Introduction

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Field Scouting in Flax
• Cutworms
º Typical Damage: Notched, wilted, dead, or cut-off plants (weed or crop seedlings). Plants missing from rows, bare
patches appearing in field.
º When and How to Monitor: Look for cutworms, and evidence of cutworm feeding, when monitoring in late May to
mid-July. Often cutworms will be close to the cut or shriveled plants that they have just damaged. Cutworms will
sometimes be most abundant in patches or a specific area of a field. In areas of the field where cutworm damage is
noticeable, check around damaged plants in a 0.25 m2 (50cm x 50cm) area. Use trowel or shovel to carefully search
through top 5 cm of soil for cutworm larvae. Multiply the number of cutworms found by 4 to get the number
per m2. Repeat in several locations to get an accurate assessment of what cutworm levels are.
º Economic Threshold: 4-5 larvae/m2. Sometimes it is most economical to just treat infested patches, and not whole
fields.
• Aphids
º Typical Damage: Extract plant fluids from the stems, leaves and developing bolls. Can cause fewer seeds to be
produced.
º When and How to Monitor: The easiest way to detect aphids in flax is to sample the upper portions of the plant
with an insect sweep net when the crop is in full bloom, or tap plants over a white tray or bucket. If aphids are
found, fields need to be more closely inspected by randomly sampling plants. To inspect plants, lightly tap the
plants on a white surface, such as a tray or the canvas of a sweep net, to dislodge the insects. Plants can be severed
at the base prior to tapping if desired. Inspect a minimum of 25 plants at full bloom and 20 plants at early green
boll randomly in the field to provide an accurate estimate of aphid density. Record total number of aphids and
calculate average per plant.
º If control is not warranted at full bloom, aphid densities should be assessed again at the green boll stage.
º Economic Threshold: Varies with crop value and control costs, but generally about 3 aphids per main stem at full
bloom or 8 aphids per main stem at the green boll stage.
º The yield loss of flax is 0.3346 bushels/acre per aphid per plant for crops sampled at full bloom and
0.1275 bushels/acre per aphid per plant for crops sampled at the green boll stage.
º The potato aphid is highly susceptible to attack by fungi (especially in years of high rainfall and humidity in late
June and July). Aphid populations sampled at full bloom that have many diseased insects should be sampled
again at the early green boll stage to determine the effect of the disease on aphid densities.
• Beet webworm
º Nominal Threshold: >10 larvae/m 2
Flax Insect Management Chart
Insect
Application LD
Insecticide
Preharvest
50
Rate/Acre
(A=aerial; (Mammalian
(and insecticide group 1 )
interval (days)
G=ground) Toxicity) 2
Belowground and Surface Feeders
Wireworms
No insecticides registered for the control of wireworms in flax.
Cutworms Coragen (D) 101 ml 1 A or G >5,000
Decis 5EC /Poleci (P) 80 ml (Decis)
40 A or G 395
162 ml (Poleci)
Matador (P) 34 ml 7 A or G 64-110
Pounce/Perm-UP (P)
Ambush (P)
73-158 ml
57-121 ml
Treat prior to
6 leaf stage
G 1030
Chlorpyrifos (OP) 0.354-0.486 L 21 A or G 205-418
Sap Feeders
Potato Aphid Lagon/Cygon 480 EC/
0.18 L 21 A or G 60-450
Cygon 480-AG (OP)
Lygus bugs Voliam Xpress (D+P) 91 ml 7 A or G 98