Knowing when to scout for potential corn pests is one of the key components to a successful pest management program. Many insect pests occur in corn across Iowa, but not all of them develop economically damaging populations. Most problems occur when corn is still young and the plant stand is more likely to suffer serious injury. This scouting calendar will help you focus your efforts on what insects to watch for during specific corn growth stages. Refer to current or past issues of the ICM newsletter for information on economic thresholds and treatment recommendations.
| Corn Growth |
Corn Stage |
Insect |
Calendar |
Comments |
| Preemergence |
Seed-VE |
seedcorn maggot |
May |
Most common during cool, wet spring or in fields with animal manure or recent green vegetation |
Emergence and
early whorl |
VE-V3 |
true white grub |
May |
Most common in areas adjacent to willow and cottonwood trees; also in fields after pasture |
Emergence and
early whorl |
VE-V3 |
wireworm |
May |
Most common following pasture or CRP grasses |
Emergence and
early whorl |
VE-V3 |
corn flea beetle |
May |
Populations higher in central and southern Iowa |
Emergence and
early whorl |
VE-V3 |
hop vine borer |
May through
early June |
Found on lighter soils in NE quarter of Iowa (north and east of Marshalltown) |
Emergence and
early whorl |
VE-V5 |
billbug |
May through early June |
Found on low ground, often associated with yellow nutsedge |
Emergence and
early whorl |
VE-V5 |
black cutworm |
300 degree
days (base 50°F)
after significant moth
flight; often mid-May to
early June |
See ICM newsletter for scouting dates |
Emergence and
early whorl |
VE-V5 |
stink bug |
May through early June |
Uncommon; mostly likely in fields planted no till into weeds |
Emergence and
early whorl |
VE-V5 |
chinch bug |
May throughearly June |
Uncommon; mostly in extreme SW Iowa following a dry summer |
| Early whorl |
V1-V6 |
stalk borer |
Late May through June;
hatch (575-750 degree days
base 41°F); begin
migration from grass
(1300-1400 degree days
base 41°F) |
Most common in fields with grassy weeds or giant ragweed; in weed-free fields, larvae will move from brome terraces and ditches into adjacent corn rows |
| Mid-whorl |
V6-V10 |
corn rootworm larva |
Early to mid-June |
Mostly in continuous corn |
| Mid-whorl |
V6-V10 |
armyworm |
Late May to early July |
Most common following no-till sod or in fields with grassy weeds, such as foxtail, or fields with rye cover crop |
| Mid-to-late whorl |
V8-V14 |
European corn borer
(first generation) |
June through early July;
begin when corn reaches
"knee height" or 200
degree days (base 50°F)
after first moth flight |
Most common in earliest planted fields |
| Tassel |
VT |
western bean cutworm |
July through early August |
Uncommon but found in western Iowa (north and west of Carroll), see ICM newsletter for scouting dates |
| Early tassel |
VT |
corn leaf aphid |
July through early August |
Uncommon but found across the state |
Tassel to
milk stage |
VT-R3 |
grasshoppers |
July through early September |
Most common along field margins and grassy areas |
| Silk |
R1-R2 |
European corn borer |
Late July through August |
Most common in latest planted fields |
| Silk |
R1-R2 |
corn rootworm adult |
Late July through August |
Most common in continuous corn |
