MANAGEMENT PRACTICES OF CASHEWNUT

Cashew nuts

Anacardium occidentale

Description

Cashew, Anacardium occidentale, is an evergreen tree in the family Anacardiaceae grown for its edible fruits (nuts). The cashew tree has a branching main trunk and characteristic domed crown. The thin foliage of the tree is limited to the ends of the branches and is made up of oval-oblong leathery, shiny dark green leaves. The leaves are smooth with pronounced veins and midrib and possess petioles which are swollen at their base. The tree produces numerous pinkish-white flowers on drooping panicles and a kidney shaped true fruit (nut) which is approximately 3 cm (1.2 in) long with a gray-brown shell and develops from a fleshy accessory fruit, sometimes referred to as the 'cashew apple'. The cashew apple is pear shaped and red to yellow in color. Cashew trees can reach a height of 12 m (39.4 ft) and have an economic lifespan of 25 years after which time they are replaced in commercial plantations. Cashew originates from Brazil.

Cashew foliage

Cashew apples

Cashew tree

Cashew fruits developing

Cashew fruits and flowers

Cashew growing wild in Panama

Cashew fruits forming

Cashew fruits ripening

Cashew fruits developing

Uses

Cashew nuts are usually eaten after roasting either as a snack or as in ingredient in other dishes. Cashew apples are also edible and can be eaten fresh or cooked in a variety of dishes. It may also be used to flavor drinks or be fermented to produce vinegar or alcoholic beverages.

Propagation

Basic requirements
Cashew trees grow only in regions with consistently high temperatures, typically between 24 and 28°C (69.8–82.4°F). The trees cannot be grown in frost prone areas as they will be killed by the low temperatures. Cashew will grow optimally in deep, well draining soils with a pH between 4.2 and 8.7. The trees have the ability to grow in sandy soils where other fruit trees will not survive. In cooler areas, they can be grown in containers and moved indoors in winter to prevent damage to the plant.

Propagation
Trees are propagated from mature seeds which can be directly sown at the final planting site or planted in polyethylene bags to produce seedlings for transplanting. Only seeds that sink when floated in water should be selected for planting. Newly emerging seedling should be grown under approximately 45% shade in the nursery and hardened off in sunlight before final planting. As the seeds have a poor germination rate 2–3 seeds should be sown per planting hole and then thinned as necessary. Seedlings should be thinned to a final spacing of 10 m (33 ft) allowing a further 10 m (33 ft) between rows.

General care and maintenance
Young trees should be provided with supplemental irrigation to help them establish. Establishment of trees is slow but mature trees can survive dry periods as their extensive root systems can access moisture deep in the soil. The area around the trunk of the tree should be kept free from weeds to prevent competition for water and nutrients, particularly during establishment. Cashews require little pruning. Pruning is limited to the removal of limbs to facilitate movement of machinery in commercial plantations and is only practices on trees that are 6 years old or greater.

Harvesting
Young trees do not produce high yields of cashews and the yield increases as the trees mature.Do not attempt to break open the seed of the cashew nut immediately following harvestas the seed contains a toxic oil. This oil causes an itchy rash of the skin and painful blisters in the mouth if eaten. Instead, the nuts should be dried for several days and then roasted before being cracked open.

Diseases

Angular leaf spot FUNGUSSeptoria anacardii

SYMPTOMS

Angular cream colored lesions with dark-brown margins on leaves of seedlings; angular black lesions with chlorotic halos on mature trees; defoliated seedlings

COMMENTS

Some dwarf types of cashew are resistant to this disease; disease is widespread in cashew growing regions of Brazil

MANAGEMENT

Currently no control measures are used

Anthracnose FUNGUSColletotrichum gloeosporoides

SYMPTOMS

Water-soaked lesions on leaves, twigs, flowers or young apples which develop into orange-brown or red lesions;

COMMENTS

Disease emergence favored by rainfall and high humidity

MANAGEMENT

A protective coating of copper-based fungicide on susceptible parts of plant can prevent the disease; fungicide should be applied when buds begin to expand through to fruit set but are not required during dry periods

Black mould FUNGUSPilgeriella anacardii

SYMPTOMS

Chlorotic spots on upper surface of leaves which spread to lower surface as infection progresses; dark-brown to black fungal patches on leaves; leaves shrivelling and dropping from plant

COMMENTS

Damage most severe on dwarf cashew varieties

Cashew weevil INSECTMecicorynus loripes

SYMPTOMS

Brown-black gummy frass (insect excrement) on trunk and branches; girdling of branches; plants dying

COMMENTS

Adults large and gray-brown with knobbly appearance; larvae legless grubs which are white with a brown head

MANAGEMENT

Remove bark from infested areas and destroy any larvae or pupae found, this process should be repeated every month for up to six months; severely infested trees should be removed and destroyed; remove all adult weevils from tree prior to destruction and also remove bark and kill all larvae and pupae

Coconut bug INSECTPseudotheraptus wayi

SYMPTOMS

Necrotic lesions on fruit which develop into hard lumps; pockmarks of fruit; spotting on kernels

COMMENTS

Adults are red-brown in color; nymphs are red-brown to green in color

MANAGEMENT

Conserve natural enemies by avoiding unnecessary applications of insecticides

Helopeltis bugs INSECTSHelopeltis schoutedeni
Helopeltis anacardii

SYMPTOMS

Deformed leaves with angular lesions along veins; leaves may drop from plant; elongated green lesions on young shoots which may exude gummy substance; dieback of shoots

COMMENTS

Helopeltis bugs are slender with long legs and antennae; antennae twice as long as body; females are red; males brown; nymphs are yellowish in color

MANAGEMENT

Monitor crop regularly for signs of damage; conserve populations of natural enemies, weaver ants can reduce populations; avoid interplanting cashew with other crops which are hosts for helopeltis bugs such as tea and cotton

                       PLANTATION & IRRIGATION OF CASHEW

Fresh seeds germinate readily, so if you know of a cashew tree in your area, or have another way of getting hold of fresh seeds (that's the whole thing, shell and all, not just the nut!), you can grow cashew trees from seed. But be aware that cashew seeds don't grow true to type, meaning, the plant you get is not identical to the parent. (It may not fruit as much or taste as nice.)

Some fruit tree nurseries stock seedling or grafted trees. Commercial growers usually propagate their own. If you have a grower in the area you may be able to buy stock of him.

If you want to grow your cashew trees from seeds you can start them in pots or put them straight in the ground. Keep them moist and they should sprout within four or five days.

Best planting time? When you can get hold of fresh seed. The sooner you plant it, the better.

Select a well drained spot (cashew trees don't like wet feet or heavy clay soils), preferably a place that has some protection from strong winds.

Mature trees need about 10 metres distance between them, and they grow to 12 metres tall.

Water and Fertilizer

Cashews grow best in sandy soils, but sandy soils don't hold much water and are generally not very fertile. The trees will still do fine without additional attention.

However, if a good crop is important to you (read: if you want to grow them commercially) then you need to supply your cashew trees with additional water and fertilizer. Irrigate during dry periods, and fertilize the trees when they actively grow, as well as during flowering and nut development. (They will mainly need nitrogen and phosphorus, and possibly zinc.)

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MANAGEMENT PRACTICES OF COCONUT

Coconut

Cocos nucifera

Description

The coconut palm, Cocos nucifera, is an erect palm in the family Arecaceae which is grown its fruits, used primarily for the extraction of coconut oil for use in cooking. The coconut palm has an erect or slightly curved stem which grows from a swollen base. The stem is smooth, light gray in color and has prominent leaf scars. The stem is topped with a crown of 60–70 spirally arranged leaves. The leaves are long (up to 7 m/23 ft), pinnately divided and composed of 200–250 tapering leaflets. The inflorescence is a spike produced at the leaf axil with 20–60 branches, each with a female flower at the base and many male flowers. The fruit is a drupe containing a single seed. It is ovoid in shape with three sides divided by ridges. The exocarp and the mesocarp make up the husk of the coconut. The seed is protected by a thick, stony shell, or endocarp, and is partially filled with a liquid known as coconut water. The edible endosperm is white and meaty and can be between 1.0 and 2.5 cm (0.4–1.0 in) thick. Coconut palms can reach a height of 30 m (98 ft), produce up to 75 fruits a year, and live for up to 90 years. The origin of the coconut is unknown although the center of genetic diversity lies in Southeast Asia.

Coconut palms with coconuts

Close-up image of coconut palm leaf

Coconut palms can reach 30 m (98 ft)

Coconut inflorescence

Coconut seed cut open to reveal flesh

Coconut seedling

Coconut propagation

Coconut drupes

Harvested coconut drupes

Uses

Coconuts are primarily cultivated for their oil. The oil is extracted from the endosperm and is used in cooking. Low grade oils are used in the production of soaps. The endosperm can be consumed fresh or dry and is commonly grated for use in baking. Young coconuts, termed waternuts, are commonly sold in tropical resorts, where the liquid is drunk directly from the shell. Coconuts may also be used to produce coconut milk by squeezing the liquid from the grated endosperm. Coconut milk is popularly used in many dishes from Southeast Asia.

Propagation

Basic requirements
The coconut palm is a tropical plant and is generally grown in humid, tropical regions. It grows optimally in areas with an annual mean temperature of 27°C (80.6°F) with in excess of 2000 hours of sunlight per year. The palm will thrive in a wide range of soils from sand to clay as long as they are well draining and well aerated with a pH between 4.3 and 8.0. Although palms are often found growing on sandy beaches, they can be successfully grown inland but will not tolerate freezing temperatures. 

Propagation
Coconut palms are propagated exclusively from seed. The seeds are ready for planting when the coconut milk can be heard sloshing around inside the seed when it is shaken. Seeds are germinated by planting in seed beds before transferring to a polythene bag or nursery beds after germination. Seeds should be planted on their sides in a shallow hole with enough soil to cover about one third of the seed. The seed should be watered regularly to prevent it drying out. Germination usually occurs after about 3 months but may take up to 6 months. 

Transplanting
Coconut seedling can be transplanted from 6 months onwards or transferred to pots and grown further in the nursery. Trees require a wide spacing and are typically planted 8–9 m (26–30 ft) apart allowing a further 8–9 m (26–30 ft) between rows. Dwarf varieties can be spaced closer together and are typically planted 7.5 m (25 ft) apart allowing another 7.5 m (25 ft) between rows

Diseases

Bud rot and nutfall OOMYCETEPhytophthora spp.
Fusarium solani
Fusarium moniliforme
Graphium spp.

SYMPTOMS

Chlorosis of youngest open leaves; leaves rapidly turning necrotic; necrotic spots on leaf bases; unopened spear leaves can be pulled away from the plant easily; removal of unopened spear leaves reveals soft, pink-red tissue with foul smell; leaf necrosis spreading through central crown leaves; woody parts of plant may have water-soaked, pink lesions with dark borders; infected inflorescences abort nuts

COMMENTS

Palms between 14 and 40 years old most susceptible; disease occurs in all coconut growing regions; diseases emergence favored by high rainfall

MANAGEMENT

Control of the disease is reliant on good sanitation practices and the use of appropriate systemic fungicides; remove all infected debris and dead trees from plantation and destroy; irrigate trees early in the day to allow surfaces to dry off during the day

Cadang-cadang VIROIDCoconut cadang-cadang viroid (CCCVd)

SYMPTOMS

Newly formed nuts more rounded than in in previous years; nuts exhibit scarring on the surface; chlorotic spots on leaves; stunted inflorescences with tip necrosis; leaves begin to decline in size and number; death of palm

COMMENTS

No vector has been identified

MANAGEMENT

There is currently no known method of controlling the disease

Coconut bug INSECTPseudotheraptus wayi

SYMPTOMS

Damged and/or aborted flowersd; sunken necrotic lesions and scars on nuts; young nuts may exude gum (gummosis) and die; many nuts fall from tree; adult insect is a brown-red with well-developed wings; nymphs are brown-red or green in color with long antennae and feed at the calyx of the nut

COMMENTS

The coconut bug is one of the most damaging pests of coconut in Africa; just two bugs per palm can cause severe damage

MANAGEMENT

Natural enemies of the coconut bug include weaver ants, conserve bushes and trees around plantation which are habitats for weaver ants or intercrop with mango, guava or citrus which are attractive to weaver ants; connect canopy with ropes or sticks to allow weaver ants to move between trees

Coconut foliar decay VIRUSCoconut foliar decay virus (CFDV)

SYMPTOMS

Some varieties which have the disease may show no symptoms, others exhibit partial yellowing of leaves which begins to spread to leaf tip; necrosis of petioles causing leaves to die and hang from palm canopy

COMMENTS

Transmitted by leaf hoppers

Coconut rhinoceros beetle INSECTOryctes rhinoceros

SYMPTOMS

V-shaped cuts in palm fronds or holes in leaf midribs caused by beetles boring into crown to feed; adult insect is a large black beetle with a curved spine on its head; larvae are creamy white grubs with brown heads and 3 sets of prolegs at the anterior (head) end

COMMENTS

Beetles are nocturnal and fly at night; also a damaging pest of oil palm

MANAGEMENT

Destroy any decaying logs in plantation by chopping and burning to kill any larvae that may be inside; remove any dead trees from plantation and destroy by burning; plant a cover crop to deter egg laying by females as they do not lay eggs in areas covered by vegetation; hooked wire can be used to extract larvae that are boring into young crowns

Coconut scale INSECTAspidiotus destructor

Scale on coconut foliage

Coconut scale damage

Coconut scale damage

SYMPTOMS

Pale yellow spots on leaves; entire leaves yellowing; leaves turning brown and dropping prematurely; adult insect is a flattened oval, resembling a scale, which is red-brown in color

COMMENTS

Insect also attacks other crops such as tea and mango

MANAGEMENT

May be possible to control coconut scale by pruning infested parts of trees and destroying by burning; chemical control may be necessary

Ganoderma butt rot FUNGIGanoderma spp.

SYMPTOMS

Older fronds turning yellow and gradually wilting and drooping; fronds collapsing and dying; internal tissue of lower stem discolored; overall reduction in vigor

COMMENTS

Fungi may enter through wounds on trunk or pruning wounds

MANAGEMENT

Spacing trees widely limits the chance of infection through root grafts; avoid damaging tree trunks with tools and machinery; remove any dead or severely damaged trees from plantation immediately, including any that have been killed by natural processes; if a site is known to be infected with the disease, the ground should be fallowed for at least 1 year prior to a new plantation being established

Gray leaf blight FUNGUSPestalotiopsis palmarum

SYMPTOMS

Small, yellow-brown spots on leaflets which develop gray centers and dark green borders; lesions coalesce to form large necrotic patches; tips of leaflets turning gray; canopy has blighted appearance

COMMENTS

Fungi will colonize young, wounded or weakened tissues; disease emergence favored by high rainfall and high humidity

MANAGEMENT

Disease usually only merits control in coconut nurseries as infection of mature coconut palms are rare; appropriate broad spectrum protective fungicides should be applied

Lethal bole rot FUNGUSMarasmiellus cocophilus

SYMPTOMS

Oldest leaves of palm turning yellow and wilting; reddish-brown rot in bole tissue; destruction of root system

COMMENTS

Some grasses such as Bermuda grass have been reported as alternative hosts fro the fungi

MANAGEMENT

Any infected trees must be uprooted and burned; area can only be replanted once soil is treated for the disease

Lethal yellowing PHYTOPLASMALethal yellowing (LY) phytoplasma

Symptoms of lethal yellowing on coconut palm

Symptoms of lethal yellowing on coconut palm

SYMPTOMS

Premature dropping of fruit; fruit with brown-black water-soaked appearance; necrosis of inflorescences; flower stalks turn black; lower, older leaves turning yellow; entire crown turning yellow; yellow leaves turn brown, dry out and hang from canopy

COMMENTS

May be transmitted by leaf hoppers

MANAGEMENT

The most effective method of managing the disease is to plant resistant coconut varieties such as Malayan dwarf or Maypan; antibiotic treatment is effective but not usually practical for large scale plantings

Mealybugs (Pineapple mealybug, Striped mealybug, Cocoa mealybug, etc.) INSECTDysmicoccus brevipes
Ferrisia virgata
Planococcus lilacinus

Coconut mealybug damage

SYMPTOMS

Flattened oval to round disc-like insect covered in waxy substance on tree branches; insects attract ants which may also be present; insect colony may also be associated with growth of sooty mold due to fungal colonization of sugary honeydew excreted by the insect; symptoms of direct insect damage not well documented but trees may exhibit symptoms of cocoa swollen shoot (see disease entry)

COMMENTS

Insects have a wide host range; often tended by ants which farm them for their sugary honeydew secretions; transmit Cocoa swollen shoot virus

MANAGEMENT

Mealybugs can potentially be controlled by natural enemies such as lady beetles but are commonly controlled using chemicals; chemical pesticides may also decrease populations of natural enemies leading to mealybug outbreaks

Red ring nematode (Coconut palm nematode) NEMATODEBursaphelenchus cocophilus

SYMPTOMS

Nuts falling prematurely; withering inflorescences; yellowing leaves which then turn brown; orange to red-brown ring of discoloration when a cross section is taken of lower stem

COMMENTS

Nematode spread to palms via American palm weevils and sugarcane weevils

MANAGEMENT

If a tree becomes infected it should be removed and destroyed; control of the disease is currently limited to efforts to control the weevil which transmits the nematode to the palms

Stem bleeding disease FUNGUSChalara paradoxa

SYMPTOMS

Soft, yellow rot on trunk; affected areas are dark and turn black as they mature; a reddish-brown liquid may ooze from rotting regions and spill down trunk

COMMENTS

Fungi enter the trunk through wounds

MANAGEMENT

Avoid wounding palms with machinery and tools to reduce disease incidence; disease can be controlled with applications of the fungicide benomyl where registered; infected trees should be removed and destroyed as soon as possible

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MANAGEMENT PRACTICES OF ONION

Onion

Allium cepa

Description

Onion, Allium cepa, is an herbaceous biennial in the family Liliaceae grown for its edible bulb. The stem of the plant is a flattened disc at the base and the tubular leaves form a pseudostem where their sheaths overlap. The leaves are either erect or oblique and there are 3–8 per plant. The onion plant produces pink or white flowers clustered on stalks. The bulbs are formed just above the flattened stem of the plant by overlapping leaves. The bulb is made up of several layers, each corresponding to a leaf. They are are generally oval but shape can be variable and occur in clusters of 3–18 to a plant. The bulb is protected by a membrane which turns to a papery coat. Onion plants can reach a height of 50 cm (20 in) and are grown as annuals, harvested after one growing season. Onion may also be referred to by cultivar and these include red or purple onion, shallots and spring onions or scallions. The origin of the onion has not been conclusively determined although it is likely to be somewhere in South East Asia where the gene pool is most diverse.

Onion bulbs

Onion flower

Onion plants

Onion foliage

Onion bulb

Pink onion flowers

Uses

The bulb is an edible vegetable and is the most commonly used part of the onion, usually consumed after cooking although it can be eaten fresh. The stems and leaves are also edible.

Propagation

Requirements
Onions are hardy, cool season vegetables that grow best at temperatures of 12 to 24 °C (55–75 °F), growing particularly well in areas with cool spring weather and drier, hotter summer weather. They require a fertile, well-draining soil such as clay or silt loams with a pH of 5.5–6.5. The plants do not do well in acidic soils. Onions should be set out in full sun for optimum bulb development. Onions are biennial vegetables and if they are left in the ground for a second year, they will produce flowers and set seed. 

Seeds and transplants
In milder climates, onion seeds can be direct seeded as soon as the soil is workable in the Spring, 4–6 weeks before the last frost date, or even earlier if starting seeds indoors to produce transplants. The planting site should be cultivated deeply and be free of stones. Work some compost into the soil and ensure that soil has a soft crumbly texture before planting. Seeds should be sown 2.5 cm (1 in) deep allowing 10–13 cm between plants and 30–45 cm (12–18 in) between rows. Onion transplants which have been started indoors can be transplanted to the garden at a similar time to planting seeds. Transplants are best produced in cell trays by planting 2 seeds per cell. Once the seeds have germinated, the seedlings should be thinned to one plant per cell. Transplants are ready to be planted when the root system has developed sufficiently to bind the soil in the cell together. Transplants should be spaced 10–13 cm allowing 30–45 cm (12–18 in) between rows. 

Sets
Onion sets are small, immature onion bulbs which can be purchased from seed companies and garden centers for planting in place of seeds. Select the smaller sets for planting as they are less prone to bolting. Sets should be planted 2 cm (0.75 in) deep allowing 5–7.5 cm between sets and 25 cm (10 in) between rows.

General care
Onions should be watered thoroughly after planting and once every week thereafter, applying approximately 1 inch of water each time. Be careful not to allow the soil to become dry and cracked as onions have a shallow root system and this indicates a lack of water. Water adequately but do not overwater. Remove any weeds around young plants by hoeing shallowly so as not to damage the roots of the onions. Plants should be fertilized avery few weeks with a high nitrogen fertilizer.

Harvesting
When the soil at the base of the plants begins to crack, this indicates that the bulbing process has begun. Fertilizer applications should be stopped at this point. Avoid hilling the soil over the bulbs as onions mature best if they are on top of the soil. When the onion bulbs are mature, the leaves will begin to yellow and fall over. The tops can be bent right back to speed maturation. After a few days, the bulbs can be pulled and left on the soil surface to begin curing. Any damaged onions should be cooked and consumed right away as they will not store well. Onions should be cured for several weeks before storing. This can be done outdoors by placing them on a plastic sheet off of the ground, under cover if the weather is wet.

Growing green onions
Green onions, also known as scallions or Spring onions, are immature onions which are harvested before the bulbs mature. Seed can be purchased to grow onion varieties which are specifically bred to be harvested as green onions. Green onions, like regular bulbing onions can be started from seed or sets and can be grown as transplants indoors (see above). Green onions do not require the same amount of space that bulbing onions do and seed or transplants can be set out 2.5–3.8 cm (1.0–1.5 in) apart in the row. Allow 5 cm (2 in) between sets. The general care of green onions is the same as that for regular onions. They can be harvested when they reach 15 cm (6 in) in height or more. 

Transplants can be produced in cell trays

Transplanting onions from cell trays

Onion sets are small, immature onion bulbs

Diseases

Black mold FUNGUSAspergillus niger

Symptoms of black mold on onion bulb

Symptoms of black mold on onion bulb

Close up of black mold on onion scales

SYMPTOMS

Post-harvest black discoloration at neck; lesions on outer scales; black streaks under outer dry scales; entire surface of bulb turning black and shriveling

COMMENTS

Wash hands thoroughly after coming into contact with fungus

MANAGEMENT

Treat seeds with appropriate fungicide prior to planting to reduce rot in mature bulbs; avoid bruising bulbs during and after harvest; storing at temeperatures below 15°C (59°F) prevents mold from spreading but it will resume once temperature increases

Botrytis leaf blight FUNGUSBotrytis squamosa

Lesions on onion leaves caused by Botrytis leaf blight

Lesions on onion leaves caused by Botrytis leaf blight

Lesions on onion leaves caused by Botrytis leaf blight

SYMPTOMS

Small white lesions with light green halos which may expand slightly as they age; in prolonged periods of moisture fungus may develop rapidly and cause leaf blighting

COMMENTS

Disease emergence favors high humidity and warm temperatures; fungus survives on piles of crop debris or in soil; older leaves more susceptible to blighting than younger leaves

MANAGEMENT

Plant onions in single rows allowing at least 30 cm between plants to promote good air circulation and quick drying of foliage after rain; time irrigation to allow plants time to dry out sufficiently; apply appropriate fungicide sprays when plants have at least five true leaves and early symptoms of disease

Bulb mites ARACHNIDRhizoglyphus spp.
Tyrophagus spp.

SYMPTOMS

Stunted plant growth; reduced stand; bulbs rotting in ground or in storage; pest is a cream-white, bulbous mite

COMMENTS

Damage to plants by bulb mites allows secondary invasion by other pathogens and can cause bulb rots

MANAGEMENT

Do not plant successive crops of onion or garlic in same location; allow field to fallow to ensure that any residual organic matter decomposes completely - crop residues can harbor mite populations; treating garlic seed cloves with hot water prior to planting may help reduce mite populations

Downy mildew FUNGUSPeronospora destructor

Symptoms of downy mildew on onion leaves

Symptoms of downy mildew on onion leaves

Symptoms of downy mildew on onion leaves

Symptoms of downy mildew on onion leaves

Symptoms of downy mildew on onion leaves

SYMPTOMS

Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing

COMMENTS

Disease emergence favored by cool temperatures and leaf wetness

MANAGEMENT

Avoid planting infected sets; rotate crops to non-allium species for 3-4 years; plant in well-draining areas and do not overcrowd plants; destroy all infected crop debris; apply appropriate foliar fungicides taking care to apply thoroughly to waxy leaves

Fusarium basal plate rot FUNGUSFusarium oxysporum

cross section of onion bulb showing discoloration around ...

SYMPTOMS

Curving, yellow or necrotic leaves; necrosis begins at leaf tips and moves downward; wilting plants; infected bulbs may be brown and watery with rot spreading from stem plate to basal leaves; stem plates may have brown discoloration

COMMENTS

Disease emergence favors moderate to high temperatures

MANAGEMENT

Rotate with non-susceptible crops for at least 4 years, plant resistant onion varieties

Fusarium damping-off FUNGUSFusarium oxysporum

Onion plant showing wilt associated with Fusarium damping...

SYMPTOMS

Rotting seeds that are covered in mold; discolored root tips which may be pink, tan, yellow, red or black; slowly growing seedlings which wilt and die

COMMENTS

Fungus survives in soil and disease emergence is favored by moist to wet soil

MANAGEMENT

Plant only disease-free seed; treat seed with fungicide; rotate crops with cereals or grasses to reduce levels of pathogen in soil; steam treatment or fumigation of soil can help reduce levels of Fusarium in the soil

Leafminers INSECTSLyriomyza spp.

Leafminer trail on onion leaf

Leafminer damage to onion foliage

SYMPTOMS

Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larave hatch and feed on leaf interior

COMMENTS

Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year

MANAGEMENT

Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies

Leaf streak and bulb rot BACTERIUMPseudomonas viridiflava

Onion plant infected with bacterial leaf streak and bulb rot

Lesion on onion leaf caused by bacterial leaf streak and ...

Cross section of onion bulb infected with bacterial leaf ...

SYMPTOMS

Water-soaked, dark green oval lesions or streaks on leaves; tipburn of leaves; dark spots on wrapper scales of bulbs; reddish-brown discoloration of inner scales; rot developing in ring-like pattern

COMMENTS

Little is known about the pathogen; greatest damage occurs during winter; rapid spread of disease on infected plants is promoted by rainfall

MANAGEMENT

Avoid fertilizing plants during winter' apply appropriate bacteriacidial sprays

Onion maggot INSECTDelia antiqua

Onion maggot and bulb damage

SYMPTOMS

Stunted or wilting seedlings; plant will commonly break at soil line if an attempt is made to pull it up; if infestation occurs when plants are bulbing, bulbs will be deformed and susceptible to storage rots after harvest; adult insect is a greyish fly which lays white, elongate eggs around the base of the plant; the larvae that emerge from the eggs are tiny and white and bore into the onion plant; mature larvae are about 1 cm (0.4 in) long with feeding hooks

COMMENTS

Females can lay several hundred eggs during their 2-4 week lifespan; insect overwinters as pupae in the soil

MANAGEMENT

Management of onion maggots is heavily reliant on good sanitation; all onion bulbs should be removed at the end of the season as maggots will die without a food source; commercial onion growers must often rely on the application of appropriate granular insecticides and, in some cases, insecticide sprays are also required; home gardeners should try to remove any volunteer wild onion and chive plants as these can act as an infection source; floating row covers may provide protection by preventing females from laying eggs around the plants

Onion yellow dwarf VIRUSOnion yellow dwarf virus (OYDV)

SYMPTOMS

Yellow streaks on bases of of first leaves; all leaves which emerge after infection have yellow streak or are completely yellow; leaves may be flattened or crinkled; bulbs are undersized; flower stalks yellow and twisted; flower clusters small and seed is of poor quality

COMMENTS

Transmitted by several species of aphid, including the peach aphid; virus is not spread via seed or pollen

MANAGEMENT

Controlling aphids by applying insecticides is not effective due to the short amount of time aphid needs to transmit virus; other control methods include: planting sets or transplants which were produced in areas free of virus; growing plants from seed; removing any infected plants and planting more tolerant varieties

Pink root FUNGUSPhoma terrestris

Symptomatic onion roots

Pink root symptoms

Pink root symptoms

SYMPTOMS

Light pink roots which darken and turn purple; roots become transparent and water soaked; plant may look like it has a nutrient deficiency; infected seedling may die; stunted plants with undersized, shriveled bulbs

COMMENTS

Fungus colonizes plant through root tips; fungus can survive in soil down to a depth of 45 cm (17.7 in)

MANAGEMENT

Disease is most severe when onions are planted continuously or in a 1-year rotation, a rotation of 3-6 years is preferred; plant more resistant varieties; solarization and/or fumigation can help reduce the levels of pathogen in the soil

Purple blotch FUNGUSAlternaria porri

Symptoms of purple blotch on onion leaves

Purple blotch symptoms on neck of onion

Symptoms of purple blotch on onion leaves

Symptoms of purple blotch on onion leaves

Advanced symptoms of purple blotch in onion field

SYMPTOMS

Small water-soaked lesions lesions on leaves or stalk with white centers; which enlarge to become zonate and brown to purple in color with red or purple margin surrounded by yellow zone; large lesions may coalesce and girdle leaf, killing any tissue between the lesions and the leaf tip; severely infected foliage may die

COMMENTS

Disease emergence favored by wet foliage, with sporulation occuring during the night during periods of high humidity

MANAGEMENT

Cultural controls include long rotations with non-hosts and the reduction of leaf wetness by planting in well-draining soil and timing irrigation to allow plants to dry adequately during the day; some fungicides are effective at controlling the disease but should be rotated for optimal control

Pythium seed rot (Damping-off) FUNGUSPythium irregulare

Damping-off of onion seedlings caused by Pythium infestation

SYMPTOMS

Seeds water-soaked, mushy and decomposing; infected roots are gray and water-soaked; seedlings that have already emerged prior to infection collapse and die; older plants that become infected become severely stunted

COMMENTS

Disease emergence favors high soil moisture and cool temperatures

MANAGEMENT

Control of disease is dependent on minimizing soil moisture: break up compacted soil; plant in well-draining areas or raised beds; treat seeds with appropriate fungicides prior to planting

Rust FUNGUSPuccinia porri

Orange rust pustules on onion leaves

Rust symptoms on onion leaves

Close-up image of rust pustule on onion leaf

SYMPTOMS

Small white flecks on leaves and stems which develop into circular or elongated orange pustules; severe infestations can cause leaves to yellow and die

COMMENTS

Favors high humidity but low rainfall; spores can be transported over long distances by wind

MANAGEMENT

No resistance known; use only disease-free seed and plant in well-draining soil; control weeds around crop; apply appropriate protective fungicide

Smut FUNGUSUrocystis colchici

Onion plants showing symptoms of smut

Stunted onion plants infected with smut

SYMPTOMS

Dark, thickened lareas on cotyledons (seed leaves) which may become large and cause leaves to bend downwards; raised blisters may be present on the base of scales in older plants; lesion mature and become covered in black powdery fungal masses; plant growth stunted; death of plant occurs within 3-4 weeks

COMMENTS

Smut can persist in soil for many years and is mainly introduced through infected sets and transplants; spores can be spread by wind, on equipment or in irrigation water

MANAGEMENT

No resistance to disease known in onion; plant onions during periods which promote rapid growth; plant only health sets and transplants - if smut is present in the soil they will not become infected

Thrips (Onion thrips, Western flower thrips) INSECTThrips tabaci
Frankliniella occidentalis

Onion thrips nymphs feeding on onion leaves

SYMPTOMS

Discolored, distorted tissue; scarring of leaves; severly infected plants may have a silvery appearance

COMMENTS

Thrips are most damaging when they feed on onions at the early bulbing stage of development; both onion thrips and western flower thrips have an extensive host range and can be introduced to onion from other plants

MANAGEMENT

Natural enemies include some species of predatory mite, pirate bugs and lacewings; avoid planting onion in close proximity to grain fields as thrips populations build up on these plant in the spring; overhead irrigation of plants may help reduce thrips numbers; apply appropriate insecticides at first sign of thrips damage

White rot FUNGUSSclerotium cepivorum

SYMPTOMS

Older leaves yellowing; stunted growth; death of all leaves; fluffy white growth on base of bulb which spreads up bulb to storage leaves

COMMENTS

Fungus can survive in soil for 20 years and is one of the most damaging diseases of Allium crops worldwide, causing major crop losses

MANAGEMENT

Fungicide treatment may not be effective at controlling white rot under conditions which are favorable to the fungi's development and control may have to rely on cultural methods: avoid transferring soil or plant material between sites; treat seeds with hot water prior to planting; use a long term rotation with non-allium crops; apply appropriate fungicides if available

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