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Production Papers

Managing Flea Beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) in Canola with Seeding Date, Plant Density, and Seed Treatment

^a Dep. of Agric., Food and Nutr. Sci., 4-10 Agriculture/Forestry Centre, Univ. of Alberta, Edmonton, AB, Canada T6G 2P5
^b 142 Rogers Rd., Saskatoon, SK, Canada S7N 3T6

^* Corresponding author (lloyd.dosdall{at}ualberta.ca)

Received for publication April 2, 2005.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Fall seeding of canola can increase equipment and manpower efficiencies for producers, hasten crop maturity, and improve seed quality, but no previous studies have examined effects of this practice on infestations of flea beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae), the major pests of crop seedlings in North America. Field experiments were conducted at Vegreville, Fort Saskatchewan, and Lethbridge, AB, Canada from 1998 through 2000 to determine the effect of fall versus spring seeding of canola (Brassica napus L. and Brassica rapa L.) on feeding damage by flea beetles. Interactions with seeding rate and seed treatment on flea beetle damage also were investigated. Flea beetle damage was greater on plants of B. rapa than B. napus, on spring-seeded canola than on plants seeded in fall, and on plants that developed from seed treated with Vitavax Single (containing carboxin) than on plants treated with Vitavax rs (containing carboxin, thiram, and lindane). Mean flea beetle damage per plant declined with an increase in seeding rate. Canola seeded in fall reached 50% flowering about 10 d earlier than plants seeded in April and about 20 d before plants seeded in May. Fall-seeded plants matured 5 to 21 d earlier than plants seeded in April and about 10 to 30 d before plants seeded in May. Seeding in fall enabled plants to progress beyond the vulnerable cotyledon stage by the time that most flea beetle injury occurred. Seeding canola in fall, at rates selected to achieve vigorous plant stands, is an important component of an integrated management strategy for flea beetles, with the potential for substantially reducing insecticide use in this crop.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
THE FLEA BEETLES Phyllotreta cruciferae Goeze and Phyllotreta striolata Fabricius (Coleoptera: Chrysomelidae) are chronic pests in canola production systems in North America, estimated to cause yield losses of many tens of millions of dollars (CAD) annually (Burgess, 1977a; Lamb and Turnock, 1982; Madder and Stemeroff, 1988). Adults of both species overwinter primarily in leaf litter and turf of shelterbelts and emerge in spring to injure crop seedlings (Burgess, 1977a, 1981). The most severe crop damage occurs when adults feed on cotyledons and stems of seedlings, causing loss of photosynthetic capability, wilting, or host plant mortality (Westal and Romanow, 1972). Plants that recover from flea beetle injury often have reduced biomass, delayed maturity, and reduced seed yield and quality (Putnam, 1977; Lamb and Turnock, 1982; Lamb 1984).

In recent years there has been increasing interest in the adoption of fall dormant seeding of canola in the Northern Great Plains of North America. Several advantages have been attributed to seeding canola in fall rather than at more conventional times in spring (Kirkland and Johnson, 2000; Clayton et al., 2004a). Increased equipment and labor efficiencies result from spreading out seeding dates of canola relative to other crops. Crop development is advanced, resulting in early maturity and reduced risk of preharvest frost damage and grade loss. Seeding canola in fall, rather than at more traditional times in mid-May, can increase yields by approximately 40% and improve seed oil concentrations by 5% (Kirkland and Johnson, 2000; Johnston et al., 2002). Improvements in yield and quality of fall-seeded canola have been attributed to the advantages gained from enhanced utilization of early-season soil moisture and the timing of flowering and seed maturation to occur during cooler and moister periods of the growing season (Kirkland and Johnson, 2000; Johnston et al., 2002). However, benefits from fall dormant seeding of canola have not always been realized. Karamonas et al. (2002) reported yields that were 4 to 31% less in fall-seeded than in spring-seeded canola, and Clayton et al. (2004a) found that 46% lower plant densities associated with fall-seeded canola resulted in substantially reduced yields compared with canola seeded in spring.

In spite of the potential benefits that can be gained from fall dormant seeding of canola, the primary drawback to its widespread adoption has been difficulty with plant stand establishment. Failures to establish adequate canola densities in fall-seeded systems were usually attributed to soil crusting that prevented or hampered emergence in spring and warm fall soil temperatures that sometimes caused premature germination and subsequent seedling mortality from frost (Kirkland and Johnson, 2000; Angadi et al., 2003). However, stand establishment was found to improve when canola was dormant-seeded into stubble rather than fallow, resulting in less soil crusting (Kirkland and Johnson, 2000). The potential for reduced risk of stand failure associated with fall seeding was improved further with the recent development of polymer seed coatings that can prevent premature germination when atypical warm fall environmental conditions occur (Chachalis and Smith, 2001). A polymer seed coating designed to prevent fall germination by impeding the imbibition rate of water in seeds has been developed for canola under the trade name Extender (Zaychuk and Enders, 2001). Johnson et al. (2004) and Clayton et al. (2004b) found that Extender improved seedling density and seed yield when soil temperatures after fall seeding were above 5°C.

The effects of fall versus spring seeding of canola on feeding damage by flea beetles have not been investigated previously. This study was undertaken to investigate the impact of seeding on two dates in fall (October to November) and one date in early spring (late April), compared with a "normal" seeding date in spring (mid-May), on feeding damage by flea beetles, and to determine the effect of different seeding rates on infestations of these pests for both fall and spring plantings. Additional objectives were to assess the impact on flea beetle infestations of utilizing seed treated with a synthetic polymer (Extender) designed to reduce moisture uptake versus seed treated with more conventional coatings (Vitavax Single and Vitavax rs). We also compared relevant agronomic characteristics, such as seedling establishment, flowering and maturity dates, and seed yields, associated with canola planted on the different dates.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Study Sites and Experimental Designs
The study was conducted at Vegreville (53°30' N, 112°03' W), Fort Saskatchewan (53°43' N, 113°13' W), and Lethbridge, AB (49°37' N, 112°39' W) from 1998 to 2000. Soil type was Black Chernozemic loam (35% sand, 34% silt, and 31% clay) with pH 6.3 and 7.2% organic matter at Vegreville, Black Chernozemic loam (33% sand, 39% silt, and 28% clay) with pH 6.1 and 7.4% organic matter at Fort Saskatchewan, and Dark Brown Chernozemic loam (37% sand, 30% silt, and 33% clay) with a pH of 7.8 and 2.3% organic matter content at Lethbridge.

Treatments were assigned to experimental units in a randomized complete block design having four replications. The design included factorial combinations of seeding date (described below), seeding rate (7.5, 10.0, and 12.5 kg ha^–1), seed treatment (described below), and canola species (B. rapa cv. Reward and B. napus cv. Q2). Each treatment plot measured 6 by 2 m and comprised eight rows spaced 20 cm apart; 20 cm was not seeded on each side of the plot to aid in harvesting.

A coulter double-disc no-till drill was used to seed plots into wheat (Triticum aestivum L.) stubble on four dates (two in fall and two in spring) at Vegreville and Fort Saskatchewan and on two dates (one in fall and one in spring) at Lethbridge. Fall seeding dates for Vegreville were 14 and 31 Oct. 1998 and 27 Oct. and 8 Nov. 1999; spring seeding dates were 29 Apr. and 18 May 1999 and 25 Apr. and 18 May 2000. Fall seeding dates for Fort Saskatchewan were 14 and 27 Oct. 1998 and 22 Oct. and 8 Nov. 1999; spring seeding dates were 29 Apr. and 17 May 1999 and 25 Apr. and 16 May 2000. Fall seeding at Lethbridge occurred on 14 Nov. 1998 and 22 Nov. 1999; in spring, plots were seeded on 5 May 1999 and 7 May 2000. Seed treatment formulations included seed coated with Vitavax Single containing fungicide only (22.5 mL kg^–1 carboxin), Vitavax rs with both fungicides and insecticide (22.5 mL kg^–1 containing carboxin:thiram:lindane at 1:2:15 g a.i.), and Extender with a germination-inhibiting polymer (Zaychuk and Enders, 2001).

Fertilizer was broadcast on the plots at the time of seeding according to the soil test recommendations for canola production, so total available quantities of N, P, K, and S were approximately 200, 40, 200, and 60 kg ha^–1, respectively. Weed control of the plots was achieved by hand weeding. Rainfall was monitored at each site during the period from seeding to harvest using tipping-bucket rain gauges.

Data Collection
Growth stages of canola were recorded weekly for each treatment plot beginning 14 d after the final spring seeding date using the key of Harper and Berkenkamp (1975). Canola seedlings were counted at each study site along a 1-m length of one row within each plot approximately 20 d after the final spring seeding date.

Adult flea beetle migrations were monitored with 12.7- by 7.6-cm yellow sticky cards (Phero Tech Inc., Delta, British Columbia) placed at 10-m spacings along the perimeter of the study sites. The cards, attached to wooden stakes, were about 10 cm above the soil surface and were collected and flea beetles counted twice weekly beginning 10 d after the final seeding date. Flea beetle damage was assessed at each site (location x year combination) on two dates in spring. The first or "early" assessment date occurred when yellow sticky cards indicated that flea beetles had emerged from their overwintering sites and were invading the research plots. At this time, beetle numbers per card ranged from 34 to 80 adults per card. The second or "late" assessment date occurred approximately 1 wk later. On each assessment date, 25 seedlings were randomly selected from the middle two rows of each treatment plot and rated according to the scale of Palaniswamy et al. (1992) where 0 = no damage and 10 = 100% of leaf area damaged by flea beetles.

At maturity, plots were harvested and threshed with a Hege plot combine. Grain samples were dried at approximately 20°C for 1 wk until they reached constant moisture. Seed was then cleaned and seed weights recorded for each plot.

Data Analysis
Flea beetle populations and damage were negligible at Fort Saskatchewan in both years of the study; consequently, flea beetle damage data were analyzed from the Vegreville and Lethbridge sites only. The Fort Saskatchewan data were incorporated in analysis of fall dormant versus spring seeding effects on canola plant stand establishment, time to flowering and maturity, and crop yield. Seeding dates (early/late fall and spring) and seed treatment formulations (Vitavax Single, Vitavax rs, and Extender) were combined into a single effect called seeding treatment for the statistical analysis.

The semicategorical nature of the flea beetle damage assessment data (rating scale values) and consequent non-normal distribution of data necessitated the use of a generalized mixed linear model. The analysis was conducted separately for each sampling date with the GLIMMIX macro of SAS (Littel et al., 1996) with blocks and sites (location x year combinations) as random effects, and species, seeding treatment, and seeding rate as fixed effects. A Poisson distribution and log link function model specifications were used for the analysis. Seedling density and yield data were analyzed with the PROC MIXED procedure of SAS (Littel et al., 1996) with blocks and sites (location x year combinations) as random effects and canola species, seed treatment, and seeding rate as fixed effects.

Site was considered a random effect for all analyses to extend conclusions across canola-growing regions. A combination of variance estimates and P values was used to determine the importance of site x treatment interactions. Site x treatment interactions for flea beetle damage were further explored with an analysis of variance conducted separately for each site, and results were used to understand how environmental and cropping conditions corresponded with treatment effect variability among sites. Contrasts were used to make specific comparisons among levels of the seeding treatments for all analyses. Treatment effects were considered significant at P < 0.05.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Environmental Conditions
Precipitation during the growing season in 1999 approximated 30-yr averages with a total of 21.2, 24.3, and 22.7 cm of rainfall received at the Vegreville, Fort Saskatchewan, and Lethbridge study sites, respectively. Lethbridge plots were invaded by large numbers of cabbage seedpod weevil adults, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), when plants were in the bud to early flowering stages. Infestations caused destruction of buds ("bud-blasting"), in addition to loss of seed yield and quality, especially in fall-seeded plots. The weevil invasion made it impossible to discern whether yield losses were attributable to flea beetles or weevils, so plots were not harvested at the end of the season.

In 2000, dry soil conditions persisted until mid-June at Vegreville and Fort Saskatchewan. However, precipitation after that time permitted good crop establishment, with a total of 19.2 and 21.4 cm of rainfall received during the growing season at Vegreville and Fort Saskatchewan, respectively. Snow melt soil moisture at Lethbridge was sufficient to permit good germination and uniform emergence of seedlings, but drought conditions persisted there throughout the season with only 0.5 cm of rainfall received between emergence and harvest. Plant racemes developed with few pods, and any seeds that did develop were very small. Consequently, plots were not harvested at Lethbridge.

Canola Stand Establishment
Seedling density was affected by canola species (P < 0.001) (Table 1). Densities were greater for B. napus than B. rapa, regardless of seeding date or seed treatment formulation (Table 2).

Plant density increased with seeding rate (P < 0.001), and seeding rate interacted with seeding treatment (Tables 1 and 3). Increasing seeding rate from 7.5 to 12.5 kg ha^–1 significantly increased plant density for 9 of 10 seeding rate by seed treatment combinations (Table 3). Seeding rate increases from 7.5 to 10.0 kg ha^–1 and from 10.0 to 12.5 kg ha^–1 were associated with significant increases in plant density more frequently in spring than in fall (Table 3), and this effect was greater for B. napus than B. rapa (data not shown).

Flea beetle damage was affected by host plant species (Table 1) and varied between the two assessment dates (data not shown). For example, mean damage ratings to plants of B. rapa on the early and late assessment dates were 1.94 and 2.08, respectively, compared with 0.68 and 1.31 for B. napus on the same dates. Damage levels per seedling often were lower and more similar among the different canola species, seeding dates, and seed treatment formulations for the early assessment date than for the late date. Species differences in susceptibility were approximately similar in magnitude for both assessment dates although the analysis determined that these differences were significant only for the late assessment date (P < 0.001) (Table 1).

Seeding date and seed treatment formulation significantly affected flea beetle damage (Table 1). This interactive effect was associated with higher flea beetle damage ratings in later seeding dates and for the Vitavax Single seed treatment (without insecticide) than for Vitavax rs (with insecticide) on the late assessment date, regardless of canola species (Table 1; Fig. 1) . For example, on the late assessment date, mean flea beetle damage to plants seeded in spring and treated with Vitavax Single was approximately twice that to plants seeded in fall or plants seeded in spring and treated with Vitavax rs (Fig. 1). The interaction between canola species, seeding date, and seed treatment formulation varied among sites for the late flea beetle damage assessment date (site x species x seeding treatment interaction; P < 0.05 and total site variation > 25%) (Table 1). The site x seeding treatment portion of this interaction corresponded to greater flea beetle damage to plants treated with Vitavax Single for spring than fall seeding at all sites and was especially prominent at Lethbridge in 1998 to 1999 (Table 1; Fig. 1 and 2) . This site x seeding treatment interaction was also associated with responses at Lethbridge in 1999 to 2000 and Vegreville in 1998 to 1999; mean flea beetle damage to plants of B. rapa treated with Vitavax Single was greater when plants were seeded in spring than in fall (P < 0.05) (Fig. 3) , but the same treatment difference did not occur for B. napus plants.

View larger version (22K): [in this window] [in a new window]   Fig. 1. Mean flea beetle damage ratings per canola plant seeded on two dates in fall and two dates in spring with different seed treatment formulations. Damage ratings are summarized from the latest of two assessments. The bar represents the LSD0.05 for interaction among factors averaged across sites, canola species, and seeding rates for each damage assessment date.

View larger version (23K): [in this window] [in a new window]   Fig. 2. Mean flea beetle damage ratings per canola plant seeded in fall and spring at Lethbridge and Vegreville, AB in 1998 to 1999 and 1999 to 2000 with different seed treatment formulations. Damage ratings are summarized from the latest of two assessments. The bar represents the LSD0.05 for interaction among factors averaged across canola species and seeding rates for each damage assessment date at each site.

View larger version (30K): [in this window] [in a new window]   Fig. 3. Mean flea beetle damage ratings per plant of Brassica rapa and Brassica napus seeded in fall and spring at Lethbridge and Vegreville, AB in 1999 to 2000 and 1998 to 1999, respectively, with different seed treatment formulations for the late damage assessment date. The bar represents the LSD0.05 for interaction among factors averaged across seeding rates at each site.

Significant seeding date, seed treatment, and seeding rate interactions occurred at Lethbridge in 1998 to 1999 and 1999 to 2000, although a site x seeding treatment x seeding rate interaction was not detected when data were analyzed with site as a random effect (Table 1). Mean flea beetle damage per seedling did not differ among seeding dates when canola was seed-treated with Vitavax rs, regardless of seeding rate (Fig. 4) . However, when seed was treated with Vitavax Single, the increase in flea beetle damage for spring- versus fall-seeded canola was substantially greater at seeding rates of 7.5 and 10.0 kg ha^–1 than at 12.5 kg ha^–1.

View larger version (27K): [in this window] [in a new window]   Fig. 4. Mean flea beetle damage ratings per canola plant grown at Lethbridge, AB in 1998 to 1999 and 1999 to 2000 and seeded in fall and spring at three rates with different seed treatment formulations. The bar represents the LSD0.05 for interaction among factors averaged across canola species for the late damage assessment date.

	DISCUSSION

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In our studies, fall-seeded canola was in the three to four true-leaf stages of development when flea beetles invaded plots in large numbers, but spring-seeded canola was still in the cotyledon stage. Flea beetle feeding damage to canola apical meristems can prevent a compensatory response (Gavloski and Lamb, 2000), but by the time of greatest flea beetle injury, plants seeded in fall had well-developed, enlarged apical meristems making them less susceptible to flea beetle damage. Moreover, plants in the true-leaf stages are no longer reliant on the cotyledons for photosynthate production and so would withstand considerably more feeding pressure from Phyllotreta spp. than spring-seeded plants still in the cotyledon stage. Damage to canola seeded in fall was low on both assessment dates (<30% of leaf tissue eaten), especially compared with plants seeded in spring (up to 70% of leaf tissue consumed). Seeding in fall enabled plants to progress beyond the vulnerable cotyledon stage by the time that most flea beetle damage was inflicted, resulting in less feeding damage per seedling without application of insecticide.

Seed treatment with Extender increased seedling emergence when canola was seeded in early fall although its impact on improved plant stands was evident in 1998 to 1999 but not in 1999 to 2000 (Table 4). The dramatic differences between the two field seasons in the effectiveness of Extender for enhancing seedling survival can be attributed to the variation in environmental conditions between years. In 1998 to 1999, the onset of winter was delayed by an extensive frost-free period in fall; however, when snow cover did develop, it remained throughout winter. Conditions in 1999 to 2000 were quite different. An initial period of frost and snow cover in November was followed by unseasonably mild temperatures during December. Snow cover disappeared, and many seedlings probably germinated at that time, only to be killed when seasonable temperatures returned in late December and January.

Failure to establish adequate fall-seeded canola plant stands even with polymer seed coatings, as we found in 1999 to 2000, is consistent with results of Clayton et al. (2004a) and Johnson et al. (2004). In order for fall seeding to be widely adopted by growers, technologies will need to be developed to prevent premature germination, and a more thorough understanding must be gained of the factors associated with plant stand failure (Johnson et al., 2004). However, once fall seeding technologies are perfected, our results indicate that this strategy has the additional benefit of reducing crop losses from flea beetle infestations and enabling production of canola with substantially less insecticide than is currently used.

We found no differences in flea beetle damage to canola seeded in early spring compared with late spring (Fig. 1 and 2). However, we expected that hastened plant development with early-spring seeding should have enabled plants to better resist damage compared with late-spring seeding if seedlings developed beyond the cotyledon stage when flea beetle invasion occurred. Additional site-years of flea beetle infestation data could better resolve this question, but damage levels to seedlings planted in early versus late spring are likely to vary depending on the timing of flea beetle emergence from their overwintering sites. Peak spring emergence of flea beetles occurs when soil temperature at their overwintering sites warms to 14 to 15°C (Ulmer and Dosdall, 2005). Because canola growth and development occur at soil temperatures lower than those needed for maximum flea beetle emergence (Thomas, 2002), early-spring seeding may enable plants to develop beyond the cotyledon stage and so escape excessive flea beetle damage in some sites and years. Our data suggest that fall seeding can more reliably impart this advantage to canola than seeding in spring. However, even in the absence of flea beetle pressure, seeding in early spring is still an appropriate agronomic strategy. Early-spring seeding may hasten development and so increase the probability that plants will avoid heat stress during flowering. Clayton et al. (2004a) found that early-spring seeding significantly increased yield in comparison with seeding later in four of 10 site-years. Seeding earlier, therefore, can be associated with an increased probability of higher yields in the absence of flea beetle feeding pressure, and when flea beetles are abundant, early seeding may help seedlings escape extensive damage.

Flea beetle damage to canola declined with an increase in seeding rate (Fig. 4), which concurs with previous results of Dosdall et al. (1999). Flea beetle damage ratings are based on the percentages of cotyledon and true leaf tissue consumed by adults. In dense plantings there is much more seedling leaf biomass than when stands are less dense, so damage by a given population of flea beetles is greater per seedling when plant density is low. Increasing seeding rate has potential usefulness for reducing flea beetle damage without the addition of seed treatment insecticide. We found that seeding canola in spring at 12.5 kg ha^–1 without an insecticidal seed coating reduced flea beetle damage to levels comparable to those achieved by seeding with an insecticidal seed treatment at 7.5 or 10.0 kg ha^–1. Increasing seeding rate to reduce crop damage by flea beetles is a strategy compatible with management of other canola insect and weed pests. For example, damage to taproots by larval root maggots (Delia spp.) (Diptera: Anthomyiidae) also declined with increasing seeding rates (Dosdall et al., 1996, 1998), and higher canola seeding rates reduced crop losses from weeds (O'Donovan, 1994; Harker et al., 2003; O'Donovan et al., 2004).

Treatment effects on yield were minimal, indicating that canola often compensated for the levels of flea beetle damage observed in this study. Injury to canola seedlings in our studies was lower than is often observed in other regions of the Northern Great Plains where flea beetle outbreaks can cause considerable stand losses (e.g., Lamb, 1984); compensation for feeding damage would be less likely to occur in those regions. Compensation by canola seedlings for flea beetle herbivory is a function of whether the insects destroy the apical meristems and the degree to which cotyledons are defoliated (Gavloski and Lamb, 2000). In our studies, mean flea beetle damage to spring-seeded canola at Vegreville did not exceed 40% of the leaf tissue eaten, but damage at Lethbridge was greater. We could not assess yield at Lethbridge due to drought and injury by other insects, but it is unlikely that plants at Lethbridge would have compensated as well because 60 to 80% of leaf tissue was eaten by flea beetles in some instances.

Lack of association between treatment effects for flea beetle damage and canola yield may also have been a function of soil moisture availability. Seed yields of both canola species were unusually low in 1999 at Vegreville, regardless of seeding date. Drought occurred at Vegreville in 1998, and even though rainfall approached normal levels in 1999, it is probable that residual soil moisture levels were too low to enable plants to achieve the level of seed yield that would be expected under normal moisture conditions.

Flea beetle control throughout the Northern Great Plains is routinely reliant on insecticidal seed treatment applications as a precautionary measure to protect against excessive feeding damage (Lamb and Turnock, 1982). Our data suggest that these treatments are often not necessary with fall seeding because under this management regime, plants rarely sustained more than 20% damage to their leaf tissue, a level for which canola can readily compensate (Gavloski and Lamb, 2000).

Results of our study have important implications for the integrated management of flea beetles in the production of canola in the Northern Great Plains. At present, brassicaceous oilseed crops are protected with insecticidal seed treatments followed by additional foliar sprays if beetle populations are exceptionally high or feeding damage extends beyond the time when the seed treatments are effective. Efforts to develop canola cultivars resistant or partially resistant to flea beetles have been made (Lamb, 1988; Palaniswamy et al., 1992; Gavloski et al., 2000), but after more than 15 yr of research, no resistant varieties are yet available to producers. Predation and parasitism are minor causes of flea beetle mortality (Burgess, 1977b; Burgess, 1980; Wylie and Loan, 1984), and biological control is not a promising strategy (Lamb, 1988). Consequently, integrating effective cultural control practices with insecticidal applications provides the most realistic management approach for these pests.

Several cultural strategies, determined from this study and from earlier research, can be combined to minimize the need for insecticidal intervention. Here we found that seeding in fall enabled seedlings to escape severe flea beetle injury because plants were in the true-leaf stages by the time that most flea beetle damage occurred. We also found that increasing seeding rate reduced flea beetle damage per plant, and planting B. napus rather than B. rapa resulted in less crop damage. Other effective strategies from previous research that can also be utilized in an integrated approach include growing canola in a zero-tillage regime rather than with conventional tillage (Dosdall et al., 1999) and planting large rather than small seeds (Bodnaryk and Lamb, 1991) at wide row spacings (Dosdall et al., 1999). Combining such cultural strategies may not completely eliminate the need for insecticidal intervention, but in the vast areas of cropland where flea beetle infestations are chronic, implementing these strategies should enable growers to substantially reduce insecticide use in canola production.

	ACKNOWLEDGMENTS

 
This research was funded by the Alberta Canola Producers Commission; the Alberta Agricultural Research Institute; Alberta Agriculture, Food and Rural Development; and the Alberta Research Council. We thank P. Conway, N. Cowle, and M. McFarlane for providing technical assistance, and K. Zaychuk of Grow Tec Ltd. for providing the seed and seed treatments used in this study.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

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