SYMPTOMS: Loss of stand before emergence or due to above-ground cutting from worm feeding on seedlings. Also, below-ground tunneling, irregular holes, dead plants.
TIME OF ATTACK: VE-V8
CONDITIONS FAVORING: Reduced tillage and abundance of broadleaf weeds prior to planting.
MANAGEMENT: Early tillage and good weed control. Scouting and application of insecticide if/when reach threshold.
CORN ROOTWORM
FORMS: Western, western variant, northern (larvae and adults).
SYMPTOMS: Root systems with scars or elimination of roots due to larvae feeding on and tunneling into roots. Adults feed on and clip silks; western and southern species feed on leaf tissue.
TIME OF ATTACK: Larvae: V4-R2; adults: V8-R5.
CONDITIONS FAVORING: Continuous corn in general, but rotation may not be a help when it comes to variants that lay eggs in soybeans.
SYMPTOMS: First generation: Foliar shot hole injury of mid-whorl corn, tunneling into midribs, boring into stalks. Second and third generation: leaf feeding and boring into stalks, tassels, around ear
TIME OF ATTACK: First generation: V6-VT; second generation: V12-R6; third generation: R2-R6
CONDITIONS FAVORING: First generation: early planted corn; second generation: late-planted corn.
MANAGEMENT: If significant infestations are detected prior to stalk boring, chemical treatment may be applied. Control should be based on projected yield, infestation level, yield loss figure for number of borers per plant, projected level of control, market value of crop, insecticide costs.
FALL ARMYWORM
FORMS: common and fall
SYMPTOMS: Ragged leaves to complete defoliation for armyworm; whorl and ear-feeding for fall armyworm.
TIME OF ATTACK: VE-V12, armyworm; V12-R6, fall armyworm.
CONDITIONS FAVORING: Wet spring seasons; no-till corn planted in grassy cover crops, sod or hay.
MANAGEMENT: High-risk areas not scoutable may warrant use of preventive treatment. Scouting and rescue treatment is preferred. Easy to control if detected early.
SOUTHWESTERN CORN BORER
SYMPTOMS: First generation: leaf feeding, tunneling into midribs and boring into stalks. Second generation: leaf feeding, boring into stalks, tassels and around ear zone. Larvae tunnel down through center of stalk.
TIME OF ATTACK: First generation: V6-VT; second generation: V12-R6
CONDITIONS FAVORING: Sandy soils
MANAGEMENT: First generation: insecticides, with critical timing. Once borers enter stalks, they cannot be controlled. Avoid late-planted corn; use fall tillage options.
SPIDER MITES (TWO-SPOTTED)
SYMPTOMS: Fine, spider-like webbing on underside of leaf; will start on lower leaves and move up plant, piercing plant cell walls and removing contents causing leaf to dry up and die.
TIME OF ATTACK: Close to tassel when temperatures start to warm.
CONDITIONS FAVORING: Moisture-stressed fields and hot, dry, windy weather with low humidity and little rainfall. Fields with insecticides for European corn borer, western bean cutworm; fields next to grasses, ripening wheat, alfalfa.
MANAGEMENT: Reduce moisture stress if possible; treat only heavily infested areas. Corn reaching full dent stage is unlikely to benefit from treatment.
STINK BUG
SYMPTOMS: Seeds fed upon may be shriveled, deformed, shrunken or may bear a dark spot and depression at the feeding site. Damage to ears of corn varies greatly with the development stage at which fed upon. Damage early in development can lead to severe deformities and abscission, while damage near harvest may result in small dark spots at the feeding site.
TIME OF ATTACK: Younger plants up to V15
CONDITIONS FAVORING: Edges/sides of fields, including those adjacent to wooded habitat.
MANAGEMENT: Stink bugs may be controlled with a variety of insecticides, however, many crops have specific action thresholds that should be observed to provide the most economically efficient control.
WESTERN BEAN CUTWORM
SYMPTOMS: Untasseled corn: feeding on pollen in the developing tassel within the flag leaf; tasseled corn: feeding on silk in the ear and on kernels.
TIME OF ATTACK: VT and on
CONDITIONS FAVORING: All corn is susceptible to infestation.
MANAGEMENT: Properly timed insecticide treatments based on currently accepted economic guidelines.
WIREWORMS
SYMPTOMS: Worms feed on the seed or seedling causing wilting and, at times, plant death. Gaps along row.
TIME OF ATTACK: VE-V8
CONDITIONS FAVORING: Corn following sod, old hay fields, other grassy conditions.
MANAGEMENT: Seed treatment or planting-time insecticide if an average of 1 or more wireworms/bait station when scouting. No rescue treatm
