Management calendar May 1-15 One-half inch or more of rain or irrigation within four days of a surface application of manure moves the manure ammonium-nitrogen into the soil. This is equal to incorporation for ammonium availability; however, more ammonium is lost with each day of delay. Manure incorporation is not needed to utilize the organic-N credit. For more information check the NU NebGuide Determining Crop Available Nutrients from Manure", G97-1335, available from your local Cooperative Extension office.

In NU Cooperative Extension field trials in south central and southeast Nebraska since 1997, crop specialists compared the productivity of corn and sorghum side by side in dryland farmers' fields. They used management practices appropriate to each crop and area. Research found sorghum usually yielded better in fields expected to yield below 120 bushels per acre. However, if yields are expected to be above 140 bushels per acre, corn usually will yield more, said Steve Melvin, extension educator in Frontier County and formerly an extension educator in Nuckolls County, where some of the research was conducted. The yields in the 120 to 140 bushels per acre range would be similar for the two crops.

The 2001 results in south central Nebraska show when it is fairly dry during the corn grain-fill period and extremely dry later during the sorghum grain-fill period, corn will outyield sorghum, Melvin said. The previous years' data show the opposite is true with a little rain later in the summer.

These trials emphasize there are distinct advantages to having both corn and sorghum in the same year, said Roger Elmore, crops specialist at the South Central REC near Clay Center. "You don't know what kind of weather you'll have. Planting corn and sorghum spreads out the risk and provides excellent crop rotation benefits," he said.

IANR specialists have rotated field trials in Gage, Lancaster, Nuckolls, Otoe and Webster counties over the past five years.

The 2001 trials were in Webster and Lancaster counties. In Webster County, where it was extremely hot and dry during late summer, 18 corn hybrids were planted in the same field with 19 sorghum hybrids. Both crops were planted no-till into wheat stubble. Corn yields ranged from 108 to 160 bushels per acre with an average of 138 bushels per acre. Sorghum yields ranged from 108 to 148 bushels per acre with a 135-bushel per acre average.

In Lancaster County, which also was dry much of the summer, 60 corn hybrids and 35 sorghum hybrids were no-tilled into bean stubble. Corn yields averaged 129 bushels per acre and ranged from 104 to 171 bushels per acre. The sorghum plot had a poor stand and only 11 commercial hybrids were included in these comparisons. They averaged 115 bushels per acre and ranged from 95 to 131 bushels per acre.

The last five years of data from Nuckolls and Webster counties show sorghum yielding 126 bushels per acre and corn 112 bushels per acre, giving sorghum a 14 bushel per acre advantage over corn.

Three years of data from Gage, Lancaster and Otoe counties resulted in 139-bushel-per-acre corn yields and 130-bushel-per-acre sorghum yields, giving corn a nine-bushel-per-acre advantage at these higher yields.

The plots in south central Nebraska were planted no-till into wheat stubble each year except 1997 when the stubble was disked once. The southeast plots were planted no-till into soybean stubble two out of the three years. The excellent yields in these plot are directly related to the water saving practice of no-till farming, Melvin said.

"Another observation from these trials is that dryland corn hybrid selection is more critical than for grain sorghum," Melvin said. "The variation between the top and bottom yielding corn hybrid was 20 bushels per acre more then for the sorghum."

Side-by-side corn and sorghum fields.

Grain sorghum seed costs less than seed corn, which leads to lower overall production costs than with corn. The lower cash price for sorghum is offset by equally lower production costs, these trials showed. If yields are similar for corn and sorghum, returns are similar. So, if sorghum outyields dryland corn, it will produce better returns.

The market price also makes a difference. During the last couple of years, grain sorghum prices have been a few cents a bushel below and occasionally above corn prices, said Roger Selley, extension farm management specialist.

Traditionally the grain sorghum price is based on the feed value and sorghum is less valuable for a feed source. However, today other factors are influencing grain sorghum prices. For example, grain sorghum is a better base for dog food and more is being exported to Mexico, he said. "The price depends on what's happening in the market place now," he said. "There's been a shift, but the question is how long these conditions will prevail.

Sandi Alswager
Newswriter
IANR News and Publishing

The growing point for recently planted corn is near where the seed was planted. If there was some soil moisture, especially from a recent rain, there should be little damage from the frost. Recent tillage also can affect the potential for damage by creating a direct path from the cold air down into the soil and seed cavity. At this point, however, even if the leaves have emerged and are burned back, there should not be any permanent damage to the plants.

Spring grains such as oat and spring wheat are able to tolerate fairly low temperatures at their current growth stage. Winter wheat will tolerate low temperatures as long as the growing point is near ground level. The growing point will not be in danger until it gets close to the boot stage. Even then it is quite well protected. It becomes very vulnerable after the head has emerged and pollination is taking place. No place in Nebraska has reached that point.

Alfalfa weevil

According to growing degree accumulations, alfalfa weevil activity should have begun in most of the state by now. Weevil larvae usually begin causing noticeable damage at about 350 GDD (48 degree base).

Clover leaf weevils (CLW) are occasionally a problem in dry springs but are very vulnerable to a fungus disease, and so haven't been pests since the late 80s early 90s when spring rains were rare. 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. The chart below compares the alfalfa and clover leaf weevil. Both the alfalfa weevil and clover leaf weevil feed on first cutting alfalfa as larvae and regrowth of the first cutting as adults. While research conducted in northeast Nebraska has shown that clover leaf weevil larvae 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.

Weevil management
Several methods can be used to reduce weevil populations. At this time of year, economic infestations are usually dealt with by insecticide use or early harvest, depending on the alfalfa's height. Other non-chemical control methods that have been used for alfalfa weevil management include flaming, flooding, crushing of eggs and larvae, disking or harrowing, seeding dates, and use of resistant varieties. The easiest way to begin weevil management is to select a resistant or tolerant variety that will yield well in your area. The grazing of alfalfa in fall and winter is becoming more popular and will reduce overwintering egg populations, particularly in southern areas where a significant number of eggs, as well as adults, may overwinter.

In a recent Oklahoma study, cattle reduced the density of weevil eggs by over 60%. Grazed alfalfa may not be as attractive to egg-laying females in the spring although more research needs to be done to determine the factors involved. 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 small (1/16 to 3/8 inch in length) and a pale yellowish green, which turns to a darker green when they are larger. These legless worms have black heads and a white stripe the length of the back. The alfalfa weevil larvae, which curl into a C-shape when disturbed, spend nearly all their time on the plant.

Total precipitation for April 16-21 generally ranged from 0.50 - 1.00 inch across the eastern half of the state. Northeast Nebraska received the most generous amounts, with totals decreasing considerably toward western Nebraska. The recent activity has provided some surface moisture for planting, but has not reduced drought concerns.

The Nebraska Agricultural Statistics Service (NASS) reported dismal topsoil and subsoil levels for most of the state as of April 21. The percent of fields reporting topsoil as short to very short are: Panhandle (64%), north central (26%), northeast (42%), central (90%), east central (64%), southwest (89%), south central (89%), and southeast (53%). Subsoil condition continues to remain poor with the percentages of fields reporting short to very short conditions as follows: panhandle (70%), north central (42%), northeast (43%), central (89%), east central (78%), southwest (74%), south central (84%), and southeast (63%).

To add insult to injury, snowpack in the Colorado and Wyoming mountains which feeds the Platte watershed was only 80% of what it was by the end of March last year. This represents less than 60% of the historical average. Even after a heavy snow April 19-21, snowpack water equivalents rose less than five percent. Streamflow projections for this summer are for less than 60% of normal flow if normal precipitation is received for the period.

It is anticipated that further reservoir draw downs will occur this summer for Enders, Harlan, McConaughy, and Swanson. Irrigation delivery restrictions are a certainty for Enders and Swanson users, with initial estimates placing deliveries at six inches for the season. No restrictions are anticipated for McConaughy this year, but a below normal snowpack this winter would likely force authorities to visit the issue next spring.

Weather outlooks do offer some rays of hope. Forecasts for the next week point to several systems working across the state. Because of recent storm activity, there may be more moisture at the surface to feed these systems and improve rainfall prospects. The large temperature fluctuations experienced between each of the systems means that severe storm activity will likely occur.

It is important that these systems deliver rainfall in a consistent manner. Rainfall deficits for the year are running two to five inches across the state. This represents 30%-60% of normal precipitation, depending on location. Areas that have been hardest hit and need to see significant moisture are central and southwest Nebraska and the Nebraska Panhandle.

Precipitation outlooks for May do not give us any direction as there are equal chances of receiving below normal, normal, or above normal precipitation across the entire state. However, the 90-day outlook for the May - July indicates a tendency toward above normal precipitation for the entire state, with the highest probabilities assigned to the eastern two-thirds of Nebraska. It is extremely unusual for 90-day outlooks to indicate a wet bias across the central Plains during the summer. Due to the nature of thunderstorm activity, models generally assign a climatology ranking to summer precipitation forecasts, meaning equal chances of below normal, normal, or above normal conditions. That is precisely what the forecasts are indicating for the June-August, July-September, and August-October periods.

After analyzing the 90-day outlooks, it appears that the wet forecast for the May-July period indicates that June is contributing to the above normal tendency of the three-month precipitation forecast. However, it also indicates a bias toward drier than normal conditions in August. This would be consistent with a building El Nino event forecast to reach full maturity by December. The one thing researchers are not clear on is how El Nino events will contribute to precipitation and temperature trends during the next 20 years. The Pacific Ocean has undergone a 20-year circulation oscillation from a warm phase to a cold phase. Since model input for long-lead outlooks favors the warm phase, there is some model uncertainty to whether the cool phase will exhibit similar climatic influences around the globe during El Nino events. Time will tell.

Option is a new postemergence herbicide in corn that has just been labeled. It is being manufactured by Aventis and is a sulfonylurea herbicide with ALS mode of action. It's primary spectrum of control is grassy weeds.

The program, which will be held from 8:30 a.m. to 5 p.m., is designed for entry level scouts who will be working for crop consultants, industry agronomists and farm service centers across Nebraska and neighboring states, said Keith Glean, program co-coordinator and NU extension educator. Trainers are NU faculty and representatives from ag industry.

Topics include: corn and soybean growth and development - how to stage the growth of corn and soybeans and why this is important to pest control; corn and soybean insect pests - identification, damage and life cycles; natural enemies - predators, parasites and pathogens; weed identification; crop diseases; nutrient deficiencies; and sampling methods including scouting do's and don'ts. Past participants give the training high marks, Glean said.

Registration is $65 before May 7 and $75 after. A total of 5.5 CCA credits is anticipated for Integrated Pest Management 4.0, Crop Production, 1.0 and Soil Fertility 0.5.

This training is part of the NU Cooperative Extension Crop Management Diagnostic Clinics. Three other clinics are planned. A mid-summer diagnostic clinic July 18 will include: crop production management decisions, soybean pests, sprayer management, fertilizer application equipment, crop nutrient management planning, herbicide mode of action, insects, diseases and weeds.

The Aug. 20 clinic will address late season pest management, nutrient management, and tillage options and the Sept. 4 clinic will be on precision farming.

Field updates

Mechanically removing the tops.
Cattails can be kept in check, and eventually controlled, by repeatedly cutting the tops. If possible, cut plants below the water line. If they must be cut above the water line, raise the water level in the lagoon to submerge the cut stems at least 8 inches. Research in Iowa (Weller, 1975) found that cutting shoots two or three times during the growing season before flower production reduced a cattail stand by 95-99% in one year. A single cutting in August followed by submergence resulted in 80% control. It is important to remove all dead and live cattail stems to achieve this control.

Power equipment that has been used to cut cattails includes tractor-mounted sickle mowers and hand-operated power trimmers equipped with metal cutting wheels instead of strings. Hand scythes, machetes (corn knives) and long-handled shovels also have been used to manually cut cattails close to the shoreline.

Hand pulling.
Where feasible, pulling rather than cutting will result in faster control because the plant structures (crowns, rhizomes, and roots) which store the energy will be removed. Repeated pulling so plants never grow taller than 3 feet above the water surface will prevent seed production. Sometimes the rhizomes become so intertwined, it is nearly impossible to pull the plants out by their roots. In this case, use a shovel to first divide the clumps into square foot sections and then pull them.

Using a contact herbicide.
A contact herbicide only kills the green tissue that comes in contact with the herbicide and does not move through the plant as a systemic herbicide does. Thorough coverage of the green tissue is essential for effective control. Expect plants to regrow from the roots. Treat three to four times during the growing season to prevent seed production and to eventually starve the root system.

Reward is the most common contact herbicide used. Use 1 to 2 quarts per acre broadcast in at least 50-100 gallons of water or 0.75 oz per gallon for spot spraying to either add 0.25% to .50% solution (1 or 2 quarts per 100 gallons) of non-ionic surfactant (such as X-77).

Using a systemic herbicide.
Systemic herbicides applied to the foliage are absorbed into the plant tissues and then moved (translocated) throughout the entire plant. The optimum treatment period is from late boot stage (noticeable bulge caused by the flowering structure growing up through its protective sheath) to early flowering (green cattail head freshly emerged from the boot).

Typical products include:

2,4-D ester (4L) + Methylated seed oil (MSO) or crop oil concentrate (COC). Use 1.5 gallons per acre in at least 150 gallons of water (carrier) for broadcast or a 1% 2,4-D solution for spot spraying. To either add 0.5% of MSO or COC.

AquamasterTM or aquatic glyphosate + non-ionic surfactant (NIS). Use approximately 4.5-6 pints per acre broadcast or 0.75% solution (1 oz per gallon) for spot spraying. To either add 0.5% solution of NIS.

Be sure you only use glyphosate products registered for aquatic uses. As always read and follow all label directions and use restrictions.