Armyworm (True)
Pseudaletia unipuncta |
(TAW) |
Early Season- 25% of
plants damaged or some plants are being killed.
Late Season - Feeding occurs above the ear on 10 to 20% of plants. |
Armyworm (Fall)
Spodoptera frugipera |
(FAW) |
75% or more of whorl stage plants
are damaged and live larvae can still be found. If larvae are 1 inch or greater, control
is not justified. |
Billbugs
Sphenophorus spp. |
(BB) |
None established. Rescue
treatments may be warranted when the damage is widespread and live adult billbugs can be
found. |
Black cutworm
Agrotis ipsilon
|
(BCW) |
Seed leaf emerged - 2% of plants
cut
Two leaf stage - 3% of plants cut
Three leaf stage - 5% of plants cut
Four leaf stage - 7% of plants cut
Five leaf stage - Seldom an economic problem at this stage
Note: If larvae are longer than 1 1/2 inches, treatment is not
warranted even if the threshold is reached because larvae have done most of their damage
and will pupate soon. |
Corn flea beetle
Chaetocnema pulicaria |
(CFB) |
5 or more beetles per plant prior
to the 4th-leaf stage or if the infestation is so severe that some plants
are being killed. |
Corn leaf aphid
Rhopalosiphum maidis |
(CLA) |
If 50% of the plants have more
than 100 aphids per plant and plants are under drought stress or 3% or more
of the plants have their tassels and upper leaves heavily infested, plants are under
moisture stress and aphid populations are increasing. |
Corn root aphid
Anuraphis maidiradicis |
(CRA) |
None established. |
Corn rootworm larvae
(western)
Diabrotica virgifera |
(WCRW) |
1.0 per plant in 1st year corn;
1.5 per plant in second year or more of corn. See Sequential Sampling Charts (pgs. 58
& 59) |
Corn rootworm larvae
(northern)
Diabrotica barberi |
(NCRW) |
2.0 per plant in 1st year corn;
3.0 per plant in second year or more of corn. |
Corn rootworm adult
(both species) |
(CRW) |
5 beetles per ear and the corn is
less than 50% brown silk. |
European corn borer
Ostrinia nubilalis
|
(ECB) |
First generation -
75% of plants showing whorl feeding and live larvae are found.
Note: More dynamic and accurate thresholds can be calculated using
Table 14.
Second generation - 50% of plants with an egg mass.
Note: More dynamic and accurate thresholds can be calculated (See
Table 15). |
Garden symphylan
Scutigerella immaculata |
(GS) |
None established. Treat if a
significant area in the field is affected. |
Grape Colaspis
Colaspis brunnea |
(GC) |
None. Follow replanting
guidelines (Penn State Agronomy Guide). |
Grasshoppers
Melanoplus spp. |
(GH) |
7 or more grasshoppers per square
yard. After pollen shed, (differential) control is justified when grasshoppers are feeding
on leaves (redlegged) above the ear level. |
Japanese beetle
Popilla japonica |
(JB) |
3 or more beetles per ear and 50%
or more of plants are still in green silk. |
Seed corn maggot
Delia platura |
(SCM) |
None. Follow replanting
guidelines. (Penn State Agronomy Guide). |
Slugs
Deroceras laeva
Arion fascistus
D. reticulatum |
(SLUGS) |
50% of leaf area removed per
plant and plants are less than the V6 stage of development. |
Sod webworm
Crambus spp. |
(SWW) |
None established. Use black
cutworm thresholds. |
Stalk borer
Papaipema nebris |
(SB) |
See Table
13 for thresholds. |
Thrips
Anaphothrips obscurus |
(TP)
|
None established. |
White grub
(True)
Phyllophaga spp. |
(WG) |
1 or more per square foot of soil
at the soil-root interface. |
Wireworm
Elaterid species |
(WW) |
2 or more per 10 shovels of soil or
1 or more per grain bait trap. |
