Late season insect infestations can be impacted by corn maturity; particularly, on corn that is planted late or maturing
later than surrounding fields. Later planted fields are very attractive to females of the second-generation corn borers,
corn earworms, and fall armyworms as green silks are preferred oviposition sites. Additionally, corn rootworm adults
also prefer green silks or pollinating corn and these fields can become ovipositional sites that may result in
significant injury the following season.
LATE SEASON CORN PESTS, VT TO R6
|
Corn Growth Stage |
|
VT |
R1 |
R2 |
R3 |
R4 |
R5 |
R6 |
BELOW GROUND INSECT PESTS |
CORN ROOTWORM LARVAE |
|
|
|
|
|
|
|
ABOVE GROUND INSECT PESTS |
CORN EARWORM |
|
|
|
|
|
|
|
CORN LEAF APHID |
|
|
|
|
|
|
|
CORN ROOTWORM ADULTS |
|
|
|
|
|
|
|
EUROPEAN CORN BORER |
|
|
|
|
|
|
|
FALL ARMYWORM |
|
|
|
|
|
|
|
GRASSHOPPERS |
|
|
|
|
|
|
|
JAPANESE BEETLE |
|
|
|
|
|
|
|
STINK BUGS |
|
|
|
|
|
|
|
WESTERN BEAN CUTWORM |
|
|
|
|
|
|
|
ABOVE GROUND NON-INSECT PESTS |
TWO SPOTTED MITE |
|
|
|
|
|
|
|
Table 1. Late season corn pests, VT to R6.
Corn earworm
Unlike the Western bean cutworm, corn earworms are cannibalistic so rarely is there more than one per ear. This species
has a wide color variation from black to green (Figure 1). Usually more of a significant pest of sweet corn then field
corn.
Figure 1. Corn earworm. Picture courtesy of R.L. Croissant, Bugwood.org.
Corn leaf aphid
The aphid is blue-green, pear shaped, and wingless (Figure 2). It has short antennae and purple spot at the base of the
cornicles. Usually first found in the whorls spreading to the tassel later in the season.
Figure 2. Corn leaf aphid. Picture courtesy of Eric Burkness, Bugwood.org.
Corn Rootworm Complex
The major corn rootworm species are the Northern corn rootworm (Figure 3) and the Western corn rootworm (Figure 4).
While the larval stage is the most damaging, adults can clip silks and interfere with pollination; however, silk
clipping is rarely of economic concern. For more information, see https://www.cropscience.bayer.ca/Stories/2021/Grow-Your-Knowledge/Management-of-the-Corn-Rootworm-Complex
Figure 3. Northern corn rootworm. Picture courtesy of Daren Mueller, Iowa State University, Bugwood.org.
Figure 4. Western corn rootworm. Picture courtesy of Frank Peairs, Colorado State University, Bugwood.org.
European corn borer
Depending on geography, late season corn can be infested with European corn borer larvae from the single generation type
(Northern locations) or larvae from second generation of the two generation type (majority of Midwest) (Figure 5).
Larvae can be found in the stalk, ear, and ear shank. Scout for insect frass (excrement) in leaf sheaths, holes in the
stalk, shank, or ear. Feeding can reduce nutrient and water transfer, increase risk of stalk diseases, and stalk
lodging.
Figure 5. European corn borer. Picture courtesy of Frank Peairs, Colorado State University, Bugwood.org.
Fall armyworm
The identifying characteristic for the fall armyworm larva is the white inverted Y-shape suture between the eyes (Figure
6). Moths are usually attracted to late developing corn or late planted corn as they do not overwinter in the Corn
Growing Region and fly into the Midwest from the southern states.
Figure 6. Fall Armyworm. Picture courtesy of Frank Peairs, Colorado State University, Bugwood.org.
Grasshoppers
Early season injury is usually confined to field margins, but as the majority become adults, movement into the field
increases. Grasshoppers feed on leaves, silks, and ear tips, and when populations are very high, the entire plant can
become stripped.
Figure 7. Two-striped grasshopper. Picture courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.
Japanese beetle
The Japanese beetle can clip silks and injure developing kernels at the tip of the ear. Like adult corn rootworms, the
silk clipping is rarely of economic concern.
Figure 8. Japanese beetle. Picture courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.
Stink bugs
Injury to corn is most severe when stink bugs feed on the immature ear prior to tasseling, but the damage becomes
evident after pollination. The feeding injury causes the ear to be deformed. Feeding after pollination on developing
kernels, while concerning, is not as injurious as feeding on the developing ear.
Figure 9. Green stinkbug. Picture courtesy of Frank Peairs, Colorado State University, Bugwood.org.
Western bean cutworm
The western bean cutworm attacks the ear and can be identified by the brown bars behind the head (Figure 10). Typically,
unlike corn earworm, more than one larva can be found in the ear.
Figure 10. Western bean cutworm. Picture courtesy of Mike Weiss.
Two spotted spider mite
Two spotted spider mites are more of an economic concern during hot dry weather, when populations can expand extremely
quickly. Its host range includes a wide variety of plants, including corn.
Figure 11. Two spotted spider mite.
Legal Statements
Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may
vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts
of these conditions on the grower’s fields.
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