NDSU

2000 Flea Beetle Insecticide Study
Large Plot Trial  

Jan Knodel, Crop Protection Specialist
Brian Jenks, Weed Scientist

Introduction
Canola, Brassica napus L. and B. rape L. are a high quality edible oil crop.  Flea beetles are the primary insect pest of canola in the Northern Great Plains, capable of eliminating seedling stands or in less severe cases, reducing yield and seed quality.   Currently, the most effective management measure is the use of insecticides for managing the overwintering generation of flea beetles that emerges 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.  Data were collected on the efficacy of different insecticides from a large plot study to mimic a grower’s field.

Material and Methods
Four treatments were evaluated for crucifer flea beetle management on canola during 2000:  untreated control, foliar spray of Capture (FMC), and two seed treatments - new formulation of Gaucho (Gustafson) and Helix (Novartis).  Brassica napus cv. 357RR was seeded on May 5, 2000 for the Gaucho, Capture, and control treatments at 8 lbs. of seed per acre.  The Helix seed treatment was seeded later on May 9, 2000 due to rain which prevented its seeding on May 5, 2000.  Treatments were arranged in a randomized complete block design with three replicates per treatment.  The large plots were 30 ft. (wide) x 160 ft (long).  Gaucho was treated with Gustafson’s new fungicide package (thiram, allegiance, carboxin) and the insecticide gaucho.  Helix (Novartis) treated canola seed had the apron XL, dividend, maxim for the fungicide package and adage for the insecticide.

 Flea beetle populations were monitored weekly using sticky yellow trap cards.  Three assessments were taken to evaluate flea beetle damage at 2-2.5 weeks after planting (or 1-1.5 weeks after emergence):

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 determined the percent incidence.  Any plant with pitting or other feeding punctures was considered damaged.  This also provided the plant stand count (# plants/foot).

2)      A total of ten plants per plot (or 30 per treatment) were randomly collected along this 16 ft long section for flea beetle damage ratings.  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 leaf area damaged by flea beetles was determined by using a computer image analysis system (CID, Inc.).  A total of two plants per plot or eight per treatment were scanned into the computer for leaf imaging analyses.

Capture was applied on May 23, 2000 at a rate of 2.1 fl. oz. per acre using a tractor sprayer with a 15 ft. boom that extended over one half of the plot.  The 30 ft. plot width was covered by driving and spraying along both sides of the plot.  Both seed treatments were also rescued with a foliar application of capture on June 5, 2000 due to the heavy flea beetle pressures.  Roundup was applied on June 10, 2000 for weed control.  The canola was swathed on August 8, 2000, and combined on August 15, 2000.  The following data were collected from each experimental unit: yield (lbs./acre), and test weight (lbs./bushel). 

Data were analyzed using SAS ANOVA procedure and LSD test.

Results and Discussion
Population Dynamics of the Crucifer Flea Beetle:
During 2000, the flea beetle activity started mid-May and continued until early July (Fig. 1).  The numbers of flea beetles at Minot had a high average trap catch of 923 beetles per trap week with the peak occurring between June 25 and July 3.  The duration of the feeding period was approximately 1.5 months long.  In 1999, the population trends were similar - started to increase in late May and continue for a month long (Fig. 1).  However, the numbers were lower in 1999 with an average trap catch of 290 beetles per trap week during peak activity.  The majority of the canola crop in the North Central Region was planted during early-mid May, which provided opportune time for the emerging flea beetles to infest.  Unfortunately, some canola fields had to be rescued with one or more applications of a foliar insecticide regardless of whether the seed was treated or not.

Flea Beetle Damage Assessments: (Table 1)
There were no significant differences among the treatments for plant stand counts.  The mean plants per foot of row was 4.6.  Capture had been sprayed only one day prior to the damage assessments so one would expect the damage levels to be similar to the untreated check.  Helix had the lowest incidence of flea beetle damage but was only significantly lower from Capture and the untreated check.  Helix also had the lowest damage rating and was significantly lower from the Gaucho, Capture, and the untreated control.  One of the reasons Helix had lower damage is because it was planted later than other treatments.  Although the difference was only 4 days, the flea beetles became very active the weekend before Helix was planted due to the warm temperatures.  As a result, the other treatments (Gaucho, Capture, untreated check) had a longer exposure to heavy flea beetle pressures.  The percent leaf area damaged is probably the best indicator of damage.  Both Helix and Gaucho had significantly lower leaf area damaged compared to Capture and the untreated check.  For Capture, it is important to remember that it was only sprayed one day prior to the damage assessments.

Appendix I illustrates the damage among the different treatments from scanned leaf seedlings of the large plot plantings.

Harvest Data (Table 2):
The yield and test weight were not significantly different among treatments.  The treatments ranked in order from the highest to lowest yield include:  Gaucho, Capture, Helix, and the untreated control.  The test weight is an indicator of quality, and appears to be not directly influenced by flea beetle pressures or yield.  For example, Gaucho had the lowest test weight, but the highest yield.  The treatments ranked in order from the highest to lowest test weight are:  Capture, Helix, untreated control, and Gaucho.

*The untreated control, Capture, Gaucho plots were seeded on May 5, 2000 and the Helix plots were seeded on May 9, 2000.
**The Gaucho and Helix plots were rescued with a foliar application of Capture on June 5, 2000 due to heavy flea beetle pressures.

Acknowledgements
The author would like to thank the Northern Canola Growers Association, FMC, Gustafson, and Novartis for their support.  This research would not have been possible without the field assistance of G. Willoughby, D. Markle, H. Semler, L. Neal, and A. Marsland.

Control