Louisiana Corn: Dealing With Early Insects Before, During and After Planting

Highboy spraying seedling corn. ©Debra L Ferguson

Pre-plant pest management decisions

Burndown herbicides typically are applied 30 to 45 days prior to planting crops. Complete control of all weed species within in the field and on the surrounding field borders is necessary to eliminate alternate host plants of insect pests. Fields should be scouted at the time of planting to ensure the seedbeds are essentially weed-free.

The presence of heavy plant residue following burndown applications or any green vegetation on the seedbeds can create a favorable environment for arthropod pests. Incomplete termination of some weed species provides a refuge for insect pests until crop seedlings become available. Even at planting, a herbicide application or modified tillage treatment may be warranted to ensure a clean seedbed and remove alternate hosts of arthropod pests.

In addition, heavy residue from previous crops (corn, sorghum and soybeans) covers the soil surface and mediates soil temperature and moisture levels. This in turn increases the probability of insect pests such as corn earworms, corn borers and stink bugs successfully overwintering in those fields. Identifying these problems early provides producers with the information necessary to modify their insecticide use strategies at the time of planting.

At-planting and surface-applied insecticide applications should be used to manage cutworms if winter vegetation was not terminated well in advance of planting, if incomplete kill of winter weeds occurred, if any freshly emerged vegetation is observed on the seedbeds at the time of planting or if cutworms are observed in high numbers on plants in the field or along field borders.

The most common insecticides used for this application include any pyrethroid. The lowest application rates have proven to be effective preventative treatments when applied properly. Producers should apply a broadcast treatment or in a wide band over the seed furrow. Cutworms exist below the soil surface feeding on root tissue and may not be exposed to the insecticide if only part of the seedbed is treated.

At-planting pest management decisions

Soil insecticides such as Counter 15G, Lorsban 15G and Aztec 2.1G were the standard insecticide treatments applied either in the seed furrow or at planting to control seed and seedling pests in corn. However, Gaucho 600FS, Cruiser 5FS and Poncho 600FS have become standard as seed treatments and have replaced granular and liquid soil-applied insecticides on considerable acreage.

Regardless of the product(s) used, an at-planting insecticide treatment is essential for optimal seedling development. Producers should not reduce seeding rates below recommended levels when using at-planting insecticide treatments. Lower than optimal plant populations cannot consistently tolerate injury from seedling insect pests and recover to produce maximum yields.

Post-emergence and reactive pest management decisions

Generally, corn seed treatments, at existing rates, will exhibit enough residual efficacy for corn seedlings to develop beyond the susceptible stages to many above/below ground insect pests. However, when soil temperature is below 55 degrees, delayed germination and uneven emergence can increase the susceptibility of corn seedlings to arthropod pests. For producers using herbicide-tolerant crops, the co-application of foliar insecticides with post-emergence herbicides is a cost-effective practice when controlling above-ground pests. However, there are no rescue treatments for below-ground insect injury, and seedling protection is critical when planting corn in suboptimal conditions.

As conservation tillage systems continue to evolve, IPM strategies will need to adapt to address emerging pest issues. Pest managers and producers should scout fields and identify those situations that may result in pest problems. These fields should be considered high risk and managed with preventative pest management methods.

An effective IPM strategy for field corn pests should include weed-free seedbeds well in advance of planting, optimal application dates and rates of cultural practices, and discriminate use of preventative and reactive chemical control strategies for pest problems.

Most of the extension IPM recommendations do not recognize general differences in insect management recommendations between conventional and conservation tillage systems.

However, to improve the overall success of insect pest management in conservation tillage systems, crop advisors and producers should timely apply broad-spectrum herbicide treatments to control winter vegetation not only within the field but also on field borders. Many of these insect pests are highly mobile and crop advisors should scout field borders and adjacent fields to observe potential refuges for these pests. Fields should be scouted regularly during the season and treated only as needed based on insect density and changes in plant development.

Agronomic practices that enhance rapid seed germination and promote seedling growth should be used to reduce that period of time that plants are susceptible to insect pests. Chemical control strategies are effective against field corn insect pests, but the application method, product rate, and treatment timing must be adjusted for the requirements of each individual field.

Seed treatments and soil-applied insecticides are critical inputs in conservation tillage systems for field corn. Crop advisers and producers should recognize the potential for unidentified pest problems, intensify scouting practices and use all available resources to make an informed decision on the appropriate management strategy.

Southern row crop producers have incorporated significant changes in field corn production systems to decrease input costs and improve profits. These changes can significantly influence arthropod pest diversity and density as well as overall pest status. Conservation tillage systems or components of those systems have widespread acceptance among producers.

However, several of those practices including educed tillage and winter cover crops have also been demonstrated to increase problems with some insect pests. There are numerous insect pests are capable of injuring field corn annually across the Southern region, but only a select few are directly affected with a change in tillage systems. Most of these are associated with seed germination and seedling development.

There are, however, other pests that can be indirectly affected by conservation tillage production systems and occur as problems later in crop development. These indirect effects are the result of production systems that influence changes in the landscape across an entire farm or farm region. Fortunately, the impacts of insect pest problems have been minimized with the tools, technologies, and production practices that are now available.

The following table summarizes field corn pest problems common to the mid-South. The ranges of these effects are highly variable and depend on the environment of the local landscape and the production practices applied to individual fields.

Table 1. Common pest problems in mid-South field corn

Insect Effecta Description of problems
Southern corn rootworm 0 to +++ Fields to be planted to corn that contain winter weeds such as henbit is attractive to adults that lay eggs in the soil. The larvae hatch feed on corn seeds and roots. Timely vegetation management can reduce the impact of these pests.
Seed corn maggot 0 to +++ Adults prefer to lay eggs on fields with decaying crop residue. Wet soil conditions and cool temperatures can slow seedling development and make plants more susceptible for injury
Beetles 0 to + Wireworm and carrot beetle larvae as well as sugarcane beetle adults may be serious pests of seedlings in fields with heavy crop and winter vegetation residue.
Cutworms + to +++ Cutworms can overwinter in no-tillage fields. The adults of some species prefer to lay eggs in fields with dense weeds, winter cover crops, or heavy crop residue. As pre-plant vegetation is destroyed, larvae feed on crop seedlings to survive.
Slugs 0 to +++ Winter vegetation and crop residues in wet soil conditions favor slug populations and seedling injury.
Chinch bug + to +++ Plant residue provides a favorable habitat for these insects. Chinch bugs prefer fields with surface vegetation which makes control with foliar insecticides difficult.
Corn borersb 0 to +++ Several species of borers overwinter in corn stubble. Con-till can increase overwintering survival and subsequent problems in corn.
Stink bugs 0 to + Con-till fields usually have little effect on bug pests. Delayed herbicide applications can increase population in fields. Poor control of spring weeds such as marestail or primrose can increase populations. Vegetation management surrounding fields is critical to bug IPM.
Corn earworm 0 Winter survival of heliothine populations can be increased in con-till fields. Little economic injury occurs except for seed producers.

a“+++” = substantial increase in pests; “+” = some increase; “0“ = no effect; “-“ = decrease in pests.

bBorer pests include Southwestern corn borer, sugarcane borer and European corn borer.

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