NDSU

2003 Reducing Insecticide Inputs for Control of the Crucifer Flea Beetle in Canola

Janet Knodel, Area Extension Specialist/Crop Protection, North Central Research Extension Center, Minot
Lorilie Atkinson, Research Specialist, North Central Research Extension Center, Minot
Denise Olson, Entomologist, Department of Entomology, NDSU, Fargo
Bryan Hanson, Agronomist, Langdon Research Extension Center, Langdon
Bob Henson, Agronomist, Carrington Research Extension Center, Carrington

Abstract
Canola is an important crop of North Dakota agriculture.  The crucifer flea beetle, Phyllotreta cruciferae Goeze, is the major insect pest of canola, and can significantly decrease plant stands, cause uneven growth and maturity, and decrease yields.  Canola is becoming expensive to produce due to its high input costs, for example insecticides, seed, fertilizer.  The objective of this proposal was to determine if insecticide seed treatment costs ($7.00+ per acre cost) could be reduced and still effectively control the crucifer flea beetle in areas with different pressures.  The high and low rates of Helix with active ingredient thiamethoxam from Syngenta, and Prosper with active ingredient clothianidin from Gustafson, were evaluated at 33% treated seed : 67% untreated seed; 67% treated seed : 33% untreated seed; and 100% treated seed.  Results indicate that the 100% treated seed had higher plant stand counts and improved vigor (higher plant dry weight), and a lower incidence (% of plants damaged) compared to the 67% and the 33% treated seed.  Using 100% treated seed and the high rate of insecticide seed treatments was discovered to be crucial for protecting canola in moderate to heavy flea beetle pressures areas (Minot, Langdon, Carrington).  These data demonstrate that as the ratio of insecticide treated seed was reduced, the damage ratings were subsequently increased.  67% and 33% treated seed were not as effective in reducing the overall damage rating compared to 100% treated seed.  For example, 100% treated seed had an average damage rating across locations of 2.9, 67% treated seed had 3.1, 33% treated seed had 3.7 and the untreated check had 4.6.  When averaged across locations, the high rate of insecticide seed treatments had a slightly lower damage rating of 3.1 compared to the damage rating of 3.4 for the low rate of insecticide seed treatments.  100% Helix xtra treated seed usually had the lowest damage ratings among the insecticide treatments.  Canola seed treated with insecticides and 100% treated seed flowered earlier and were taller at the end of flowering than untreated seed, 67% and 33% treated seed.  There were little differences in flower duration and maturity date; probably due to the hot July weather which accelerated plant development.  When yield was averaged across locations, 100% treated seed had the highest yield (1338 lb/A), then 67% treated seed (1095 lb/A), then 33% treated seed (872 lb/A), and the untreated check with the lowest yield (568 lb/A).  The high and lower rate of insecticide had a difference of 313 lb/A (high rate averaged 1258 lb/A versus low rate of 945 lb/A).  In addition, the high rate had a 2x the difference of 690 lb/A from the untreated check compared to the low rate with a difference of 377 lb/A from the untreated check.  Yields were similar between insecticides when averaged across locations and percent treated seed:  1289 lb/A for Helix xtra versus 1228 lb/A for Prosper 400, and 996 lb/A for Helix lite versus 893 lb/A for Prosper 200.  There were little differences in test weight, seed weight, and percent oil among percent treated seed, high and low rates of insecticides, and insecticide treatments.

Introduction

Canola is an important rotation crop in the Northern Great Plains. Canola oil is expanding its market share due to its placement as one of the healthiest of vegetable oils. North Dakota produces 85% of US canola and production was valued at $116M in 1998, $81M in 1999, $108M in 2000, $158M in 2001, $151M in 2002 and near $160M in 2003.  The high market demand for canola makes it an increasingly important crop for growers in North Dakota.  Canola will help add diversity and provide an important cash crop to central and northeastern North Dakota. 

The crucifer flea beetle, Phyllotreta cruciferae Goeze, represents a major insect threat to canola production wherever it is grown in the Northern Great Plains.  Flea beetles can invade and reduce newly emerged plant stands within a few days.  Currently, the most effective management measure is the use of insecticides for managing the overwintering generation of flea beetles that emerge early in the spring.  The seedling stage is the most critical period, and insecticides often need to be applied as a seed treatment or as a foliar application to protect the crop from flea beetle damage.  Flea beetle populations have been at damaging levels since 1997 in north central North Dakota, and appear to be increasing based on trapping records (Knodel, unpublished).  Although post-emergence foliar insecticides can be effective, they require timely applications within a relatively small window of opportunity.  Therefore, seed treatments are obviously more convenient and commonly used.

Canola is becoming expensive to produce due to its high input costs, for example insecticides, seed, fertilizer.  Across different canola growing regions of North Dakota, canola has an estimated input cost of $58.53 per acre compared to oil sunflowers of $35.55 per acre and hard red spring wheat of $32.70 per acre.  In general, canola growers must plan for about $20 per acre higher expenses than other crops.  The objective of this proposal is to determine if insecticide seed treatment costs ($7.00+ per acre cost) can be reduced and still effectively control the major insect pest of canola, crucifer flea beetle, in areas with different pressures.  This has never been tested before in North Dakota and would result in lower the input costs as well as lower the risk of insecticide contamination in the soil.

Materials and Methods
The efficacy of using reduced ratios of insecticide treated seed was evaluated using commercially available seed treatments.  Trials assessing the different insecticide treatments were conducted in research plots located at the research extension centers in Minot, Langdon, and Carrington.  Brassica napus cv. RaideRR (Integra Seed Ltd., open pollinated) was seeded on May 2, 2003 in Minot, May 13, 2003 in Langdon and May 1, 2003 in Carrington.  The seeding rate was approximately 14-17 pure live seeds per sq. foot.  A RCB design with four replicates was used.  Experimental units were 3.5-4.1 ft. (7 rows) x 20-22 ft.  Two seed treatment, Helix with active ingredient thiamethoxam from Syngenta, and Prosper with active ingredient clothianidin from Gustafson, were evaluated at their low and high rates that are commercially available.  Three different ratios were also be evaluated for each seed treatment:  33% treated seed : 67% untreated seed; 67% treated seed : 33% untreated seed; and 100% treated seed.  This included a total 13 treatments: 

                  1) Untreated check

                  33% treated seed : 67% untreated seed

                  2) Helix lite (200 g ai/100 kg seed) seed treatment

                  3) Prosper 200 (200 g ai/100 kg seed) seed treatment

                  4) Helix xtra (400 g ai/100 kg seed) seed treatment

                  5) Prosper 400 (400 g ai/100 kg seed) seed treatment

                  67% treated seed : 33% untreated seed

                  6) Helix lite (200 g ai/100 kg seed) seed treatment

                  7) Prosper 200 (200 g ai/100 kg seed) seed treatment

                  8) Helix xtra (400 g ai/100 kg seed) seed treatment

                  9) Prosper 400 (400 g ai/100 kg seed) seed treatment

                  100% treated seed

                  10) Helix lite (200 g ai/100 kg seed) seed treatment

                  11) Prosper 200 (200 g ai/100 kg seed) seed treatment

                  12) Helix xtra (400 g ai/100 kg seed) seed treatment

                  13) Prosper 400 (400 g ai/100 kg seed) seed treatment

Flea beetle populations were monitored weekly using sticky yellow trap cards.  To evaluate flea beetle damage, assessments were taken on approximately 25, 31, 38, and 45 days after planting (DAP) using the following techniques:

1) Counting the total number of plants in a 16 ft. long section of row, and then recounting the number of plants with flea beetle damage to determine the percent incidence.  Any plant with pitting or other feeding punctures were considered damaged.  This provided the plant stand count (# plants/sq. foot).

2) A total of ten plants per plot (or 40 per treatment) were randomly collected along this 16 ft long section, and rated for flea beetle damage.  The following rating scheme was used:

1 = 0-3 pits per seedling

2 = 4-9 pits per seedling

3 = 10-15 pits per seedling

4= 16-25 pits per seedling

5 = >25 pits per seedling

6 = dead.

3) The dry weights of 10 seedlings per plot were weighed in grams to indicate the overall vigor of the plant on 25 and 31 DAP only.  All roots were removed from the seedling using a razor.

            During the field season, the following notes on crop development stages were taken:

1^st Flower: Days after planting when 10% of plants in plot have at least one open flower.

End Flower: Days after planting when 90% of plants in plot have completed flowering.

Flower Duration: Days from 1^st flower – End flower

Days to Mature: Days after planting when seeds on lower third of main raceme are dark brown to black, seeds on middle third of main raceme are turning brown or black and seeds on top third of raceme are green but firm and pliable.

Plant Height: Height from soil surface to top of main raceme in inches at the end of flowering.

Roundup (1 pt./A) + AMS was applied for weed control early in the season.  A Ronilan application was not necessary in 2003 for disease control due to the environmental conditions at Minot and Carrington.  However, Ronilan (12 oz/A at 20-50% bloom) was sprayed in Langdon.  Best management practices were used regarding fertility and harvest operations.  Plots were harvested on August 12, 2003 in Minot, September 2, 2003 in Langdon, and August 18, 2003 in Carrington.  Yield (lbs/A), test weight (lb/bu), and seed weight (gm/1000 seeds) were obtained at the end of the season to facilitate agronomic comparisons.

Data Analysis:  Data were compared between treatments using Analysis Variance (ANOVA) (Zar 1984), and Fisher’s Protected LSD (SAS institute 1991).

Results and Discussion

Flea Beetle Populations:

During 2003, the spring emergence of flea beetle was delayed due to the cool, wet early May.  In late May, flea beetles were ready to emerge as the canola seedlings were emerging.  This was the major peak of activity, and spring emergence continued until late June.  Flea beetle populations were high in Minot and Langdon, and even moderate-high in Carrington during 2003 (Fig. 1).  The total number of flea beetles captured from May 1 to July 1 includes:  11,047 for Minot, 5,159 for Langdon, and 11,051 for Carrington.  The average trap catch was 85 beetles per trap day in Langdon, 181 beetles per trap day in Minot and Carrington.  Langdon had a lower than expected total number of flea beetles and average trap catch, because canola seedlings in the trapping area were almost completely defoliated by flea beetles making the trapping area less attractive.  However, flea beetle pressures were very high in Langdon killing most of the canola seedlings in the untreated plots.  Trap data from Carrington recorded lower numbers of flea beetles in May due to the delayed planting and emergence of the untreated canola for the trapping area.

Plant Stand, Incidence, and Dry Weight (Table 1 & 2):

For plant stands at Minot on 25 DAP, the 100% treated seed of Helix xtra and Prosper 400 had significantly higher plant stand, about 13 plants per square foot, compared to the untreated check, 8 plants per square foot.  At Minot on 31 DAP, the following treatments had significantly higher plant stand counts than the untreated check:  100% Helix xtra, 100%, 67%, and 33% Prosper 400, 100%, 67%, and 33% Prosper 200.  At Langdon and Carrington, no difference were observed in plants per square foot on 25 and 31 DAP, probably due to heavy flea beetle pressures in plots.

Incidence measures the percent of plant damaged by flea beetles.  At Minot, the following treatments had a significantly lower incidence at 25 DAP than the untreated check:  33% Helix xtra, 33% Prosper 400, and all treatments at 67% and 100% treated seed.  100% and 67% Helix xtra, 100% Prosper 400,  and 100% Prosper 200 also had lower incidences than 67% Prosper 200, and all treatments at 33% treated seed.  At Langdon and Carrington, no differences were observed for incidences at 25 DAP, probably due to heavy flea beetle pressures and flea beetles moving into plots earlier than at Minot.  At 31 DAP, there were no significant differences in incidence regardless of the location, which suggests heavy flea beetle infestations in the plots.

For dry weight at Minot on 25 DAP, 100% Prosper 200, 67% Helix xtra, and 67% Helix lite had significantly higher dry weight than the untreated check, but was not significantly different from the remaining seed treatments.  There were no differences in dry weight at 25 DAP at Langdon and Carrington.  At 31 DAP, dry weight of all seed treatment ratios was significantly higher than the untreated check at Minot.  100% Helix xtra and 100% Prosper 400 had the highest dry weight among the seed treatments.  At Langdon and Carrington on 31 DAP, only 100% Helix xtra had significantly higher dry weight than the untreated check.   

These data indicate that the 100% treated seed had higher plant stand counts and improved vigor (higher plant dry weight), and a lower incidence (% of plants damaged) compared to the 67% and the 33% treated seed.  In Table 2, these data are averaged across locations.  In general, the insecticide treatments and treatments with 100% treated seed had higher plant stand counts.  The high rate of seed treatment also had slightly higher plant stand counts, average of 9.6 for both Helix xtra and Prosper 400, compared to low rate of seed treatment, averaged of 9.2 for Helix lite and 9.4 for Prosper 200.  At 25 DAP, the insecticide treatments and treatments with 100% treated seed also had lower incidences (or percent of plant damaged) than the untreated check.  For example, 100% treated seed average 70%, 67% treated seed average 75%, and 33% treated seed average 91% compared to the untreated check of 100%.  The high rate of insecticides also had a lower incidence of 74% compared to the low rate of insecticide of 83%.  Differences between Helix xtra (73%) versus Prosper 400 (75%) and Helix lite (82%) versus Prosper 200 (83%) were small when averaged across locations.  At 31 DAP, incidence of insecticide treatments was similar to the untreated check due to waning insecticide residuals and heavy flea beetle pressures.  For dry weight, the differences were more observable at 31 DAP.  Again, the insecticide treatments and treatments with 100% treated seed had higher plant dry weights.  For example, 100% treated seed average 0.345 g/10 plants, 67% treated seed average 0.290 g/10 plants, and 33% treated seed average 0.234 g/10 plants compared to the untreated check of 0.083 g/10 plants.  The high rate of insecticides also had a higher dry weight of 0.312 g/10 plants compared to the low rate of insecticide of 0.268 g/10 plants.  Differences between Helix xtra (0.327 g/10 plants) versus Prosper 400 (0.298  g/10 plants) and Helix lite (0.281 g/10 plants) versus Prosper 200 (0.254 g/10 plants) were small when averaged across locations.

Table 1.  Plant Stand and Incidence