Cutworms: What’s causing bare spots, and how can SWAT MAPS help?

Cutworms are a pest mainly in canola and pulse crops but can become a problem in cereals and other crops as well. There are many different species and damage will be very similar with all of them, so identification is key to determining which ones you are dealing with in your field. Their damage can be localized to small areas within a field or widespread across an entire region and populations can persist for years. Cutworm development progresses from egg through larval instars to pupa then adult, with the larvae causing crop damage. There can be one or multiple generations per year depending on the species.

Figure 1: Cutworm curled when disturbed (Source Rachelle Farrell Senior Precision Agronomist with Croptimistic Technology)

Figure 2: Multiple species of cutworm within single field. (Source Rachelle Farrell Senior Precision Agronomist)

Scouting and Identification

When looking for cutworms, look for bare patches in the field, holes in leaves, wilted plants, or plants that have been chewed near the soil surface. Cutworms will curl up when disturbed. Pay close attention to hilltops — typically in SWAT Zones 1-4 — compacted areas, pulse stubble, fields with high trash and weedy patches. Cutworms move quickly through a field so if there is a suspicious area, action should be taken within 24 hours to control them. They will bury themselves below ground during the heat of the day and come out when the soil temperature begins to drop.

By using SWAT MAPS you can target your search for cutworms to be much more efficient. You can start by looking at SWAT MAPS Zone 1 and expanding out from there.

Figure 3: Damage to field caused by cutworm (Source: J. Robert Byers, AAFC)

Figure 4: Dying plants with stems cut close to ground (Source: Canola Council of Canada)

Thresholds

There are important considerations when determining if you should spray including insect size, level of infestation, crop stage, environmental conditions, and existing plant stand. The key is determining what kind of damage you have. Plants can handle some minor feeding and may have the opportunity to regrow, but if entire plants are clipped off below ground then there will be losses.

Table 1: Economic Threshold of Various Crops

SWAT MAPS Opportunities

Talk to your SWAT MAPS Service Provider about how they can help you with cutworm problems, as cutworms often prefer hilltops and/or sandy areas of the field. These areas are often occurring in SWAT MAPS zones 1-4. Entire fields do not need to be sprayed just a spot here and there and because spraying once soil temperatures have dropped in the evening or night can make it difficult to see where to spray the field, an on/off prescription can be created to spray only in the areas that need it. Proper ground truthing is required in order to determine exactly which zones would need to be sprayed but with proper scouting techniques and talking with your SWAT CERTIFIED Service Provider you can feel confident you are spraying only where it is needed.

Figure 5: Example On/Off Prescription

Depending on the field and level of damage there can be significant savings when applying an on/off prescription and you can be confident knowing that you are targeting the cutworms where they are exactly. This will help eliminate the need to randomly drive around the field guessing where would be a good area to spray.