Organic pest management of cabbage flea beetles

Description

The following tools and techniques are meant to provide some examples of organic pest management (IPM) tactics for cabbage flea beetles (scientific name Phyllotreta cruciferae) using the “Four T” method.

Target

Our target is the adult of the cabbage flea beetle adults. These are tiny, black, and shiny beetles that have a burstlike jumping action that looks like the jumping action of fleas. Cabbage flea beetles are beetles and not related to fleas at all.

Timing

General calendar time: adults emerge between late May through early June (in Minnesota)
Degree days: adults emerge between 150-250 degree days

The time to control these beetles adults is when they emerge from the ground in the spring. In Minnesota, and around the Twin Cities metropolitan area, the general window for cabbage flea beetle emergence is around late May (around May 20) through early June (around June 1).

We can improve the precision of our timing by using a simple degree day calculation formula. This formula asks us to take the average daily temperature (the daily high temperature and the daily low temperature divided by 2) and subtract it by the lowest average temperature a typical insect begins to move (50 degrees F). If the number at the end of it is over 50, we count that as insect “degree days”.

By using the simple degree day formula, growers can narrow the window of time that insects emerge to a week’s time or less – and this precision can affect which tool you use as well as when and how you use it in the field.

Tool(s)

Tool #1: Yellow sticky cards (Type of tool: Mechanical/Monitoring)

For all-sized plots: Place yellow sticky cards at regular intervals. around perimeter and within plot area at at least one day before earliest expected emergence. Suggested placements:

  • For a very small (12×12 sq. ft. or less) plot, place at least one trap at each corner, and one or two within the plot.
  • For a small (18×18 sq. ft or less) plot, place one trap every three to six feet around the perimeter of the plot and at least three to four at selected intervals within the plot.
  • For a moderate (24×24 sq. ft.) plot, place one trap every four to six feet around the perimeter of the plot and place additional sticky traps within the plot area.

Tool #2: Plant a “trap crop” (Type of tool: Cultural)

For small to very large plots: Plant a cool-hardy “trap crop” among your primary crop that is attractive to the adult cabbage flea beetles and that will distract them and perhaps diffuse their feeding time and energy.

  • Plant radishes in mid-to-late April

Tool #3: Spray insecticidal soap with neem oil (Type of tool: Chemical)

Insecticidal soap with neem oil basically coats the insects with a soap-like substance that slows them down. In addition to the slick interference that the oil portion of the spray may have on their movement, the neem oil. If they come into contact with it (or better yet, if some is ingested) the neem oil’s natural antifeedant properties interferes with their digestion and/or willingness to feed. Without feeding, the cabbage flea beetles don’t get as strong as they need to be. Females who don’t feed are less likely to lay as many eggs as they might otherwise lay.

Tool #4: Use row cover material to protect crops

Row cover material may be time intensive to setup, take down, and store, but its effectiveness is guaranteed to protect against cabbage flea beetles and many other adult plant-feeding insects. In addition to protection from insects, row covers may also provide additional protection from sun/wind exposure, heavy rains, hail, and other weather-related pressures.

Technique(s)

Technique for tool #1

Attach yellow sticky cards on long (eight to 10-inch wooden craft/popsicle sticks) using hot glue gun. Place the yellow sticky card at least three-to six inches from the plants you intend to monitor. Place at least 3 to four inches of the stick into the soil so that the stick is firm in the ground and not easily blown away. Press down around the stick so that it remains firm in the ground.

Technique for tool #2

Plant radish seeds in mid-to-late April. In rows or in areas that will be accessible for cabbage flea beetles. The idea behind these radishes is that they will grow taller and be more attractive to the early “waves” of cabbage flea beetle adults that emerge from overwintering. You may decide if you want to kill these early-emerging adults with a strong dose of Pyganic (a neuro-toxic pesticide derived from chrysanthemums) so that they do not transfer to your primary crop or perhaps douse them with a healthy dose of insecticidal soap with neem oil in the hope that they are slowed down and perhaps will ingest the neem oil and decide not to feed. (See tool #3)

Technique for tool #3

So you’ve decided to spray insecticidal soap with neem oil. If they ingest the insecticidal soap with neem oil, the soap part may slow them down and the neem oil may suppress their appetite. Either way, you may still have the cabbage flea beetles, visible, but they may not be doing anything, so you’ll have to watch them to make sure. A second or third treatment of insecticidal soap with neem oil may help prevent additional damage if the first treatment wears off within four or five days.

Technique for tool #4:

Use row covers in conjunction with any of the other three tools (or all four) to maintain protection and

Control measures outside of the season

Flea beetles lay eggs close to the base of plants. Larvae hatch from these eggs and feed on plant roots during the growing season. If you receive regular and high pressure from cabbage flea beetles, you may consider applying beneficial nematodes after the adult flea beetles reach their peak in mid to late July. The beneficial nematodes, if they establish, should provide pressure to future populations of cabbage flea beetles within the soil areas where they overwinter.

For more information

Contact Green Noise LLC at leavesofnoise@gmail.com

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