Corn insect management

Francis P. F. Reay-Jones

 

Grain yield reductions and losses in grain quality due to insect pests are a constant problem in the Southeast. Control options include cultural practices to prevent or avoid injury, transgenic Bt corn, at-planting insecticides (including seed treatments), and foliar insecticides (Table 1). Because of economic reasons, growers cannot afford to invest a substantial amount of money on foliar insecticides on corn.

 

Bt corn and insecticide coated seeds are relatively new technologies, and have not yet been evaluated in replicated studies in South Carolina. Some of the recommendations in this chapter refer to work conducted at NCSU and UGA. Insecticide recommendations can be found in the Clemson University 2008 Pest Management Handbook for Field Crops and online at http://www.clemson.edu/edisto/corn/insect_control/.

 

Table 1. Major insect pests of corn in South Carolina.

Insect	Description of feeding habit	Methods of control
Wireworms	Feed on planted kernels resulting in poor germination and stunted seedlings	Insecticide, tillage, control of winter weeds
Cutworms	Girdling of stalk at soil surface	Avoid planting corn on sod or weedy land, selected Bt hybrids, insecticides
Sugarcane beetles	Burrow into stalk above base of roots	Plant early and do not plant corn after sod
Billbugs	Chew into stalk and cause bud leaves to wilt and die	Crop rotation, weed removal in and around corn field, insecticides
Corn earworms	Feed on leaves in whorl and on ear tissue near ear tip	Insecticides, selected Bt hybrids, plant early
Fall armyworms	May feed on all above ground parts of corn plant	Insecticides, plant and harvest early, control grassy weeds
European corn borers	Burrow into stalk anywhere on plant, resulting in broken stalks	Crop rotation, plow under old corn residue, selected Bt hybrids and insecticides
Southern corn rootworms	Larvae feed on roots and leaf bud while adults feed on any plant tissue	Plow under weeds or cover crop early, selected Bt hybrids, insecticides
Southern cornstalk borers	Burrow into base of stalks	Crop rotation, early planting and plow under old corn residue, selected Bt hybrids, insecticides
Lesser cornstalk borers	Tunnel into corn seedling	Crop rotation and early planting, selected Bt hybrids, insecticides

 

 

1. Transgenic corn:

Bt corn. Several types of Bt corn are available, each characterized by an ‘event’ (i.e. a successful insertion of the genetic package into a plant) and Cry proteins. In a nutshell, there are Bt corn for stalk borers, Bt corn for rootworm and stacked Bt corn for both stalk borers and rootworms.

 

Bt corn for stalk borers. The two main types of Bt corn for stalk borers are YieldGard (event MON810, Cry protein Cry1Ab) and Herculex (TC1507, Cry1F). Both provide excellent control of stalk borers (European corn borer, southern cornstalk borer). The activity in seedling and whorl stage is greater in Herculex, which provides good early season control of cutworms, lesser corn stalk borer, and fall armyworm. YieldGard has greater activity in ears and kernel. Corn earworm control is good in YieldGard and poor in Herculex. These hybrids will be particularly useful in late planted and no-till corn. Another available Bt corn for stalk borers is Agrisure (Bt11, Cry1Ab), similar in efficacy to YieldGard.

 

Bt corn for rootworm. Herculex RW (DAS59122-7, Cry34/35Ab1) and YieldGard-RW (MON863, Cry3Bb1) provide good control of rootworm (but no control of grubs and wireworm). Rootworms are not currently widespread pests in South Carolina, and these products should generally not be needed. Another available Bt corn for rootworm is Agrisure RW (MIR604, mCry3A), similar in efficacy to YieldGard RW. YieldGard VT Rootworm (MON88017, Cry3Bb1) uses a new methodology to insert genes into the corn plant, and has a similar efficacy to other rootworm products.

 

Stacked Bt corn for stalk borers and rootworms. Available products are Herculex Xtra, YieldGard Plus, Agrisure CB/LL/RW, and YieldGard VT Triple, which combine the Cry proteins (and efficacy) of the stalk borer and rootworm Bt corn.

 

Refuge requirements for Bt corn for stalk borers (see dealers for complete refuge requirements)

 

- 50% of Bt corn planted on farm

- Blocks can be internal (within Bt field) or external (in separate field within ½ mile of Bt field to maximize random mating; ¼ mile is however preferred.

- In field strips: at least 4 rows wide to reduce effect of larval movement (6 rows preferred)

 

Bt corn for rootworm has specific regulations that differ from stalk borer Bt corn (see

http://www.epa.gov/oppbppd1/biopesticides/pips/bt_corn_refuge_2006.htm

for EPA requirements). The major difference is that refuges must be either adjacent to or within the Bt field, rather than within ¼ mile of the Bt field. This is due to the poor flight ability of corn rootworm adults.

 

2. Insecticides at planting:

Table 2 lists the efficacy of insecticides used at planting in corn in Georgia (Dr. David Buntin, UGA). Granular, liquid and seed treatment insecticides can be used. Seed companies are using more and more seed treatments (Poncho [clothianidrin] and Cruiser [thiamethoxam]), and seeds without such treatments are becoming harder to find. Both provide systemic activity for aphids, thrips and leafhoppers for 2-3 weeks, as well as the control listed in Table 2.

 

Table 2. Relative efficacy of insecticides for at-planting use in corn in Georgia (reprinted with permission from D. Buntin, University of Georgia).

Product	Seed-corn maggot	S. Corn root-worm	Wire-worm	Grubs	Lesser corn-stalk borer	Cutworm	Bill-bug	Sugar-cane beetle
Counter 15G	++	++	++	++	-	-	+	-/+
Lorsban 15G	++	++	-/+	-/+	++	++	-	-
Force 3G	++	++	++	+	+	+	-	-/+
Capture 2EC LQ	++	++	++	+	+	+	-	-
Furadan 4F LQ	++	++	++	+	++	+	+	+
Regent 4SC LQ	++	++	+	+	+	+	-	?
Poncho 250 ST	++	++	+	-/+	+	-	-	-/+
Cruiser 250 ST	++	++	+	-/+	+	-	-	-/+
Poncho/Cruiser 1250 ST	++	++	++	++	++	+	+	+

Rating: - indicates poor activity; + indicates fair activity; ++ indicates good activity.
LQ = Products require specialized equipment for liquid injection in-furrow.
ST = seed treatments, applied by seed dealers.

 

3. Foliar insecticides:

Seedling corn is particularly sensitive to insect damage. Recommendations for UGA state that yield loss occurs when 10% of plants are destroyed or severely damaged. In general, corn beyond the 5-7 leaf stage can withstand a good amount of defoliation before insecticides are required. Insecticides and rates are listed in the corn insecticide recommendations (http://www.clemson.edu/edisto/corn/insect_control/).