Introduction

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Field Scouting in Corn (Field Corn)
• 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 corn 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. At each stop, examine
100 plants in a row. Calculate percentage of plants cut off or showing leaf feeding.
º Economic Threshold: When 3-6% of plants are cut and small larvae less than 1 inch present. Sometimes it is most
economical to just treat infested patches, and not whole fields.
• European corn borer
º Typical Damage: Shot-holes in leaves. Holes in stalk, tassels and ears. Damage may cause stalk breakage prior to
harvest or cobs to fall to the ground. Nutrient flow in the plant may be restricted, resulting in smaller cobs.
º When and How to Monitor: Begin looking for European corn borer when field scouting in early July. At 5 locations,
examine 10 plants for young larvae and egg masses. Calculate percentage of plants infested. Scout every
5 to 7 days until the end of July or larvae start to tunnel into the stalks.
º Economic Threshold: The level of European corn borer where control becomes economical depends on the value of
the crop, and cost of control. Information on determining specific economic thresholds for European corn borer in
corn can be found at http://www.gov.mb.ca/agriculture/crops/insects/european-corn-borer.html, or from your
local agriculture office. These thresholds are based on a 5% yield loss per corn borer per plant on average. If the
majority of larvae have bored into the stalk, do not apply insecticide, as they are ineffective once the larvae have
entered the stalk.
Insect
Insecticide
(and insecticide group 1 )
Rate/Acre
Preharvest
interval (days)
Application
(A=aerial;
G=ground)
LD 50
(Mammalian
Toxicity) 2
Belowground and Surface Feeders
Cutworms Seed Treatments
Fortenza (D) 83-167 ml /
100 kg seed
Foliar Sprays
Matador/Silencer (P) 34 ml 14 A or G 64-110
Mako (P)
UP-Cyde (P)
Pounce/Perm-UP (P)
Ambush (P)
Chlorpyrifos (darksided,
black, redbacked) (OP)
71 ml
115 ml
73-158 ml
57-121 ml
0.971 L (Pre-plant
treatment),
0.486-0.971 L
(seedling treatment)
21 G 242-542
355
Treat prior to
6 leaf stage
G 1030
70 G 205-418
Pyrifos 15G (OP) 75 g per /
70 G 2250
100 m of row
Wireworms Fortenza (D) Seed Treatment
Cruiser Maxx Corn (N) 83 ml Cruiser 5FS /
100 kg seed
Poncho 600 FS (N)
33.3-66.6 ml of
Poncho 600 per
80,000 unit of seed
A seed treatment containing
Cruiser 5 FS and Maxim Quattro.
>5,000
Seed Treatment Seed Treatment 2,000
Nipsit Inside (N)
33.3-66.6 ml per Seed Treatment Seed Treatment 3,044
80,000 unit of seed
Sombrero (N) 0.16 mg per kernel Seed Treatment Seed Treatment N/A
Insect Control