cole crops.pptx

8/22/2019 cole crops.pptx

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Pests and nutritional

disorders of colecrops


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AlternariaLeafspot

SYMPTOMS AND SIGNSThe two Alternaria species, A. brassicae and A. brassicicola, causesimilar symptoms;small, dark specks first develop on leaves and laterenlarge into circular, tan spots (0.25-0.5 inch in diameter). The spotscaused by A. brassicicola tend to be darker than those caused by A.brassicae. If conditions are favorable, dark green spores of the

pathogen will grow on the spots. Such growth causes the spots to haveconcentric rings in them. Old leafspots become papery in texture andmay tear. When the dry tissue falls out, a shothole effect results.


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Bacterial LeafspotPathogen: Pseudomonas

syringae

SYMPTOMS AND SIGNSBacterial leafspot infections start as small, dark specks on leaves. Asdisease develops, numerous water-soaked leafspots appear. Leafspotsremain small (0.125 inch or 3 mm in diameter). Older leafspots turn tanand may or may not have a purple border around them. Leafspots arevisible from both top and bottom sides of leaves. Symptoms on transplantsmay resemble downy mildew symptoms.


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Black LegPathogen: Phoma

lingam

SYMPTOMS AND SIGNS

The most serious symptoms occur on stems near the soil line whereelongated, sunken, brown lesions form. These lesions may girdle thestem, resulting in stunting, wilting, and general poor growth of theplant. If the lesions enlarge, the stem may break, causing the plant tofall over. Lesions usually contain minute, spherical, dark structuresthat are the fruiting bodies of the pathogen. If conditions are right,

pink masses of spores exude from these structures. If seedlings areinfected early, they may die. Less important are the leafspots thatmay develop on foliage. Leafspots are circular, light tan, and containthe dark, spherical fruiting bodies of the pathogen. The diseasedamages the water-conducting tissue, andblackened streaks of xylem can be seen by cutting open the stem.
http://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-FO.003.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-FU.003.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-BT.001.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-BT.001.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-FU.003.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PLIN-FO.003.html


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Black Rothogen:Xanthomonas campestris

SYMPTOMS AND SIGNS

Black rot symptoms vary depending on the environmental conditions.Early in disease development, typical symptoms consist of angular or V-shaped chlorotic lesions along the leaf edges. With time these lesionswill dry up and turn tan or brown. Black veins are often seen withinthese tan lesions, though they may not always develop. Severelyinfected leaves may wither and drop off the plant. If systemic infection

has taken place, the vascular tissues in petioles and main stems canalso turn black. If temperatures are cool, however, symptoms may notbe expressed. Atypical symptoms, such as small, brown specks, mayalso occur and mimic other bacterial diseases.
http://www.ipm.ucdavis.edu/PMG/X/D-CC-XCAM-FO.020.htmlhttp://www.ipm.ucdavis.edu/PMG/X/D-CC-XCAM-FO.020.html


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ClubrootPathogen: Plasmodiophora

brassicae

SYMPTOMS AND SIGNSDuring initial stages of clubroot, aboveground symptoms may beabsent. When present, foliar symptoms consist of stunting,yellowing, wilting, and other signs of a dysfunctional root system.Extensive galling, swelling, and distortion of the roots and hypocotylare the main symptoms of the disease. Galled and clubbed roots areoften invaded by secondary rot organisms such as soft rot bacteria;this results in the rapid decay of roots, further decline of infected

plants, and release of additional inoculum into the soil.
http://www.ipm.ucdavis.edu/PMG/P/D-CC-PBRA-FS.006.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PBRA-RO.008.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PBRA-RO.008.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PBRA-FS.006.html


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Downy MildewPathogen: Peronospora

parasitica

SYMPTOMS AND SIGNSInfections begin as irregular yellow patches on leaves; thesechlorotic lesions later turn tan to light brown. If conditions are

favorable, white fluffy growth of the fungus develops on theundersides of leaves. If disease development is extensive, leavesmay take on a blighted effect as a result of numerous infection sites.Systemic infections can cause internal black streaks and patches toform in stems and floret branches of broccoli and cauliflower. Earlysymptoms on transplants may resemble bacterial leafspotsymptoms. Severely diseased seedlings may be stunted or die.
http://www.ipm.ucdavis.edu/PMG/P/D-CC-PPAR-FO.009.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PPAR-BL.001.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PPAR-BL.001.htmlhttp://www.ipm.ucdavis.edu/PMG/P/D-CC-PPAR-FO.009.html


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Fusarium YellowsPathogen: Fusarium

oxysporum

SYMPTOMS AND SIGNSIn California this pathogen affects primarily cabbage. Symptomsconsist of yellowing of the lower leaves, often on one side of theplant. These leaves later turn brown and drop off. A browndiscoloration of the water-conducting tissues (xylem) is characteristicof this disease. With time the entire plant may yellow, wilt, andcollapse.


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Phytophthora Root RotPathogen: Phytophthora

megasperma

SYMPTOMS AND SIGNSThe external surfaces and internal tissues of

infected roots are water-soaked and dark in colorand are rotted. Leaves, especially older ones, firstturn purple-red and later yellow and then wilt. Theplant may be stunted, and with time, the entireplant wilts. The stem near the soil line may turnblack and become soft


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Rhizoctonia DiseasesPathogen: Rhizoctonia

solani

SYMPTOMS AND SIGNS

On cole crops, Rhizoctonia causes two types ofdisease symptoms: damping off (or wirestem)and bottom rot.


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RingspotPathogen: Mycosphaerella

brassicicola

SYMPTOMS AND SIGNSIn California, this disease occurs primarily on Brusselssprouts. Symptoms consist of circular leafspots (0.5 inch indiameter) that range in color from light brown to black.With time these spots develop concentric rings much like atarget pattern. Small spherical fruiting structures may alsobe observed within the leafspots. If disease is severe,some defoliation may take place. This pathogen may also

infect the sprouts, causing dark lesions on outer leaves.
http://www.ipm.ucdavis.edu/PMG/M/D-CC-MBRA-FU.003.htmlhttp://www.ipm.ucdavis.edu/PMG/M/D-CC-MBRA-FU.003.html


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Sclerotinia Diseases

Pathogens: Sclerotiniasclerotiorum, S. minor

SYMPTOMS AND SIGNSTwo species ofSclerotinia cause disease on cole crops.Sclerotinia minoronly infects stems or leaves in close contactwith the soil. Once infection takes place, water-soaked, brownnecrotic areas develop on these structures. The necrotic areasrapidly turn into soft, watery rots. Plants then wilt and collapse.Profuse amounts of white mycelial growth and numerous small(up to 0.125 inch or 3 mm), black, hard resting bodies calledsclerotia, form on the outside and inside of the stems. Sclerotiniasclerotiorum can also infect lower leaves and stems, causing thesame type of symptoms as S. minor. In addition, S. sclerotiorumforms tiny, brown, mushroomlike bodies (apothecia) that releaseaerial spores, which can infect any of the upper leaves and

flowers. If conditions are right, these spores cause a watery, softrot of these tissues as well. Sclerotinia sclerotiorum forms


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Verticillium WiltPathogen: Verticillium

dahliae

SYMPTOMS AND SIGNSThe older, lower leaves of plants turn yellow and wilt. Theseleaves eventually turn brown and drop off the stem, usuallywhen plants approach maturity. The water-conducting tissues(xylem) of the stems and roots become black. Overall growth

of the plant may be stunted.
http://www.ipm.ucdavis.edu/PMG/V/D-CC-VDAH-FO.001.htmlhttp://www.ipm.ucdavis.edu/PMG/V/D-CC-VDAH-FO.001.html


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White RustPathogen:Albugo

candida

SYMPTOMS AND SIGNSThe fungus infects leaves and floral parts, causingdistinctive white, raised pustules to form underneath theplant epidermis. These blisterlike pustules sometimes resultin twisted, deformed growth of the stem, leaves, or flowers.When mature, the epidermis covering the pustule willrupture, releasing powdery white sporangia (a type ofspore) that can be carried by winds or splashing water ontoneighboring host plants. Severely infected leaves canwither and die.


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White SpotPathogen: Pseudocercosporella

capsellae

SYMPTOMS AND SIGNSThis fungus causes circular, light tan leafspots that are up to 0.5 inchin diameter. Sometimes dark streaks and splotches develop in thespots. If conditions are favorable, the characteristic white growth ofspores may be observed on the leafspots


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Beet ArmywormScientific Name: Spodoptera

exigua

DAMAGEBeet armyworms candestroy seedlings, consume

large portions of leaves, orstunt growth by feeding onbuds. However, seriouseconomic damage to colecrops is uncommon


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Cabbage AphidScientific Name: Brevicoryne

brassicae

DAMAGECabbage aphids do not normally affect seedlings but build up afterthinning or transplanting. Large colonies can stunt or kill small plants,but the most serious problem is contamination of the harvested crop.Dense populations cause leaves to curl around them, making themharder to reach with pesticide applications.
http://www.ipm.ucdavis.edu/PMG/B/I-HO-BBRA-CD.009.htmlhttp://www.ipm.ucdavis.edu/PMG/B/I-HO-BBRA-CD.009.html


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Cabbage LooperScientific Name:Trichoplusia ni

DAMAGEAlthough seedlings are occasionally damaged, most injury occurs afterheading. Loopers eat ragged holes into leaves, bore through heads andcontaminate heads and leaves with their bodies and frass. Young plantsbetween seedling stage and heading can tolerate substantial leaf damagewithout loss of yield.
http://www.ipm.ucdavis.edu/PMG/T/I-LP-TRNI-CD.012.htmlhttp://www.ipm.ucdavis.edu/PMG/T/I-LP-TRNI-LV.042.htmlhttp://www.ipm.ucdavis.edu/PMG/T/I-LP-TRNI-LV.042.htmlhttp://www.ipm.ucdavis.edu/PMG/T/I-LP-TRNI-CD.012.html


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CutwormsScientific Names:Agrotis

ipsilon

DAMAGESeedlings or young plants are cut off at or just below ground level;often several plants in a row will be wilted or cut off. Losses can beespecially severe in fields seeded to a stand or recently thinned.Occasionally cutworms will bore into cabbage heads, but this is notcommon. Damage often recurs in the same fields and same parts offields from year to year; damage is worst where large numbers of


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Diamondback MothScientific Name: Plutella

xylostella

DAMAGEDiamondback moth infestations aremost serious when they damage the

crowns or growing points of youngplants or Brussels sprouts. This injurycan severely stunt growth.Sometimes diamondback mothcaterpillars may also bore into headsof broccoli or cauliflower, or in the

flower buds of stalks, causingeconomic injury and contamination.Injury to leaves is not usually serious,except when the wrapper or capleaves of cabbage are injured.


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Leafminers

Scientific Name:Liriomyza spp.

DAMAGE

Leafminers can reduce the plant's photosynthetic capacity,render edible leaf portions unmarketable, and provide anentrance for pathogenic organisms.


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Secondary and micro-nutrients

Calcium (Ca)Cole crops have a high calcium requirement. Deficiencies may occuron acid soils, on soils with very high potassium, or on very dry soilswhere calcium uptake is reduced. Deficiencies cause a conditionknown as tip-burn, where the tips and margins of leaves becomepaler and paper thin, and eventually die back. Tip-burn is thus much

more of a problem with cabbages and Brussels sprouts, because itcan affect the edible part of the plant. Most deficiencies occur wherethe absorption and translocation of calcium within the plant arereduced by environmental factors. Drought and high temperatureconditions favourthe occurrence of tip-burn and it is thus often more prevalent insummer crops than in those grown over winter. The use of calciumnitrate, or similar materials, as foliar sprays, can alleviate thecondition.Magnesium (Mg)Magnesium deficiencies occur mainly on acid soils, on very light soilssubject to leaching or on soils with a very high potassium level. Itmay be corrected by spraying with 5 kg/ha of magnesium sulphate.

Nutritional requirements


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Molybdenum (Mo)Cole crops are very susceptible to a molybdenum deficiency, with caulifloweraccepted as being a very good indicator plant for such deficiencies. Inseedbeds the first indication of a deficiency is a yellowing of the foliage,similar to that of a nitrogen deficiency. Young developing leaves becomedistorted, particularly in cauliflowers, showing the so-called "whiptail"symptoms; the mid-rib of the leaf develops normally, but the leaf blade does

not fill out properly resulting in narrow, distorted leaves. The curds tend tobe small, open and loose. Leaf symptoms on other cole crops are much lessobvious than on cauliflowers. Spray the plants with sodium- or ammonium-molybdate at the very first signs of deficiency, at the rate of 125 g in 500 lwater per hectare. Should the deficiency be severe, a follow-up spray using60 g of the chemical may be applied. Malformed leaves will not recover, butsubsequent growth should be normal. Do not over-supply molybdenum as itcan harm the plants. Molybdenum may also reach toxic levels in humantissues, but the levels of the element derived from consumption of thesevegetables is less than from other sources. Routine spraying may benecessary in areas where molybdenum deficiency occurs. Adequate liming ofacid soils before planting will increase the availability of molybdenum.


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Boron (B)Soils in the high-rainfall areas of KZN are often low in available boron,and deficiencies may be expected on such soils. Should deficiencies beknown to occur, cole crops, especially cauliflower, will respond well tofoliar sprays of, for example, Solubor. Usually 3 kg will correct suchdeficiencies. Where any bean crop is included in the rotation, ratherunder- than overapply boron, because high rates of boron can be verytoxic to these crops (toxicity symptoms may be manifested in beanswhen soil boron levels are above 5 ppm). A deficiency is characterised byan internal discolouration and cracking of the stem at the base of the

head. A roughness, almost a cork-like appearance, on the lower surfaceof the mid-rib of the leaves, also occurs. Deficiency causes a browning ofcauliflower curds. Internal cracking of the stem of broccoli, without anydiscolouration, is common when the plants grow rapidly, especially atlower plant populations. This symptom should not be confused with aboron deficiency, which causes an internal discolouration.Manganese (Mn)

Soil manganese is most available to plants on acid soils and may evenreach toxic levels on very acid soils. Deficiencies of this element areencountered only on soils with a pH (KCI) of over 5.5. The deficiency maybe corrected by a foliar spray of 5 kg/ha of manganese sulphate, or 2 to 3kg/ha of manganese oxide, as soon as the deficiency is observed. Thedeficiency initially causes yellowish mottled areas to develop between

the veins of the younger leaves. This finally results in an overall paleappearance. Toxicity levels of manganese and aluminium can be reached


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Iron (Fe)Deficiencies only occur on calcareous, alkaline soils with a pH(KCl) of over 7,0. Symptoms are very similar to those caused bymanganese, and also occur first on the younger leaves.Yellowing is normally more intense than is the case with amanganese deficiency. A foliar spray with 1% iron sulphate orchelate should overcome the problem

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