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To estimate surviving plant stands, you will want to count plants in at least three places in the affected field. Count plants in at least 1/100 of an acre. Use Table 1 to determine the length of row necessary to achieve 1/100 of an acre. (You also could sample 10 areas within a field, each representing 1/1000 of an acre.) The total linear feet of row necessary to end up with 1/100 of an acre for different row widths is shown in Table 1.
Now determine if the standing plants will survive or whether there are "skips" that need to be accounted for. Were skips the result of seed that hadn’t emerged yet but will, or were they due to damage from insects, disease, frost, hail, etc? Considering the recent cool weather, it’s possible that the seed just hasn’t emerged yet. If this is the case, will they be able to break through the crust? If flooding is the cause, how long were plants flooded?
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When assessing your soybean crop, first determine seedling health. The loss of leaf tissue is not as important as damage to or loss of stem buds. Soybean must have viable buds remaining on the stem to survive. They should show signs of growth within four to seven days after the storm. When counting viable soybean plants, count any plant that appears to have intact or expanding buds or leaves. Sample an area at least 1/1000 of an acre; see Table 1 for the proper row lengths for a given row width. It is best to sample 5-10 areas within the field. An easy method is to pick a number of rows, 30 for example, and walk diagonally across your field, stopping every 30 rows and counting the number of plants in the given row width (Table 1).
Record your values from the 5-10 areas sampled and calculate the average number of plants. Next take this average and divide it by the row length you used, to determine the number of plants you have per foot of row. If you have drilled soybean, use a population hoop to estimate the number of plants per acre.
At the South Central Agricultural Laboratory (SCAL) near Clay Center, we have studied the effect of stand reductions in soybean at various growth stages during 2003 and 2004. The earliest stand reduction occurred at V3 (three trifoliates). Although none of the soybean crop in the state was at this stage when the storms came through last week, it is useful to look at this data and see the minimal impact losing plants early on in the season has. Although the loss in yield varied a little between the two years of research, we can average them to get a close idea of what the response would be this year. The uniform loss of plants at V3 caused a linear decrease in yield as severity increased. A 25%, 50% and 75% reduction in stand reduced yields only by 3.6%, 7.9%, and 12.1% relative to the control.
This loss in yield is for irrigated soybean in the yield range of 55-75 bu/A. In 2004, yields were reduced more than in 2003 but even in 2004, yields were only reduced by 16.4% from the 75% stand reduction at V3. Remember that these yield losses occurred from stand reductions at V3. Therefore, considering the storms affected the soybean crop much earlier than V3 we would not expect yield
losses to be greater than what occurred at V3.
Although it is saddening to walk into soybean fields that are much sparser than they should be; if you have a healthy, fairly uniform stand of soybean, it likely will not pay to replant. With lower soybean populations you will want to pay more attention to weed pressure throughout the season since you will
have reduced shading from the soybean canopy. Also remember that when soybean branches out, pod
height will be lower and these plants will need extra attention at harvest.
Lori Abendroth
Soybean replanting guidelines
Some soybeans were just starting to emerge last week when severe storms rolled through. The
resulting floods and soil crusting may necessitate replanting in some areas. Crusted soils can
reduce the total population of soybean due to reduced emergence and plant viability. The following
guideline can help determine whether replanting is economical in your situation. Remember too that
once soybeans emerge they often can compensate for these situations by branching out.Table 3. Deriving plants per acre from field measurements of plants per row. An optimum planting rate is 150,000 seeds per acre in Nebraska and therefore the table increases up to roughly 150,000 plants per acre because this would be the maximum plants that would be possible. This table is from Soybean Replant Decisions by Iowa State University. 38 36 30 20 15 13,800 14,500 17,400 26,100 34,800 27,500 29,000 34,800 52,300 69,700 41,300 43,600 52,300 78,400 104,500 55,000 58,100 69,700 104,500 139,400 68,800 72,600 87,100 130,700 174,200 82,500 87,100 104,500 156,800 96,300 101,600 122,000 110,000 116,200 139,400 123,800 130,700 156,800 137,600 145,200 151,300 159,700
Research and Extension Associate
Roger Elmore
Extension Crops Specialist
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Consider insect control options with replanting
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For example, replanting corn now will likely increase the likelihood of injury from second generation European corn borers and possibly corn earworms. Later planted corn also may be attractive to corn rootworm beetles in August, as the early planted corn fields reach the brown silk stage. Corn rootworm beetles will fly to nearby fields if they are in the green silk stage. If abundant, rootworm beetles could interfere with pollination of the late planted corn by feeding on the silks. Also, if this late planted field is replanted to corn in 2006, there’s a good chance that rootworms will be a problem. In soybeans, later planted fields will be green later in the season and may attract bean leaf beetles in August and September.
If you used an insecticide at planting in corn and are replanting now, you may still want to use an insecticide. Although the risk of injury from seedling insects such as wireworms and seed corn maggots is reduced with a later planting, there is no post-emergence treatment for these insects. If you think there is moderate to heavy pressure from rootworms in the field, an insecticide at planting may be important. Rootworm larvae will be hatching out of eggs in late May and early June and can severely injure the root system of small plants.
If you used a planting time insecticide in corn, read the label before re-using it in a replant situation. Many insecticides have a maximum amount per season that can be used on a field. If you want to treat the replant crop, you may need to use a different insecticide. If you are considering switching to a different crop such as soybeans when you replant, check the label of what you applied earlier in the season. Some insecticides have restrictions on how soon you can plant to another crop. For example, Aztec 2.1 G has a 30-day plant back restriction for any crops after corn.
Bob Wright
Extension Entomologist
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If fertilizer had been recently applied to the soil surface, without incorporation or a gentle rain of 0.5 inch or more to move nitrogen into the soil profile, substantial nitrogen loss may occur in runoff. Rainfall was very intense in some areas last week, with total precipitation exceeding 10 inches in some areas, resulting in severe erosion and loss of nutrients on or near the soil surface.
Denitrification
The primary nitrogen loss mechanism from saturated, fine-textured soils may be denitrification. This is the process of anaerobic bacteria present in soil converting nitrate-N into gaseous forms (nitric oxide, nitrous oxide, dinitrogen) which can be lost to the atmosphere. In fields where most fertilizer nitrogen was applied preplant, likely four to eight weeks ago, much of the N may have been converted to nitrate by the microbial process of nitrification. This nitrate is then susceptible to loss via denitrification or leaching.
Leaching
If nitrogen existed in soil in the nitrate or urea forms, significant leaching loss may have occurred, more so on coarse-textured soils. Some of this nitrogen may have leached deep enough into the root zone to be unavailable to the crop, at least early in the season. Continued precipitation or irrigation may leach this nitrogen out of the root zone entirely.
For more information on soil processes influencing nitrogen management, view the Nitrogen Chapter of the Cooperative Extension publication, Nutrient Management for Agronomic Crops in Nebraska.
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Unfortunately, there are many variables interacting to influence the potential for nitrogen loss from heavy rainfall, making it difficult to estimate how much fertilizer N has been lost, and whether producers should apply more fertilizer. Figure 1 and Table 1 can be used to help derive rough estimates of potential loss. For anhydrous ammonia applied 6 weeks ago, perhaps at least 50% of the nitrogen has been converted to nitrate. If soils have remained saturated for a week, perhaps 10-20% of the nitrate nitrogen has been lost to denitrification, with additional loss due to runoff or leaching. Whether remaining nitrogen will be adequate to optimize yield potential depends on the initial application rate, and growing conditions during the rest of the season.
Soil sampling is one option to evaluate what is left, but results may be difficult to interpret. If nitrogen fertilizer has been banded, many samples will be required to integrate what the plant will have access to. Samples should be collected to a depth of three feet in one foot increments. Consider having samples analyzed for ammonium as well as nitrate, since substantial nitrogen from many fertilizer sources may remain in the ammonium form. Interpretation of soil test results for both ammonium and nitrate may require help from a soil scientist. Even then accurate prediction of fertilizer nitrogen availability will be difficult.
If producers can sidedress nitrogen or apply it through an irrigation system, they may want to supplement loss they believe may have occurred. The challenge will be to know what rate to apply. Over-fertilization will increase the cost of production and potentially increase the loss of nitrogen to the environment, while under-fertilization will reduce yield.
Carefully monitoring the crop for N status may be the best option, primarily between now and silking, especially if producers have the option to sidedress, fertigate or apply nitrogen with high clearance equipment. Most corn hybrids will take up the majority of their nitrogen requirement in this period. Visual observation for signs of nitrogen deficiency (lower leaves yellowing, inverted "V" yellowing pattern of leaf tips) is one option, although yield potential may be reduced by the time nitrogen deficiency is visually evident. A chlorophyll meter may be useful in detecting nitrogen stress before it can be seen. To calibrate chlorophyll meter readings, it is best to have one or more strips in the field with nitrogen applied at a rate high enough to be non-yield limiting to serve as a reference. For more information on the use of a chlorophyll meter to manage nitrogen, see NebGuide 1171, Using a Chlorophyll Meter to Improve N Management..
Richard B. Ferguson
Extension Soils Specialist
With the heavy rainfall, widespread flooding was reported on the Platte, Wood, and Blue rivers.
At Grand Island, streamflow rates on the Platte River were running approximately 220 cubic feet
per second (cfs) prior to the event, peaking at 8000 cfs two days after the event. On May 17 the
Platte had a streamflow rate of 1000 cfs, which was close to the long-term normal.
You didn’t need to be under the down bursts to feel the effects of flooding. The Blue River at
Dorchester peaked out at 10,000 cfs on May 12. Prior to the event, streamflow rates were
measured at 72 cfs and as of May 17 stood at 1270 cfs. The previous record streamflow rate for
May 12 at Dorchester was slightly above 1100 cfs.
While it’s difficult to gauge the long-term impacts of this widespread event on the drought,
small ponds and shallow aquifers likely saw significant improvements. We’ll probably be able to
determine the degree of improvement to the Platte River in a couple weeks. The degree to which
streamflow rates stay above the 220 cfs rate measured prior to the event will give us details about
the significance of this record-setting event.
One thing is certain: These storms resulted in flooding, the magnitude of which hasn’t been
seen in the central Platte River valley since 1967. Even the 1993 flooding across the central
United States did not cause such an intense flood in central Nebraska.
Al DutcherMay 11 rains set 100-year records
Heavy rain fell in the central Platte River valley May 11, with unofficial reports of more than 11
inches in 6-8 hours. The highest official report was from Wood River with 10.63 inches. This is
well short of the state record rainfall of 13.15 inches in 24 hours set May 8-9, 1950 in York.
According to statistics for May 11, Grand Island recorded a 100-year 24-hour and 12-hour event,
while Hastings recorded a 100-year, 6-hour event. In fact, over five inches of rain fell within a
90-minute period at Hastings, which statistically would exceed a 200-year event.
State Climatologist
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Next, make sure you take into account crop safety and application timing. For example, a certain herbicide may have good activity on many grass and broadleaf weeds but it has a label restriction that does not allow it to be applied to corn over 12 inches tall. All herbicides carry some timing restriction and pushing that limit can easily result in crop injury or reduced weed control, and in the end, it can result in lost income from yield loss.
Often, efficacy is influenced by the rate used. Choose a herbicide that allows 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. Caution should be used when increasing rates of most herbicides as this can also increase the possibility of crop injury.
Finally, follow label recommendations regarding additives. Many labels will suggest adding crop oil, AMS, or other additives to enhance herbicide uptake or movement into the plant. The right additive can change average weed control into 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.
Brady Kappler
Extension Educator, Weed Science
Producers interested in getting the best weed control for the lowest cost can check product
efficacy. We compared efficacy of a variety of glyphosate-based products (generic and brand
names) on weed control over three years at six locations in Nebraska. Weed species composition
in our studies included: velvetleaf, common waterhemp, sunflower, kochia, Russian thistle,
lambsquarters, and a mix of foxtail species. Depending on the year or location, we tested the
following glyphosate-based products at two rates (label rate and half-rate): Roundup Ultra,
Roundup UltraDRY, Roundup UltraMAX, Roundup WeatherMAX, Touchdown w/IQ,
Cornerstone, Clearout 41 Plus, GlyphoMAX, Glyfos Xtra, and Glyphomax Plus.
All herbicides provided excellent weed control (more than 90%) regardless of the rate or brand
name. For example, there was no significant difference in the level of weed control for Roundup
Ultra Dry and the generic product, Clearout 41 Plus. Similarly, the level of weed control was not
significantly different between Roundup WeatherMax and the generic, Clearout 41 Plus or any
other herbicide tested. These findings are similar to those reported by colleagues in other states.
Generic glyphosate-based products can provide a valuable tool for weed control in glyphosate-
tolerant crops, especially to those producers who are interested in lowering crop production
inputs by reducing weed control costs. Perhaps, more importantly, producers should select the
appropriate herbicide rate for the weeds present, environmental factors and herbicide costs, rather
than choosing a glyphosate trade name.
In addition, with the growing popularity of the relatively inexpensive generic glyphosate-
based products, there is an even grater need for their proper use. Their value can be preserved
only by proper management and use. This becomes even more important when other Roundup-
Ready crops become more readily available (e.g. Roundup-Ready corn and Roundup-Ready
alfalfa). It is easy to fall into a trap of overusing glyphosate when one glyphosate-resistant crop is
grown after another.
Proper use of glyphosate-based technology, as a component of an integrated weed management
program, is the key to preserving the long-term benefits of this technology while avoiding many
concerns about its use or misuse. Glyphosate is a valuable herbicide, the kind of product that gets
discovered once in a 100 years, and should be preserved for future generations.
For more details about proper use of herbicide-tolerant crops, especially Roundup-Ready
technology, see the Extension NebGuide, Use of Herbicide Tolerant Crops as a Component of an Integrated Weed Management Program.
Stevan Knezevic
Normally, new shoots don't begin to emerge on intact plants until late May, but last week I
found new shoots starting almost everywhere I looked.
Check your fields to see if many of your alfalfa plants are developing new shoots. If they are,
start harvesting as soon as convenient because alfalfa doesn't develop these shoots until plants are
ready to start their next growth cycle. And since these shoots are the next growth cycle, try
to avoid cutting them off because if you remove them, your alfalfa will have to start developing
new regrowth all over again.
If you don't find many new shoots, wait until alfalfa blooms like normal. Of course, this
spring has been anything but normal. I think the above normal heat units that alfalfa received in
late March and early April is causing this difference. And the many nights of freezing
temperatures also probably helped by influencing the flow of growth hormones from the growing
point near the top of the plants. Those freezes also might prevent your alfalfa from blooming
normally later this spring, so even if you see no shoots now, keep watching. They will show up
eventually, even if your plants don't bloom.
Bruce Anderson
Grazing wheat, even if it has headed out, can provide feed for cattle
and delay the use of other pastures. This will allow them to use limited soil moisture more efficiently
and develop higher carrying capacity. If you do graze your wheat, be sure to feed a magnesium supplement to avoid potential problems with grass tetany.
Wheat hay can be harvested whenever it becomes convenient, but I
recommend cutting before much grain fill occurs or leaves start to turn in
order to maintain good forage quality from the leaves and stem. Before
feeding the wheat hay, make sure you have it tested for nitrates,
especially if plants experience much drought stress before harvest.
Comparing glyphosate products: Research shows few differences
The proliferation of glyphosate-based products into the glyphosate-resistant crop market is
unprecedented. Currently, there are more than 40 glyphosate-based herbicides registered for use
in Nebraska. As distributors try to remain competitive, they’ve dropped product prices for
growers.
Integrated Weed Management Specialist
Alfalfa developing early;
watch for new shoot growth
Most years, first harvest of alfalfa occurs when plants begin to bloom. This spring, though, many
alfalfa fields are using a different signal to tell us they are ready to be cut – they’re sending up
new shoot growth from the base or crown of alfalfa plants.
Extension Forage Specialist
Salvaging poor wheat stands
Long-term damage from early May frosts and storms should be fully apparent now in wheat. In some fields stands are going to be spotty or grain heads empty enough to cause you to consider destroying the wheat and replanting the field to something else. Before you do, consider grazing or cutting the wheat
for hay. After all, destroying the wheat will make it a total loss and
cost valuable soil moisture if you use tillage, and you have no guarantee
of sufficient rainfall to support a different crop.
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Staying aware of where soybean rust is throughout the growing season will be critical to managing the disease. Two University of Nebraska resources will provide real-time information. The Soybean Rust Web site is a focused site with links to pertinent Web sites for managing soybean rust in Nebraska.
Another resource is a toll-free Soybean Rust Hotline with recorded updates specific to Nebraska, including soybean rust locations and conditions and management changes throughout the growing season. The hotline number is (877) NebRust or (877) 632-7878. This hotline is funded by the Nebraska Soybean Board.
UNL Cooperative Extension also has several publications related to identification and control of soybean rust. To order copies, contact your local Cooperative Extension Office or the IANR Publications Distribution Center, Box 830918, University of Nebraska, Lincoln, NE 68583-0918, as indicated below. Publications include:
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