Flea Beetle Control Starts Early

REGINA - May 9/05 - SNS -- Saskatchewan Agriculture and Food reminds canola and mustard seed growers that ability of flea beetles to maintain large over-wintering populations has made them persistent spring pests.

Saskatchewan Agriculture and Food's Insect Specialist Scott Hartley offers some insight into managing their impact on crops.

"Your best indicator of what flea beetle populations will be like this spring is what the population was last fall," says Hartley. "Flea beetles over-winter as adults within leaf litter, grass and vegetative debris within fields, beneath hedges and shelterbelts, in poplar groves, and in association with canola stubble and volunteer cruciferous plants."

Initially, when the temperature warms up in spring, they will start feeding on early emerging volunteer canola and related weeds such as wild mustard, flixweed and stinkweed.

"The economic impact of flea beetle damage will not be felt until the canola seedlings start to emerge and become the next food source for the beetles," explains Hartley. "Producers should base their flea beetle management decision on populations observed the previous fall."

Flea beetles feed on the above ground plant components of brassica crops (canola, mustard and rapeseed). The effect of feeding activity on crop development varies with the part of the plant that is targeted, as well as crop development and the intensity of the attack.

The crop can usually compensate for the destruction of individual plants, provided large portions of the crop are not totally destroyed and growing conditions are favorable. Feeding damage is most severe when beetles attack the growing point (apical meristem) because it limits the ability of the plant to recover, most often resulting in death. Cool spring conditions in 2004 slowed seedling development, as well as flea beetle activity. The insects fed closer to the ground surface, girdling the young stems and killing the plants that were most severely affected.

"In essence, younger plants are more susceptible to high feeding pressure. We recommend constant monitoring to ensure the action threshold is not crossed. This is the point where 25 per cent of leaf tissue has been removed or consumed. It is the level where the plant can withstand a little more damage while giving producers sufficient time to implement appropriate action."

According to Hartley, the use of insecticide seed treatments represents an attractive option when the infestation is expected to be intense.

"Whether producers opt for a seed treatment with just a fungicide or a combination of insecticide and fungicide, the coated seed is the best way to ensure constant protection. The insecticide in the seed treatment is systemic — it grows within the plant and is fatal to the flea beetles when plant tissue is consumed.

"However, the newer seed treatments do not repel the beetles, and therefore, with high populations and heavy feeding, a foliar spray may still be required. The higher rates of the seed treatments have provided the best control under these conditions. Seed treatments containing an insecticide are not registered for on farm use, and must be applied by commercial seed treaters."

Regular monitoring for flea beetle damage is important. "When assessing economic thresholds, it is important to consider growing conditions, as well. When flea beetle feeding is combined with poor plant growth during hot, dry weather, canola can tolerate less flea beetle feeding than if plants are growing under more ideal conditions."

Hartley also points out that research is currently being conducted to develop flea beetle resistant canola varieties.