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Early Insect Problems in Corn

Most early season damage to corn by insects is caused by wireworms, white grubs, or cutworms. These insects are often associated with fields that have been in a pasture or CRP situation previously, where grasses have been allowed to grow for more than one year. It is very rare to see these problems in continuous corn, although there are always exceptions to the rule. These insects are underground feeders (wireworms and white grubs), or feed on the surface or below the surface of the soil (cutworms), and so detection is through observing plant damage and digging in the soil around plant.

Wireworms

Wireworms are the larvae of click beetles. The adult beetles prefer to lay eggs in grasses and the larvae can remain in that stage for up to 6 years, depending on the species. Wireworms are our earliest corn pests, as they may feed on the seed before germination, causing reduced plant emergence. Later feeding may kill or stunt small emerged plants. All wireworm feeding is done under ground. Wireworms are white, yellow, orange, or brown with hard shells, which give these insects the name. As stated earlier, they tend to be more numerous in fields that have been in grass/pasture or fields that have had grassy weed problems. Wireworms prefer cooler soil temperatures, under 70 degrees, so early planted fields and heavy surface residue fields may have higher risk than tilled fields.

There is no rescue treatment available for wireworms, so farmers with a high probability of problems need to use a planting time treatment to prevent stand reduction. The recent development of seed treatments like Cruiser and Poncho has really reduced the incidence of wireworm damage. They are excellent early season stand protectors. One potential problem with seed treatments is they are becoming so commonly used that resistance is a possibility. Granular soil insecticides and liquids also work well.

White Grubs

White grubs are the larvae of May (or June) beetles. They also prefer to feed on grasses and very rarely affect crops other than corn. There are two basic types of grubs. Annual grubs complete their development in one year and are not considered serious pests. Three year grubs, however, can damage corn severely in the last two years of their larval stage. The larvae overwinter deep in the soil, and as the soil warms they begin feeding on plant roots. Damage to corn may not occur until the corn is in the 2 to 6 leaf stage. This is difficult because up to the time of feeding the stand may look fine. Often grub damage is near shelter belts where the adults may congregate to feed and mate.

Like wireworms, there is no treatment available to rescue damage from white grubs. Again, high risk areas need to be treated at planting time. Products for white grub control are similar to wireworm control.

If wireworm or white grub damage is serious enough to warrant a replant, the use of planting time products is recommended, although the odds for damage diminish with the warming of the soil.

Scout Emerging Corn for Cutworms

Cutworms and other insects may hinder emerging corn plants this spring even if seed was treated with insecticides or Bt corn hybrids were used. High populations of insects may overwhelm the protection provided by controls, such as insecticides applied at planting time whether liquid, granular or seed treatment or whether it was a Bt corn hybrid. Also in some cases products are not labeled for the full spectrum of insects we may encounter in Nebraska . For example, Herculex I Bt corn hybrids list black cutworm on the label, but not other soil cutworm species.

Cutworms can cause serious damage to corn in the first couple weeks after emergence so it is important to scout fields for damage. Several species of cutworms attack corn. The severity and the area affected will vary greatly, depending on species involved, previous crop history and weather conditions. The black cutworm does not overwinter in Nebraska , and infestations depend on moth movement in southerly winds in the spring. Fields with winter annual weeds or abundant crop residue are more attractive to the egg-laying moths in the spring. Other cutworm species (dingy, army, sandhills) overwinter as partly grown caterpillars. Remember that early detection of a problem is essential because most of the cutting occurs within seven days of plant emergence.

Generally, a postemergence "rescue” treatment should be considered if cutting is observed on 5 percent or more of plants and the worms are one inch or less in length.

Rescue treatments are effective in controlling soil cutworms. Ambush 2E, Asana XL, Baythroid, Lorsban 4E, Mustang Max, Warrior, Proaxis, Pounce 3.2EC, or other insecticides with similar active ingredients will give satisfactory control as post-emergence sprays. If soil is dry or crusted, rotary hoeing immediately before or after Lorsban application may enhance control. The other insecticides are pyrethroids and should not be incorporated.

For more information about insecticide products and rates, visit UNL's Department of Entomology's Web site at http://entomology.unl.edu. For more information about managing cutworms, consult UNL Extension NebGuide G1154, Corn Cutworms, available at local extension offices or online at http://www.ianrpubs.unl.edu/sendIt/g1153.pdf . (KJ)

Windmills, Wells, and Water Quality

Is that old windmill contaminating your drinking water - or a neighbor's?

Probably not, but the well below can be. Often, these wells are deteriorating and no longer used, but the well shaft is still a direct connection from the ground surface to the underlying aquifer. This can allow surface runoff to flow directly to the water-bearing zones, often carrying organic wastes, fertilizers, and other chemical residues such as pesticides and petroleum products into the groundwater. Small animals can fall into these wells, further adding to the contamination. Contaminants that enter an old, out-of-service well can migrate to in-service water supplies such as a new well on the property, or a neighbor's well.

Unused wells, especially those that are old and/or in disrepair, or that do not meet current standards as an inactive well, pose a major threat to groundwater quality and represent a serious threat to human health and safety. State law refers to these as illegal wells.

There are thousands of these wells on farmsteads, acreages, and other rural areas throughout the state. Often, when a new well is drilled, the property owner neglects to properly decommission the old well. Or, even though a well may not have been used for several years, the owner continues to put off having it sealed.

While a windmill tower can be a sure sign, wells can be present at many other locations too. Rural property owners, field scouts, and others who walk around old farmsteads and similar areas should carefully observe for any signs that a well might exist. Some signs include: concrete pads where the legs of a windmill tower once stood; depressions where an old well pit or the walls of a dug well may have collapsed; an old stock tank in an over-grown area; a small area that is fenced off, especially if there are also pipes sticking out of the ground; flat stones, a concrete slab, old boards, metal sheets, or other items that could be covering an old well shaft; and many others. Sometimes there are no signs. For example, one landowner discovered a 36-inch diameter, 50-foot deep dug well when the front wheel of his tractor dropped into it. He did not know that this well was there, despite having grown up on that farm. (This well has now been properly filled and sealed.)

Nebraska regulations require that illegal wells be decommissioned by a licensed Nebraska Well Contractor. This process includes removal of well equipment (pump, piping, etc), disinfection, sealing, filling, capping, and reporting. The cost of decommissioning a well depends on several factors including accessibility, construction technique and materials, diameter, depth, and condition. Generally this is not particularly expensive. For example, in conjunction with a special water quality educational program in the Shell Creek Watershed in northeast Nebraska, 14 out-of-service domestic and livestock wells were decommissioned during 2005 and 2006 at an average cost of $313 per well.

Because of the importance of protecting water quality, nearly every Natural Resources District (NRD) offers an attractive incentive to assist well owners with the cost of decommissioning. Payment rates vary by NRD, but typically these programs will pay for 60 to 75% of the costs. The Lower Elkhorn NRD will reimburse well owners 75% of the approved costs for decommissioning, up to a limit of $500 for drilled wells or $700 for dug wells. With these cost-share payments, out-of-pocket expense to the well owner will often be less than $100 - a small price to pay to help assure that water quality and human safety are protected.

If there is an unused well on your property, begin the decommissioning process today. It = s okay to keep the windmill for decoration or as a yard light support, but have the well properly sealed and do your part to protect groundwater quality and human health and safety. (DPS)

David P. Shelton
Extension Agricultural Engineer

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