EXTENSION 
INSTITUTE OF AGRICULTURE AND NATURAL RESOURCES         
UNIVERSITY OF NEBRASKA-LINCOLN 
NORTHEAST RESEARCH & EXTENSION CENTER       
601 EAST BENJAMIN AVENUE, SUITE 104
NORFOLK, NE 68701-0812
PHONE: (402) 370-4000 
FAX (402) 370-4010

Current Soybean Aphid Situation in Nebraska

In late June after we published our last newsletter we received reports of soybean aphids scattered across eastern Nebraska . This is typical of what we have experienced the last few years. Recent weather forecasts indicate a hot period coming up. If that is the case aphids should not develop rapidly and predators may keep them in check. However, this can only be verified by regular field reports. Fields must be scouted at least once a week to determine aphid population trends. Once again, we are receiving calls asking about treating low levels of aphids with an insecticide during a late glyphosate application. This is not a good idea at this time because: 1) We don't know if aphid populations will increase to economic levels, and; 2) This will eliminate predators which may actually worsen the situations by causing flare-ups of aphids that migrate into fields or flare-ups of spider mites which are more common in soybeans in dry years. See newsletter #10 for full soybean aphid recommendations. (KJ)

Western Bean Cutworm

We have seen an increase of moth numbers in our light trap at Concord . Now would be a good idea to scout fields for egg masses and small larvae in whorls or tassels. See newsletter #10 for full recommendations. (KJ)

Cowpea Aphid

Cowpea aphids, Aphis craccivora, were found in alfalfa a couple of weeks ago in Dixon County . The grower cut the alfalfa and so far no further reports are in but in a dry year this insect could become a problem. This insect was first reported in Nebraska in Knox Co. in 1999. In 2002 economic levels occurred in some fields in northeast Nebraska in late July. Since many growers were in the process or close to harvesting the third cutting, most chose to take the cutting and watch the regrowth. Some fields were treated in 2002.

The cowpea aphid is easily distinguished from other aphids in alfalfa largely because it is the only black aphid found infesting the crop. In general, it is a relatively small aphid, less than 2 mm long. An excellent color image of the cowpea aphid can be found on the internet:http://www.ipm.ucda v is.edu/PMG/A/I-HO-ACRA-AD.004.htm l . Non-winged and winged adults are usually shiny black, while the smaller nymphs may appear to be a dull gray to black. The first half of the antennae is white, and the legs are usually a creamy white color with blackish tips. In alfalfa, these aphids prefer to feed on young terminal growth, but can be found infesting leaves, blooms, and stems. Damage symptoms include yellowing, wilting, and dieback. In general, legumes can be seriously damaged, either by direct insect feeding or by the transmission of virus diseases. This aphid produces a considerable amount of honeydew upon which sooty mold grows. The honeydew also makes the alfalfa sticky, which causes problems with harvest.

The cowpea aphid is generally distributed across North America and has been reported in at least 28 states and in three Canadian provinces. This aphid species also has an extensive host range with a marked preference for legumes. Other known host plants are apple, carrot, cotton, cowpea, dandelion, dock, goldenrod, kidney bean, lambsquarters, lettuce, lima bean, pinto bean, peanut, pepperweed, pigweed, red clover, shepherdspurse, vetch, wheat, white sweet clover, and yellow sweet clover. The aphid lives throughout the year without producing sexual forms and they are always parthenogenetic viviparous females (ready to produce live offspring at birth).

Threshold suggestions for cowpea aphid control are similar to those of blue alfalfa aphid: 10-12 per plant in alfalfa under 10 inches tall or 50 per sweep of a net, 40-50 per plant or 200 per sweep in alfalfa over 10 inches. Insecticide tests at the Haskell Ag Lab showed good control with Mustang Max, Warrior, and Lorsban. (KJ)

Grape Colaspis Beetles Feeding on Corn Leaves

In two separate situations last week area consultants in Cuming County reported finding grape colaspis beetles feeding on corn leaves. While the beetle feeds on a variety of plants, corn is not considered a favorite.

The grape colaspis is a rare (in Nebraska ) pest of corn usually found in the southern counties, whose larvae feed on the root hairs. The damage appears earlier than corn rootworm and can be confused with wireworm or white grub injury, since the feeding causes stunting and purpling of young corn plants. The grape colaspis usually causes root damage to corn planted after red clover, or more infrequently sweet clover, alfalfa, or soybeans.

Adults emerge in mid-June to early July in the corn belt. Females lay eggs and the larve feed on roots in the late summer and early fall. Unlike corn rootworms, the larvae overwinter. Adults have been reported feeding on corn silks but rarely leaves.

Colaspis beetles are similar in size to corn rootworm beetles but are more of a brownish color with light stripes. The larvae are smaller and more rounded than corn rootworm larvae, and appear slightly curved (comma shaped). Most larval feeding should be complete in Nebraska and some adults should now be visible in some fields. (KJ)