Last Weekly Newsletter
This will be the last weekly newsletter of the season. We may have more depending on the growing conditions for the rest of the year. A survey will arrive later to gather information on how we can improve the newsletter. (KJ)
Corn Rootworms and Extended Diapause
Recently there has been concern from growers and consultants that corn rootworm damage has been increasing in rotated fields. The suspicion is that we are seeing more damage from the northern corn rootworm.
Two species of corn rootworms attack corn in northeast Nebraska , the western corn rootworm, Diabrotica virgifera , and the northern corn rootworm, Dibrotica barberi. Both overwinter in the egg stage, hatch and feed on the roots of corn as larvae in June and July, and emerge as adults in July and August to start the cycle all over again. The majority of corn rootworms in Nebraska are westerns, but in the northeast where temperatures are generally cooler we have a larger percentage of northerns than the rest of the state.
As stated earlier, corn rootworms overwinter, or diapause, in the egg stage. In the past, the surest way to avoid corn rootworm damage was to rotate crops. The eggs would hatch in the non-host crop and the rootworm larvae would starve. However, a certain percentage of northern corn rootworm eggs overwinter for more than one year. This is called “extended diapause”. If enough eggs in a field overwinter for more than one year, a strict corn/soybean rotation could have problems with corn rootworms. This phenomenon has been seen in southwest Minnesota, southeast South Dakota, and northwest Iowa .
Lately, extended diapause has been confirmed as far south as the University of Nebraska 's Mead field lab east of Wahoo, and in some places further west. This is an indication that the trait is spreading south and west. To make matters more complicated, northern corn rootworms will leave corn fields in the adult stage to feed on the pollen of many plants. For example, they may concentrate in a corn field that had a late season pigweed problem. This would result in higher numbers of eggs being laid in that field and set it up for a problem 2 years down the road.
Entomology staff at the Northeast Center 's Haskell Lab have put out emergence cages in several area corn-after-soybean fields to try to gauge the extent of extended diapause. Preliminary results are that we are catching some northern corn rootworm adults out of every field, although mostly in non-economic numbers. However, this phenomenon will bear careful attention. You can be sure it will be of increasing interest in the near future, and one of the subjects of our winter meetings. (KJ)
Saltcedar Control
Saltcedar ( Taramix ramosissima), also known as tamarisk , is a new invasive weed introduced from Eurasia and found in Nebraska = s wetland habitats in all soil types. It is a perennial deciduous or evergreen shrub or small tree from the tamarisk family (Tamaricaceae) that reproduces both by seeds and perennial structures such as the taproot and stem. The root system is extensive with the primary taproot easily growing at least 15 ft deep. Once the water table is reached, secondary root branching becomes profuse. The plants (trees) can grow as individual trees or in sparse groups. The woody stem is erect, up to 20 ft tall, dark-brown or reddish-brown highly branched saplings. Leaves are small, scale-like (as in many cedar trees) with many divisions on slender highly branched green stems. In Nebraska , it can flower from June to August, with small pink flowers positioned on the top of the main woody stem and branches (saplings) in the finger-like clusters. The flowers produce small, numerous, and tufted seeds that can be carried long distance by wind and water. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal.
Saltcedar was sold as an ornamental plant species, but escaped and became naturalized along streams, canals and reservoirs in much of Western USA . In addition, in early 1900 saltcedar was purposely planted along stream banks for soil erosion control. Saltcedar has detrimental effects on the ecology of the natural habitat through several means. The high evapo-transpiration rate of saltcedar can lower the water table in streams and canals. The salt excreted from the leaves to the soil surface under the plant inhibits germination and growth of competing species. Thus the name A saltcedar @ is derived from the salty residue that collects on the small scale-like leaves that resembles cedar foliage. As a result, many wildlife species are negatively affected by habitat changes and native species displacement due to encroachment of saltcedar. In addition, the sticky salty substance exuded by the leaves can also damage the plumage of birds. With loss of habitat most wildlife species move to more diverse native plant communities.
Due to its detrimental nature to the wildlife habitat and land in general, it is a concern to many privately and government managed lands. The guidelines for control include: (1) treat young or regrown plants under 6 ft tall because they are easily sprayed and controlled than taller trees, (2) treat areas previously root plowed, mowed or areas where saltcedar appears to be newly invading, (3) treat area with tree densities fewer than 150 plants per acre, (4) spray foliage to wet (no dripping) especially terminal ends, and allow two full growing seasons before follow-up management. (5) Time herbicide application towards the later part of the season, but not too late. September and August treatments are much better than May, June or October. (6) Broadcast treatments can be done using airplane, helicopter or high-clearance sprayers with a water volume of a least 15 gall per acre for better penetration into the dense canopy. Arial application can be effective using a global positioning spray system matched with the survey maps, allowing the pilot to locate saltcedar sites and exclude sensitive areas such as cottonwood groves and other vegetation. For broadcast treatments Habitat (imazapyr) is recommended at the rate of 3 pints per acre. (7) Individual trees can be also controlled with Habitat at 1% volume/volume (v/v). Habitat is absorbed through foliage and roots and is translocated throughout the plants. Complete kill of plants may not occur within a month or two. In addition, a mix of Roundup (0.5% v/v) and Habitat (0.5% v/v) is also very effective. Roundup is added to the mix to reduce the cost of the treatment since Roundup (or any generic glyphosate) can be as much as 4-5 times cheaper that Habitat alone. (8) Do not treat irrigation ditches and water for domestic use. Do not use near desirable trees and near homesteads. Clean equipment with water following spraying. (SK)
The Corn Stalk Nitrate Test 
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