Diamonds Are Not a Farmer’s Best Friend

The southern winds blew all spring and have left us wondering, “Did they bring the diamondback moths with them?”

What Are Diamondback Moths?

Diamondback moths are a pest on the Canadian Prairies, which migrate from the south to the north on the wind currents in the spring. They prefer brassica crops, which means on the prairies they feed mainly on canola. Diamondbacks can have up to 4 generations per year, so the damage period can depend on when they arrive, and how many generations there are.

The moths are 8-9 mm in length when resting, and they have 3 diamond-like markings on their back. The adult moths lay eggs on the leaf surfaces which can hatch to larvae in 4-8 days. Since the diamondback can have up to 4 generations per year, there can be all life stages in one field at the same time. 

Once the larvae hatch, they can feed up to 21 days. First on internal leaf tissue, then outer leaf tissue, flowers and buds. When the larvae reach maturity, they are a bright green worm around 12 mm (½”) long with a slight taper at each end. When the larval stage is complete, they pupate. This can last anywhere from 5 to 15 days. They then emerge as an adult moth, and start the whole process over again. The whole diamondback life cycle can vary from 21-51 days, depending on the environment and food conditions. 

What To Watch For

There are a few different monitoring techniques that can be used. The first would be pheromone traps, which are set out to predict early warnings of infestations. Unfortunately though, these traps are only an estimate or a predicting tool and regular monitoring in July and August is necessary. 

When it comes to scouting for these pests, you will be looking for the diamondbacks in the larval stage. It is important to identify them at this point in the life cycle as this is when they feed on the plant. Sweep nets can be utilized, but keep in mind there are no threshold numbers set for this method. Since diamondbacks can feed on all parts of the plant, the sweep net will not accurately collect the larvae in that testing area. If diamond back larvae are found in the sweep net, closer inspection is required of the crop. 

The best method of scouting is to visit 5-10 different areas in the field and remove plants in an area the size of a square foot. You will then lightly beat the plants on a clean surface, such as the hood of your truck or the tailgate. The larvae will fall off the plant, and you will be able to assess the populations. The action threshold is 20-30 larvae/ft2 or 2-3 larvae/plant. 

When you are assessing damage it is important to take into account the stage(s) of the larvae and the crop. Once leaf tissue begins to die off as the plant matures, the larvae will move up the plant and feed on pod and stem tissue.  This can quickly lower the yield potential of the crop.

How To Control Them

As with most pests, there are beneficial insects that can help naturally control populations. This can range from insects, to parasitoids, or fungi. The presence of these factors are important to take into account when deciding if you have reached the action threshold or not.

If the application of an insecticide is warranted, there are many options on the market. Insecticide would be applied if you have determined that your crop has reached the action threshold and needs another form of control to prevent further damage. There are different products available but it is important to be cautious of the preharvest interval and the impact on beneficial insects found in the field. 

If you need help monitoring for diamondbacks, or help deciding which control option would be the best fit for your operation, reach out to your SynergyAG agronomist or sales representative.

Niki Beingessner CCA, PAg

Sales Agronomist – Yorkton, SK

Sources:

Canola Council

Government of Saskatchewan