Areas of the state received 1-3 inches of rain last week, delaying planting in many areas. Photo by Brett Hampton

May 16, 2003

Median autumn freeze (32oF) date. Half of all autumn freezes will occur before the dates shown on this map and half will occur after (based on 47 years of records, 1949-1995). From the NU NebGuide, Autumn Freeze Probabilities (G96-1312). (Link to larger version.)

A review of Midwest research on the effects of late corn planting dates and fall frosts can be helpful at this time. It is clear that delayed planting usually reduces corn yields. A recent report by Golden Harvest summarized yield across several "northern" Cornbelt locations including Hastings, North Platte and Waterloo, Nebraska. The trials were conducted from 1993 to 2001.

The greatest yield potential occurred with a May 7 planting date. Yield potential declined slowly during mid-May and dropped rapidly in late May and early June. For example, yield potential with a May 19 planting date was about 94% of maximum while that of May 29 was about 83%.

Of course, every year is different and planting late in 2003 may actually enhance yield. The Golden Harvest work from all north and south locations also shows that grain moisture contents at harvest increased about 1% for every four- to five-day delay in planting date.

In addition to the issue of potentially lower yields with delayed planting is concern about the possibility of frost occuring before crop maturity. One of the NebGuides (G1312) listed in the Sources section includes data for autumn frost probabilities in Nebraska. A map (above) from the NebGuide shows the median probability of a 32º fall freeze and indicates that in a large portion of southeast and south central Nebraska, half of the freezes would be likely to occur before October 6 and half would be likely to occur afterward. Ideally I'd like to have corn mature at least two weeks before this date.

We also should consider measures of crop maturity, which can become somewhat confusing given the variety of measurement systems available. While there is no single standard, researchers Bob Nielsen (Purdue University) and Peter Thomison (Ohio State University) clarified the relationship between hybrid comparative relative maturity (CRM) and growing degree days (GDD). The CRM system they used is similar to that of Pioneer Hi-Bred International and is thought of as days required from planting to maturity. The equation generated for this relationship was:

Table 1. Relationship between CRM and GDD for days to physiological maturity (black layer) (86/50) for 'normal' planting dates. CRM GDD 100 2408 105 2533 110 2657 115 2782 120 2906

For every day increase in CRM, GDD requirements appear to increase about 25 units. Table 1 shows this relationship too.

Based on this table, a 115 CRM hybrid would use about 2800 GDD to mature with a normal planting date. The last five words are important! Research cited by Nielsen and Thomison shows that:

1) although delayed planting shortens the growing season, corn hybrids adjust to this well, and

2) adapted hybrids can be planted into early June without major risks of fall frost injury.

Many producers, especially those in no-till, also have been concerned that weed size may exceed the range of most preemergence herbicides by the time they are applied this year. Many of these products contain atrazine and have burndown properties. One can expect to control 4-inch broadleaf weeds at 1.5 lb and 2-3-inch broadleaf weeds with 0.75 - 1 lb. of atrazine.

Atrazine's postemergence activity can be increased by including an oil additive or applying with UAN as the carrier; however, you will not need both and adding oil to a mixture of fertilizer and atrazine will injure the crop. If you have planted Roundup Ready corn, you can add glyphosate to the mixture. Keep in mind that glyphosate activity may suffer when mixed with other herbicides or UAN so use the 1 quart rate. Another option with Roundup Ready corn would be to use Field Master, which contains both Harness Xtra and Roundup as a premix. Also, if you are considering adding 2,4-D to the mixture, the entire field should be at the spike stage to avoid injury to the corn.

Additionally, please note that Balance is not registered post-emergence. If used post-emergence, injury may occur. Also, DO NOT use Balance on lights sandy soils with low organic matter. Also, crop oil concentrate (COC) can be added with some mixtures to enhance weed control but be sure to check the label as it may injure the crop.

See CropWatch Tables for this issue for a list of postemergence corn herbicides.

Consider several factors when choosing a postemergence herbicide. The first and most important is its efficacy on the weed species present. You obviously want a herbicide that works well, but some herbicides provide better control on some weeds than others. Also consider crop safety and timing of the herbicide application. For example, one herbicide will have good activity on many grass and broadleaf weeds, but should not be applied to corn over 12 inches tall. All herbicides carry some type of timing restriction and pushing those limits can easily result in crop injury or reduced weed control. In the end that can mean lost dollars from yield loss.

Often, efficacy is influenced by the rate used. Choose a herbicide that will allow you to use the required rate for different weed sizes. For example, 24 oz/ac of glyphosate will do well on most velvetleaf plants in the 1–3 inch stage; however, if you are dealing with 4-8 inch weeds, increase the rate to 1 qt/ac. Use caution when increasing rates of most herbicides because this can increase the possibility of crop injury. Finally, follow label recommendations regarding additives. Many labels will suggest adding crop oil (COC), AMS, or othe additives to enhance herbicide movement or uptake into the plant. The right additive can really help provide great weed control; however, the wrong additive can cause serious crop injury and/or poor weed control, which once again translates into yield loss. As always, read and follow the label recommendations and restrictions for maximum herbicide efficacy and crop safety.

Now you can add the labeled rate of Steadfast (0.75 oz/ac) or Accent (0.67 oz/ac) to the rate of Lumax for your soil. This tank mix should be applied before the corn is 5 inches tall. Only use NIS as the additive. The use of MSO, UAN, and AMS is not recommended and COC may cause injury to the corn.

Grasshopper nymph identification guide.

The recent damp weather likely had a minimal effect on the survival of summer feeding grasshoppers. Grasshopper species that overwintered as nymphs were too large to be susceptible to wet conditions, and most grasshoppers that hatch in the spring were still in the egg stage, well protected from the weather. If rainy weather patterns continue through the end of May and into early June, the effect on spring hatching grasshoppers would be significant.

One of the bright spots of the recent rainfall has been the improvement in range and pasture condition. Cool season grasses have been growing rapidly and now may have a better chance to keep ahead of spring and summer feeding grasshoppers. Even though rangeland conditions have improved, it is essential that grass growth and grasshopper populations be monitored. Many of the state's grasslands are still suffering from the effects of drought, overgrazing and severe grasshopper infestations in 2002. These grasses need additional time to recover from the stress they have experienced.

With the high potential for a large number of grasshoppers and the fragile condition of grasslands, it will be important that producers start looking for hatching grasshoppers and identify problem areas. Collecting grasshoppers with a sweep net is the easiest way to determine where grasshopper hatching beds are located. After the hatching areas are identified, producers should determine the number of grasshoppers in a square yard. These counts are important to help determine the potential severity of an infestation. To estimate densities, identify a point at a distance of about 10 feet, visualize a square foot area around that point and, while walking toward the location, count any grasshoppers that move out of the area. It is important to check the vegetation in the square foot area carefully and count small grasshoppers that were not previously flushed from the area. The square foot count should be repeated 18 times in areas of different slope and vegetation. Divide the total number of grasshoppers counted in the 18 samples by two. This result is the number of grasshoppers per square yard. The procedure should then be repeated in different areas surrounding cropland or in different areas of rangeland and pastures.

There are over 100 species of grasshoppers in Nebraska. Of these only a handful are important pests of rangeland and pastures. Most of these grasshoppers feed exclusively on grasses and sedges and tend to be wasteful when they feed. They climb on leaf blades and clip them off, causing the blades to fall unconsumed to the ground. At high grasshopper densities, this clipping behavior results in a much greater loss.

Four species typically cause problems in crops. Although these grasshoppers will be found in pastures, they prefer to feed on a mixture of broadleaf plants and grasses. These grasshoppers can be abundant in weedy pastures or crop borders. When the weeds are either completely consumed or become dried down, the grasshoppers will move to adjacent crops and can cause severe damage. It is important to identify the species present because other rangeland and pasture infesting grasshoppers seldom move to crop plants to feed.

Producers also will need to monitor the growth of young grasshoppers, particularly if they are abundant. Grasshopper controls should target the 3rd and 4th instar nymphs (when they are about ½ to 3/4 inch long). Grasshopper nymphs are much easier to control than the adults because they can be killed with less insecticide. Also, adult grasshoppers are more mobile and more apt to spread, requiring controls over a greater area in order to protect crops and pastures. The growth stage of grasshopper nymphs can be determined by looking at the size of the individual and the length of the wing pads. The wing pads are posterior to the pronotum or saddle shaped structure just behind the head. The tips of the wing pads of 3rd instar nymphs point down and not toward the back. The tips of the wing pads of 4th instar nymphs point upwards and toward the back and do not extend beyond the 1st abdominal segment. With a little practice producers can easily see the wing pads and made a positive determination of the nymph growth stage.

Producers can protect their rangeland, pastures and crops if they survey their land for spring hatching, summer feeding grasshoppers. After the grasshoppers have gained some size (1/2 inch), the number of individuals per square yard should be determined as well as determining the growth stage and species present. Once this information has been gathered, producers can make informed control decisions based on established economic thresholds. These thresholds are available in two University of Nebraska NebFacts: A Guide to Grasshopper Control in Rangeland, NF97-329 and A Guide to Grasshopper Control in Cropland, NF97-328. (NF328 has been recently revised and will be rereleased in May.) These NebFacts are available from your local Cooperative Extension office or on-line.

The most important point to remember is that grasshoppers should be controlled well before they reach the adult stage.

Fortunately, the rate of human infection for West Nile Virus is relatively low. People can only contract it if bitten by an infected mosquito. Only one out of five people bitten by an infected mosquito will have mild symptoms of the disease, such as headache, body aches and fever. Only one of 150 people will develop more serious symptoms, such as high fever, neck stiffness and paralysis due to brain inflamation. Older people and those with a compromised immune system are most likely to suffer severe disease symptoms. Birds, primarily crows and blue jays, and horses are the main animals suffering from the disease, although a few dogs, squirrels and other animal species also have been identified with it.

A vaccine available to protect horses is estimated to be 90-95% effective. Horses must be vaccinated twice about three weeks apart in the first year and at least once each year thereafter to provide protection from the disease. The vaccination or booster should be administered before the onset of vector mosquitoes.

Unfortunately, there is no vaccine to protect humans. Human protection depends on avoiding mosquitoes.

Tips for avoiding mosquitoes

• Human exposure to mosquitoes is greatest at twilight so avoid mosquito-infested areas then.
• Wear light-colored clothing that covers the body, including the arms and legs. Mosquitoes are attracted to exposed skin and darker clothing.
• Use mosquito repellents, particularly those with N,N-diethyl-meta-toluamide (DEET). DEET provides protection from mosquitoes for three to five hours, depending on how much of the active ingredient is in the formulation. The higher the percentage, the longer the repellence lasts, up to a maximum of five hours. An insecticide, permethrin, can be applied to clothing but NOT to skin. It both repels and kills mosquitoes.

Mosquito control will lessen the potential threat to humans.

• Empty all containers holding water for more than a week, including bird baths, wading pools, ponds, house gutters and eaves and kids toys. Poorly drained areas that puddle, such as from machinery tracks, and discarded tires provide potential egg-laying areas for mosquitoes.
• Add fish or provide a means of agitation for small ponds to help reduce mosquito populations.
• Regularly treat with residual insecticides flowers, shrubs, evergreen trees and other vegetative areas that provide resting areas for mosquitoes.
• In some farm situations where eliminating mosquito-breeding areas is not practical, such as near irrigated fields, a larvicide application may be an effective control method. Several larvicides are well suited for farms, including Bacillus sphaericus. B. thuringiensis israelensis (B.t.i.), Temephos, growth regulators, oils and mono-molecular films. These larvicides can only be applied by certified pesticide applicators. Check with an applicator to determine which product would best suit your situation, and what type of control activities should be conducted.

"What we found was that without the bacteria Bradyrhizo-bium, which 'fixes' the nitrogen that plants utilize, soybean yields can be dramatically reduced," said Barney Gordon, agronomist-in-charge of the university's North Central Kansas Experiment Field.

Comparison yields for inoculated and non-inoculated soybean trials with and without added nitrogen. Treatment Yield Not inoculated - 0 nitrogen 39 bu/ac Not inoculated - 60 pounds nitrogen per acre 44 bu/ac Inoculated - 0 nitrogen 45 bu/ac Inoculated - 60 pounds nitrogen per acre 47 bu/ac

Researchers studied the role of inoculants in fields at three sites: 1) near Scandia under irrigated conditions on Crete silt loam soil, nine years after soybeans were last planted; 2) on a dryland field near Manhattan on Wymore silty clay loam, five years after soybeans; and 3) in a Geary County field on a dryland Muir silty clay loam, where soybeans had been grown within the last two years. Depending on location, the study examined 6 to 13 inoculant treatments, including a no-inoculant check.

Average yields for all treatments for the Scandia, Manhattan and Geary County sites were 67, 24 and 55 bushels per acre, respectively. (Hail damage at the Manhattan site reduced yields.) The no-inoculant check yields were 50, 24 and 55 bushels per acre, respectively.

In the field where soybeans hadn't been grown for nine years there was a 17 bushel per acre decrease without inoculants. In the two fields where soybeans had been grown more recently, there was no yield difference.

"There are some situations when seed should be inoculated even when soybeans have been previously planted," said Scott Staggenborg, northeast area Extension crops and soils specialist. "Those situations include when the field has been flooded, when the soil pH is very low, or if the soil is sandy with minimal organic matter."

A separate three-year study at the Northwest Research and Extension Center near Colby examined whether an emergency application of nitrogen would compensate for the lack of an inoculant. The study site was a field that had never been planted to soybeans. The researchers looked at four inoculant-nitrogen combinations.

Using an inoculant provided a yield increase of six bushels per acre in a field where soybeans had never been planted. The research also indicated that a rescue application of 60 pounds of nitrogen per acre would compensate for not planting inoculated soybeans.

"Based on these data," Staggen-borg said, "if a farmer did not use an inoculant when one should have been used, added nitrogen fertilizer could eliminate most of the yield loss. This should be considered an emergency solution, though, because the cost of the nitrogen fertilizer is considerably more expensive than the cost of the inoculant."

Mary Lou Peter
Kansas State University News

Nitrogen fertilizer recommendations for manured soils* and corn after alfalfa. (From ISU Cooperative Extension publication, Nitrogen Fertilizer Recommendations for Corn in Iowa). Grain and Soil test Recommended N rate fertilizer nitrate Excess** Normal prices Rainfall Rainfall ppm N -- lb. N/acre -- Unfavorable 0-10 90 90 (1 bu buys 11-15 0 60 7 lbs. of N) 16-20 0 0*** > 20 0 0 Favorable 0-10 90 90 (1 bu buys 11-15 60 60 15 lbs. of N) 16-25 0 30 > 25 0 0 * A field should be considered manured if animal manures were applied with a reasonable degree of uniformity since harvest of the previous crop or in two of the last four years. ** Rainfall should be considered excess if rainfall in May exceeded five inches [in Iowa]. *** Adding 30 lbs. N/acre may have no detectable effects on profits, but producers could reasonably elect to apply this rate.

The featured guest, Dallas Virchow, NU Extension wildlife management project coordinator, will talk about how to determine which control measures might work best in a particular situation.

“Some control measures will work in some landscapes but not in others,” he said. He’ll also talk about how to apply those control measures safely and effectively.

The May 23 NU Market Journal will look at refinancing options for ag operations. David Goeller, NU beginning farmer program coordinator; and Cary Sandell, a Wells Fargo banker, will talk about why farmers and ranchers might want to consider refinancing certain kinds of debt.

This show will also address concerns and potential impact of the new country of origin labeling law. The fifth USDA “listening session” on the law was held May 9 in Kearney. The May 23 Market Journal will include a review of what was said there and an analysis of the hearings’potential impact on the law and on the beef industry.

With six more hearings scheduled nationwide between now and June 26, the country of origin labeling law (COOL) debate is far from over. Darrell Mark, NU Extension agribusiness marketing specialist, attended the Kearney hearing and videotaped interviews with some of the producers, packers, and other beef industry representatives there. He'll share clips from those interviews and offer his analysis of what is likely to happen next in the debate over COOL.

Acreage to be harvested for grain is estimated at 1.65 million acres, up 9% from last year. This would be 94% of the planted acres, up from last year’s 92% and the ten-year average of 93%. As of May 4, topsoil moisture supplies were rated mostly adequate in the major wheat growing areas. Disease and insect pressure to date has been light.

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