Canola (Rapeseed) and Mustard

Stem and Leaf Diseases � Fungal

SCLEROTINIA STEM ROT, Sclerotinia sclerotiorum

Symptoms. Infections usually begin on the dead blossoms and spread out from them. The stems develop water-soaked spots which later may be covered with a cottony white growth. As the disease progresses, affected portions of the stem develop a bleached appearance, and eventually the tissues shred. Girdling of the stem results in premature ripening and in lodging of plants. Hard black bodies, the sclerotia, are formed inside the stem and occasionally on the stem surface. Basal stalk infections rarely occur. Yield loss of 10 to15% has occurred in Saskatchewan, Manitoba and North Dakota; occasionally losses of 50% have occurred in Manitoba.
Survival and Spread. See description under Dry Edible Beans -- White Mold.
Other Crops Affected. See description under Dry Edible Beans -- White Mold.
Control. Plow down infected crop refuse in the spring. Use crop rotation; do not plant highly susceptible crops more than once in four years, including dry edible beans, sunflowers, mustard and canola. Use at least a five year rotation for severely infested fields. Avoid planting next to a field that had severe Sclerotinia in the past four or five years. Control broad-leaved weeds. Plant thoroughly cleaned seed. Avoid dense stands of canola.

ALTERNARIA BLACK SPOT, Alternaria brassicae and A. raphani

Symptoms. The first symptoms are grayish leaf spots surrounded by a yellow halo. A few weeks before maturity, circular black spots develop on leaves and pod. Seeds may be infected. The black spots may develop a target pattern of concentric rings. Severe black spot infections on pods contribute to shattering.
Survival and Spread. Survives in the soil, on infected crop residue, in the seed, and on weed hosts (eg. wild mustard). Disease development is favored by relative humidities above 80% and wind dispersal of spores.
Control. Crop rotation helps reduce disease carryover but does not eliminate airborne spores from another field. Clean seed to remove shrunken seed that may be infected with black spot and have low viability. Use seed with high germination (over 90%). Swath badly infected crops early to minimize shattering losses and seed shrinkage due to black spot.

WHITE RUST, Albugo candida

Symptoms. White to creamy yellow pustules develop on the lower leaf surface. The pustules, about 1/16 inch in diameter, later coalesce to form patches on the lower leaf surface. Tan-yellow spots develop on the upper leaf surface opposite the pustules. Pustules may also form on the pods. Infected flowers develop a "staghead" in which the flowers are sterile, malformed and green, and various flower parts may be thick and club-shaped and greatly enlarged. Most turnip or Polish varieties of canola as well as brown and oriental mustard are susceptible. Yield losses are about 1% for each 1% of staghead observed in a field. Yield losses in Manitoba are usually less than 10%.
Survival and Spread. Survives on crop refuse and on seed. Favored by rains and cool temperatures, especially at flowering.
Control. Argentine varieties are resistant. If growing Polish type canola, select resistant varieties. See current variety recommendations for information on susceptibility. Use at least a three year crop rotation. Control volunteer canola and susceptible mustard-type weeds in the rotation.

BLACKLEG, Leptosphaeria maculans

Symptoms. A virulent strain produces round to irregular spots on cotyledons and leaves. The spots are white to gray with numerous black fruiting bodies. Basal stem cankers form that are white to gray, sunken, and covered with black fruiting bodies. Spots on leaves and stems may be surrounded by a purple border. Canker development leads to premature ripening and lodging of infected plants. Flowers may be blighted. Pods may develop spots and seeds may be infected and shriveled. Symptoms of the mild strain are similar except that stem cankers are only superficial and very few black fruiting bodies form.
Survival and Spread. Overwinters in infected crop stubble and is seed-borne. Initial spread is from airborne spores; secondary spread is by splash-dispersed spores and is favored by 70°F. Stem canker development is favored by 75°F day temperatures and 60°F night temperatures. Phenoxy herbicides may increase plant susceptibility to black leg. Also survives on wild mustard.
Control. Plow down infected crop residue. Use a four year crop rotation. Avoid planting next to a field that had blackleg in the past two years. Plant varieties that have some resistance to blackleg; many Argentine varieties are moderately susceptible and some are moderately resistant. Polish varieties are highly susceptible. See current variety recommendations for information on variety susceptibility.

DOWNY MILDEW, Peronospora parasitica

Symptoms. Leaf spots initially are angular, translucent, light green, later developing into grayish-white irregular necrotic (dead) patches. The stems of flower clusters become swollen. Frequently associated with white rust. May develop late in the season on turnip-type (Polish) canola varieties.
Survival and Spread. Survives as spores in infected crop residue and on susceptible weeds (eg. wild mustard). The downy mildew fungus is spread by wind-borne spores. Disease development is favored by long periods of dew, damp and cool weather, and by low light intensity.
Control. Destroy crop refuse; crop rotation.

Pod and Seed Diseases � Mycoplasmal

ASTER YELLOWS, Aster yellows mycoplasm

Symptoms. Flowers of infected plants are swollen, distorted and sterile. Seed pods that are formed are small, green and bladderlike. Levels of infection rarely exceed 1% of the plants in a field.
Survival and Spread. The aster yellows mycoplasm is spread by the aster leafhopper, which blows in each year from overwintering areas farther south. Neither the aster leafhopper nor the aster yellows mycoplasm overwinters in North Dakota.
Control. No practical means is available.

Root Diseases � Fungal

BROWN GIRDLING ROOT ROT, cause undetermined

Symptoms. Infected plants ripen prematurely. A grayish brown dead area can be found at the base of affected plants or on the tap root.
Survival and Spread. Soil-borne.
Control. Crop rotation. Control wild mustard and related weeds.

Sunflower

Stem and Leaf Diseases � Fungal

DOWNY MILDEW, Plasmopara halstedii

Symptoms. Pre- and postemergence damping off occurs on seedlings. Leaves show yellowing at the base of the upper surface and along the main veins; on the lower surface a downy white growth of fungus spores develops along main veins during humid weather. The plant is stunted, with shortened internodes. Few plants produce flowers; heads are malformed. Roots are swollen and stubby.
Survival and Spread. Soil-borne; fungus survives 14 years in soil. Plants are infected if infested soil is water saturated at or shortly after seedling emergence. Most severe in low spots in field. Fungus can be carried by runoff water and spores can also be wind-borne.
Control. No hybrid is resistant to all of the new downy mildew races that have appeared since 1980. Seed treatment with metalaxyl fungicide provides excellent control.

RUST, Puccinia helianthi

Symptoms. Cinnamon-colored pustules develop on leaves, primarily on the lower surface, with round yellow areas surrounding the pustules. Pustules may also occur on bracts, petioles, and stalks if disease is severe. Pustules turn black late in the season when winter spores form.
Survival and Spread. Overwinters on infected sunflower crop residue. Spreads by wind-borne spores.
Control. Control volunteers. Resistance varies, but no hybrid is resistant to all known races.

SCLEROTINIA STALK AND HEAD ROT (WHITE MOLD) Sclerotinia sclerotiorum

Symptoms. The entire plant wilts suddenly. Often occurs in patches in the field. A brown soft rot develops on the stalk, usually at the base but occasionally on the upper stalk. Later, the brown area develops a bleached appearance. In wet weather a cottony white growth develops on the rotting stalk; later, tufts of cottony growth develop into hard black fungus bodies called sclerotia. Sclerotia also form inside the stalk. Roots may be stubby, brownish colored, and with cottony white growths on the surface. Later, sclerotia form on the surface and in the center of the taproot. Head infection, which comes from wind-blown spores, is less common than stalk infection. White cottony growths form on the head, the tissues are shredded and brown, and large black sclerotia form in the back (receptacle) of the head. Later, the heads develop a bleached appearance. Head rot and upper stalk rot occur in long periods of wet weather.
Survival and Spread. Soil-borne as sclerotia, which survive five or six years in the soil. Can be borne as sclerotia mixed with seed. In wet weather, sclerotia in the soil produce tiny mushroom-like bodies called apothecia that release millions of airborne spores. The fungus may be introduced into previously clean fields in years when head rot is severe. These spores infect the heads or upper stalk if plants remain wet for 42 consecutive hours. The result is middle stalk rot and head rot. Favored by sandy soils and center pivot irrigation. Basal stalk infection occurs when roots come in contact with sclerotia in the soil. Basal stalk rot is more common than middle stalk or head infection from airborne spores.
Other Crops Affected. Dry edible beans, mustard, and canola (rapeseed) are very susceptible. Other susceptible crops include field peas, garbanzo beans (chickpeas), lentils, safflower and soybeans. Potatoes are infected occasionally. Flax and buckwheat are only rarely attacked. Many broad-leaved weeds also are susceptible.
Control. Plow down infected crop refuse in the spring. Use crop rotation; do not plant highly susceptible crops more than once in four years, including dry edible beans, mustard, canola (rapeseed) and sunflowers. Use at least a five year rotation for severely infested fields. Avoid high plant populations. Avoid planting next to a field known to have had white mold. Control broad-leaved weeds.

VERTICILLIUM WILT, Verticillium dahliae

Symptoms. Plants show a general wilting, which often develops about flowering time. Leaves show a mottled pattern, with yellow between the veins; the yellow tissue turns brown with a yellow margin; the main veins are green. A cross section of the stem shows brown vascular bundles.
Survival and Spread. Soil-borne. Remains for several years in infected crop refuse and broad-leaved weeds.
Other Crops Affected. Potatoes, sugarbeets, many garden vegetables.
Control. Many oilseed hybrids are tolerant. Non-oilseed hybrids are not tolerant and require crop rotation: do not plant until refuse of a susceptible crop is completely rotted. Do not rotate with potatoes.

PHOMA BLACK STEM, Phoma macdonaldii

Symptoms. Large black elliptical spots develop on the stem. These spots have a definite margin. When spots are numerous, the stalks become hollow and weakened and lodging may result. Soon after a spot begins to develop, the base of the petiole dies and the leaf hangs dead on the stem; Phoma spots at the axils of most leaves can result in a wilted appearance of the entire plant. Dark brown spots may also develop on the back of the head; a target pattern of black fungus fruiting bodies forms in these spots. A black area may develop at or below the soil line and girdle the plant. This is called Phoma girdling and is a common cause of early dying.
Survival and Spread. Survives in crop refuse. A few seeds may be infected. Spread is by rain-splashed spores and stem weevils.
Control. Crop rotation and stem weevil control may help.

PHOMOPSIS STEM CANKER, Phomopsis (= Diaporthe) helianthi

Symptoms. A large light brown stem lesion forms on the area surrounding the point of attachment of the leaf to the stem. Phomopsis resembles a "brown Phoma," but the lesion is much larger (up to 6 inches) and light brown instead of black. The stalk pith may be severely rotted. The disease frequently starts with infection of the lower leaves. Infection starts at the leaf margin, and a brown lesion spreads down one or more leaf veins towards the petiole and eventually to the stem. Foliar symptoms may be confused with Verticillium, but Phomopsis produces less chlorosis, and in Verticillium the leaf lesions are delimited by veins.
Survival and Spread. The fungus overwinters in sunflower crop refuse above the soil surface. The disease is most severe under conditions of prolonged high temperatures and high humidity.
Control. The disease can be reduced by thorough discing in the fall to bury crop residue, and by crop rotation.

ALTERNARIA LEAF AND STEM SPOT, Alternaria zinniae and Alternaria helianthi

Symptoms. Circular to angular spots develop on the leaves. The spots are uniformly dark and often associated with the main veins. Dark-colored elliptical spots, streaks, flecks, or diamond-shaped spots without a definite margin may occur on the stem or leaf petiole. Dark circular spots may also occur on the back of the head. Seedling blight may occur if seedlings emerge in rainy weather in a field with infected crop residue.
Survival and Spread. Survives on infected crop residue. Spread is by airborne spores. Favored by wet weather and warm temperatures.
Other Crops Affected. Safflower and cocklebur.
Control. Crop rotation and burial of infected crop residue. Avoid planting into field with infested sunflower stubble.

SEPTORIA LEAF SPOT, Septoria helianthi

Symptoms. Watersoaked spots develop on the leaves. These spots are roughly circular and develop gray to tan centers with dark brown margins surrounded by an area of yellow. Spots may merge, producing irregular dead areas on the leaves.
Survival and Spread. Survives on infected sunflower crop refuse. Spread is by water-splashed spores and is favored by rainy weather or center pivot-irrigation.
Control. Crop rotation and burying crop refuse.

Stem and Leaf Diseases � Bacterial

APICAL CHLOROSIS, Pseudomonas tagetis

Symptoms. Severe yellowing develops on the uppermost leaves of sunflower plants. Part or most of the leaf may be yellowed. This condition may develop anytime from emergence until the flower buds appear. Affected plants usually recover, but seedlings may be killed.
Survival and Spread. Seed-borne.
Control. Unknown, but at present the disease is not severe enough to require control.

Head Diseases � Fungal

RHIZOPUS HEAD ROT, Rhizopus spp.

Symptoms. The head develops a soft, mushy brown rot. In severe cases, shredding may occur, but no sclerotia form in the head. When the head is broken open, very tiny black fruiting bodies, much smaller than the head of a pin, and threadlike fungus strands can be seen with a hand lens or magnifying glass. Occasionally Rhizopus will develop when heads are only a few inches in diameter and cause the head to droop or fall off as if the neck had been cut. This symptom can be confused with head clipper damage.
Survival and Spread. Rhizopus spp. are present everywhere and can attack whenever warm moist weather occurs. It may enter head tissue wounded by birds or hail. It is also associated with sunflower moth or midge injury.
Control. Unknown, but reducing bird and insect damage to heads may help reduce Rhizopus head rot.

BOTRYTIS HEAD ROT, Botrytis cinerea

Symptoms. A soft brown rot develops at the bracts or the center of the head and may spread to involve the entire head. In wet weather the brown tissues develop a velvety gray-brown surface.
Survival and Spread. The fungus is present everywhere and only needs cool, wet conditions to develop.
Control. Unknown, but currently not a severe disease.

SCLEROTINIA STALK AND HEAD ROT (WHITE MOLD), Sclerotinia sclerotiorum

See description under Sunflower -- Stem and Leaf Diseases.

Flax

Stem and Leaf Diseases � Fungal

WILT, Fusarium oxysporum f. sp. lini

Symptoms. Leaves turn yellow and drop. Branches are affected first, then the entire plant. Branch tips are often curled. Seedling blight may occur at high temperatures. Plants can be killed at any stage.
Survival and Spread. Primarily a soil-borne disease. Survives many years in the soil. Wilt favored by high soil temperature and low moisture.
Control. Use crop rotations. Avoid moderately susceptible varieties on wilt-infested land. Resistant varieties are available. Consult current variety recommendations for variety susceptibility.

ANTRHACNOSE, Colletotrichum lini

Symptoms. Seedlings often affected: lesions appear on cotyledons when plants are 1 to 2 inches tall. Seedling blight often occurs, and stands are reduced. Red-brown zonate stem cankers may form at the soil line on surviving plants. If plants do not die, shriveled seed may be produced. Under damp conditions a salmon pink growth develops on affected plants.
Survival and Spread. Seed-borne. Overwinters on flax crop residue. Spores spread by dew and splashing rain. Favored by cool wet weather.
Control. Use disease-free, good quality seed. Use fungicidal seed treatment to kill surface-borne spores. Use crop rotation.

PASMO, Septoria linicola

Symptoms. Infection may start on seedlings, with greenish yellow circular lesions on the cotyledons, turning dark later. Greenish yellow to dark brown lesions develop on leaves. On stems, the lesions coalesce to form an alternate pattern of lesions contrasted with the green of healthy tissues, producing a "barber pole" effect. Later, stems turn completely brown. Lesions may also develop on bolls; many bolls are poorly developed.
Survival and Spread. Seed-borne. Overwinters on flax straw. Spores spread by splashing rain, wind, dew, insects and other animals. Favored by continued wet weather late in the growing season.
Control. Plant disease-free seed and use fungicidal seed treatment. Use crop rotation. Bury flax straw by tillage.

RUST, Melampsora lini

Symptoms. Rounded orange-yellow pustules develop on seedlings about mid-season. In summer, orange pustules develop on the leaves. In late summer, brown to black pustules develop on the leaves; on stems they are elongated and purplish black. Bolls break off or fail to develop.
Survival and Spread. Spores in black pustules overwinter on flax straw. Spring and summer spores are wind-borne.
Control. Use crop rotation. Do not plant on or next to land that had rust last year. Plant early. Plant clean seed free of debris. Most available varieties are resistant to the current races of rust.

Stem and Leaf Diseases � Mycoplasmal

ASTER YELLOWS, Aster Yellows Mycoplasm

Symptoms. Affects scattered plants about mid to late season. Leaves turn yellowish-green and are twisted. Plants are stunted if infection is early. Flower parts turn yellow-green, forming a rosette-like growth instead of a boll. Seed is shriveled or does not form.
Survival and Spread. Overwinters on perennial hosts in south. Transmitted by the aster leafhopper (Macrosteles fascifrons). Leafhoppers migrate from the south, arriving in May. Mycoplasm survives and multiples in the leafhopper.
Other Crops Affected. Many garden and flower plants. Also affects potatoes, causing purple top disease.
Control. All varieties are susceptible. No control is available.

Stem and Leaf Diseases � Non-Infectious

HEAT CANKER, Non-Infectious

Symptoms. Stem is girdled at the soil line and may enlarge above the injury due to inability of food to move downward into the roots. The plant may fall over. Plants less than 4 inches tall are most susceptible. May affect many plants in a hot, dry spring.
Survival and Spread. Non-infectious. Favored by dark soils and hot sunny days before plants are large enough to shade the soil; plant tissues at soil line are injured by hot soil.
Control. Plant early. Drill rows north and south for maximum shading. Use higher seeding rates.

CHLOROTIC MOTTLE, Zinc Deficiency

Symptoms. Leaves turn yellow from the edge inward. In severe cases leaves turn brown and die. Growing tips may die and side branches which are longer than the main branch form. Plants are stunted and may die.
Survival and Spread. Occurs in localized spots in field early in the season. Favored by cool soil temperatures and is most severe at soil temperatures of 45°F. High levels of soil phosphorus reduce zinc availability and intensify the symptoms.
Control. Apply zinc to problem soils that test low in zinc, especially if they are high in phosphorus.

Root Diseases � Fungal

RHIZOCTONIA SEEDLING BLIGHT AND ROOT ROT, Rhizoctonia solani

Symptoms. Brown lesions form just below soil line on seedlings. Later, the lesions may extend up to the cotyledons. Occurs in areas measuring a few feet across to an acre or more and may kill every plant. Occurs sporadically in eastern North Dakota. Favored by warm moist soil following summer fallow.
Survival and Spread. Soil-borne.
Other Crops Affected. Many.
Control. Control may not be feasible in warm wet weather. The following practices will help reduce damage: plant disease-free sound seed; use a fungicidal seed treatment; plant early on recropped crop land; avoid summer fallow land.

SEED ROT AND SEEDLING BLIGHT, Soil-Borne Fungi

Symptoms. Seeds and seedlings may be attacked before emerging. The stems of plants that emerge are attacked below the ground, causing seedling blight. Stands are reduced.
Survival and Spread. Soil-borne. Cracked and split seed coats allow entry of fungi, especially if the weather is unfavorable for rapid germination of the seed.
Control. Plant sound healthy seed. Use fungicidal seed treatment -- this is particularly necessary for yellow-seeded varieties, which are more prone to seed coat damage than the brown-seeded varieties.