Alfalfa PDF

8/3/2019 Alfalfa PDF

http://slidepdf.com/reader/full/alfalfa-pdf 1/14

39

Using herbicides during winter can be very effective in

controlling annual grasses and broadleaf weeds,

ensuring a weed-free first cut in the spring.

W M

C D O N A L D

WEED CONTROL

A large number of weeds affecting lucerne are of

economic importance. The key to reducing

production losses is the ability to recognise various weeds that have the potential to cause

damage in your situation. A weed control strategy

then needs to be built into your production

system.

At establishment

Lucerne seedlings are very susceptible to

competition. To overcome this problem, sow

into a seedbed that is free of likely troublesome

weeds, as far as is practicable. Good weed

control in the preceding pasture or crop cansignificantly reduce the weed population during

the establishment year.

In the establishment year, weeds can be controlled

with conventional cultivation before sowing,

The increased seedling vigour of winter-active

varieties promotes establishment, but it is not

enough to overcome many of our most common

weed problems.

The range of herbicides available to assist

lucerne to establish is very narrow. Most are

expensive and control only a limited range of weeds. One notable exception is the use of a

pre-sowing herbicide that gives effective controlof the problem weeds, especially annual

ryegrass and wireweed, at a reasonable cost.

If you are expecting a severe infestation of summer weeds (as is often the case underirrigation and on the North Coast), the beststrategy may be to avoid the competition. Thiscan be done by changing the sowing time fromspring to autumn or early winter, rather thanrelying on expensive herbicides to salvage thespring sowing. The same strategy can be used

where nutgrass is a problem, as chemical control

is expensive.If winter weeds, including broadleaved species,are likely to be present, either sow lucerne inspring or control weeds by prior cultivation or

with a herbicide, subject to the availability of irrigation or a reliable rainfall in spring.

Couch grass is particularly difficult to control inlucerne. Where couch grass is a problem, it may be necessary to delay sowing the lucerne andcrop twice to reduce the infestation. Cultivation

to bring runners to the surface during dry orfrosty periods is the main means of controllingcouch grass. Heavy grazing followed by the useof a herbicide has also had some success.

Agfact P2.2.25 Lucernefor pastures and fodder,continued –The following section covers the second half of this Agfact, dealing with:

• Weed Control,

• Pests and Diseases

• References

The bulk of the text and illustrations dealing with lucerne for pasture and fodder is containedin the first section.

Please follow this link to visit the first section.

http://www.agric.nsw.gov.au/reader/17117

http://www.agric.nsw.gov.au/reader/17117



40

R T R O U N C E

Golden dodder is a serious parasitic weed of lucerne. It

must be identified and eradicated early.

Alternatively, a post-emergent herbicide is nowavailable, but the cost may be prohibitive exceptunder irrigated hay conditions.

In established lucerne

Good management reduces weed problems in

established lucerne. Herbicides are useful if they

are used correctly, but they are much moreexpensive than good management. Sometimes

they can temporarily depress the growth of the

lucerne, allowing further weed invasion. In many

situations herbicides are an essential part of

management to allow profitable production.

If management procedures fail or are

inappropriate, many weeds can be controlled by

herbicides. Herbicides should never be a

substitute for good management, but they can be

a valuable aid in a sound management program.Sometimes herbicides are essential if lucerne is to

survive and flourish. In places where weeds grow

very vigorously – for instance, in summer grass

on the North Coast – you must use a herbicide if

you want good quality lucerne.

Control of winter-growing grasses and broadleaf

weeds (‘winter cleaning’) is generally cost-

effective in irrigated hay crops because of the

relatively low cost and the combined advantages

of quality, yield and possibly increased stand life.

Grazing management

Rotational grazing, as described in the section on

Grazing management , maintains a vigorous stand

that resists invasion by weeds reasonably well.

The stocking rate should be high enough to make

full use of the available feed as far as practicable.

Fertiliser management

Lucerne is very responsive to nutrients such as N,

P, S and K, but too much fertiliser can encourage

weeds such as barley grass, especially if

competition is low. Good paddock records and

soil tests are valuable aids in monitoring changes

in soil fertility, allowing you to determine fertiliser

needs more accurately.

Crop rotation needs to be considered to manage

fertility built up by lucerne. as well as for many

other benefits.

Cutting, slashing and burning

Cutting hay or slashing in early spring may helpto control many erect-heading weeds. Other weeds, such as couch grass and khaki weed,thrive on regular cutting. Burning may help to

remove weedy or insect-infested trash, andgenerally does little damage to well-established

lucerne on moist soil.

The nutritive value of a lucerne-based pasturemay not be improved by removing weeds. Whenlucerne is cut at the correct stage of growth, many

weeds are young and highly nutritious. Forexample, first-cut grassy lucerne hay can have thesame feed value as grass-free hay. However,grass-free hay attracts a premium on the market,and this may justify expenditure on herbicide. Itmay also be worthwhile to reduce grass seedcontamination in wool.

As lucerne pastures thin and weeds invade, thepractice of drilling in a winter cereal or foragegrass (for example, ryegrass) can reduce weedinvasion and maintain livestock production whileusing soil nitrogen, thus reducing the bloat riskand prolonging the life of the remaining lucerne.

For information on the herbicides that areavailable and the weeds they control, see theWeed control in lucerne and pastures booklet,available from NSW Agriculture regional anddistrict offices.

PESTS AND DISEASES

A great number of insects and related forms canbe found in lucerne. Some are pests that can be

very damaging when conditions favour them, butmany are harmless, and some are useful naturalenemies of lucerne pests.

The most important pests of grazing andhaymaking stands are aphids, blue oat mite, red-

legged earth mite, lucerne flea, cutworms, sitona weevil, white-fringed weevils, lucerne leaf roller,lucerne leafhopper and – in tablelands and slopesdistricts – wingless grasshopper. Occasionally



41

DISEASES OF LUCERNE

The effects of Phytophthora root rot are evident in this

irrigation bay. Note that there is less damage on the

better drained bank.

W M

C D O N A L D

Severe damage caused by Phytophthora root rot

G S T O V O L D

The initial signs of crown or root rot damage can

be detected by wilting and dead stems.

W M

C D O N A L D

G S T O V O

L D

The crown rot symptoms of Colletotrichum trifolii.

Note the dark ash discoloration in the split crown.

Common crown rot. Note the brown discolouration

extending into the root.

A N I K A N

D R O W

other, usually minor, pests such as lucerne crownborer, heliothis and weed web moth may also besignificant.

Seed crops may also be severely affected by thrips,heliothis , lucerne seed wasp, lucerne seed-webmoth and green vegetable bug. (See Growing

lucerne for seed section.)

A variety of diseases also affect lucerne, andsome of them can cause considerable loss inproduction. The most important of these are

Phytophthora root rot, a range of crown rots,stem nematode, Australian lucerne yellows,bacterial wilt and various leaf spots.

All of these pests and diseases are listed inTables 7 and 8.



42

Table 7. Major diseases of lucerne

Symptoms Occurrence Spread Control

Phytophthora root rot (Phyt ophthora medicaginis ) – fungusWilting, purple, yellowing andreddening of plants. Sometimesonly a few shoots are affected.

Taproot rots away after darkbrown to black sunken lesionsappear.

State-wide. Most common duringextended wet weather or aftertoo much irrigation, especially

on poorly drained clay soils.Symptoms appear in late springand summer.

Surface drainage water, soil. Select free-draining soils. Goodirrigation layout essential,especially for heavy soils. Sow

resistant varieties.

Ant hracnose and Colletotrichum crow n rot (Colletotrichum trifolii) – fungusAnthracnose: Scattered deadshoots appear throughout thestand, with elongated deadareas on the lower stem withblack dots (fungal fruitingbodies).Crown rot: Shoots suddenly wiltand turn yellow with crown rot.

Areas of dead and discolouredtissue in the crown often extendinto the taproot (dead tissueturns black with age).

State-wide, but most severe innorthern districts. Associated

with high humidity and summerrainfall or irrigation.

Survives on dead organic matterin the soil. Spores are spread bymachinery, rain or irrigation

water.

Use resistant varieties.

Common crow n rot (combination of several fungi, primarily Acrocalymma medicaginis , Phomopsis sp. and Phoma medicaginis ) – fungiFirst signs are wilting followedby death of individual shoots.Initially only portion of thecrown may be affected.Internally, the crown and uppertap root show a reddish-brownrot, with red flecking in the most

recently affected tissue where A.medicaginis predominates. Olderrotted tissue is dry and crumbly.

The presence of lighter brown to whitish rotted tissue, borderedby black ‘zone’ lines indicatesthat Phomopsis is thepredominant cause.

State-wide. Often followsconditions of stress ormechanical injury. High-crownedvarieties are more subject toinjury, and therefore moreprone to the disease.

Spores on machinery and duringrain or irrigation. Fungi cansurvive for a long time on deadcrowns.

Avoid practices that causemechanical injury to crowns.Crop rotation can help.

There are no known resistantvarieties.

Stem nematode (Ditylenchus dipsaci ) – tiny w ormlike organism, 1 m m longDwarfing; distortion; swollenshoots; leaves clustered towardsends of stems. Plants die in

patches.

Most common on irrigated flatsand in river valleys in slopesdistricts. Favoured by cool,

showery weather. Most obviousin spring.

Contaminated hay, seed,machinery, floodwater and thefeet and bodies of animals. May

remain dormant in diseasedtissue for up to 6 years.

Sow resistant varieties. Graze orplough out. Rotate crops. Usecertified seed.

Bacter ial w ilt (Clavibacter michiganense s sp insidiosum ) – bacteriumYellowing, small leaves; generalstunting of plants. Poor growthafter cutting and grazing.

Southern, central and coastalriver valleys. Less so in northerninland regions. Losses can besevere, especially underirrigation.

Plant material, especially hay;also seedborne. Injured plantsbecome infected.

Sow resistant varieties. Usecertified seed.

Common leaf spot (Ps eudopeziza medicaginis ) – fungusSmall, dark spots containingraised, dark-brown fungal

fruiting bodies on leaves andsometimes stems. Severeinfections cause leaf yellowingfollowed by leaf drop.

State-wide, but especially inhumid, higher rainfall areas.

Especially evident in spring andautumn on mature stands.

Spores that are on fallen leafletsare spread by wind and rain.

Infection is encouraged in thickstands.

Cut or graze to remove infectedmaterial. Infection builds up

gradually on growing plants.



43

Table 7. Major diseases of lucerne continued

Symptoms Occurrence Spread Control

Rust (Uromyces striatus ) – fungusRed-brown pustules onundersurfaces of leaflets, andsometimes on stems.

State-wide, especially in wet, warm conditions.

Airborne spores in warmshowery conditions.

Cut or graze to remove infectedmaterial.

Pepper spot, burn (Leptosphaerulina trifolii ) – fungusSmall, pinhead-sized spots onleaves (pepper spot) may coalesceto kill the whole leaf (burn) andcause extensive leaf drop.

State-wide, but especially inhumid, high-rainfall areas.Usually a problem in latesummer-early autumn.

Airborne spores released fromspots on leaves. Also spread byrain splash action. Usuallyappears on older growth.

Cut or graze at correct stage of growth.Difficult to prevent losses in extendedperiods of showery weather.

Stemphylium leaf spot (Stemphylium botryo sum ) – fungusLight brown, scattered spots.Margins of spots often dark brown.

State-wide, but more common where good autumn/winter rainoccurs or under irrigation.

Airborne spores. Fungus surviveson diseased fallen leaves.

Cut or graze to remove infectedmaterial.

Dow ny mildew (Peronospora trifoliorum ) – fungusLight green or yellow areas onupper leaf surfaces. Light brown

fungal growth on undersides ofaffected leaflets. Stems may alsobe affected.

State-wide, in wet areas withhigh humidity. Attacks seedling

stands only.

Present in infected leaflets andcrop debris. Spread by airborne

spores.

Not necessary. Clears up in warm, dry weather.

Damping off (Pythium spp.) – fungusPatchy establishment. Extensiverotting of primary root on youngseedlings.

State-wide, especially in coastalregions and tablelands. Infection

worse where seedlingemergence is retarded (e.g. wet,cold soil).

Present in soil. Avoid sowing in wet or cold weather.Irrigate before rather than after sowing.Seed treatment with a registeredfungicide is useful.

Sclerotium w ilt (Sclerotium rolfsii ) – fungusWilting, rotting of crowns andstems, sometimes extending intothe tap root. White fungal growthcovers the surface of rotting tissue.Small, (1 mm) blackish-brown,spherical resting bodies of thefungus are produced on the surfaceof affected tissue.

Most common in coastal districts, where high rainfall andhumidity favour the disease.Young stands are most affected.

Fungus survives on organicmatter in the soil.

Control broad-leaved weeds that mayhost the fungus. Rotate lucerne withcereals.

Black stem (Phoma medicaginis ) – fungusElongated, dark-brown to blacklesions occur on the lower stemparticularly, but may also affectthe leaves. Stems and young shootsmay be killed.

Usually only a problem in higherrainfall coastal and tablelandareas during spring and autumn.

Spores of the fungus spread byrain splash and on farmmachinery.

None recommended. Disease will clearup in warm, dry weather

W itches' broom – a phytoplasma-like organism

Dwarfing, fine shoots, rounded,small leaves. Crown often rots.

State-wide, but more commoninland.

Brown jassid (leaf hopper) in warm, dry weather.

Graze or plough out non-productivestands, killing all plants.

Australian lucerne yellow s – a phytoplasmaLeaves are bright yellow orreddish. The inside of bark, whenpeeled off the tap root, shows amarked yellow to orangediscolouration. This discolouredlayer appears as a ring in crosssection. The inner, woody portionof the root remains white andunaffected, unlike in bacterial wiltor Fusarium wilt, where this portion

of the root is discoloured. Initially,infected plants produce spindlyshoots and usually die after one ortwo seasons.

Riverina and western areas.Develops in mid- to latesummer. Infection can be severein hot, dry summers.

Probably transmitted byleafhoppers.

Plough out if heavily infected. Rotatecrops.



44

DISEASES OF LUCERNE

Alfalfa mosaic virus. A very conspicuous disease but rarely

of economic importance

G S T O V O L D

Leaf diseases such as Stemphylium leaf spot can

reduce yields, especially in humid environments or

under irrigation.

W M

C D O N A L D

Leaf rust can cause severe damage.

G S T O V O L D

Pepper spot

G S T O V O L D

Common leaf spot

G S T O V O L D

Bacterial wilt can be a problem in some river valleys,

especially in southern NSW. Note the yellow

discoloration of the tap root.

G

S T O V O L D



45

DISEASES OF LUCERNE

Australian lucerne yellows, a problem in drier areas of NSW. Left: Foliage symptoms. Right: Root symptoms

L P I L K I N G T O N

A N I K A N D R O W

Distorted regrowth caused by stem nematode

infect ion

Discoloration in roots caused by stem nematode

infection

W M

C D O N A L D

G S T O V O L D



46

Table 8. Main insect pests of lucerne

Pest Damage Significance Control

Spott ed alfalfa aphid (Therioaphis trifolii ) – SA A

Adults 1.5–2.0 mm, long, wingless or winged. Yellow or yellowish green with six or more transverse rows ofdark dots on the back. Winged formshave smoky areas along the wingveins.

Nymphs are born alive and resemble wingless adults, but are smaller.

Sucks sap mainly from the undersideof the lower leaves. Also injects atoxin and secretes large amounts ofhoneydew, which hosts sooty mould,giving it a black sticky appearance.

Seedlings are especially susceptible.

Veins of affected leaves become whitened or yellowish then turnyellow, and plant may defoliate frombase upward.

Active from spring to autumn, butusually most numerous in autumn.

Can kill seedlings or establishingstands and defoliate older stands ofsusceptible varieties.

Honeydew may interfere with cutting,drying and baling of hay and reduceits quality.

Establish and maintain vigorousstands of resistant varieties throughadequate and timely watering,fertilising and weed control. Resistantvarieties, parasites and predatorsnormally control this pest.

Chemical control sometimesnecessary, especially on seedlings, toprevent rapid buildup, especiallyafter cutting or grazing.

Blue-green aphid (Acyrthosiphon kondoi ) – BG A

Adults 2–3 mm long, wingless or

winged and bluish green to green.Winged forms have uniformly darkantennae.

Nymphs are born alive and resemble wingless adults, but are smaller.

Sucks sap mainly from terminal buds,

upper leaves and upper stems.Damaged plants become stunted, with small, distorted leaves andshortened internodes, and turnyellowish. Severely damaged plantsdie from top down.

Seedlings are particularly susceptible.

Active from autumn to spring, but

usually most numerous in spring.Cool, wet conditions in summer alsofavour BGA build-up.

Loss of production in spring, summerand autumn, and loss of plants in winter, can be serious. Severelydamaged plants have significantlyreduced yield in next regrowthperiod.

Heavy infestation may preventnormal flowering of seed crops.

Establish and maintain vigorous

stands of varieties with highresistance through adequate andtimely watering, fertilising and weedcontrol.

Regularly check establishing standsand the regrowth of establishedstands after cutting or grazing.Populations can increase veryrapidly.

Cutting or grazing in early spring candelay buildup and assist control bypredators, parasites and fungaldiseases.

Varietal resistance is effective butnot always adequate to preventdamage by heavy infestations.Chemical control is sometimesnecessary, especially in seedlingstands.

Pea aphid (Acyrthosiphon pisum ) – PA

Adults 4–5 mm long and wingless or

winged, with a pale green or yellowgreen body (sometimes tingedpinkish). Winged forms have bandedantennae.

Nymphs resemble wingless adults butare smaller.

Sucks sap from leaves, stems and

terminal buds.

Tops of infested plants have smallleaves and spindly stems. Leavesbecome yellow and wilt and the topsof the plants die.

Active from spring to autumn, but

usually most numerous in spring andautumn.

Normally a minor pest, but heavyinfestations can cause seriousdamage. May occur in association with blue-green aphid.

Heavy infestation may preventnormal flowering of seed crops.

Varieties with resistance to blue green

aphid are less affected by pea aphid.

Cutting or grazing in early spring candelay build-up and assist biologicalcontrol by predators, parasites andfungal diseases.

Chemical control sometimesnecessary to prevent loss ofproduction in spring, summer andautumn.



47

Blue oat mite (Penthaleus major ) – BOM and Red-legged earth mite (Halotydeus destructor ) – RLEM

Adult mites are eight-legged, ovaland about 1 mm long.

BOM has a rounded dark brown toblue-black body, bright red or pinkishred legs and mouthparts and a reddot in the centre of the lower back.

RLEM has a somewhat flattened blackbody, pinkish orange legs andmouthparts and no red streak.

Mites feed by rasping and suckingaction on cotyledons and leaves ofseedlings and first-year plants and on

leaves of older plants.

Damaged seedlings and plantsprogressively show yellowing andthen whitening of cotyledons and/orleaves.

Primarily pests of seedlings and first-year plants in autumn, winter andspring. Can also severely reduce

vigour, palatability and winterproduction of older plants.

Heavily infested seedlings and first-year plants from autumn sowingsmay be killed or become stunted and

weak.

Both pests prefer light, sandy orloamy, well drained soils.

Spray in spring of previous year toreduce over-summering RLEMpopulations.

Clean fallow and eliminate weedsfrom around paddock perimeter forat least one month before sowing.

Sow insecticide-treated seed andapply a bare ground spray and/orone or more foliar sprays. Also sprayheadlands and surroundingvegetation if infestation severe.

Inspect established stands weeklyafter autumn break and spray whenmite numbers increase sharply. Twosprays a few weeks apart, plus afurther spray in spring, may be

needed.

BOM and RLEM differ in theirsusceptibility to insecticides.

Lucerne flea (Sminthurus viridis )

Wingless, globular, up to about 3 mmlong and grey-green or yellow-green

with dark patches. Hops about whendisturbed

Over-summers as eggs, which hatchin the autumn (autumn break).

Very young nymphs make smallmembranous ‘windows’ in leaves.Older nymphs and adults eat outlarger patches. Badly infested fieldslook whitish, and total defoliationmay occur.

Primarily a pest of seedlings andfirst-year plants, but may alsodamage established plants. Severeinfestations can kill seedlings fromautumn sowings and seriously reduce

winter production of establishedplants.

Clean fallow and eliminate weedsfrom around paddock perimeter forat least one month before sowing.Liming before sowing also helps.

Sow insecticide-treated seed andapply one or more foliar sprays ifnecessary. Also, spray headlands and

surrounding vegetation if infestationsevere.

Inspect established stands weeklyafter autumn break. Spray when fleanumbers increase sharply. Two sprays4 weeks apart about 1 month afterthe autumn break can prevent laterproblems.

Cutw orms (Agrotis spp.)

Caterpillars grey-brown, green-grey,brown, green-brown, light to darkgrey or nearly black, often with darkspots on back and sides. Length 25–

50 mm when fully grown.

Feed on leaves and stems ofseedlings, first-year plants andestablished plants.

Sporadic pests throughout year.

May eat out or thin large patches ofseedling or first-year stands andseverely check regrowth ofestablished stands after cutting orgrazing.

Clean fallow and eliminate weedsfrom around paddock perimeter forat least one month before sowing.

Regularly check seedlings, first-yearstands, and regrowing establishedstands in evening or at night forcutworms. Early detection is essential.Use insecticides if needed.

Sitona w eevil (Sitona discoideus )

Larva up to about 5 mm long with alegless, slightly curved white bodyand orange-brown head.

Adult 3–5 mm long and greyishbrown with a short, broad snout andthree yellowish white stripes on

thorax.

Early-stage larvae feed within or onthe root nodules. Older larvae feedon lateral roots and taproots.

Adults make scallop-shaped notchesalong leaf margins and also chewstems of seedlings, first-year plants

and established plants. Heavyinfestations can defoliate establishedplants and may kill seedlings or first-year plants.

Persistent heavy larval attack on hayor grazing stands less than about 4years old may cause significant yieldloss. Often present but only anoccasional problem. Damagegenerally most serious in spring andautumn, but adults may also feedactively during warm weather in

winter. Damaged seedlings mayproduce stunted and weak first-yearplants.

No chemical treatment is available forlarvae.

Egg laying can be greatly reduced orprevented by controlling adultinfestations in April–May. Checkseedling and first-year stands regularly.

Spray established stands if weevils arenumerous and damage is worseningnoticeably.


Table 8. Main insect pests of l ucerne continued



48


Table 8. Main insect pests of lucerne continued

W hite-fringed w eevils (Graphognathus leucoloma )

Adults: 10–13 mm long and darkgrey to blackish brown with two

whitish bands along each side ofhead and thorax, and a whitish bandalong outer margin of each wingcover. Adults cannot fly, but all canproduce eggs.

Larvae: legless, with slightly curved white, greyish white or yellowish white bodies, indistinct pale headsand black mouthparts. Up to 13 mmlong and 6 mm wide.

Larvae feed on the roots of seedlingsand first-year plants.

Larvae also burrow well into taprootsof established plants and make deepgrooves to about 20 cm below crown.

Adults make scallop-shaped notchesalong leaf margins.

Heavily infested seedling and first-year stands can be so badly damaged

that resowing is necessary.Established plants can support highnumbers of larvae with no apparenteffect on productivity or longevity,provided they are not placed underadditional stresses such asinadequate fertiliser, grazingmismanagement or severe drought.

Can progressively thin stands, whichthen require replanting.

Feeding by adults is seldom serious.Insecticides against adults fromDecember–February may reduce

larval numbers.

No chemical treatment available forlarval control in establishing stands.

Free ground of larvae before sowinglucerne by thoroughly cultivating inOctober–November and then sowing weed and legume-free cereal or grassforage crops for at least 2 years. Sownew stands as far away as possiblefrom older stands.

Lucerne leaf roller (M erophyas divulsana )

Young caterpillars pale yellow. Oldercaterpillars up to 15 mm long, withslender yellowish green or greenbodies and dark heads. Whendisturbed they wriggle backwardsand drop from the leaves.

Populations cycle every 4–5 weeks insummer and can attack at any stageof crop growth. Caterpillars aresometimes most abundant in seedcrops shortly before flowering. Feedon the terminal leaves and floweringstems, webbing them together.

A sporadic pest of grazing or haycrops in spring, summer and autumn.Heavily infested plants becomestunted and yield and quality of hayseriously affected.

Sometimes, also severely reduces podset of seed crops.

Damage often most important inmoisture stressed unirrigated stands.

As a guide, spray grazing or haystands when about 30% of terminalsare rolled in the first half ofregrowth.

If the stand is approaching maturity,early cutting or grazing may be anacceptable alternative.

Cutting or grazing when eggs orsmall larvae are present and then at

4–5 week intervals can keepnumbers low.

Maintains optimum soil moisturelevels.

W ingless grasshopper (Phaulacridium vittatum )

Adults: 12–15 mm long and grey orbrown, usually with two white stripesalong each side and orange-redshanks of the hind legs. Most haveshort scale-like wings, but some arefully winged.

Hopper stages: smaller and dullbrown to almost black.

Feed on the foliage and stems.Heavily infested stands severelydefoliated or eaten out.

Can be severe pest in summer andautumn, mainly on the tablelandsand upper slopes.

Infestation usually most common indry weather.

If wingless grasshopper is a problemcontact local Rural Lands ProtectionBoard for advice about spraying.

Only margins of stand may needtreatment if hoppers are moving infrom outside.

Lucerne crow n borer (Corrhenes stigmatica , Zygrita diva )

Adult beetle: 10–13 mm long anddark orange-yellow with variablenumber of irregular black spots andtransverse bands. It also has a pair oflong, slender black antennae.

Larva: legless, whitish and up toabout 20 mm long and 5 mm wide.

Larvae tunnel inside the crown shootsand taproot. Tunnels surrounded bydry rotted, brown and shreddedtissue.

Damaged plants occasionally wilt anddie.

Usually a sporadic minor pest ofstands older than 2 years, in northernand central inland areas. Sometimesinfests young stands. No te : Detailedinvestigation in southern Queenslandin 1970s showed that lucerne crownborer was an insignificant cause oflucerne decline.

Plough out heavily infested stand in winter and re-sow paddock with twosuccessive cereal or grass foragecrops. Sow new stands as far away aspossible from affected older stands orland infested with alternative hostplants.



49

Table 8. Main insect pests of l ucerne continued


Lucerne leafhopper (Aust roasca alfalfae )

Adults wedge-shaped, yellow or yellowishgreen and about 3 mm long.

Nymphs resemble adults, but wingless andsmaller.

Note: Do not confuse these with the greenor bright green and about 3 mm long,vegetable leafhopper, which seldom warrants concern. It produces a whitestipple pattern on the leaves when it feeds.

Sucks sap from the conductive tissuesand also injects a toxin. Heavyinfestations cause leaves to turn yellowand fall and can stunt plants.

Mainly a sporadic pest ofgrazing and hay standsin summer and autumn.Infestation promoted byhot dry conditions, andmoisture stressed,unirrigated stands areusually most at risk.

As a guide, spray if there are 20 or moreadults and/or nymphs per sweep of a 35-cm -diameter net. Early cutting or grazingmay be an acceptable alternative tospraying if hay stand is approachingmaturity, but could induce movement intonearby crops.

Thrips (Thrips spp.)

Adults: slender, 1–1.5 mm long andyellowish brown, brownish or blackishbrown with narrow fringed wings.

Nymphs: smaller, orange-yellow oryellowish and wingless.

Feed on immature flower buds whilstentire flowering stem is inside generalbud sheath, producing dead greyish

white ‘blasted buds’ and bare stems or‘stripped racemes’.

Also feed on the petals and tiny pods inunopened flowers and on the developingpods in opened flowers. Damagedflowers and very young pods may fall.Older damaged pods become distortedand hold mixture of malformed orshrivelled brown seeds and normalseeds.

Can cause considerabledamage to seed crops inspring, summer and

autumn.

Regularly inspect crops, from whenregrowth is about 15 cm high until flowerscommence opening. Look for thrips-

damaged leaves that have silvery whiteblotches. Also, gather handfuls of stemsand shake them into a white plasticbucket or similar container to dislodge thethrips.

Insecticide treatments, before the flowersbegin to open, may be necessary. Ifadjacent thrips-infested hay stands areclose to harvest, consider delayingtreatment to ensure that any migratingthrips are also controlled.

Heliothis (Helicoverpa spp.)

Newly hatched caterpillars 1–1.5 mm long with dark-spotted white bodies and darkheads. Young caterpillars (up to about 15mm long) have dark heads and paleyellow, greenish or brownish bodies,usually with conspicuous upper body hairsin dark bases and narrow dark stripesdown the back and along each side.

Commonly a pest of seed crops atflowering. Early-stage caterpillarsinitially feed inside flower buds andthen on tiny pods in opened flowers.Damaged flower buds and flowers donot set seed.

Larger caterpillars feed on the foliage,flowers and developing pods.

Caterpillars often causeconsiderable damage toseed crops in spring,summer and autumn.

Heliothis outbreaks canalso heavily infest non-flowering hay stands andseverely reduce the yieldand quality of hay,usually in spring.

Keep a close watch during flower buddevelopment and flowering for very small(1–5 mm long) caterpillars. Earlydetection is essential. One well-timedtreatment is usually sufficient if smalllarvae are present.

Note: In heliothis outbreaks heavyinfestation may occur before and/orduring early flowering and at least twosprays (the first at or before earlyflowering and the second as determinedby follow-up inspections) will probably beneeded.

Follow pesticide resistance managementpractices.

Lucerne seed w asp (Bruchophagus roddi )

Adults are about 2 mm long, with blackbodies and brown or yellowish brown legs.

Eggs laid into developing seeds insidepods from one quarter to half formed.One larva develops in each seed,destroying it.

Can very badly damageseed crops. Drylandcrops generally most atrisk.

Carefully watch crop from start of podformation until pods over half formed foradult wasps. Early detection is essential. Anumber of management practices canreduce infestation. Moisture stress duringpod formation favours infestation.Irrigation reduces losses.



50


Table 8. Main insect pests of lucerne continued

PESTS OF LUCERNE

High numbers of aphids can severely affect lucerne

productivity

L

T U R T O N

Spotted alfalfa aphid L T U R T O N

L T U R T O N

Blue-green aphid

Lucerne seed-w eb moth (Etiella behrii )

Young caterpillars are white to cream with a shiny black head and shield

behind the head. Older caterpillarshave brownish heads and shields andcream to green bodies, usually withseveral dark red or purplish stripesdown the back and along each side.Length 16–20 mm when fully grown.

Infestation usually commences duringearly podding. Newly hatched

caterpillars bore into developing podsand initially feed within, and then on,the seeds. They emerge when aboutthree quarters grown and sometimesmake webbed shelters in centre ofclusters of older pods.

Late-stage caterpillars chew holes inolder pods and eat seeds.

Sporadic pest of seed crops insummer and autumn. Damage has

ranged from slight reduction toalmost complete seed loss.

No specific chemical control measuresare recommended.

Moisture stress during early poddingfavours infestation. Irrigation reduceslosses.

Green vegetable bug (Nezara v iridula )

Adults: 12–18 mm long, green withthree or four yellowish white spots

along the front margin of thetriangular area between the wingbases.

Final stage nymphs: wingless andmostly green to brown-black, withorange, yellowish white, pink orpurplish red markings. Averagelength 14 mm.

Suck sap from the leaves, stems andimmature seeds in pods. Large

numbers clustering on pods canprevent seed development.

Damaged seeds shrivel and turnbrown.

Sporadic pest of seed crops in latespring, summer and autumn.

Check regularly during poddevelopment for adults and nymphs.

If necessary, spray using sufficient water to directly contact the bugs.



51

PESTS OF LUCERNE

A white-fringed weevil larva (inset) in the crown

of a lucerne plant

W M

C D O N A L D

L T U R T O N

Blue oat mite

L T U R T O N

Earth mite damage. Red-legged earth mite (inset)

and blue oat mite are major pests of lucerne

during establishment.

W M

C D O N A

L D

Leaf damage caused by Sitona weevil (inset:

adult). Note the characteristic u-shaped notches

on the leaf margins. Severe damage caused by lucerne flea (inset)

W M

C D O N A L D

L T

U R T O N

W M

C D O

N A L D

Lucerne leaf roller

L T U R T O N

L T U R T O N



52

© 2002 State of New South Wales—NSW AgricultureThis publication is copyright. Except as permittedunder the Copyright Act 1968 (Commonwealth), nopart of the publication may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owner. Neithermay information be stored electronically in any form

whatever without such permission. Acknowledgements

The authors wish to thank Neil Griffith, District Agronomist, Maitland; Dr Chris Bourke, Principal

Research Scientist, Orange; Mary Anne Lattimore,District Agronomist, Yanco; Dr Alan Kaiser, Special

Livestock Officer, Wagga Wagga; Gordon Stovold,

Senior Plant Pathologist, Alstonville; and Ian Daniels,

Soil Scientist, Tamworth, for their valuable comments

on technical issues in this publication.

ISSN 0725–7759

Edited by Ann MunroeProduced by staff of NSW Agriculture

Orange, December 2002

REFERENCES AND FURTHER READING

Crocker G and Lodge G 1981. Potassium carbonatespeeds up haymaking. Agricultural Gazette of NSW

33–36

Hill MJ and Donald GE 1996. Australian Temperate

Pastures Database , compiled for National PasturesImprovement Committee (CD ROM). CSIRO, AnimalProduction

Mickan F 1999. What happens when hay heats?

Agriculture Notes AG0206, Victorian Department of Natural Resources and the Environment(www.nre.vic.gov.au)

Moran J 1996. Forage Conservation – Making Quality

Silage and Hay in Australia. Agmedia, Agriculture Victoria

Lolicato S and Lattimore M 1988. Irrigated Lucerne –

A Guide to Profitable Irrigated Lucerne Hay Production in Northern Victoria and Southern NSW .2nd Ed. Agriculture Victoria, NSW Agriculture, Murray Darling Basin Commission

NSW Agriculture 1999. ENTOpak: a Compendium of

Information on Insects in Cotton (Contains guidelinesfor using lucerne as part of integrated pest control incotton.)

NSW Agriculture annual publication. Insect and Mite

Control in Field Crops

NSW Agriculture biennial publication. Weed Control in

Lucerne and Pastures (Available from district offices of NSW Agriculture.)

NSW Agriculture Red gut in sheep. Agfact A3.9.23

Sund JM, Barrington GP and Scholl JM 1966. Methodsand depths of sowing forage grasses and legumes.Proceedings 10th International Grassland Congress,319–326

Topcrop 2002. Lucerne Pests and Disorders – the Ute

Guide . (Covers identification of diseases, insects,disorders of lucerne. Available from NSW Agriculture.)

Wolfe EC 1983. Pasture Species – Persistence or

Productivity? Proceedings Riverina OutlookConference, Wagga Wagga

For information on soil acidity and salinity seeNSW Agriculture’s web page(www.agric.nsw.gov.au) under ‘Natural Resourcesand Climate.

For a summary of information on sowing and

managing lucerne , look under ‘Pasture Planner’by selecting ‘Field Crops and Pastures’, then‘Pastures’ on NSW Agriculture’s web page(www.agric.nsw.gov.au).

Alfalfa PDF

Documents

Transcript of Alfalfa PDF