Losses from Corn Earworm have been estimated as high as 7% and populations may reach economic infestations of 35 million acres across the entire United States. Between the difficulty of effectively controlling Corn Earworm with insecticides and the damage generally being overlooked until harvest, many farmers have elected to accept the lost yield potential. New tools are becoming available to combat Corn Earworm and help protect yield potential.
There are usually two generations in much of the Midwest. Corn Earworms migrate in from the south with winds and storms from southern states. Moths typically lay eggs in corn and other host crops. The first generation larval stage feeds in the whorl of corn and other food sources, although first generation damage is generally minimal.
First generation moths lay eggs on corn silks, and larvae travel down silks within one hour of hatching. The larvae then feed on kernels for the most of the larval stage.
Planting early can help avoid peak moth flights, and corn with tight husks can help reduce feeding potential. Several foliar insecticides are labeled for control of Corn Earworm; however, the contact needed between larvae and foliar insecticides for good efficacy is rare due to larvae burrowing down the silks soon after hatching.
Sources: K.A. Cook and R. Weinzierl. 2004. Corn Earworm Insect Fact Sheet.Univ. of Illinois Integrated Pest Management. K. L. Steffey and others. 1999. Handbook of Corn Insects. Entomological Society of America.
Western corn rootworm (WCRW) and northern corn rootworm (NCRW) follow very similar life cycles. They both complete one generation per year and have four developmental stages; egg, larvae, pupa and adult. Eggs, which are yellowish and oval shaped, overwinter in the soil and tend to hatch in late May to mid-June and produce larvae Egg hatching and larvae development is dependent upon soil temperature and hatch typically begins at about 500 Growing Degree Days (GDD). In many areas, crop rotation is the best method preventing larval root damage.
There are three larval stages that are commonly referred to as instar stages. Each instar stage occurs every 7 to 10 days and larvae increase in size throughout this time period. Larvae are bright white in appearance with a brown head capsule during the 1st instar stage and are typically 1/8” in length. 2nd instar are ¼” in length and have more of a creamy white appearance. 3rd instar larvae are approximately ½” in length and are more yellowish in color with a dark brown or black head capsule.
Scouting is an integral part of CRW management. The extensive data sets from numerous university and on-farm trials have shown selecting a product with transgenic B.t. trait technology is the most consistent form of CRW larval control compared to conventional methods. Scouting is also an integral part of successful CRW management. Root damage ratings are a good measurement of current control methods and efficacy, but do little to help plan control strategies for successive years.
Adult CRW beetle counts are a key component in assessing the potential number of eggs that may be laid in a field the following year. CRW beetle populations are dependent on the CRW emerging from within the field and also those that immigrate from other fields. Because future CRW populations and densities are independent of the performance of the B.t. trait technology or any other insect management tactics employed during the existing crop season, scouting should serve as the primary source of information used to formulate an effective control strategy for the following year. Scouting becomes increasingly important for growers in high pressure areas that utilize practices conducive to increasing CRW populations.
A few examples of production practices that may favor CRW populations include: planting continuous corn, late planted corn fields relative to others in the area, and planting late maturity hybrids such as those used for silage. Full season hybrids used by many silage growers are often prime targets for escalating CRW beetle populations since they pollinate later in the season when other desirable adult CRW food sources have deteriorated.
Western Bean Cutworm
Western Bean Cutworm is a relatively new pest to the Midwest. Although it was a pest of dry bean, it is now a serious threat to corn in some parts of the Corn Belt. Properly identifying Western Bean Cutworm and understanding its thresholds can help determine if control options are needed.
Corn fields in the late-whorl stage are target locations for females to begin laying eggs. Egg masses of 5 to 200 are usually laid on the upper surface of the top leaves, and most are laid during peak moth flight in late July or early August. Timing of moth flights must be compatible with the corn stage for ear feeding. Larvae first feed on pollen, then on corn ears for several weeks before they drop to the soil and overwinter.
Western Bean Cutworm larval feeding damages corn through reduced grain yield and quality. Pollination may be poor if silks are damaged from feeding. Once the ear is formed, Western Bean Cutworm feed on developing kernels and can destroy as much as 50 to 60% of them. Losses may be compounded by subsequent fungal and mold infections associate with larval waste products.
Scouting for Western Bean Cutworm should start when moth flights begin, usually in mid-July. Check 20 consecutive corn plants at five different locations in the field. An insecticide application has been historically recommended if 8% of the plants contain and egg mass of if young larvae are found in the tassel.
Sources. E. Cullen. 2008. Wisconsin Crop Manager. Volume 15 Number 22, Aug 7, 2008; R. Seymour and others. 2004. Western bean cutworm in corn and dry beans. Univ. of Nebraska Ext. NebGuide G1359; B. Wright and R. Seymour. 1996. Western bean cutworm management. Univ. of Nebraska Extension. PM Guide. http://entomology.unl.edu. 6/10/09; K.L. Steffey et al. 1999. Handbook of Corn Insects. Entomological Society of America.