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Newsletter Renewal Time

It's a little later than usual, but it's time to gear up for the new crop production season and time to re-subscribe to the Northeast Nebraska IPM-Crop Production Newsletter.

The subscription rate for 2008 will remain at $20.00. For this reasonable sum you can expect objective information on pest management, fertility, irrigation scheduling, crop development, and other crop management information on a weekly basis during the growing season. This newsletter is designed specifically for Northeast Nebraska . The subscription fee basically covers our costs for supplies and stamps.

If you have access to the Internet, the newsletter can be read free of charge at http://nerec.unl.edu/ipm/ipm1.htm . If you do access the newsletter regularly on the Internet, we do ask that you call Pat Bathke at 402-584-3837 or email her at pbathke1@unl.edu so we can get a handle on how many people are using the information. Also, if you want an e-mail reminder of when the newsletter is on the web you can subscribe to a listserve that will automatically contact you when the letter is ready. To subscribe to the listserve, send an e-mail message to: LISTSERV@UNL.EDU and in the Message Field (Not subject) type SUBSCRIBE IPM. Do not include a signature, as LISTSERV will try to interpret each line as a command. If you have any problems, contact Pat.

For another option for subscribing to the IPM newsletter reminder or other agricultural listserves, go to http://nerec.unl.edu/aglistserv.htm . Just click the listservs you would like to receive and fill in the form. You'll receive any newsletters, ag notices, etc., that are sent.

Please fill out the accompanying form and get it to us as soon as possible so you can receive our weekly update on conditions influencing crop production in northeast Nebraska . (KJ)

Alfalfa Weevil and Clover Leaf Weevil in Alfalfa

The majority of alfalfa weevils overwinter as adults, and then become active and lay eggs. However, some eggs overwinter as well, and hatch earlier. This has resulted in some areas in Nebraska (Panhandle and the northern tier of counties) being hit with 2 flushes of weevils in the spring. In the last few years some areas of the state have received damage to regrowth after the first cutting due to a combination of late larval feeding and adult feeding. This is something to be aware of after the first cutting.

Getting back to the present, based on growing degree days, alfalfa weevil larvae should be feeding, and small pinholes may be visible in the new alfalfa growth near the tips of the plants as soon as next week. While alfalfa weevil damage has been spotty in much of Nebraska over the past few years, the potential for damage always exists. While things are very busy as row crops are to be planted, those of you who are growing high quality alfalfa hay should take the time to monitor fields for weevils over the next few weeks.

Clover leaf weevils (CLW) are occasionally a problem but are very vulnerable to fungus disease and so haven't been pests since the late 80's early 90's when spring rains were rare. The dry conditions over the past several years in western Nebraska may have aided them in building their populations, although recent rain could have knocked populations down. Clover leaf weevil larvae will be in the debris around the crowns during day. Scratching in the soil around the crowns and counting the number of larvae found per crown will help give a better idea of clover leaf weevil infestation. Their brown heads will help distinguish them from the black-headed alfalfa weevil. Table 1 will compare the alfalfa weevil and the clover leaf weevil.

Both alfalfa weevil and clover leaf weevils feed on first cutting alfalfa as larvae, and regrowth after the first cutting as adults (and sometimes larvae). While research conducted in northeast Nebraska has shown that clover leaf weevil larva feeding does not cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting.

It is essential that fields be monitored for alfalfa weevil feeding now. Damage consists of small holes and interveinal feeding on the newest leaflets near the stem tips. The larvae are a small (1/16 to 3/8 inch in length), pale yellowish green, becoming a darker green when larger. These legless worms have black heads and a white stripe the length of the back. The alfalfa weevil larvae spend nearly all their time on the plant. They curl into a C-shape when disturbed.

Once the alfalfa is about 4-6 inches or so in height, take a bucket, carefully cut some stems at ground level (30 to 50 per field, from various spots in the field) and shake the stems against the side of the bucket. Average the number of weevil larvae per stem. Use the following charts to aid you in making a decision on whether to control alfalfa weevils. Each chart has been developed for a different alfalfa value. To treat or re-sample depends on the average number of weevils per stem, the stem length, and the value of the alfalfa. When alfalfa reaches a certain height, it may be more profitable to cut the alfalfa early rather than to treat. The graphic charts shown here are examples, and you should use the $105/ton chart and adjust to the price you feel your alfalfa is worth.

Insecticides registered to control alfalfa weevil larvae include Ambush, Baythroid, Cythion, Furadan, Guthion, Imidan, Lannate, Lorsban, Mustang Max, Penncap M, Proaxis, Pounce, Sevin, and Warrior. Check the labels or see the Entomology Website at http: / /entomology.unl.edu/instabls/instabls.htm to find the use rates. (KJ)

Early Soil 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. (KJ)

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. (KJ)

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. (KJ)

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, Cobalt, Lorsban 4E, Mustang Max EC, Warrior, Proaxis, Pounce 3.2 EC, or other insecticides with similar active ingredients (generics) will give satisfactory control as post-emergence sprays. If soil is dry or crusted, rotary hoeing immediately before or after Lorsban (chlorpyrifos) 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)

David P. Shelton
Extension Agricultural Engineer

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