Prepared: August, 1999
Canola Production Regions in Montana
1. Counties in the northern region of Montana
Total for northern region = 19,794 acres
2. Counties in the central region of Montana
Total for the central region of Montana = 4,745 acres
3. Counties in the northeastern region of Montana
Total for the northeastern region of Montana = 4,282 acres
4. Counties in the southeastern region of Montana
Total for the southeastern region of Montana = 1,215 acres
5. Counties in the northwestern region of Montana
Total for the northwestern region of Montana = 739 acres
6. Counties in the southern region of Montana
Total for the southern region of Montana = 548 acres
7. Counties in the southwestern region of Montana
Total for the southwestern region of Montana = 440 acres
Canola is a member of the mustard family that was developed in the 1970s. Also known as rapeseed, canola acreage increased dramatically during World War II as it was used as a lubricant for steam ships, but its use declined with the advent of the diesel engine.
Canola, or rapeseed, grown in the past has had moderate levels of a compound called erucic acid. Research in the 1960s indicated the acid could be harmful. A breeding program initiated in Canada began producing rapeseed varieties with low erucic acid content. In 1978, varieties with less than 2 percent erucic acid were trademarked as "Canola."
In 1985, the USDA granted canola oil the GRAS (Generally Recognized as Safe) status for use in foods. This led to sales of canola oil in the United States, with only part of the demand met by U.S. producers. Canola oil has achieved worldwide commodity status and is extensively used in Japan, Canada and other countries.
Canola varieties don’t all have the same growth habit. Spring canola is planted early spring and completes its seed production late in the summer. Winter canola, not widely grown in Montana, is planted in the fall (like winter wheat). Plants become established in the fall and go dormant and vernalize during the winter period. Growth is resumed in late March or early April, with plants producing many bright yellow flowers by early May. Maturity is generally reached in late June, similar to that of winter wheat.
There are two types of canola commonly used in Montana; Brassica rapa or the Polish canola and Brassica napus or Argentine canola. Argentine canola tends to yield higher than Polish and has a higher oil content (1-2%) but it requires a longer growing season (7 to 14 days more than Polish). It also has a greater risk of frost damage. Polish canola is an early maturing variety, can be seeded later in the spring and still reach maturity before the first frost. It does have lower yield than Argentine. In the hotter, drier climates, it can be seeded early so that it flowers before the July heat.
Planting Considerations:
The goal is to get the crop out of the ground quickly so as to reduce seedling exposure to soil-borne diseases and prevent weeds from getting a competitive edge.
Spring canola is gaining increasing acceptance as a specialty crop to be grown in rotation with Montana's traditional small grain and forage crops in the cooler farming environments of Montana. Winter canola also seems to have good potential as more winter hardy varieties are developed.
Soilbed Preparation:
The tillage-planting system required for canola production varies between soil zones and soil types, and from year-to-year. The system used depends upon soil moisture, weeds, previous crop, trash cover, insects and diseases, soil erodability, fertilizer placement and machinery availability. There is no one best system as each specific situation will require its own special treatment. A successful practice in one location may be a disaster in another. Successful systems result in:
Canola Seedbed Requirements:
For canola the seedbed should be reasonably level, uniform, well packed, free from weed growth, warm, sightly lumpy on the surface and moist throughout its depth. if possible, the soil surface should have a good granular structure with 30 to 45 percent fine material (granules up to 1 millimeters in size) and the rest ranging up to 5 millimeters in size with only enough larger lumps to prevent wind erosion. It is also desirable to have a moderate amount of semi-rotted crop residue uniformly scattered over the surface and throughout its depth to provide protection from erosion and to reduce crusting. No-till works exceptionally well for canola as seed-to-soil contact is optimized.
Seedbed Firmness:
A firm well-packed seedbed provides excellent soil moisture and oxygen contact with the seed. Prior to seeding, the seedbed should be firm enough so that heel marks are barely visible. You should sink no deeper than the thickness of the sole on a normal work boot. This will also provide better depth control with the seed drill. Packing the soil reduces the size of the pores in the soil surface. the more packed the soil the greater the proportion of small pores relative to the number of large pores. Packing consolidates the soil surface and reduces soil moisture vapor loss from the large pores of the soil. However the soil granules should not be pulverized or packed so tightly that the supply of oxygen to the seed or seedling roots is restricted. A soil with fine or small granules is less well drained and is more poorly aerated than soils with large granules.
Crop Nutrition:
Canola benefits from a proper fertilization program. Soil testing is the most effective monitoring device a grower can have to manage a fertility programs. Adequate levels of nitrogen, phosphorus, and potassium are essential for rapid stand establishment.
Both winter and spring canola types are heavy nitrogen users. Canola will show greater response to high nitrogen levels than wheat and barley. It needs a total availability of 150 pounds of nitrogen to produce 2,000 pounds of grain per acre in as shown in Canada. Growers can use two methods of nitrogen application. An early spring application is as effective as split applications. A split application of 35 to 50 pounds preplant nitrogen with the remaining nitrogen applied as a topdress in early spring (not past the rosette stage) is also effective. Excessive preplant nitrogen levels will increase canola's chances of winterkilling. If the canola crop follows a nitrogen fixing legume, reduce the nitrogen application. Canola is sensitive to fertilizer burning due to furrow applications of both nitrogen and sulfur.
Canola's phosphorus and potassium requirements are similar to those needed by high yielding wheat crops. Production fields need a pH of 5.8 to 7.5. Boron is a pH sensitive micronutrient and boron deficiencies can be seen in sandy and high pH soils. Canola uses more boron than the other crops in its rotation. Growers should be careful to avoid elevating boron soil concentration to toxic levels. Boron application is done in preplant split applications.
Canola needs sulfur to take advantage of the higher nitrogen amounts. Avoid excessive sulfur levels due to the chance of increasing the glucosinolate content in the meal. If needed, apply sulfur preplant in a more available forms such as ammonium sulfate or ammonium thiosulfate rather than elemental sulfur.
Harvesting and Storage:
Direct combine harvest of canola is the most popular method in North America and Europe. Swathing is also possible when weed or humidity problems make direct harvest difficult. Harvest should not begin until moisture is below 10 percent. Harvesting above 10 percent moisture will result in dockage due to green seeds and the chance of heating damage.
Growers usually use a combine with a reel head. A combine harvest speed of 2 ½ mph is recommended to get clean seed. Canola is a difficult crop to feed into the combine but it is an easy crop to thresh. The reels should be set high and reel speed should be set to match ground speed due to the chance of shattering. Periodic inspections are essential to insure that the harvesting equipment has no openings through which canola can leak.
Swathing and threshing is practical when the fields have heavy weed infestations. Seed moisture levels should be 30 percent or lower before swathing. When the seeds in the pods are 75 percent black, the seed moisture should be about 30 percent. Threshing should start when the seed is at 10 percent moisture and no green seed is present. Swathing too early will result in green seed, lower oil content and higher seed moisture. Swathing too late will result in excessive shattering.
Seed moisture should not exceed 8 percent for long term storage. Lining the floor with a fine nylon or metal mesh screen will solve bin leakage problems. When drying seed, temperatures above 104°F can change the seed oil composition and kill germination. Seed stored below 6 percent moisture will be susceptible to damage in handling.
Summary:
Canola is a cool-season crop which can be planted on a variety of soils. Spring canola should be seeded as early as possible. Research has shown that date of seeding for canola is similar to sugar beets; late April or early May.
Winter canola should be planted in mid-to-late August to get adequate root development for overwintering and to withstand desiccation. Areas downwind from large bodies of water are most suitable for winter canola. Winter canola is often killed in March or April, after it has lost its winterhardiness and has started to grow. The lake effect reduces the large diurnal fluctuations in temperature, thereby increasing the chances of survival.
Canola should not be grown in successive years on the same land, because of the increased chance of crop losses due to diseases and insects. A 4-year rotation is recommended.
A firm, fine seedbed with adequate soil moisture is ideal. However, on heavier soil, crusting can be a problem if the soil is overworked. It is best to plant the seed to moisture, but do not go below a depth of 1 inch. A seeding depth of 1/2 inch is preferred, if moisture is adequate, because it will lead to a more even emergence and maturity.
Canola can be planted using grain drills, Brillion-type seeders or broadcasters. It should be seeded at a rate of 5 to 10 lbs/acre.. The objective is to establish 7 to 17 plants per square foot. Polish canola can be seeded at the lower end of the range because of its smaller size.
The major disadvantage of broadcasting is uneven planting depth. Good seedbed preparation before broadcasting and harrowing or packing after will help to keep seed depth constant.
Packing after planting generally improves emergence and yield, particularly if the soil may dry out before emergence. Some find that packing before the seed drill gives better seed depth control.
Spring canola is primarily grown in the cooler small-grain growing areas of Montana (northern, northeastern and central regions.) It produces excellent yields under irrigation and high rainfall conditions and gives small grain farmers another crop to cycle nutrients and break the pest cycles of continuous small grains.
Studies in Montana have shown that canola responded to all added nitrogen, phosphorous, potassium, and sulphur (N,P,K and S) fertilizers. Nitrate tests are useful in guiding nitrogen fertilizer applications.
A 1997 survey of canola growers in Montana indicated that the diamondback moth and flea beetles were the most prevalent pests.
1. Flea Beetles - Various Species
Flea beetles overwinter as adults and fly to volunteer rapeseed, canola, or wild mustards when temperature reaches 68°F. The shiny black beetles (1/10 in. long) move into canola fields just as the seedlings are emerging. Adults feed on the cotyledons and first leaves of seedlings. Eggs are laid in the soil and hatch into larvae that feed on the roots of the canola plant. The larvae feed for 3 to 4 weeks, pupate, and emerge as adults during July or early August. Emerging adults feed on any green plant tissue and then move to protected areas surrounding the field to overwinter. There can be more than one generation per year depending upon temperature. Adult feeding on the cotyledons can lead to seedling death and significant stand loss. Cotyledons can withstand up to 50% defoliation without yield loss. Damage becomes more severe when plants are stressed, particularly during periods of drought. Seedling canola plants will die if the above-ground portion is eaten entirely.
a. frequency of occurrence of flea beetles
Flea beetles are tiny insects, 2 to 3 millimeters long, which jump quickly when disturbed. Two species, the crucifer flea beetle (Phyllotreta cruciferae), which is black with a bluish sheen, and the striped flea beetle, which is black with two yellow stripes running the length of the body, are the most abundant and serious pests of canola.
b. damage caused by flea beetles
Spring feeding by adults on cotyledons and young leaves is the major cause of crop loss. Flea beetles move into newly emerging canola crops by a "creeping" action. The adults move from plant to plant into the field from hibernation sites around the field. On warm sunny days (above 68oF or 20°C), the beetles fly readily and quickly disperse across fields. In areas with lighter infestations, flight may spread the damage throughout the field where it is less noticeable and less damaging than when concentrated at the margins.
Damaged plants typically have a "shot-holed" appearance when the tissues around the feeding sites in the cotyledons and leaves die. The intensity of attack is influenced by weather conditions. Sunny, warm, dry weather increases feeding activity. Cool, damp weather slows flea beetle activity and promotes plant growth. Canola seedlings can withstand up to 75% percent leaf area removal in the cotyledon stage in dry regions without significant reduction in yield. With heavy attacks, seedlings may wilt and die, particularly when feeding is combined with poor plant growth during hot, dry weather. Unlike cereal seedlings, canola seedlings are unable to resume growth after losing all above-ground tissue. Even though surviving plants may be able to compensate for yield losses, heavy attacks can destroy the entire crop, forcing growers to reseed or leave the field in fallow. Less severe beetle damage may cause stunting and uneven maturity in growth stages. The heaviest feeding can last from May to late June when the crop is most susceptible. If the crop has good growing conditions and adequate soil moisture, it can often outgrow a moderate flea beetle attack and damage with no loss in yield. Once the crop develops beyond the seedling stage, damage does not usually occur and the adult flea beetle population often begins to decline.
Occasionally, seedling loss from plant diseases is mistaken for flea beetle damage. Damaged plants should be dug from the soil and examined carefully for evidence of disease on the shoots and roots. The effect of larval feeding on roots is not known. Although surface scars and some burrowing into the roots often result from their feeding, no effects on plant growth, vigor or yield have been observed. Feeding by newly emerged adults in August does not usually cause a loss of yield. However, if large numbers congregate in a few late-planted fields their feeding on green pods and stems causes poor seed development, reduced seed size and premature drying of the plant. Pod feeding may also result in seed loss from shattering and fungal growth on the pods. Fortunately, most crops are sufficiently advanced to avoid widespread damage of this type.
d. flea beetle life cycles
Flea beetles can have more than one generation per year. They overwinter as adults and leave their winter hibernation in April and early May. They feed on volunteer canola and mustard, or on weeds such as wild mustard, flixweed or peppergrass, then move to newly emerged canola seedlings. They mate during this feeding period. Eggs are laid in batches of up to 25, on or in the soil, and the overwintered adults begin to die off in late June. The young larvae feed on the roots of the developing canola crop. The larvae are whitish, slender, delicate, cylindrical worms about 3 to 4 millimeters long when full grown, with tiny legs and brownish heads. The larvae feed for three or four weeks and are present from about mid June to late July. They then enter a transitional stage known as a pupa, before emerging as adults in early August at which time they feed on the green tissue of any canola, mustard or cruciferous weeds that are still present. The feeding activity of these adults can continue into mid October. However, by mid September, most adults have entered a dormant, overwintering stage. In most years, they overwinter in leaf litter under hedges, windbreaks and wooded areas, but rarely in canola stubble fields.
e. flea beetle control measures
Cultural- Presently, no canola varieties are resistant to flea beetle damage. Cultivation of summerfallow fields containing cruciferous weeds and volunteer canola should be delayed until the canola crops are at the four leaf stage. It is sometimes recommended to sow at a higher seeding rate if the flea beetle population was high in the area the previous fall. Increased numbers of beetles in the fall are usually associated with increased numbers in the spring. When flea beetle populations are very high, there are no cultural controls that will effectively reduce their attack.
Chemical - General Guidelines
Examine the fields weekly, or daily in the seedling stage, and check for signs of feeding damage on various parts of the plant. Examine the entire field, make counts, and determine whether the entire field requires treatment. Frequently, insect numbers are high at the periphery of the field and decrease rapidly across the field. Canola crops can withstand some insect damage and usually compensate for it if the damage occurs early in the growing season.
Treat for flea beetles with a labeled insecticide when 25% of the cotyledons show severe pitting or tissue loss. Normally, plants are not treated once past the first true leaf stage.
Insecticides Used: RUP indicates a restricted-use pesticide
No use indicated by growers in 1997
% acres sprayed with methyl parathion (1997): 1%
Gaucho 480 (imidacloprid, 40.7%) at 16 to 32 fluid oz./hundredweight of seed.(Gustafson). For use in commercial seed treaters only. For protection of seedlings against injury by aphids, flea beetles, and wireworms
Thiodan 3EC (endosulfan) at 0.75 - 1.0 lb/acre.--- A 24(c) exemption. 24 hrs to re-entry. Do not exceed 2 applications per season. See label and 24(c) statement.
No use indicated by growers in 1997
Javelin WG(Bacillus thuringiensis ssp. kurstaki) - 0.12-1.50 lbs/acre.-- Apply as necessary to maintain control.
No use indicated by growers in 1997
In areas where pest damage from flea beetles has been light, no treatment may be required. Inspect newly emerged crops daily as flea beetles can damage crops quickly. A few flea beetles in the field and less than 25 percent damage to cotyledons and first true leaves are not cause for alarm. However, an increase in feeding damage and a delay of one or two days in dealing with a severe infestation can result in loss of fields. If plants are being lost, determine if the cause is flea beetles or seedling blight.
Spray only if necessary. If beetles are numerous on plants and the soil surface, and if beetle damage is becoming excessive on cotyledons and leaves of most seedlings, use a foliar insecticide spray. Where damage starts at the field margins, only a small portion of the field may require treatment. Apply sprays when it is sunny and warm, and the beetles are active and exposed on plants and soil. If there is a risk to honey bees, apply insecticides in the late evening or early morning. When flea beetle populations are high, more than one spraying may be necessary because of rapid reinfestation of the crop by beetles from nearby areas.
In areas where damage in the previous year was moderate, use a seed treatment containing an insecticide. If high flea beetle populations occur and the seed added treatments are not protecting the seedlings adequately, use a foliar spray.
In areas where pest damage from flea beetles has been high, using the combination of both a seed treatment and infurrow granule treatment will provide economically superior control. If hot, dry conditions occur, a foliar insecticide may also be necessary.
f. yield losses attributed to flea beetles
The 1997 survey indicated 5-30% losses for both the diamondback moth and flea beetles (5% losses in the northwestern region, 15% losses in the northeastern region, 30% losses in the central region.)
2. Diamondback Moth (Plutella xylostella L.)
a. frequency of occurrence
Population densities are dependent on the size of the spring immigration and the availability of host plants for first generation larvae. Tillage reduces the availability of cruciferous weeds and volunteer canola host plants, thus preventing the successful establishment of first generation larvae where moths arrive before canola emergence.
b. damage caused by pest
Damage to canola by young larvae is characterized by irregular small holes and surface stripping on the undersides of leaves, as well as small white mines in the leaves. The amount of leaf area lost probably causes little yield reduction in any but the most extreme cases. Older larvae may feed on the flowers, young pods and the surface tissue of stems and mature pods, usually from mid July to early August. Damage seems to be due to feeding on the surface of filling and maturing pods. The seeds under these areas do not fill properly. In severe cases, damage shows from a distance as an abnormal whitening. After an infestation is controlled in a podded crop, a new infestation is not likely to become established because of the rapid advance of the crop toward maturity. Damage is much worse when plants are drought or heat stressed. Pod damage is likely to occur if lower foliate is damaged by drought or other insects.
c. pest life cycles
Diamondback moths are weak fliers and are carried on winds in early May or in June. The number of spring migrants and their establishment is weather dependent, and infestations vary greatly from year to year. Adult moths are about 1/3 in. long with folded wings flaring outward and upward toward their tips. Adult males have a row of three diamond-shaped yellow spots where wings meet down the middle of the back when folded at rest. The small, narrow 12 millimeter (1/2 in) long moths have a wing span of about 18 to 20 millimeters (3/4 in), and are grey or brownish with white marks on the front margins of the forewings. The moths feed on wild flowers at dusk and mate and lay eggs after dark. In the main canola growing areas, most of the canola crops will not have emerged by the time the moths arrive, so that many eggs are laid on cruciferous weeds and volunteer canola. Each female lays up to 200 eggs. The minute, disc-shaped, pale green or yellow eggs are laid singly, or in twos or threes, on either side of leaves.
Small, green larvae hatch within a few days, about mid June, and enter the leaves to feed, or "mine", on the internal leaf tissue. When almost mature, usually within 10 to 30 days, the 8 millimeter (1/3 in) long, smooth, pale yellowish green larvae begin feeding on the outer leaf tissue. If disturbed, the caterpillars will wriggle violently backward and drop from the leaves on a silken thread.
The larvae pupate in delicate, whitish, open lacework cocoons attached anywhere on the plants. Adult moths of the next generation emerge within 7 to 14 days. There are at least three generations a year, and all stages may be found on the plants at the same time. The first larval generation has only leaves to feed on and is not numerous. Generally, only the second generation larvae cause yield loss when flowering and early podding are at a peak (often about the last week in July). The third generation is likely to affect only a few unusually late fields. When diamondbacks are numerous, cocoons may be noticed in dozens or hundreds on the pods of maturing plants.
d. control measures
Rainfall is a natural control agent. Young larvae are easily dislodged from plants by rain and can drown on the soil surface or in water trapped on the plants. Cool, cloudy weather during the egg-laying period reduces moth flight activity, and the longer this weather lasts the more females die before egg-laying is completed.
Diamondbacks can be controlled by recommended foliar insecticidal sprays. A severe infestation of small caterpillars is necessary to cause appreciable damage. If the leaves are beginning to turn yellow and dry up, damage will become more serious as larvae move to feed on pods. If this is the case, consider control at the lower end of the economic threshold range. This insect is notorious for multiple resistance to all types of insecticides. In North Dakota treatment is recommended when larval counts reach 25 to 30 per square foot and there is significant evidence of damage to flowers and/or pods.
f. yield losses attributed to each pest
A 1997 survey indicated 5-30% losses for both the diamondback moth and flea beetles (5% losses in the northwestern region, 15% losses in the northeastern region, 30% losses in the central region.)
3. Aphids
Occasionally aphids may become abundant in canola crops. Noticeable numbers usually appear at the tops of plants in late July to early August. The aphids frequently cover the entire top 2-3 inches of plants. In most cases, individual or small groups of plants are infested. The damage is rarely significant since the bulk of pod formation has been completed, and the damaged top few small pods contribute little to the overall yield. Spraying is not economical. Several kinds of beneficial insects, like the ladybird beetle and lacewing, feed primarily on aphids. Their populations increase as aphid populations increase, usually in numbers sufficient to control the aphids.
Diseases may attack canola at any time from seeding to maturity. These diseases come from the soil, infected seed, infected crop residue or air-borne spores from neighboring canola fields. Many of these diseases also attack other Brassica crops, such as mustard and common cruciferous weeds. Consequently, diseases are usually more severe in areas of intensive canola production.
Most fields in the more intensive production areas have some disease present each year. Disease severity varies with the year and the location, and is greatly influenced by farming practices and environmental conditions.
Soil-Borne Fungal Diseases:
Several soil-borne fungi, found in most agricultural soils, can attack canola plants. These fungi can survive in the soil or in decaying plant residues in the absence of a crop host. The fungi are almost always present because they can maintain themselves in the soil and multiply on roots of other susceptible host plants. Weeds of the mustard family and volunteer canola are attacked by these same diseases. These fungi may infect canola at any time during the growing season, especially when the plant root systems are growing under adverse conditions.
Seedling Disease Complex: (Rhizoctonia solani, Fusarium and Pythium species)
Appearance: Seeds & seedlings fail to germinate or emerge.
Emerged seedlings have constricted roots just below soil surface, topple
& die. Stands can be thin, slow to emerge or patchy.
Damage: Dead seedlings are usually compensated for by healthy
seedlings. However, in very uneven & patchy stands, yields are reduced.
Severe loss may necessitate reseeding.
Control: Use certified seed. Sow shallowly into firm, moist
seedbed with adequate fertilizer.
Chemical Control:
Thiram 42-S (Gustafson) 6.4 oz./hundred weight of seed. Recommended
to increase stands and yield from losses due to seed decay, damping off
and seedling blights.
Root Rot Complex (Primarily Rhizoctonia solani)
Appearance: Foot rot, hard brown lesions at stem base. Salmon
colored spore masses often present in lesion.
Damage: Losses are minor as lesions develop late in season.
Early lesions cause premature ripening and reduced yields.
Control: Crop rotation. Control volunteer canola and cruciferous
weeds in rotation. Use clean seed.
Sclerotinia
Sclerotinia stem rot is caused by the fungus Sclerotinia sclerotiorum.
The disease is usually most severe in wetter areas and in canola grown
in rotations including peas. The severity of stem rot varies from year
to year, and even from field to field within a region. With the right combination
of crop density and weather conditions or irrigation, heavy infections
can develop almost anywhere.
Appearance: 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. Sclerotia can remain viable
for 3 years. Basal stalk infections rarely occur.
Damage: Yield loss of 10 to 15% have occurred in Saskatchewan,
Manitoba and North Dakota; occasionally losses of 50% have occurred in
Manitoba.
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.
All registered canola varieties are susceptible to sclerotinia stem rot and a wide range of other crop species, including bean, sunflower, the mustards, lentil, field pea, faba bean, alfalfa, clover, carrot and potato are affected to some degree. Follow a rotation of at least four years between susceptible crops. Cereal and grass crops are not susceptible and will bring about a reduction of viable sclerotia in the soil through decay or germination in the absence of susceptible hosts. The control of susceptible weeds and volunteer plants in cereal crops also helps reduce levels of sclerotia. However, in some fields and areas with a history of stem rot, even a five-year absence of susceptible crops has not reduced the number of sclerotia in the soil enough to assure adequate control. Rotation also does not protect crops from infection by airborne spores originating in nearby fields.
Try to avoid sowing canola adjacent to a field in which a heavily infected crop was present the previous year. Burial of infected plant residues may reduce the production of apothecia in the subsequent crop; however, later tillage brings sclerotia back up near the soil surface. In order to keep sclerotia buried, minimum and shallow tillage should be used for cereals sown in fields where infected canola stubble has been worked down and buried. Where reduced tillage is recommended for erosion control, the chances of infection from certain diseases increase. It is therefore particularly important to use management practices which help reduce the likelihood of disease such as extended rotations and chemical control.
A seed source free of sclerotia should be used in areas where the disease has not been a problem.
In Canada, sclerotinia stem rot of canola can be controlled by spraying fungicides during flowering. Protection of the crop is necessary only during flowering because of the critical role petals play in infection.
Alternaria Black Spot, Alternaria brassicae and A. raphani
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. Altenaria 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.
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
Blackleg, caused by the fungus Leptosphaeria maculans (Phoma lingam)
occurs in a mild or weakly virulent form and a virulent or more
aggressive form. The virulent strain of blackleg is considered to be a
serious threat to canola production in Canada but may not likely be a problem
in Montana.
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. No pesticdes
are registered for blackleg control in Montana.
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. No data is available for Montana.
Control: No practical means is available.
Root Diseases – Fungal
BROWN GIRDLING ROOT ROT, cause undetermined; most probably Rhizoctonia spp.
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.
Weeds can be the most limiting factor in canola production. Some weeds are easily controlled; others are difficult or costly to control because they are closely related to canola or because no effective herbicide is available. Since conditions vary from farm to farm, preventative and physical, cultural and chemical weed control practices must be selected that suit the conditions in the area.
A 1997 survey conducted in Montana indicated that kochia, wild buckwheat, Canada thistle, annual mustards, wild oats and volunteer grain were the most prevalent weed problems. Losses of 10-30% losses were indicated.(Reports of 10% losses in the northwestern region, 10-30% losses in the northern region, 10-20% losses in the northeastern region, 20% losses in the central region)
Other problem weeds can be:
Weeds that cause major problems in canola are the perennial types, shade tolerant weeds and tall-growing, early-germinating weeds such as wild oats. Among the more troublesome weeds that are not controlled in a normal canola crop with lower cost herbicides are the closely related cruciferous weeds:
These weeds are easily controlled in cereal crops; however, dormant seeds and seeds from escapes will germinate and set many more seeds in the canola crop. This results in a gradual buildup of weed populations if canola becomes more frequent in the rotation. This emphasizes the need for a proper rotation when growing canola. Other difficult-to-control or expensive-to-control weeds in canola are:
In a crop rotation, canola following cereals is generally a good weed control practice becaruse broadleaf weed populations should have been reduced by herbicides and grassy weed populations should have been reduced by competition. Barley is especially good in competing against grassy weeds.
Effects of Weeds on Canola:
Canola is uncompetitive in the seedling stage but can develop so that it closes its canopy quicker than wheat and can later become very competitive. It is important to establish a vigorous uniform crop. High seeding rates will help the crop compete against weeds during the early growing season. Delayed planting of canola has been used to control early germinating weeds, but in many areas crop yield is decreased by delayed planting.
Weeds can result in reduced yields because they compete with the crop for light, moisture and nutrients. Weed competition reduces canola plant growth and leaf area resulting in increased flower, pod and seed abortion. Yield losses will depend on the kind of weed, its population, time of emergence, the crop and the timing of control. Weeds also result in:
Many of the hard-to-control weeds listed earlier fall into this category. Weed control is equally important in non-canola years.
Herbicides:
Canola is extremely sensitive to drift or soil carry-over from some herbicides such as Harmony Extra and Express. Sprayer contamination from these herbicides also can be very damaging. To avoid injury, be sure to clean out spray tanks and booms very well before applying herbicides to canola.
Resistance to groups of herbicides is an increasing reality in many parts of canola growing areas. Keep accurate records of all herbicides used and regulary rotate among herbicide groups:
Herbicide groups:
Assure (quizalofop)
Rate used: 5 to 12 oz. product/acre was used by growers in
1997.
Time: Apply to emerged weedy grasses or volunteer grains with
height ranges specified on the label (between 2 and 10 inches tall, depending
on species). For best results, apply when grases are in the 3-leaf to early
tillering stage.
% acres sprayed with Assure (1997): 22%
Remarks: For control of certain emerged annual grass weeds,
volunteer corn, volunteer cereals and quackgrass in canola. Quackgrass
may require 2 treatments. Approved for ground and aerial applications.
Always include a nonphytotoxic petroleum-based crop oil concentrate or
a nonionic surfactant. Rate is dependent on weed species, size, density,
and environment. Use high label rates on larger weeds, higher populations
and in arid areas. Subsequent flushes of grasses require additional treatment.
Refer to and follow all supplemental and regular label instructions.
Caution: Reduction in grass control is possible when Assure
II is applied immediately before or after a postemergence broadleaf herbicide.
Wait at least 24 hours after applying Assure before applying a broadleaf
herbicide. In fields already treated with broadleaf herbicide, wait 7 days
before applying Assure. Do not mix with any other pesticide. Do
not apply within 60 days of harvest. Do not apply after crop reaches flowering
statge. Do not apply through any irrigation system. Do not exceed 18 oz
of product per acre per season.
Poast 1.5 EC (sethoxydim)
Rate used: 1.5 to 2.5 pts/acre. The 1.5 pt/acre rate was most
widely used (1997).
Time: Apply to actively growing annual or perennial grasses
at the appropriate stage of grass grwoth as indicated on the label.
% acres sprayed with Poast (1997): 28%
Remarks: Always adda nonphytotoxic oil concentrate to the
spray tank at 2 pints/acre. Poast is most effective on actively growing
agrasses before they reach the maximum size indicated on the label.
Caution: Control may be erratic if grasses are stressed due
todrought, temperature extremes, insect damage, herbicide injury, etc.
Do not apply if rainfall is expected within 1 hour following application.
do not cultivate with 5 days before application or with 7 days after application.
do not apply within 30 days of harvest.
Treflan MTF (4EC) (trifluralin)
Rate used: 1 to 2 pts/acre in the spring (1997)
Time: Apply preplant incorporated in the spring
% acres sprayed with Treflan (1997): 20%
Remarks: Residual preemergence control of annjual grasses
and certain annual broadleaf weeds. Weak on nightshade, mustards and sunflower
family weeds. Use lower rates on coarse-textured, low organic matter soils.
incorporate twice, once with 24 hours. Incorporate to a depth of 1 to 2
inches. Allowing five (5) days or more interval between first and second
incorporation often improves weed control with Treflan. Conducting the
second incorporation after soil temperatures have reached 50oF
and just prior to seeding often is beneficial.
Caution: Do not plant sugarbeets for 12 months after a spring
application of Treflan or 14 months after a fall appliciation. Corn, oats
and sorghum should not be planted for 14 months after a spring application
and 16 months after a fall application. Do not combine with fertilizers,
fungicides or insecticides. Treflan may cause injury to stressed crop seedlingsrtain
emerged annual grass weeds, volunteer corn, volunteer cereals and quackgrass
in canola. Quackgrass may require 2 treatments. Approved for ground and
aerial applications. Always include a nonphytotoxic petroleum-based crop
oil concentrate or a nonionic surfactant. Rate is dependent on weed species,
size, density, and environment. Use high label rates on larger weeds, higher
populations and in arid areas. Subsequent flushes of grasses require additional
treatment. Refer to and follow all supplemental and regular label instructions.
Caution: Reduction in grass control is possible when Assure
II is applied immediately before or after a postemergence broadleaf herbicide.
Wait at least 24 hours after applying Assure before applying a broadleaf
herbicide. In fields already treated with broadleaf herbicide, wait 7 days
before applying Assure.Do not mix with any other pesticide. Do
not apply within 60 days of harvest. Do not apply after crop reaches flowering
statge. Do not apply through any irrigation system. Do not exceed 18 oz
of product per acre per season.
Reeves Petroff, Montana PIAP SLR, PO Box 173020, Room 712, Leon Johnson Hall, Montana State University, Bozeman MT 59717-3020. Phone: (406) 994-3518, Fax: (406) 994-6029. E-mail: rpetroff@montana.edu.
Perry Miller, Asst. Prof. of Cropping Systems Land Resources and Environmental Sciences PO Box 173120, Rm. 334 Leon Johnson Hall Montana State University Bozeman MT 59717-3120 PH. 406-994-5431 FX. 406-994-3933 E- mail. pmiller@montana.edu
Database and web development by the
NSF Center for Integrated Pest
Managment located at North Carolina State University. All materials may be used freely
with credit to the USDA.