Managing Flea Beetles

By Shelleen Gerbig, BSA, P.Ag, SARDA Ag Research and Dr. Maria Angelica Ouellette, Ph.D., NPARA

Adult Flea Beetles (Phyllotetra spp.) feed on the cotyledons of newly emerged canola seedlings and cause significant damage to the crop, sometimes requiring costly reseeding operations. Rapidly growing canola seedlings may outgrow the pests as older plants can withstand the feeding pressures. Seed-coated insecticides are the first level of control and often the best, but they require the beetle to feed on the plant to take effect. Large populations of the beetle may damage the crop even if the seed-coated insecticide is effective. If seeding occurs in cold, wet soil and germination is delayed, seedling canola plants may be adversely affected by flea beetles. Seed-applied insecticides are only effective for 2-3 weeks after seeding. Foliar applied insecticides are available, but the time to effectively spray is compressed. Foliar-applied insecticides also have a greater risk of affecting non-target native pollinators such as birds and bees. Relying only on chemical means to control flea beetles could cause problems in the future as the pests may develop resistance to the chemicals, and beneficial insects (flea beetle enemies) are destroyed. Therefore, it is imperative to combine cultural control methods to reduce the need for chemical insecticide applications.

In 2020, SARDA Ag Research, MARA (Makenzie Applied Research Association), and NPARA (North Peace Applied Research Association) started a joint project to evaluate the effectiveness of various cultural methods of control for flea beetles. Increased seeding rate (Dosdall et al. 1999), late seeding date (mid-May to early June) (Cárcamo et al. 2008) and larger seed size (Elliot et al. 2008; Bodnaryk and Lamb 1991) have been some of the agronomic methods used to reduce flea beetle populations. Our trials will also look at the species of flea beetles that affect our crops in the Peace Region. We have three common species; one native species, the crucifer flea beetle and the striped flea beetle. The striped flea beetle is likely the most common in the Peace Region, but it holds the dubious distinction of being the most difficult to control.

To evaluate flea beetle pressures, we designed an experimental trial. The treatment parameter was early and late seeding dates, and split-plot parameters were seed size (< 2.2mm, >2.2.mm and mixed) and seeding rates (3.7, 7.4 and 11.1 lb ac-1). The canola seed used for the trials was not treated with insecticides but with fungicides. We assessed the following parameters during this experiment: a) Fleabeetle individuals were counted from sticky traps every three days from canola emergence up to the second cotyledon leaf. Sticky traps were swapped at the third counting and taken back to the shop to identify flea beetle by species (native, crucifer and striped). b) Visual assessment of the leaf damage percentage and c) canola stand counts at emergence, fluorescence and maturity.

2021 was the second year of the trial, and 2022 will be the final year. The total fleabeetle population tended to increase until the two-leaf cotyledon stage, while leaf damage percentage showed a maximum point followed by a decline. Canola leaves quickly grow, providing an abundance of food for the fleabeetles. Ample food signals flea beetles to reproduce, so populations increase. The percentage of leaf damage declines because the leaves and plants are actively growing, and the surface area expands faster than the flea beetles can feed on the leaves.

We found the seeding date impacted the number of striped and native fleabeetle species. More striped and native flea beetles were in the later seeded canola than earlier. The native flea beetle has increased in numbers compared to the other two species, which disagrees with previous literature arguing that striped and crucifer fleabeetles are more common. There were differences in yield between the early and late seeded crops. Canola sown at the lowest rate (3.7 lb ac-1) yielded more if sown later in the season than earlier. In addition, canola stands emerging from large and mixed-size seeds produced more than those from small seed sizes. The number of plants at emergence, fluorescence and maturity was greater in the late seeded than in the early seeded.

The data from the 2022 season will align our data and provide guidelines for Integrated Pest Management of Flea Beetles in Canola in the Peace Region.

We want to thank our partners and funders of this project; NPARA, MARA, SARDA Ag Research and Canola Agronomic Research Program (CARP).

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Sticky card traps for flea beetle