Agronomic Crops

suggested Planting Dates for Corn
South Mississippi: February 25 – March 15 South-Central: March 5 – April 10
North-Central: March 15 – April 20 North Mississippi: March 20 – April 25
resholds
Making insect management decisions based on established treatment thresholds rather than applying treatments based on
schedules or presence of pests is a proven method of reducing insect management costs. Effective use of thresholds requires frequent,
intensive scouting to get accurate estimates of populations of various pest species that may be present in a field.
Treatment threshold is the pest population level at which treatment must be applied to avoid economic loss that would be
greater than the cost of the treatment. resholds can vary, depending on species of pest present, stage of crop development, yield
potential of the crop, cost of the treatment, market price, populations of other pests present, number of beneficial insects, potential
for flaring secondary pests, ability to control secondary pests, and other factors. e thresholds recommended in this guide vary according
to pest species and stage of crop development, but fixed thresholds cannot fully consider the many other factors that can
influence a treatment decision.
Additional Information
In addition to this publication, you can get several other Extension publications on corn insect biology and
management from your county Extension agent.
Information Sheet 864 – Corn Fertilization
Information Sheet 1548 – Corn Plant Population
Information Sheet 1563 – Minimizing Alflatoxin in Corn Information Sheet 866 – Corn Planting Dates
Insecticide Resistance and Resistance Management
CAUtIon: Recommendations of specific insecticides are based on information on the manufacturer's label and performance
in a limited number of tests. Levels of insecticide resistance, environmental conditions, and methods of application by growers may
vary widely. For this reason, insecticide performance will not always match the safety and pest control standards indicated by
experimental data.
Insecticides are listed alphabetically, not in order of their effectiveness. Effectiveness of a particular insecticide can vary greatly
from field to field, depending on previous insecticide use, pest species, levels of resistance, and many other factors. A group of insecticides
recommended for control of a specific pest will vary in cost, effectiveness against the primary target pest, and secondary
pests controlled. When selecting insecticides, growers must consider each of these factors plus the need to rotate among different
insecticide classes to limit insecticide resistance problems.
Classes of insecticides: Effective resistance management requires rotation among the various classes of available insecticide
chemistry. Often when one insecticide in a class fails because of insecticide resistance, other insecticides in the same class will also
be ineffective. Selection of an insecticide from a different class will improve the chances of obtaining control. Growers need to be
very aware of the type of insecticide chemistry being used. Classes of insecticides recommended in this guide are identified by the
following abbreviations:
Avermectins – (AV) Chloro-nicotinyl – (CN) Organophosphate – (OP) Pyridine Carboxamide – (PC)
Biologicals – (B) Insect Growth Regulators – (IGR) Oxadiazine – (OX) Spinosyns – (SPN)
Carbamate – (C) Organochlorine – (OC) Pyrethroid – (P) Tetronic Acid – (TA)
Diamindes – (D) METI-Acaricides – (M)
Bt Corn
Bt is a bacterium that occurs naturally in the soil. Bt, or Bacillus thruingensis, produces crystal-like proteins (cry proteins) that
can kill certain insects once ingested. Bt corn hybrids express cry proteins. erefore, Bt corn hybrids are protected from certain insects,
depending on what cry protein(s) the plant expresses.
e Bt corn hybrids planted in the Midsouth resist southwestern corn borers, European corn borers, and sugarcane borers. Before
2009, the commercial Bt corn hybrids expressed one protein to protect against lepidopterian pests. In 2009 Bt corn hybrids
became available that expressed two proteins to protect against lepidopterian pests, corn earworms, and fall armyworms. In 2010,
Bt corn hybrids became available that express multiple proteins to control these pests.
Bt corn hybrids protected against western and northern corn rootworms are of little value in Mississippi. ey were developed
for use in the Corn Belt and have little or no efficacy on southern corn rootworms.
Refuge requirements for the Bt corn hybrids in cotton-growing regions depend on the number of proteins expressed in the
plant. Bt corn hybrids expressing one protein can be planted to only 50 percent of a grower’s acreage. Bt corn hybrids expressing
two or more proteins can be planted to 80 percent of a grower’s acreage. For specific information regarding refuge location and
refuge configurations, see your local Extension agent or seed dealer.
46 Corn