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Introduction
| Seed
treatments for insect pest control | Conclusion
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Introduction
In the past three years, a new
generation of insecticidal seed treatments has been introduced to canola
cropping systems in western Canada. The new seed treatments feature
chemistry that is considered to be less environmentally harmful than
lindane, the product recently withdrawn from the seed treatment market. In
2003, seedling canola was attacked by flea beetles, cutworms, and
wireworms in densities much greater than those reported in years when
lindane was the sole product being used. This presentation discusses
issues relating to crop losses from these pest species, and will present
strategies for improved integrated control of seedling pests in the
post-lindane years.
Seed
Treatments for Insect Pest Control
Lindane, an
organochlorine insecticide used commonly as a seed treatment for flea
beetle control in canola during the 1980’s and 1990’s, was recently
withdrawn from the market in Canada due to concerns that emerged regarding
its volatility, persistence in the environment, and its potential
carcinogenic and endocrine disruptive effects. The replacement products
for lindane comprise a new generation of insecticides in the neonicotinoid
class. Gaucho®, produced by Gustafson, contains the active insecticidal
ingredient, imidacloprid. Gaucho® is marketed at two rates: Gaucho Canola
System® is the lower dosage and Gaucho Platinum® is the higher rate.
Gaucho Platinum® therefore provides a longer period of protection from
flea beetle herbivory than Gaucho Canola System®, but it also costs more.
Helix® and Helix XTra® are produced by Syngenta, and contain the active
insecticidal ingredient, thiamethoxam. Helix XTra® contains a higher
dosage of thiamethoxam than Helix®. Both Gaucho® and Helix® are formulated
to contain fungicides in addition to the insecticides, to provide
protection from a broad spectrum of seed and seedling diseases.
In
2003, Alberta canola producers encountered outbreak densities of flea
beetles throughout much of the province, especially the Peace River region
and in southern Alberta. The reasons for the outbreak are unknown, but are
likely associated with the hot, dry conditions experienced during 2002.
Although most growers used one of the new flea beetle seed treatment
formulations, substantial crop losses still occurred in several
areas.
Although there has been some concern regarding the efficacy
of the new neonicotinoid insecticides for flea beetle control, there can
be little doubt that the products are effective. Both imidacloprid and
thiamethoxam kill adult flea beetles by systemic action: when flea beetles
feed on cotyledon tissue grown from seed treated with these insecticides,
they are poisoned and die. Both products were tested extensively prior to
registration, and field trials confirmed that they were effective. For
example, during 140 trials conducted in 1999 and 2000, canola grown from
plants treated with Helix® and Helix XTra® out-yielded, on average, canola
grown with the lindane treatment by approximately 5% or two bushels per
acre.
One reason for the extensive crop damage caused by flea
beetles during 2003 could relate to the extended emergence period of
overwintered flea beetle adults. Research conducted in southern Alberta
during 2003 determined that flea beetles emerged over a period
encompassing at least four weeks (Figure 1). Although peak emergence
occurred during a one-week period, substantial numbers still emerged for
two weeks before and two weeks after the emergence maximum.
Figure 1. Mean
numbers of overwintered flea beetle adults collected per emergence
trap
(sampled area = 1 square meter per trap) in various
shelterbelt sites near Lethbridge,
Alberta in 2003.
In addition to increased damage from flea beetles, growers also
experienced substantial crop losses from cutworms and wireworms in 2003.
Although both pest groups occur commonly throughout Alberta’s cropping
regions, extensive damage from these pests is a relatively new phenomenon.
Widespread insecticidal spraying occurred in 2003 for cutworm control,
primarily the redbacked cutworm, pale western cutworm, and army cutworm.
One possible explanation for the increased damage caused by these pests
relates to differences in efficacy between the new neonicotinoid seed
treatments and lindane. The new seed treatments are not effective against
these pests, but it is probable that lindane provided some
control.
For the 2004 field season, Gustafson has reduced the
suggested retail price of the Gaucho Canola System® from $7.00 per acre to
$4.97 per acre. This price reduction of the seed treatment can allow
growers to apply a foliar spray if necessary and still maintain their
costs for flea beetle control at or near the former cost of the
product.
In view of the danger of crop loss to canola posed by flea
beetle and cutworm infestations, growers should employ an integrated
management strategy. Some recommendations are given below for agronomic
practices that can be implemented for minimizing drop damage from these
pests.
1. Monitor Insect Populations. Foliar insecticides
are registered and effective against flea beetles and cutworms, but it is
critical that growers carefully monitor pest populations to avoid
unnecessary spray applications. Crops should be monitored in the cotyledon
stage, the stage most susceptible to flea beetle damage. When damage is
estimated to occur to the extent that 25% of the cotyledon tissue is
consumed by flea beetles, foliar sprays should be applied. Cutworm control
is recommended when population densities are approximately 4 to 6 larvae
per square meter. Canola crops should also be monitored for flea beetle
infestation levels late in the season, in the pod stage. High numbers of
adults suggest that infestation levels will also be high in the following
year, and provide an early warning for producers.
2. Follow
Recommended Agronomic Practices. Seeding too deep can produce
late-emerging, poorly competitive seedlings with little tolerance for
attack by insect pests. By contrast, seeding into a firm seedbed where
good soil to seed contact exists can promote rapid germination, good
seedling vigor, and competitive stands that can more readily withstand
some feeding damage by insect pests.
3. Maintain Adequate Plant
Stands. Some growers have responded to the comparatively higher costs
of the new seed treatments (compared with lindane), by reducing seeding
rates. Although it can be possible to develop adequate plant stands by
seeding as low as two kilograms of seed per hectare, this does not allow
the stand to fill in if some plants are consumed by flea beetles,
cutworms, and wireworms. By maintaining higher seeding rates, growers face
less risk of yield losses if insects destroy some seedlings.
4.
Consider Reduced Tillage for Flea Beetle Control. Research has shown
that flea beetle infestations are reduced in reduced tillage systems,
compared with conventional tillage. Flea beetles prefer warm, dry soil
which occurs more rapidly in conventional tillage than in reduced tillage.
There have been many examples of growers who experienced substantially
less flea beetle damage to canola when employing a reduced tillage regime
than with conventional tillage.
5. Consider Wider Row Spacings
for Flea Beetle Control. Research has determined that flea beetle
infestations decline with wider row spacings, compared with narrow row
spacings. For a given seeding rate, growers should consider using wider
row spacings to reduce the attractiveness of canola crops to invasion by
these pests.
6. Plant Vigorous Varieties. Vigorous, rapidly
growing seedlings are less susceptible to flea beetle damage than more
slowly developing plants. For optimal flea beetle management, growers
should consider selecting the most competitive, rapidly growing canola
varieties.
Conclusion
The new generation of seed treatments
presents new challenges for growers. Even though the new neonicotinoid
products are not registered for use against cutworms, growers can still
limit losses from these pests by integrated management strategies. In
years of outbreak densities of flea beetles, growers should consider using
canola seed treated at the high rate of insecticide for more prolonged
control. Careful monitoring can enable applications of foliar insecticidal
sprays before crop losses from flea beetles and cutworms are excessive.
Seeding at the recommended rate, or slightly higher, and in a reduced
tillage regime can further reduce flea beetle infestation levels and crop
damage.
Lloyd M. Dosdall and Bryan J.
Ulmer
Alberta Agriculture and University of Alberta
Department of Agricultural, Food and Nutritional
Science
Agriculture-Forestry Centre
University of Alberta
Edmonton, AB T6G
2P5
lloyd.dosdall@ualberta.ca
bulmer@ualberta.ca |
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