- June 10th, 2025
By John Doe
Hectares of razed crops abound in Manitoba as a virus has decimated the crop. The
culprit has been determined to be Barley Yellow Dwarf Virus, which is transmitted from
aphids from the Southern United States. Usually this virus cannot over winter in Canada
and is only brought to Canada from aphids carried by the wind. However due to climate
change, the virus is now able to survive Canadian winters, thus attacking the crop at an
earlier and more crucial stage in development. The Provincial Government of Manitoba
has issued a state of emergency as the entire crop has been decimated, with losses
numbering in the billions. According to agronomist Dr Smith, since the virus can now
overwinter here, eradication is impossible and the whole canola industry in Manitoba
may be a “relic of the past”.
The preceding scenario is fictitious but the possibility of its occurrence is not
beyond plausibility. The virus is a real threat to this crop currently but cannot overwinter
so the late onset of this disease is not an immediate threat to the canola industry. Climate
change and global warming is another reality that this scenario presents. However,
despite the possibility of the perfect eclipse of these two aspects is not a death certificate
for the canola industry in Canada but rather a catalyst for the industry to work on resistant
strains and proper IPM to prevent disaster should this scenario become a reality.
Therefore, to understand the scenario one must understand the canola crop, barley yellow
dwarf virus and its transmission, the effect on global climate change on pest ecology, and
finally the options available to combat this disease.
Canola (Brassica campestris), is grown for its seeds that is in turn used to
produce edible oil. What makes it ideal for human consumption is that it contains lower
levels of erucic acid than other rapeseeds. It is also an excellent livestock feed because of
its lower levels of the toxin glucosinolates. Canola was originally naturally bred from
rapeseed in Canada by Keith Downey and Baldur R. Stefansson in the early 1970s, but it
has a very different nutritional profile in addition to much less erucic acid. The name
"canola" was derived from "Canadian oil, low acid" in 1978. A product known as LEAR
(for low erucic acid rapeseed) derived from cross-breeding of multiple lines of Brassica
juncea is also referred to as canola oil and is considered safe for consumption.
Once considered a specialty crop in Canada, canola has become a major North
American cash crop. Canada and the United States produce between 7 and 10 million
tons of canola seed per year. Annual Canadian exports total 3 to 4 million tons of the
seed, 700,000 tons of canola oil and 1 million tons of canola meal. The United States is a
net consumer of canola oil. The major customers of canola seed are Japan, Mexico,
China and Pakistan, while the bulk of canola oil and meal goes to the United States, with
smaller amounts shipped to Taiwan, Mexico, China, and Europe. World production of
rapeseed oil in the 2002–2003 season was about 14 million metric tons.
Canola was developed through conventional plant breeding from rapeseed, an
oilseed plant already used in ancient civilization. The word "rape" in rapeseed comes
from the Latin word "rapum," meaning turnip. Turnip, rutabaga, cabbage, Brussels
sprouts, mustard and many other vegetables are related to the two canola varieties
commonly grown, which are cultivars of Brassica napus and Brassica rapa. The negative
associations due to the homonym "rape" resulted in creation of the more marketingfriendly name "Canola". The change in name also serves to distinguish it from regular
rapeseed oil, which has much higher erucic acid content.
Hundreds of years ago, Asians and Europeans used rapeseed oil in lamps. As time
progressed, people employed it as cooking oil and added it to foods. Its use was limited
until the development of steam power, when machinists found rapeseed oil clung to water
or steam-washed metal surfaces better than other lubricants. World War II saw high
demand for the oil as a lubricant for the rapidly increasing number of steam engines in
naval and merchant ships. When the war blocked European and Asian sources of
rapeseed oil, a critical shortage developed and Canada began to expand its limited
rapeseed production. After the war, demand declined sharply and farmers began to look
for other uses for the plant and its products. Edible rapeseed oil extracts were first put on
the market in 1956–1957, but these suffered from several unacceptable characteristics.
Rapeseed oil had a distinctive taste and a disagreeable greenish color due to the presence
of chlorophyll. It also contained a high concentration of erucic acid. Experiments on
animals have pointed to the possibility that erucic acid, consumed in large quantities, may
cause heart damage, though Indian researchers have published findings that call into
question these conclusions and the implication that the consumption of mustard or
rapeseed oil is dangerous. Feed meal from the rapeseed plant was not particularly
appealing to livestock, due to high levels of sharp-tasting compounds called
Plant breeders in Canada, where rapeseed had been grown (mainly in
Saskatchewan) since 1936, worked to improve the quality of the plant. In 1968 Dr Baldur
Stefansson of the University of Manitoba used selective breeding to develop a variety of
rapeseed low in erucic acid. In 1974 another variety was produced low in both erucic acid
and glucosinolates; it was named Canola, from Canadian oil, low acid. A variety
developed in 1998 is considered to be the most disease- and drought-resistant variety of
Canola to date. This and other recent varieties have been produced by gene splicing
techniques. An Oregon State University researcher has determined that growing winter
canola for hybrid seed appears possible in central Oregon, USA. Canola is the highestproducing oil-seed crop, but the state prohibits it from being grown in Deschutes,
Jefferson and Crook counties because it may attract bees away from specialty seed crops
such as carrots which require bees for pollination. Canola was originally a trademark but
is now a generic term for this variety of oil. In Canada, an official definition of canola is
codified in Canadian law.
Canola oil has been claimed to promote good health due to its very low saturated
fat and high monounsaturated fat content, and beneficial omega-3 fatty acid profile. The
Canola Council of Canada states that it is completely safe and is the "healthiest" of all
commonly used cooking oils. It has well established heart health benefits and is
recognized by many health professional organizations including the American Dietetics
Association, and American Heart Association, among others. Canola oil has been
authorized a qualified health claim from the US Food and Drug Administration ] based on
its ability to reduce the risk of coronary heart disease due to its unsaturated fat content.
Genetically modified canola which is resistant to herbicide was first introduced to
Canada in 1995. Today 80% of the acres sown are genetically modified canola.
Contamination of conventional canola crops from neighboring genetically engineered
fields has been a serious problem for Canadian canola farmers. It is very difficult for
farmers to grow non-GM crops because of the frequent contamination.
The most high-profile case of contamination is Monsanto Canada Inc. v.
Schmeiser, where Monsanto sued Percy Schmeiser for patent infringement because his
field was contaminated with Monsanto's patented Roundup Ready glyphosate tolerant
canola. The Supreme Court ruled that Percy was in violation of Monsanto's patent
because the crops were growing on his land, but he was not required to pay Monsanto
damages since he did not benefit financially from its presence. On March 19, 2008,
Schmeiser and Monsanto Canada Inc came to an out of court settlement whereby
Monsanto will pay for the clean-up costs of the contamination which came to a total of
$660 Canadian. Also part of the agreement was that there was no gag-order on the
settlement and that Monsanto could be sued again if any further contamination occurred.
Introduction of the genetically modified crop to Australia is generating considerable
controversy. Canola is Australia's third biggest crop, and is often used by wheat farmers
as a break crop to improve soil quality. As of 2008 the only genetically modified crops in
Australia were non-food crops: carnations and cotton. In 2003, Australia's gene
technology regulator approved the release of canola altered to make it resistant to the
herbicide Glufosinate ammonium.
Barley Yellow Dwarf Virus is a virus that is transmitted via aphids to the
following crops: barley, oats, wheat, maize, triticale, canola and rice. This virus is
commonly referred to as BYDV, and its anatomy is that it is a positive sense singlestranded RNA. This means that its developmental orientation is in the positive direction
of the RNA sequence. Within this species are two categories, Subgroup I and Subgroup
II. Subgroup I has less severe diseases such as MAV, which is carried by grain aphid
(Stiobion avenae). Subgroup II is commonly called Cereal Yellow Virus and it is often
carried by bird-cherry aprids (Rhopalosiphum padi.)
The pathology of the plant results when aphids feed on the phloem on the leaves
of susceptible plants, in this case canola. Once inside of the plant, it uses the plant to
reproduce its own genetic material. This process requires significant energy that is
diverted from plant development, hence the symptoms of the disease. The cultivar of the
affected plant is the major determinate of the severity of the symptoms, as is plant
development stage, viral strain and environmental conditions. More often than not, it is
mistaken for another disease or environmental condition. The onset of symptoms occurs
about fourteen days after initial infection. Plants that are affected have the following
symptoms: yellowing-reddening of the foliage, stunted growth, leaves that are in a rigid,
upright position, reduction in root growth, delayed or no heading leading to a reduction in
overall yield.
Again, the virus is transmitted when the aphids feed on the phloem of susceptible
plant leaves. During feeding, the virons go to the aphid hindgut. The coat protein of the
virus is recognized by the hindgut antibodies and permitted passage into the hemolymph
where it can remain for an indefinite period of time. However, the virus is incapable of
reproducing in the aphid, making it only a carrier of the virus. Actively transported to the
salivary gland, where it is excreted in saliva when the aphid feeds upon the host plant.
In regards to how this disease spreads, there are two dispersal methods. One is
dispersal by non-winged aphids that are pre-existing in the field, and colonize newly
emerged crops, otherwise known as “green-bridge transfer”. This type is much more
damaging to a crop because it infect during a time essential for growth of a new plant.
The second method is by winged aphids migrating into crops from elsewhere. These then
reproduce and the offspring spread to neighboring plants. This is the case with current
infestation of Canola in Manitoba from airborne aphids from the warmer Southern United
The effect on yields vary greatly depending on the host species and the variety
that is being grown. Another variable to be considered is the dispersal method and the
rate of infection. Severe losses occur mostly when the onset is during early development
of the plant and yield losses can be up to fifty percent. Even at fifty percent, such losses
can be disastrous to a grower because rotation is difficult for this pest due to the large
number of host crops it can potentially infect.
Management of this pest includes cultural methods such as tilling under these
“green bridges” which prevents the non-winged aphids a corridor to move into a field or
area. Insecticide is recommended to be applied ten days before cultivation but can also be
used at crop emergence. Synthetic pyrethroid insecticides are the most effective at doing
this task. Drilling dates prior to mid-October favors attacks from winged migrant aphids.
However yield penalties may be experienced from late drilling. Insecticide sprays in this
instance are therefore aimed at killing the aphids before significant spread can occur.
The biggest catalyst for a potential problem is that if the virus is able to
overwinter in Northern Latitudes, the infestation remains there in the soil and therefore is
present regardless of planting date, making it difficult to prevent infestation. Due to the
range of affected crops, rotation would not be viable because most cereal crops are
susceptible to this disease. However, one must first understand the role of global climate
change to better understand the scenario.
One of the biggest threats to agricultural production in the 21st century is the
prospect of global warming. The implications of this effect are much more than the crops
but also the local ecology, which due to climate change is being altered. This leads to
disruption in the ecological balance between pests and their predators. It will also allow
pests into regions previously unaffected due to unfavorable conditions. According to the
IPCC, the planet temperature has risen 0.3 to 0.6 degrees. The most rapid increase during
this period has been 1925-1944 and 1978-1997. Despite the seemingly trivial increase in
world temperature, this is not fully descriptive of the problem facing many ecological
systems. Most of the areas with the greatest change are in the northern latitudes and occur
mostly during the winter, where the range has changed by four degrees Celsius. This has
effects on things such as reproductive processes and range of many species. Aphids date
of flight migration has changed by 3-6 days (Fleming and Tatchel). If the warming trend
accelerates, this could be earlier or allow a greater flow of aphids during warmer weather.
Plant pathology depends on three factors, pest, environment and host to infect.
Often referred to as the pest triangle, all factors are needed to be present to allow the
disease to manifest. Should any of these factors become out of balance, the possibility for
a disease epidemic becomes plausible. The major factors of climate change such as
temperature, rainfall and carbon dioxide can severely impact the pest triangle. Changes in
temperature potentially effect both host and pest. For example, rust becomes much more
problematic in grass crops when temperature increases but some forages become more
resistant to fungi as temperature increases. The temperate regions with winterkill are
more likely to suffer problems from longer warm periods that are better suited for
pathogenic activity.
An example of this is a model for potato/tomato blight (phytophthora infestans)
which demonstrated that this fungus reproduction and infection is most successful during
periods of high moisture and temperatures from forty-five to eighty degrees Fahrenheit.
If warmer temperatures onset earlier in the season, the threat of an earlier blight which
could decimate the crop becomes more probable and the reality of higher pesticide use.
The effect of increased moisture will vary depending on the crop that is affected. For
example, some pests such as apple scab are more likely to infect when moisture is higher
but some pests such as powdery mildew prefers lower moisture for infestation. More
frequent and longer periods with increased moisture could result in periods of longer
windows of favorable conditions for pests. Potential host crops that are limited by
moisture to produce a greater canopy may be able to do so. This translates into more
moisture being held in place, thereby increasing potential for pathogenic infection. The
final aspect of global warming is increased Carbon Dioxide production, which effects are
also dependent upon crop and pest. As mentioned before, elevated carbon dioxide could
lead into greater canopy growth that would trap moisture. Lower rates of decomposition
in plants could leave crop residue where pests can over winter, which could lead to earlier
and more severe epidemics due to higher amounts of innoculum. Another dimension of
increased carbon dioxide is that the host plant could undergo physiological changes that
could make it more resistant to infestation.
.In regards to the pest triangle, many events would have to align to make the scenario in
canola the disaster that was presented. There would need to be increased moisture,
temperature and carbon dioxide for all effects of this potential disaster to come to
fruition. However, the effects can be avoided by farming practices and biotechnology.
Many of these negative effects are beyond control but many cultural practices
could prevent many of the worst effects. Row spacing and population density in the field
could resolve the problem with a closed canopy facilitating moisture retention. If plants
are growing bigger canopies and if planting takes that into consideration, the canopy will
not fully close. This will allow moisture to escape and reduce but not eliminate the rise of
pathogens. However weeds need to be taken into consideration or the prevention of one
pest allows the emergence of another pest. Another cultural method of control is planting
when effects are minimal. Even if a pest can overwinter in an area, there is a period
where it will be less able to affect a young crop and planting accordingly should diminish
risk. However, other pest pressures and climate still have to be considered when
changing planting date to avoid the pathogen. The final way to manage the pest would be
the use and development of resistant varieties as has been done in cereal crops. However
in regards to barley yellow dwarf virus, there is not much to be done besides using a
resistant variety if the scenario does become reality. This is why integrated pest
management is very important in any cropping system.
In conclusion, the scenario is pure fiction but using the pest triangle that includes
a proper host, the pest itself and proper environmental conditions, one can see the
possibility of such a scenario. The issue being is that there is not too much one can do to
treat this problem of barley yellow dwarf virus. However, if cultural practices such as
rotation of crops and spacing are used, the economic pitfalls of such a scenario could be
made much less destructive rather than the catastrophic scenario previously mentioned.
Therefore, to understand the scenario one must understand the canola crop, barley yellow
dwarf virus and its transmission, the effect on global climate change on pest ecology, and
finally the options available to combat this disease.