

3 amitroleboratedicambaprometonDCPAatrazinetable saltdiuronmonuronchloroxuronprometrynAMS

Almost Nontoxic siduronpropazinebromacil

3 picloramdalaponbenefin

3 Use restricted to licensed or certified applicator.

Atlas A

WeedolAquacipe

TYPES OF HERBICIDES

NONSELECTIVE HERBICIDESNonselective herbicides kill all plants to which theyare applied. These herbicides are used in placeswhere no plant growth is wanted. Lumber yards,railroad tracks, fence lines, driveways, and parkingareas are a few examples of areas where thesechemicals are used. Examples of some weed killersin this category are Atratol, Aatrex, and Roundup.

Nonselective weed killers sometimes may alsobe used as selective weed killers. Examples of this

10 2 drops to 1 teaspoon(less than 1/6 oz.)

150 1 teaspoon to 1 ounce400

various brands 500 1 ounce to 1 pint (or up toAnsar, Daconate 700 1 pound)Phytar 560 830(for comparison) 1,240Lorox 1,500Ansar, Sodar • 1,800Herban 2,500Weedazol 2,500Borax, Borascu 2,500Banvel 2,900Pramitol 2,980Dacthal 3,000Aatrex 3,080(for comparison) 3,320Karmex, Krovar 1 3,400Telvar 3,600Tenoran 3,700Caparol 3,750Ammate 3,900

Tupersan 5,000 1 pint to 1 quart orMiloguard 5,000 1 to 2 poundsHyvar X, X-L, X-P 5,200Krovar 1Tordon 8,200dowpon 9,300Balan 10,000

FIGURE 20-I Relative toxicity of some herbicides to mammals. Chemicals listed for information only, not for use.


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type of substance include Atratol and atrazine (Aa-

trex). Used at a rate of 2 to 4 pounds of activechemical per acre, it kills only small weeds or se-lected weeds; if application is increased to from 5to 10 pounds per acre, it kills all plants.

SELECTIVE HERBICIDESSelective herbicides are just what the name implies-chemicals that kill some plants but not others. Thisis by far the largest group of weed killers. Weedcontrol in a particular crop can be accomplishedsafely and effectively with selective weed killers.These chemicals are designed to kill the weed butnot the crop.

In some cases , a selective weed killer that killsbroadleaf plants will not kill grasses which have nar-row, bladelike leaves. This makes it possible to spraya lawn with 2,4-D to kill dandelions, which have abroadleaf, and-not kill--the grasses ,-which-have-nar-rowrow leaves . Since corn is a grass, broadleaf weeds ina com field can be killed with a selective herbicidewithout damaging the corn. The herbicide 2,4-D isone of the best known selective weed killers used tokill broadleaf plants without killing grasses.

Herbicides that have the potential to kill a par-ticular crop at high concentrations can be used atlow concentrations to kill young weeds that aregrowing in the crop and not damage the crop. Byapplying the weed killer at a low concentration,young tender weeds are killed and the older, moremature crop plant is not harmed . Strawberries areprotected from weeds in this way.

THE EFFECTOF HERBICIDESHerbicides work by upsetting the metabolism, orlife functions, of the plant (figure 20-2). The planteither starves to death or wears itself out due to theincreased rate of activity caused within its systemby the chemical. Herbicides are designed to affectthe metabolism of some plants and not others.

The following are some specific examples ofthe effect of herbicides.

ATRAZINEAtrazine is widely used to kill both broadleaf weedsand grassy weeds in corn and turf grass sod as wellas those in tree and shrubbery plantings.

APPLICATION Atrazine may be appliedpreplanting (before planting has taken place); pre-

emergence (before emergence of seedlings above-ground); or postemergence (after seedlings havegrown above ground but before the crop matures).However, it must be applied before the weedsreach a height of more than 11/2 inches. The chem-ical is usually applied with an ordinary sprayer.

BEHAVIOR IN THE PLANT The chemicalis absorbed through both roots and foliage. Itmoves through the plant in the xylem or wood andaccumulates in the stem tips and leaves of plants.Atrazine kills the plant by preventing photosynthe-sis from occurring. Since the plant cannot manu-facture food , it starves to death. Plants such as cornare not killed by atrazine when applied in usualdosages because they are able to break down thechemical before any harm is done to them. Cyan-azine (Bladex) also works as a photosynthesis

__ inhibitor.

2,4-D2,4-D is a systemic herbicide and is widely used tocontrol broadleaf weeds. Most dicot (broadleaf)plants are susceptible to the chemical at normal ap-plication rates.

APPLICATION Application is usually by spraydirected on the plant foliage . Both plant leaves androots absorb 2,4-D.

BEHAVIOR IN THE PLANT The chemicalmoves through the plant phloem or bark. Move-ment is more rapid in fast-growing plants andtherefore plants in active growth are killed moreeasily. The chemical 2,4 -D causes abnormal growthin the weed and affects respiration, food reserves,and cell division.

FIGURE 20-2 A weed killer was used to kill this weed.The roots are killed and the top dries out and turnsbrown. (Ed Reiley, Photographer)


Page 4

DACTHALDacthal is used to control annual grasses and cer-tain annual broadleaf weeds.

APPLICATION Application is generally atplanting time before the weeds come up. Thechemical is usually diluted with water and appliedas a spray.

BEHAVIOR IN THE PLANT Dacthal is notabsorbed by leaves and it does not move throughthe plant. Rather, it kills sprouting seeds. The exactway it acts is not yet known.

The weed killer Treflan kills weeds in a similarmanner.

SIJMMEL-R-YThe three herbicides just discussed kill weeds inthree different ways:

•• atrazine

,0 2,4-D

• Dacthal

prevents photosynthesis

upsets cell division, respiration,and food reserves

destroys sprouting seeds(specific action not yet known)

All weed killers do not fall into these threegroups, but they are representative of a great per-centage of herbicides.

APPLICATIONOF HERBICIDESHerbicides are either sprayed with ordinarysprayers or applied already mixed in fertilizers orin granules. The same type of equipment is used aswith, insecticides. However, a sprayer that is usedto apply herbicides should not be used to apply in-secticides - or fungicides unless it is thoroughlycleaned. This does not mean simply rinsing out thesprayer; it must be washed with a substance thatneutralizes the herbicides, such as ammonia. Readand follow the directions carefully; otherwise,enough herbicide may remain in the sprayer todamage desirable plants sprayed for insects or dis-eases. When using small hand sprayers, a separatesprayer should be used for the • application ofherbicides.

TIME OF APPLICATIONApplication of herbicides must be made at one ofthree times to avoid injuring desirable plants.

PREPLANTING Herbicides are mixed into orsprayed onto the soil or seed bed. Some herbicidesare effective only when incorporated with or mixedinto the soil; others need no mixing. Read the labelbefore buying.

PREEMERGENCE Treatment is made beforeany plant growth appears or after the crop comesup but before the weeds appear. Read the label tosee if the chemical should be applied before thecrop emerges or after the crop emerges and beforethe weeds emerge. When used at the recommendedconcentration, these chemicals usually preventseeds from germinating or kill only small tenderweeds without damage to desirable plants.

POSTEMERGENCE Applications must bemade very selectively in terms of the chemical used.These chemicals are applied after the crop plant hascome up.

CALIBRATION OF SPRAYERSIt is extremely important that the proper amount ofactual chemical be applied to a particular areawhen spraying herbicides. Even if the right mixtureor concentration of spray is in the spray tank, it ispossible to apply the wrong amount of weed killer.To avoid this problem, the sprayer should be prop-erly calibrated or adjusted before use. The correctamount of active chemical must be applied on ameasured area for the most effective control.

LARGE SPRAYERS The first step in the cali-bration of large sprayers is to measure and mark offan acre. Spray the acre with water and refill thespray tank, measuring exactly how many gallons ofwater are required to refill the tank, the amount ofwater applied to the acre. This is the rate of appli-cation per acre. If 10 gallons of water are appliedper acre and 2 pints of chemical are to be applied


Page 5

per acre, there 2 pints of chemical are added to each10 gallons of water. For example, for a 100-gallontank, add 20 pints, or 2.5 gallons, of chemical.

Caution: The rate of travel over the area andthe sprayer pressure must be the same as in thetrial run.

SMALL HAND SPRAYERS Follow these stepsto calibrate a small hand sprayer.

1. Lay out an area measuring 10 feet x 100 feet(1,000 square feet).

2. Fill the sprayer with water.

3. Spray the 1,000-square-foot area.

4. Measure the number of pints of water re-quired to refill the sprayer to the same levelas before. This is the number of pints ap=plied per 1,000 square feet.

If 8 pints (1 gallon) is sprayed on the 1,000square feet of land, and 21/4 teaspoons of chemicalare required per 1,000 square feet, add 21/4 tea-spoons of chemical to each 1 gallon of water. Thisis the same rate as 1 pint per acre. (One acre is43,560 square feet.)

Caution: Spray with the same pressure andspeed of application as in the trial run.

Another way to determine the amount of waterthat was applied to the 1,000-square-foot area is tomeasure the length of time required for the appli-cation. Spray into a container for the same lengthof time and measure the amount of water collected.

Caution: Use the same spray pressure as whenspraying the 1,000-square-foot area.

DRIFTAny substance that is sprayed can blow or drift in thewind. If a herbicide drifts onto a nontarget plant,there is a chance that this plant will also be damagedor killed. When spraying herbicides, use spray noz-zles that apply large droplets of spray. These largerdroplets do not blow or drift as much as a fine mistand greatly reduce the danger of damage to other

crops nearby. Tomatoes and tobacco are injured es-pecially easily if 2,4-D drifts over them. Injury ofother crops by drifting chemicals is a greater problemwith herbicides than with other types of pesticides.

BREAKDOWNOF HERBICIDESMost herbicides are broken down in the soil by soilmicroorganisms and eventually become harmlessmaterials. The length of time required for thisbreakdown varies from several weeks to severalyears. Read the label for recommendations. If a her-bicide persists or stays in the soil for a year or more,it may kill or damage the crop planted in that soilthe following year or later in the same season. Cropsthat are not damaged by the chemical should beplanted there until the soil is clean enough for cropsthat could be damaged by the herbicide.

Since preemergent herbicides are only effectivein controlling germinating weed seeds, they mustbe applied on clean, cultivated soils before weedseeds germinate. Of all the preemergent herbicides,only Chloro-IPC, Casoron, and Preemerge willcontrol existing chickweed as well as germinatingchickweed seeds.

These recommendations should be used onlyas a guide in selecting the proper test herbicide.Under no circumstances should a herbicide be ap-plied over the entire nursery without first spendingone growing season testing it in a limited areaunder the same soil conditions and the same grow-ing program. Herbicides are noted for not beingequally dependable under all growing conditions.

Always read herbicide labels for instructions,including the species that have been cleared for usefor that herbicide. Even when materials are used asrecommended, the manufacturer cannot be heldresponsible for injury when it is applied to orna-mentals not listed on the label.

WHY HERBICIDESSOMETIMES FAILWhy herbicides are sometimes ineffective is a verycomplex question. The following are some of themore common reasons for failure.


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INCORRECT SELECTIONOF THE HERBICIDEUnsatisfactory weed control may result from use ofthe wrong herbicide. It has been noted that manyweed killers are selective, that is, they kill only cer-tain weeds. Therefore, it is most important that theright chemical be selected to control a specific weed.This requires accurate identification of the weed tobe controlled. To use herbicides effectively, the ap-plicator must be able to accurately identify weeds.

IMPROPER APPLICATION-_--OF-THE-HERBICIDE

Herbicides are designed for application in a varietyof ways and at various stages of the growingprocess. Poor application and poor timing of ap-plication are reasons for herbicide failure. For ex-ample, preemergence herbicides must be spreadevenly on the surface of the soil. To make contactwith sprouting weed seeds, the entire soil surfacemust be covered with the chemical; if not, the her-bicide could be rendered ineffective.

Some chemicals also must be washed into thegermination zone by rainfall or irrigation withinseven to ten days after application. If no rain oc-curs or irrigation is not possible, poor weed con-trol will result. Preplant weed killers such asEptam must be mixed into the soil immediatelyafter application; if not, they evaporate into theair. Much of the active chemical is thus lost andcontrol is poor. Postemergence weed killers suchas 2,4-D must be sprayed onto the plant to bekilled or over the roots of the plant so that thechemical can be absorbed into the plant. The chem-ical 2,4-D also works most effectively if the weedsare in active growth.

Sprayer calibration is also very important forproper application of the herbicides. This may in-volve tests to determine the proper amount ofchemicals to apply per acre of land. Too low a rateresults in poor weed control; too high a rate couldkill the crop as well as the weeds.

ENVIRONMENTAL VARIABLES

THE MATURITY OF THE WEEDS Weedmaturity is an important variable; most weeds arekilled more easily when they are young and in ac-tive growth. In fact, this in the only time manyweed killers work effectively. An old, hardenedplant requires much more chemical, or may evenrequire a different type of weed killer. An exceptionto this is the herbicide glyphosphate (Roundup),that works better on mature plants.

RAIN Rain that falls just after application of theherbicide can be an advantage with some preemer-gence chemicals. However, excessive rain can-leach ---or wash the chemical through the soil or off foliageand dilute it so much that weeds are not con-trolled. Roundup is washed off easily. It . requiressix to seven hours to move into the plant.

SOIL TYPE AND ORGANIC MATTER CON-TENT The type of soil and its organic contentaffect the amount of active chemical that must beapplied. Some chemicals are absorbed or held onthe surface by clay particles and organic matter.There are two dosages for some chemicals. For ex-ample, Dacthal is recommended in doses of 10 to15 pounds of active ingredients per acre. Tenpounds is recommended for sandy soils, and 15pounds for silt and clay soils. A soil high in humusabsorbs and makes some of the weed killer inactive,requiring a higher rate of chemical application.

Not all chemicals are affected by organic matterin the soil to the same degree. For example,dalapon is not absorbed at all, whereas Dacthal iseasily absorbed and would be greatly affected byorganic matter level of the soil.

Weed control with chemicals is not a simple job;many variables must be considered to achieve effec-tive control. Herbicides have limitations and are nota magic cure-all for weed problems, but if used care- .fully and accurately, good results can be expected.

Caution should be exercised in the use of any ofthese chemicals.

n insect? - fulda · 2011. 2. 15. · ment and the bodies of warm-blooded animals. one chemical...

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