Healthy, uniform plant population essential to optimum yield Louisiana corn producers should seriously consider the use of a soil insecticide when planting their crops this spring, says LSU AgCenter specialist Jack Baldwin.
"Early planting and establishing a healthy, uniform plant population both are essential to obtain optimum corn yields in Louisiana," says Baldwin, an entomologist with the LSU AgCenter. "Although soil insects can be rather unpredictable, heavy infestations can reduce stands to levels where the field must either be replanted or planted to a different crop."
The Southern corn rootworm is one of the soil insects that can reduce stands of corn, according to Baldwin, who says the adult stage of this pest is the spotted cucumber beetle - an insect that becomes active in the early spring and lays its eggs in the soil of future corn fields.
"Henbit and legumes are highly attractive to spotted cucumber beetles prior to corn planting," Baldwin explains, adding, "After hatching into the larval stage, the rootworm then feeds on seedling corn plants after the field is planted."
The LSU AgCenter entomologist says that unlike other rootworms that overwinter in the egg stage and feed primarily on corn, the Southern corn rootworm overwinters as an adult and feeds on many types of plants. It can be a problem in corn fields that were planted to other crops the preceding year, but it is not necessarily a problem in corn following corn, he says.
"In Louisiana, rootworms and other soil insects tend to be a bigger problem in reduced tillage or stale seedbed fields that are not plowed in the spring," Baldwin says. "These fields are prepared in the fall and planted the following spring after a burndown herbicide is applied to kill weedy vegetation or cover crops.
"Most soil insects usually are present when the herbicide is applied and subsequently feed on emerging corn plants after planting."
The LSU AgCenter specialist says eight soil insecticides are recommended in Louisiana for rootworm control. These include Lorsban 15G, Furadan 4F, Counter 20CR, Force 3G, Thimet 20G , Mocap 10G, Regent 4SC and Aztec 2.1G.
"These products all have their respective advantages and disadvantages," he says. "Differences can be found in price, method of application and spectrum of insect control other than the Southern corn rootworm."
Furadan and Regent are liquid insecticides that are sprayed in-furrow, and all the others are granular products that require granular applicators.
Moving to another pest, Baldwin says the chinch bug, although not a true soil insect, also is often an early-season pest of seedling corn.
"This pest is most damaging when seedling corn lacks vigor because of drought and other adverse growing conditions," he says.
Furadan, Counter, Lorsban, Thimet, Regent and Aztec can all provide at least partial control of this pest when applied at planting as a soil insecticide, according to Baldwin.
Cutworms also can be an-early season threat to successful stand establishment, the LSU AgCenter entomologist says.
"These caterpillars hide in the soil or under vegetative trash during the day and then cut seedling plants just above the soil surface at night," Baldwin explains. "Later in the spring when plants are larger, these worms sometimes bore into the crown of the plant just below the soil surface."
Baldwin says serious cutworm problems almost always occur in reduced tillage fields but that soil insecticides which also have cutworm activity include Lorsban, Force and Aztec.
Recommended foliar insecticides (Lorsban, Asana XL, Ambush, Pounce and Warrior T) can be used in combination with soil insecticides that have no cutworm activity, Baldwin advises, saying in that situation, the foliar material is sprayed either in-furrow or in a band behind the planter.