WIREWORMS or CLICK BEETLES: several species, including Conoderus spp., and CORN WIREWORM, Melanotus communis, Elateridae

ADULT: Adults are smooth or with very short hairs, slender, medium to dark brown or gray, and 1/2 to 7/8 in. long. They have a large tooth-like projection between the rear legs that fits into a groove on the undersurface of the abdomen. Beetles feign death when disturbed and can then upright themselves from their backs by quick flexion at the juncture of the thorax and abdomen.

EGG: They are deposited in soil near plant roots, particularly around grasses, during summer months.

LARVA: Wireworms have narrow, hardened, creamy yellow to orangish-brown bodies.  Characteristic hardened projections on the next to last abdominal segment can be used to identify them to species.  They have three pairs of short true legs and no prolegs.  Wireworms take two to several years to complete larval development and can reach 1 1/4 in. long.

PUPA: Larvae pupate in soil for 2 wk. Pupae are naked with developing legs, antennae and wings completely visible.

GENERATION TIME: 2 to several years.

DAMAGE: Larvae attack seeds, roots and crowns of plants below the soil surface. They chew into the base of plants and then hollow out the stem, eliminating the growing points.  Young plants first exhibit severe wilting and desiccation of youngest leaves.  Such damage to young plants results in stand loss.  Soil within 8 in. diameter around affected plants should be excavated in search of larvae in or near these plants.  Wireworm damage symptoms are nearly identical to those of lesser cornstalk borer, although young plants damaged by the latter are much more likely to send up suckers than those damaged by wireworms. Lodging results following strong winds and rains when roots have been pruned or damaged by larval feeding.

CONTROL: Corn planted to weedy fields, or in rotation from pasture or sugarcane, are often exposed to very large wireworm populations.  If infestation density is in question, then fields should be sampled for these pests to determine the best treatment strategy before corn in planted.  Baits of oat, corn or potato buried in fields and recovered in 2 to 3 wk work well to monitor wireworms.  Summer flooding of fields is an effective cultural control, providing it is maintained for at least several weeks.  Water temperature should be above 82 degrees F for maximum control.  Rotation through a cycle of rice has been shown to eliminate the need for wireworm treatment in the subsequent crop.  Pesticides are available for pre-plant broadcast and at-plant banded applications. Formulations, rates, and pre-harvest intervals of insecticides labeled for wireworm control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).

Table 1.  Chemical control of wireworms in sweet corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
carbofuran (Furadan) 4 F 2.5 fl oz / 1000 row-ft 30 feed forage in-furrow at plant
chlorpyrifos (Lorsban) 4 E 4 pt 35 grain, fodder; 14 ** broadcast pre-plant
chlorpyrifos (Lorsban) 15 G *** 8 - 16 oz / 1000 row-ft 35 grain, fodder; 14 ** banded or in-furrow at plant
diazinon (D-z-n) 50 W 6 - 8 lb 7 broadcast pre-plant
diazinon (D-z-n AG500) 4 EC 3 - 4 qt 7 broadcast pre-plant
diazinon (D-z-n AG600) WBC 76.5 - 102  fl oz 7 broadcast pre-plant
dichloropropene (Telone II, C-17) See labels See labels See labels
ethoprop (Mocap) 6 EC *** 1.4 - 2.9 fl oz / 1000 row-ft   banded at plant, not in-furrow
ethoprop (Mocap) 10 G  *** 10.5 oz/1000 row-ft   banded at plant, not in-furrow
phorate (Thimet) 20 G 6 oz / 1000 row-ft 30 banded at plant, not in-furrow
tefluthrin (Force) 3 G 4 - 5 oz / 1000 row-ft   in-furrow at plant
terbufos (Counter) 15 G 8.0 oz / 1000 row-ft   banded or in-furrow at plant
terbufos (Counter CR) 20 G 6.0 oz / 1000 row-ft   banded or in-furrow at plant
**harvest or grazing of forage or silage
***check label for other application techniques and rates


Table 2.  Chemical control of wireworms in field corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
carbofuran (Furadan) 4 F 2.5 fl oz / 1000 row-ft 30 feed forage in-furrow at plant
chlorpyrifos (Lorsban) 4 E 4 pt 35 fodder, grain; 14 grazing, silage broadcast preplant
chlorpyrifos (Lorsban) 15 G 13.5 lb; 8 - 16 oz / 1000 row-ft 35 fodder, grain; 14 ** broadcast preplant; banded or in-furrow at plant
dichloropropene (Telone) II, C-17 see label see label see label
ethoprop (Mocap) 6 EC 1.4 - 2.9 fl oz / 1000 row-ft   banded at plant, not in-furrow
ethoprop (Mocap) 10 G 10.5 - 21.5 oz /1000 row-ft   banded at plant, not in-furrow
phorate (Thimet) 20 G 6 oz / 1000 row-ft 30 banded at plant, not in-furrow
tefluthrin (Force) 3 G 4 - 5 oz / 1000 row-ft   banded or in-furrow at plant
terbufos (Counter) 15 G 8.0 oz / 1000 row-ft   banded or in-furrow at plant
terbufos (Counter CR) 20 G 6.0 oz / 1000 row-ft   banded or in-furrow at plant
**harvest or grazing of forage or silage
***check label for other application techniques and rates