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EUROPEAN CORN BORER MOTHS ARE FLYING

European corn borer moths have been active in Nebraska since the end of May, and non-Bt corn fields need to be scouted if the corn is above 16 inches in extended leaf height. We expect populations to peak some time in the next two weeks.

As non-Bt corn grows it will become susceptible to the first generation of corn borers. While we haven't seen a bumper crop of moths in our black light traps since Bt corn became commonly used, we should not be complacent about the European corn borer in non-Bt cornfields.

Timely and accurate scouting is the key to managing European corn borer in standard (non-Bt) corn hybrids. Remember that conditions are localized and each field should be scouted to make accurate decisions.

Corn borer larval survival depends on several factors. High humidity and warm temperatures are ideal for establishment of larvae in the whorl. Egg masses are white, with 5 to 40 eggs in each mass, and laid on the underside of leaves near the midrib. The masses look like fish scales flattened against the leaf. In four to seven days the heads of the developing larvae will be visible, and the eggs will appear spotted. This is the “blackhead” stage, and these eggs normally hatch within 24 hours. As the larvae enter the whorl to feed on the developing tissue, the feeding scars (shot-holes) appear as the leaves emerge from the whorl. Larvae will remain within the whorl for 7 to 14 days before boring into the stalk.

Corn that is less than 16 inches with extended leaf height (distance from the ground to the tip of the leaf pulled up vertically, about six-leaf stage) is unlikely to support young larvae because of the presence of a substance known as DIMBOA, a natural resistance factor. As the plants grow, the level of DIMBOA decreases, so plants above the 16-inch extended leaf height will generally support corn borers. First generation corn borers prefer taller plants for egg laying, therefore, the earliest planted fields are more likely to have higher populations. Scout these fields first, but do not neglect other fields because any cornfield is a potential target and should be scouted.

Now that Bt corn is being planted widely, be sure you know whether the field you are scouting was planted to Bt corn. In Bt corn, corn borer injury to whorl stage plants should be limited to a few tiny pin-holes where larvae initially fed before ingesting a lethal dose of Bt toxin. However, seed lots may contain a small percentage of off-type seed (typically less than 4%) which does not produce sufficient toxin levels to kill corn borer larvae. If greater than 4% of plants show significant leaf feeding damage in a Bt cornfield, check to confirm it is corn borer causing the injury. Other caterpillars such as corn earworms or common stalk borer are not completely controlled by Bt corns currently available, although they may reduce populations.

If you believe that corn borer is causing the injury, contact a representative of the company that sold the seed to investigate the situation more completely.

To determine the need for treatment, scout at least 20-25 consecutive plants in at least 4-5 places in the field (100 plants minimum per field). The scouting locations should be randomly selected and representative of the field as a whole. At each scouting location, randomly select the first plant that will be sampled. If you do not and always start sampling at an infested plant, the counts may be inflated by as much as 5%. Count the number of plants showing shot-hole feeding and determine the percent of infested plants. Next, pull the whorls from at least two randomly selected infested plants in each set of 20-25 plants. Unroll the leaves and count the number of larvae in the whorl and determine the number of larvae per infested plant. Young corn borers usually suffer from 60-85% or higher mortality due to natural enemies, weather and disease, so try to wait to make treatment decisions until most of the borers are second instar. This will allow you to take advantage of natural larval mortality.

Use the information gathered from field scouting to complete the accompanying worksheet. This takes you through the calculations needed to estimate the preventable loss if an insecticide is used. Compare the preventable loss to the total cost of insecticide application. An insecticide application is economically justified if preventable loss exceeds the total cost of insecticide application. A worksheet interactive version of the worksheet is available on-line.

Insecticide treatments will be effective only if borers are still feeding in the whorl. Treatments made after corn borers begin to bore into the stalk (when they are about half grown) will not be effective. Based on research data, the best control is achieved with aerial or ground applied granular formulations or liquid applications through sprinkler irrigation systems, which provide the best penetration of insecticide into the whorl where the corn borer larvae feed.

In this example a $20 application would more than pay for itself by preventing a $90.00 loss. All of the above numbers are variable and are unique to each field and farm management operation. Use the formula several times using different figures for yield, price, and cost of application to see how each one affects the outcome. Use the figures closest to your situation to make the final determination. CAUTION: With the high price of corn you can “pencil out” a justification for treating for corn borers at very low numbers. You must realize that you must have a certain “minimum” number of corn borers to affect yield. Generally, corn borer numbers should average above 1 per plant to get a yield reduction. Even lowering that threshold to ½ borer per plant could save unnecessary application.

Many insecticides are registered for control of first generation European corn borers and most will do a good job if applied properly at the right time. The Bt-based insecticides Dipel, Condor, M-Peril and others are effective and do not reduce populations of corn borer natural enemies. Refer to the UNL Department of Entomology Web site at http://entomology.unl.edu/instabls/ecb1st.htm for a list of suggested insecticides.

Additional information on first generation European corn borer management is available in “ First Generation European Corn Borer Scouting and Treatment Decisions, ” NebFact 98-364. (TH&KJ)

COMMON STALK BORER DAMAGE SOON VISIBLE

Common stalk borers will be moving into corn from nearby grassy areas and damage will soon be visible. At first, large shotholes can be seen, and later, as the stalk borers burrow into the plant, the plant looks very ragged and stunted. Common stalk borer damage is occasionally confused with corn borer damage, but is nearly always confined to a few rows that border grassy areas. The larva is pale white, with dark brown to purplish stripes that converge to form a saddle shape along the middle of the body. Once the larvae have entered the stalks, there is no control available. (KJ)

INTEGRATED MANAGEMENT OF EASTERN REDCEDAR IN GRASSLANDS OF NEBRASKA

Summary: Integrated management of eastern redcedar on pasture and grassland should be based on a combination of cultural, mechanical, biological, and chemical tools to keep this invasive tree under control and protect grass land production and profits. We recommend to use tree-height as a determining factor for control options. Burning, cutting, digging, mowing, burning, use of goats and broadcast herbicide application is effective on trees up to 2 ft tall. Cutting and individual-tree herbicide treatments work well on 2-10 ft tall redcedar. Trees that are over 10 ft in height are most effectively and economically controlled by cutting. The bottom line is “control trees while they are small”.

History and Biology : Eastern redcedar ( Juniperus virginiana L.) is one of 13 juniper species native to the United States . It is the most widespread tree-sized conifer and is native to every state east of the 100th meridian. Throughout this vast range, eastern redcedar grows on many soils and under varying climatic conditions. This adaptability has enhanced eastern redcedar's recent spread into areas where it was formerly rare or absent. Eastern redcedar is a dioecious species, which means individual trees are either male or female. Staring in the 6 th or 7 th year of growth, female trees produce small, berry like fruits that are eaten by many birds and some small mammals, which indirectly helps spread the seed via droppings. Digestion actually improves germination.

Impact of eastern redcedar: Eastern redcedar is a problem on grasslands primarily because it reduces forage production and livestock handling. Developing trees alter the microclimate, which encourages a shift from desirable warm-season native grasses to introduced cool-season grasses such as Kentucky bluegrass. Heavy infestations make livestock handling more difficult. All these adverse effects can be reflected in lower rental rates or sale prices for infested grassland. Established infestations usually get worse over time due to overproduction of seeds and established trees et bigger, thus shading grass benight even more. On many sites complete coverage by eastern redcedar can be expected, resulting in total loss of grass production unless controlled. Control measures should be initiated as soon as possible, both to improve effectiveness and reduce total control costs.

Integrated Management of Eastern Redcedar : Integrated management has been commonly described as “a multi-disciplinary approach utilizing the application of numerous alternative control measures”. In practical terms, it means developing a management program based on a best method, or a combination of methods for the particular site, which could include mechanical, biological and chemical practices.

As previously described, Nebraska 's eastern redcedar infestations have developed over several decades. Likewise, management of these infestations is best viewed as a long-term or on-going effort, both to reduce the initial infestations and prevent them from redeveloping to economically damaging levels. It is best to begin treatment as soon as possible, once treatment has begun considerable time is gained to continue long-term management. The emphasis should be on management of the infestation, rather than eradication. Eradication is not economical, and probably not physically possible in most cases. Instead, it should be recognized that some remaining larger trees, which are the most difficult and expensive to kill, do little damage. In fact, at low levels, eastern redcedars can be viewed as a potential resource, providing livestock shelter, wildlife habitat, timber products, and aesthetic values. Most important, long-term selective management is considerably less expensive than a more intensive, short-term approach.

If the goal is to just reduce overall number of trees, and stop further spreading (eg. management of wildlife habitat), it is recommended to cut female trees only. Female trees are the ones that produce berry-like fruits. This would allow “male trees” to grow and provide much needed cover for wildlife, or land beautification, while reducing further spreading.

Manual and Mechanical control: Manual and mechanical control involves methods such as digging trees, cutting and mowing. It is very effective for small areas, and it is most efficient on trees up to 2 feet tall. Cutting is an effective method of control because eastern redcedar is a non-sprouter. Trees cut below the lowest branches will not regrow. A variety of handheld or motor-powered cutting tools can be used. Hand-held tools (shears, saws, spade, shovel, heavier hoe) are effective on small trees (<5ft tall), while larger trees require a chain saw or vehicle-mounted shears. The equipment varies from tractor pulled PTO driven shredders to hydraulic drive devices that mount on skid steer loaders. Most of the shredders can easily handle up to 3-4 inch stem diameter trees, while some can cut tress up to 15 inches. In general, cutting is a method that can be time consuming and labor intensive. Cutting alone also fails to remove all of the problem because fallen trees continue to occupy space. Thus, all cut trees should be gathered and burned, or permanently removed from the grassland. Mowing of short trees (<3ft tall) can be conducted using shielded mower shortly after regular cutting and haying.

Biological control of eastern redcedar: Biological control is the use of natural enemies to reduce weed populations to economically acceptable levels. In the case of red cedar control, goats can be utilized as an effective bio-control agent for trees that are up to 3-4 ft tall. Experience from Nebraska suggest that most cedar trees < 24 inches tall were killed by goats utilizing paddock grazing system. The control level was reduced by 50 percent on trees 4-8 feet tall tress, however the goats managed to defoliate bottom branches and stripe bark from branches and trunks up to three inches in diameter.

Generally, goats are browsers with diets consisting of about 70% of non-grassy species, which indicates that they should not compete with cattle for grass. Goats prefer non-grassy species, but they would eat grass if no other species are available. This also suggests that goats in general can help in controlling many plant species that cattle do not eat, including various noxious weeds (eg. leafy spurge, thistles). Goat production can be also a profitable livestock enterprise that provides income through meat and milk production, and leasing fees for goat leased to control various invasive forbs and shrubs. Important factors in managing goats include the use of appropriate stocking rates and quality fencing. In essence, the number of goats needs to be adjusted to the amount of plant material needed to control.

The grazing strategy with the goats should vary depending on the management goals set for the pasture. Adding one or two goats per cow and letting the goats and cattle run together is an excellent maintenance strategy for pasture with moderate to low cedar infestation. However, if the goal is to get a quicker response and try to suppress denser stands then the area needs to be fenced off using temporary fencing. Thus per acre stocking rate should be at least 10 goats/acre of land infested. This stocking rate with moderate cedar infestation should result in significant damage to the trees within 30 days. Higher stocking rates would be better, but will require moving the fence more often. Trees and other perennial plants have high energy reserves in their root systems and repeated defoliation over a few years is required to control them. Cedar trees however, will not resprout and thus, if the goats remove most of the needles and/or bark, the tree will eventually die. Other issues that need to be addressed before getting goats may include predator control (eg. coyotes) and perhaps learning how to raise goats for meat production. A good place to start is at the ATTRA - National Sustainable Agriculture Information Service web site. The page “Goats: Sustainable Production Overview, Livestock Production Guide” http://www.attra.org/attra-pub/goatoverview.html has information on numerous topics relating to meat goat production.

Many ranchers in other parts of the US have run cattle and goats together for decades. They view goats both as a profitable part of their business and as a very important part of their grazing land management program.

Use of prescribed fire for redcedar control: This method is inexpensive and very effective against smaller trees. Its effectiveness declines as tree size increases, however there were cases of successful burning of tall trees. Adequate fine fuel (usually, last year's dead grass) is necessary for satisfactory results. Safety also is a concern since many managers lack experience with fire and the equipment required to conduct fires.

The controlled use of fire is a large subject in itself. It is beyond the scope of this publication to provide detailed instruction on conducting prescribed fires. Two other Nebraska Extension publications provide information on the use of fire in general and on how to safely conduct fires. They are NebGuide G88-894, Grassland Management with Prescribed Burning, and Extension Circular 90-121, Conducting a Prescribed Burn. A fire plan should be prepared and a prescribed burning permit obtained from the local fire jurisdiction, as required by state law. Specialized fire equipment can be purchased. Two sources are the Ben Meadows Company, 3589 Broad St., Chamblee, GA 30341; and Forestry Suppliers, Inc, Box 8397, Jackson, MS 39284-8397.

Chemical control of eastern redcedar: Herbicides can also be considered for control of this tree species, however, they should be viewed as just another tool in the integrated management program. Depending on the application method and chemical type, the use of herbicides can be time consuming and expensive, especially when used on denser tree infestations or large tracts of land. Effectiveness also is variable depending on the tree size and label directions and/or restrictions. Therefore, always read and follow herbicide label directions. Herbicide information on control of troublesome plant species, including eastern cedar, is update annually in the Guide for Weed Management in Nebraska (EC-130). In general, herbicides for eastern redcedar control can be used for broadcast application or individual-tree spraying.

Broadcast treatments: Broadcast application is the most common method of applying herbicides in agricultural settings. The key message for the efficacy of broadcast treatments in eastern redcedar control is: “the shorter the tree the better control”.

Since tree height was the most important factor influencing the level of chemical control (tree injury) with broadcast treatments, the herbicide efficacy data from Nebraska study was categorized by tree height (Table 1). Recommended herbicides for trees that are up to two feet tall include: Surmount, Grazon P&D and Tordon (Table 1). However, the same herbicides will not provide satisfactory control of trees taller than 2 ft, indicating the importance of tree height. Surmount at the rate of 5pts/acre can also cause short-term grass injury in the form of leaf yellowing and top growth burning (Table 1). Cost of Grazon P+D and Tordon 22 K for broadcast applications can range from $21-$26 per acre. Since Surmount is not marketed product yet, its costs is not known.

Individual-tree treatments: Individual-tree treatments can be applied directly to the tree foliage or to the soil around tree base. Soil treatments can minimize the amount of herbicide used and the exposure to non-target species. However, soil treatments may not be effective unless applied before rainfall, preferably in Spring or Fall. Rain water is needed to move the herbicide into the root zone allowing an easier uptake by a tree. Recommended herbicides for soil application around tree base include Tordon 22K at the rate of 1 cc (ml) per every foot of tree height, Velpar-L at 4 (cc) ml and Spike 20P at 1cc (ml) per every inch of tree diameter. Cost of Tordon is about $85 per gallon, Velpar is about $65 per gallon and Spike 20P is about $9 per pound of product.

Individual-tree foliage can be also treated with various herbicides (Figure 8). Based on a study conducted in northeastern Nebraska, recommended herbicides for control of 2-10 feet tall trees include Surmount at 1.5% volume per volume (v/v), Grazon P+D at 2.0% (v/v) and Tordon 22K at 1.0% v/v (Table 2).

To help you determine volume per volume basis, for example, the 1% v/v equals 1 gall of product per 100 gallon of water. For smaller back pack sprayers use an equivalent of 1.3 oz of product per every gallon of water. Apply about 1.5 oz of the herbicide spray solution per every foot of tree height. Walk around the tree and just spray enough solution just to get a glisten (shine) on the canopy surface. Solution dripping off the canopy indicates a rate that is too high, and a likely waste of time and money. As an example, it was calculated that 1 gallon of spray solution could cover 15 individual trees that are 6 feet tall at a pressure of 20 PSI and a single nozzle type XR8002.

Grass injury in the form of temporary yellowing and burning of top growth was evident among all treatments especially for Tordon 22K. Roundup is not recommended for use in pasture settings due to poor activity on cedar trees and high injury level to the grass (Table 2). Cost of Grazon P+D and Tordon 22 K can ranged from $11-$16 per acre.

Practical hint for chemical control: Use of selective herbicide treatments should be based on a tree height. Broadcast treatments are effective only on short trees (up to 2-ft tall), while the medium height trees (2 to 10 ft) can be controlled with individual-tree treatments. For broadcast treatments use 6-8 pints of Grazon P&D or 4-5 pts of Surmount in a 20 gallon of water per acre. To prepare 1 gall of spray solution for individual-tree canopy treatments use 1.3 oz of Tordon, or 2.6 oz of Grazon P&D, or 2 oz of Surmount. For larger spray tanks adjust herbicide rates accordingly.

Take home message: Since there are many different scenarios under which eastern redcedar trees grow, they obviously can not be managed by a single IWM control method; however, if the methods are implemented in a systematic manner, significant advances in eastern redcedar control can be achieved. Obviously you can not use all of the above described techniques at once. We recommend to use the best combination of techniques for your needs. There are many ways to start developing an IWM program. The easiest start will be to try a one or two techniques and then add more practices as the time goes on or the field conditions change. Cost of control methods can also vary thus choose the operation that can fit your budget the best.

We recommend to use a tree-height as a determining factor for control options. There are many control options for trees that are up to 2 feet tall, which may include: cutting, pulling, digging, mowing, burning, use of goats and broadcasts herbicide application. Trees that are 2-10 feet tall can be controlled effectively by cutting and individual-tree herbicide treatments of soil or foliage. Trees that are over 10 ft in height are the most effectively and economically controlled by cutting. Therefore, in order to save time and labor expenses the main take-home message is to “control redcedar trees while they are small”. (SK)

Table 1. Percent eastern redcedar control and grass injury levels at about 100 days after treatment as influenced by the tree height (feet) where herbicide treatments were broadcast applied.

Table 2: Percent of eastern redcedar and grass injury at 100 days after treatment that were applied to individual- trees.

READING CROP WATER USE TABLES TUTORIAL

Listed at the Crop Water Use link is the estimated crop water use information based upon data collected near several weather stations in northeast and north central Nebraska . Each table has lines of information about a specific crop (corn, soybeans, alfalfa, potato, and grass) and specific emergence date (month day). We try to update these tables daily Monday through Friday, however, on occasion the server in Lincoln or at Norfolk may fail making it impossible for us to update the information. Thank you for your patience.

The estimated crop water use is calculated based on local weather information collected at an automated weather station near the city listed in Column 1 and is for a well-watered crop. If you tend to under irrigate, these values will be higher than you might experience when monitoring your soil water levels.

Emergence date and relative maturity selections were made based on local input about when each crop was planted in the area around the weather station location. We have tried to bracket the planting season for corn and soybeans in an effort to provide information to a broad group of producers. The other crops have a single emergence date.

•  Page down until you find the weather station closest to your field.
•  The date when the data was updated is provided on the top left side of each table. The date when the data were collected is presented a few lines down and is centered on the page.
•  Find the line of information that is closest to your field situation. An example printout is provided below. (Example: corn emerged on 5 26) in Columns 3 and 4 of line 2.
•  Read the accumulated growing degree days (GDD's) based on May 26 emergence date in Column 5 of line 2 (183 GDD's).
•  Read the calculated crop water use for the previous week, the past 3 days, and yesterday in Columns 6, 7, and 8 of line 2( 0.03, 0.03, 0.02) in inches per day. These values are averages based upon the number of days except for the information for yesterday which is based only on data for that 24-hour period.
•  Read the estimated crop water use for the next three days and next week in columns 9 and 10 of line 2
( 0.03, 0.04) inches per day. These are estimated based upon long term trends and partially on weather data during the previous 3-7 days.
•  Read the estimated stage of crop development based on the growing degrees accumulated and the relative maturity of the crop in Column 11 of line 2 (2 leaves). The crop water use estimate is the same for all relative maturities until the grain fill period. Late in the season, varieties with higher relative maturities will maintain a high crop water use rate for several days longer than low relative maturity varieties.
•  The last column provides the estimated growing degree days required for the crop to reach physiological maturity. Read 2700 in Column 12 of line 2.

Since we cannot predict when you might be harvesting your grass and alfalfa, perennial crops are assigned unrealistically high estimated growing degree days to maturity values in an effort to keep them growing throughout the summer. If you have any questions or comments about these data tables, feel free to call:
Bill Kranz at 402-584-3857 .

5/24/2006 CROP WATER USE SUMMARY

Ending on 5/24/2006

David P. Shelton
Extension Agricultural Engineer

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