|
Wheat Production
Management
Weed Control
Insect Control
Alfalfa
Ag Programs/Resources/Updates
Disease Management
|
Winter wheat seasonal water use varies widely due to weather conditions, but generally it needs 16 to 24 inches. Using a midpoint of 20 inches, water use would be 4 inches from emergence to start of spring growth, 4 inches from start of spring growth to jointing, 2 inches from jointing to boot, 2.4 inches from boot to flower, 3 inches from flower to milk, 1.6 inches from milk to dough, and 3 inches from dough to maturity. Normally it takes about 4-7 inches of water to get yield. For each inch of water above that, yield increases an average of 4-6.5 bushels per acre.
The fall and winter dry conditions may contribute to crown and root disease since dry soil warms up and cools down six times faster than moist soil. This alternating freezing and thawing will diminish the health of the wheat plant, damaging stands and decreasing yields.
Estimating wheat yields early
Wheat growers frequently need to estimate wheat yields in the spring to decide whether recropping is necessary. Determining a reasonable estimate of wheat yield allows growers to predict if it is in their best interest to destroy the wheat and plant a summer crop or leave the wheat for harvest. With little soil moisture in many areas of the state, the chance of a spring crop being successful is limited. Before making such a decision, growers should be aware of any restrictions imposed by government programs, crop insurance, or previous herbicide use.
Several methods can be used to estimate winter wheat yield potential. I will discuss two, both of which rely on several assumptions that may not be accurate for every season or situation. These assumptions presume that plants are healthy, soil moisture and nutrients are adequate, and that weeds, insects and disease are not affecting yield. Added to the uncertainty of yield estimates is wheat’s ability to compensate for changes in the environment.
Table 1 is easy to use; however, it relies on several assumptions required to make a yield estimate in the fall or early spring prior to extensive tillering or stem elongation. These assumptions include:
To use Table 1, count the number of plants per foot of row. It is best to use at least five feet of row in at least five sites within the field and calculate the average number of plants per foot of row. If the stands are uneven, for example the stand is better or worse in the wheel tracks, make sure your percentage of samples is these areas accurately represents the proportion of these areas in the whole field. Locate the column in the table that corresponds to your average number of plants per foot of row and then move down that column until it intersects with the row corresponding to your row spacing. This is your estimated yield.
Method 2
Table 2 was developed using data collected from 1994 to 1998 with the Nebraska Wheat Quality Tour. These tours were conducted near May 1, prior to head emergence in most of the state. Factors such as heavy weed, disease, or insect infestations or inadequate soil moisture at the time of the tour may suggest fewer final heads and a lower yield potential than indicated in the table. In addition, the table becomes unreliable in situations of extremely low or extremely high tiller counts, or in years when crop development as of May 1 is well ahead of or behind normal. For later season yield estimates, yield predictions can be made by substituting the actual number of heads per foot for tillers per foot.
To use Table 2, count the number of tillers per foot of row. Again, it is best to use at least five feet of row in at least five sites within the field and calculate the average number of plants per foot of row. Be sure sample sites are representative of the field. Locate the column in the table that corresponds to your average number of tillers per foot of row and then move down that column until it intersects with the row corresponding to your row spacing. This is the estimated yield. Although these multipliers may appear to be in error --- everyone knows that wheat fields in the semi-arid Panhandle usually yield less than fields to the east -- on a per head basis the multiplier is correct. Wheat fields in the sub-humid portions of the state produce more heads per acre, but typically fewer kernels per head than in the Panhandle.
For example, if your winter wheat field is in southwest Nebraska and you have an average of 30 tillers per foot of row, and your row spacing is 10 inches, multiply the table results of 40 bushels per acre by 0.9 to get a yield estimate of 36 bushels per acre.
For more information, see Estimating Winter Wheat Grain Yields (NebGuide 1429).
Bob Klein
Extension Cropping Systems Specialist
West Central REC
Army cutworm potential high in western Nebraska wheat and alfalfa
|
Army cutworm moths are active in September and October when they lay their eggs in the soil. Shortly after being laid, the eggs will hatch. As fall and winter conditions permit, these partially grown cutworms will feed on surrounding vegetation. Due to their need for winter vegetation, these cutworms are only likely to overwinter where winter wheat, alfalfa, grasses or weeds are present.
Army cutworms are most often a threat to wheat and alfalfa in early spring, just as these crops break dormancy. Alfalfa and wheat fields should be monitored immediately, before cutworms are able to delay spring regrowth. The cutworms feed at night but may be found on plants on some cloudy days. During the day, they will be found buried in the loose soil and debris or under soil clods.
Treatment decisions should be based on the number of cutworms present, the amount of damage, and the plant’s ability to outgrow this damage. In poorly growing wheat or alfalfa two or more army cutworms per square foot may warrant treatment; however, in healthy wheat or alfalfa the threshold is four or more per square foot. When determining whether treatment is necessary, it’s important to consider the plant’s ability to outgrow the defoliation damage as well as the number of cutworms present.
Various pyrethroid insecticides will provide emergency control of cutworms.
Further information on the army cutworm is available in the NebGuide, Management of the Army Cutworm and Pale Western Cutworm (G1145), available from Extension offices and on the Web. The University of Nebraska Department of Entomology Web site also has information in its Field Crops section.
Gary Hein
Extension Entomology Specialist
Panhandle REC
Be alert to early season wheat disease problems
|
Dry conditions in fall often predispose winter wheat plants to crown and root rot. This disease complex weakens plants during winter which leads to a stand decline in spring as the wheat emerges from dormancy. Infected plants may die during winter or they may initiate growth in March and then decline and die two or three weeks later. Early symptoms of crown and root rot appear as a dark brown discoloration of roots and the sub coronal internodes between the seed and the crown. Infected crowns rot to a greater or lesser degree, depending on the stage and severity of disease development. Plants will not recover from severe crown damage even with optimal growing conditions in April. Those with moderate crown and root infection tiller sparsely and yield less than healthy plants.
Individual fields affected by crown and root rot contain scattered pockets of yellow dying and dead plants. Terrace ridges and exposed slopes often show the greatest degree of loss. To diagnose crown and root rot, dig suspected plants, wash the roots and look for any dark discoloration on the roots and subcoronal internodes. Split the crown with a sharp knife and examine for discoloration. Infected crowns appear tan or brown where healthy ones are white. Often the extent of rot in the crown determines the overall health of the plant.
Other than assessing the stand to determine if it should be left or destroyed, nothing can be done to cure the problem. When assessing the stand don’t be too hasty to write it off. Give the wheat a chance to recover from winter before making that decision.
John Watkins
Extension Plant Pathologist
|
A center pivot must be capable of delivering the amount of water needed by the crop during the peak crop water use period. Table 2 illustrates the amount of water that can be applied with different system capacities and with one crop or with multiple crops whose critical water needs are at different times. For example, if a 130-acre field was planted half to wheat and half to corn, an 800-gpm system would be able to apply 0.64 inches a day to the half of the field requiring water most at that time.
To operate efficiently many irrigation districts plan to deliver a minimum of one inch of water per week. For example, if 6 inches of irrigation water is available for the summer, the maximum length of the irrigation season would be six weeks – less if water demands are greater than one inch per week. The Bureau of Reclamation has estimated that the amounts of water listed in Table 3 will be available for 2004. The district uses these estimates to determine how much to supply to water users. In districts where water is expected to be restricted, reduce the estimates if the district does not plan to deliver one inch of water every six to seven days.
In the North Platte Valley, the water availability for this year appears to be very similar to last year – less water than normal and irrigation water supplies that will likely run out early. To show what we might expect, ownership of water for the North Platte project as of February 1, was at 217,000 acre feet. This compares to 133,000 acre feet in 2003 and 315,000 acre feet in 2002. By February 1 of the past three years, water in ownership to the North Platte project water users have all been well below the average of 615,000 acre feet.
Based on current forecasts from the Bureau of Reclamation, it is estimated that only about 78% of the average irrigation demand will be met. The most critical months are still ahead and normal precipitation will be needed not only in the mountains but also in the form of spring rains to avoid yet another water short year. Irrigators with low capacity groundwater wells also will need to prepare for dry soil conditions by maintaining and preparing their systems for a potential early start. If the soil moisture is not near field capacity at planting, regardless of the crop, irrigation will need to begin earlier than usual to keep from getting too far behind. As soon as weather permits, system maintenance and repair should be initiated to avoid any unnecessary delays.
Bob Klein
Extension Cropping Systems Specialist
West Central REC
Dean Yonts
Extension Irrigation Specialist
Panhandle REC
Bill Kranz
Extension Irrigation Specialist
Northeast REC
When a dry season is expected:
Select crops suited to available water
|
The subsoil moisture is below normal (see the March 5 CropWatch), the winter precipitation has been sparse in many areas, and the long range forecasts do not indicate enough excess moisture to help many areas catch up to average levels. This is due to both drought and over-development of ground water resources in some areas.
In those areas where water is likely to be restricted, the timing of water deliveries may not correlate with crop water needs, making it important to select a crop whose water needs match when water is likely to be available (Figure 1). Soybean, for example, uses most of its water during pod fill. If water is not available then, yields will be greatly affected.
What crops are a producer’s best options, given the prospects for limited water supplies?
When we look across the state of Nebraska, varieties and hybrids have rather limited areas of adaptation. Both corn and soybean need to stay fairly close to their adapted areas. When comparing yields of potential varieties and hybrids, look within your geographic area and consider the experiences you’ve had on your farm.
Don’t throw out all your current varieties and replace them with ones you’ve never tried. It is safest to replace 25% or less of your acres with a new, untried variety or hybrid.
Crop traits
Corn. When water is limited, avoid full season corn hybrids and adjust fertility rates for a lower yield goal. A corn hybrid with a four- to five-day shorter maturity will reduce crop water use by one inch. Reducing plant population for corn can reduce water use, but populations must be planted below approximately 16,000 plants per acre before substantial water savings can be expected. With lower plant populations, weed control becomes even more important later into the season. Also, studies have shown that early water stress in corn has much less of an impact on yield than water stress during tasseling. If water supplies are limited, concentrate irrigation at tassel time (see Figure 2).
Soybean. For soybean if the soil profile is near field capacity at planting, the late flower through pod elongation periods are critical water use periods. If there is a chance water may not be available at pod fill, consider planting the soybean earlier (although frost and some insects may increase risks). Planting early may not gain you a lot of maturity, but it can help. Planting earlier may allow the plant to benefit from more rainfall events than if the crop were planted later (see Figure 3).
Sorghum. Grain sorghum irrigation is particularly applicable when limited irrigation is a management objective. Grain sorghum usually outyields corn up to the 120-140 bushel yield level where adapted. The biggest advantage with grain sorghum is seen in Figure 4 in the drought sensitivity for sorghum. While not having a critical need for water during any growth stage, if water is limited or not available, grain sorghum will go dormant and resume growth when water is available.
Dry bean. In western Nebraska dry bean is a good choice where water supplies are limited. Because dry bean is not a program crop and is considered a fruit or vegetable crop, be sure an acreage increase does not jeopardize your other bases. Early or late water stress on dry bean has been shown to depress yields somewhat; however, maintaining soil water during flowering can still produce respectable yields. Although dry bean only uses about 16 inches of water, most of it is used during July and early August. If water availability is limited to early spring, production can be reduced.
Small grains and forages. Most of Nebraska has the greatest potential for precipitation in early spring. Even though conditions are dry, excess rain during the spring can result in water loss to deep percolation or runoff. Planting small grains and forages or having winter wheat planted may allow irrigators to take better advantage of the spring rains. These crops are actively growing in the early spring and can use water that may not be useable by more traditional row crops. In some parts of the state, animal forages may be a good option for producers who also raise cattle since the cost of forage will likely increase if dry conditions persist.
Summary
Soil water conditions may change, but it appears likely that areas in Nebraska will face shortages of irrigation water. Always check with the appropriate agency before selecting crop, planting dates, and other production practices which may affect eligibility for programs.
Bob Klein
Extension Cropping Systems Specialist
West Central REC
Samples should be taken to a depth of three feet to determine residual nitrate levels. Samples may be taken less than three feet deep, but they will be slightly less accurate. (See Guidelines for Soil Sampling (G91-1000) for comprehensive overview of soil sampling recommendations). If a soil analysis is not available, assume an existing level of 9 ppm of nitrate-N per acre, which represents an average or medium soil nitrate level.
Topdressing nitrogen on wheat in spring can help avoid the potential yield depression associated with fall nitrogen applications. It also allows for the evaluation of yield potential based on stands and soil moisture. Topdressing in the spring provides a significant advantage to wheat producers because it can help them avoid investing in a crop with a low yield potential. Topdressing should be completed before April 15 or prior to jointing. Generally, wheat grain yields decrease and grain protein increases with later applications.
The optimum nitrogen rate (lbs N/acre) for winter wheat (with a maximum rate of 100 lbs N/acre for dryland, and 150 lbs N/acre for irrigated) is calculated using Equation 1.
Calculating the nitrogen rate and fertilizing winter wheat
Most winter wheat grown in Nebraska requires some additional nitrogen fertilizer for profitable production. This is true for virtually all soils in Nebraska where wheat is commonly grown unless there is a large carry-over of fertilizer nitrogen. Residual fertilizer nitrogen can be measured effectively with a residual soil nitrate test of the root zone. While the depth of the root zone is often six feet or more for wheat, most available nitrogen affecting yield is in the top two to three feet of soil.
|
Table 1 shows the nitrogen recommendations (lbs N/acre) for wheat for various nitrogen and wheat prices at several soil nitrate concentrations.
All fertilizer nitrogen sources (ammonium nitrate (33-0-0); urea (45-0-0); urea-ammonium-nitrate UAN (28-0-0); and anhydrous ammonia (82-0-0)) are generally effective for spring nitrogen fertilization. Ammonium nitrate is preferred for topdressing when incorporation is impossible because it is the least susceptible to loss from volatilization. If the nitrogen fertilizer is incorporated soon after application, all nitrogen sources should be equally effective. Base your fertilizer selection on the most economical source of nitrogen that fits the restrictions of the particular wheat production system you use.
For more information on fertilization of winter wheat and other crops visit the UNL Soil Fertility and Nutrient Management Web site.
David Tarkalson
Soil Fertility and Nutrient Management Specialist
West Central REC
|
We classify stored soil water as being 100% effective as a source of water for plants. In the spring when the soil is moist and air temperatures are low to moderate, it is impossible to kill weeds with tillage unless the weeds are buried, which also destroys the crop residue. About 89% of the water in snow that is captured is stored in the soil. A Colorado study even found that 70% of their snow came when the ground was not frozen and could be better captured.
Most herbicide applications during fallow will eliminate two tillage operations. The most economical herbicide treatment is to use glyphosate with or without 2,4-D, depending on the weed species present. Always put spray grade ammonium sulfate at 17 lbs per 100 gallons of spray solution in the tank before adding glyphosate. Surfactant may need to be added if the glyphosate does not contain a surfactant or enough surfactant. The surfactant is the last item added to the tank.
Spring is the most effective time to use herbicides instead of tillage to control weeds. When spring tillage buries the weeds, it also buries any crop residue. Some research has found that as rainfall events become less frequent in mid to late summer, soil water storage during summer fallow may be improved with a single shallow tillage operation compared to using no till exclusively.
| ||||||||||||||||||||||||
If there is little or no crop residue, such as when the previous crop was removed for hay or silage, it won’t work well to use herbicide for weed control for the entire fallow period. The photo shows the damage that can result from removing all residue. If you need to remove a crop for hay or silage, leave 6-8 rows of residue 12-20 rows apart, depending on the height of the crop, to protect the soil and crop residue from wind erosion and to trap snow.
Bob Klein
Extension Cropping Systems Specialist
West Central REC
Drew Lyon
Extension Dryland Crops Specialist
Panhandle REC
CropWatch author Bob Klein recognized
| ||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||
In Nebraska many producers have found that no-till fields are an excellent means of conserving moisture in dryland situations; however, if winter annuals are present, they will use valuable moisture that could be available to the crop.
Many people wonder why these winter annual weeds seem to have become more of a problem in recent years. One theory is that as more growers plant Roundup Ready soybeans, there is less herbicide residual to control these weeds. When conventional soybeans were planted, the herbicide program provided residual to keep many winter annuals from germinating or growing in the fall.
How can spring applications be made most effective? Timing of the herbicide application is the biggest issue. Most herbicides work best before weeds have bolted. This is why fall control is generally preferred when possible –- it’s fairly simple and typically very successful.
If spring control measures are necessary, the first step is to monitor fields early and begin spraying as soon as temperatures warm up enough for plant growth. The next step is to use the right product. Several products will control henbit and provide similar or better control of marestail, pennycress, and other winter annuals (see table).
Brady Kappler
Weed Science Educator
Apply before alfalfa green up
Glyphosate and Gramoxone Max will control emerged winter annual broadleaf and grass weeds but will have no effect on weeds germinating after application. There are no use restrictions regarding age of the alfalfa stand. Karmex can be used in alfalfa established one year or longer to control winter annual broadleaf weeds and suppress summer annual broadleaves. There is a 24-month restriction on planting crops following a Karmex application. Sencor, Sinbar, and Velpar can be used on alfalfa established one year or longer to control winter annual broadleaf weeds and downy brome. Sinbar also will suppress dandelion. Sinbar and Velpar have a 24-month planting restriction for several crops.
Apply before or after green up
Pursuit, Raptor, and Select can be used on both dormant and actively growing alfalfa. These three herbicides can be used on new alfalfa seedlings or established stands; however, Pursuit and Raptor have planting restrictions of one year or longer for certain crops. Pursuit and Raptor will both control winter annual broadleaf weeds, with Pursuit providing control of many later germinating summer annual broadleaf weeds. Raptor will also control downy brome. Select will control downy brome but will not affect broadleaf species.
Alex Martin
Varieties now have a high enough level of resistance to leafhoppers
to make a big yield difference when leafhoppers are active, and they don't
have lower yields when leafhoppers are inactive.
Seed prices still are higher for these varieties, so they should only
be used if leafhoppers are frequently a problem. Also, seedling alfalfa
plants of resistant varieties still are susceptible to leafhopper damage so
clipping injured plants and/or use of insecticides should be considered.
The most damage from potato leafhoppers usually is observed east of the
Iowa/Nebraska border. West of Highway 281 potato leafhopper damage is
infrequent so resistant varieties may not be useful. In those in-between
areas, it seems leafhoppers are becoming more common. These newer varieties
with higher leafhopper resistance should be valuable to alfalfa growers in
this region that have alfalfa as a major source of income.
Bruce Anderson
For an added twist to this crop rotation idea, consider interseeding
grasses and other legumes into your thinning alfalfa to create a high
producing pasture. Not only might you extend the useful life of your
alfalfa field by many years, you also will develop excellent grazing for
your livestock.
The most common grasses interseeded into alfalfa are orchardgrass and
smooth brome, but other grasses like tall fescue, wheatgrass, creeping
foxtail, meadow brome, and reed canarygrass also can be used. In addition,
seed other legumes like red clover for short-term pasture or birdsfoot
trefoil if you plan to graze this pasture more than three years to add
diversity to your animals' diet and help assure good legume growth for
several more years.
It is important to get these new seedlings off to an early start, so
be sure to interseed as soon as conditions allow tractor and drills to
operate properly. If your alfalfa is thick enough to form a canopy that
shades new seedlings, take a very early hay cutting, maybe during the first
week of May. This will allow sunlight to continue to reach new seedlings
below the alfalfa. Then use your good judgement on subsequent hay cuts or
starting to rotationally graze.
Both land and livestock will improve with your efforts.
Bruce AndersonEarly spring weed control best in dormant alfalfa
Pennycress, tansy mustard, downy brome and other winter annuals are common problems in established alfalfa, but often can be controlled with herbicide applications in early spring before alfalfa “green-up.” Weeds are small in spring and several herbicides will work well; however, once alfalfa breaks dormancy, herbicide options become more limited. Some herbicides require that alfalfa be established at least one year before treatment. Several of these herbicides restrict planting another crop for two years following application so planning is important. Check pro-duct labels for planting restrictions.
Extension Weeds Specialist
New alfalfa varieties resistant to potato leafhoppers
New varieties of alfalfa that resist injury from potato leafhoppers
have improved and are worth checking out. Last summer, many alfalfa fields turned yellow and
stopped growing because of potato leafhoppers. Past alfalfa varieties with potato
leafhopper resistance, offered a resistance level too low to be worthwhile.
Also, these varieties yielded less when leafhoppers were not a problem, and
seed cost was much higher.
Extension Forage Specialist
Converting thin alfalfa into high producing pasture
Most alfalfa fields start to lose stand and production ability after
cutting hay for three or four years. When this starts to happen, I usually
suggest rotating to another crop and planting a new hay field.
Extension Forage Specialist
 |
About Crop Watch |
Agricultural News |
Events |
Archives |
Markets Ag Links | Weather | Photos | Search Lisa Jasa, Crop Watch Editor | Publications | IANR |
 | ||
| Published by University of Nebraska Cooperative Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture | ||
| The University of Nebraska-Lincoln does not discriminate on the basis of gender, age, disability, race, color, religion, marital status, veteran's status, national or ethnic origin, or sexual orientation. | ||
