Number 145
June 20, 2008
1. Hail damage on soybeans
2. Delayed soybean planting: Effect on variety selection, seeding rate, and row spacing
3. Comparison of summer annual forage options
4. Wheat streak mosaic potential on fields of hailed-out wheat
1. Hail damage on soybeans
2. Replanting soybeans late: Variety selection, seeding rate, and row spacing
3. Comparison of summer annual forage options
4. Wheat streak mosaic potential on fields of hail damaged wheat
1. Hail damage on soybeans
Hailstorms have been widespread throughout most of Kansas this spring. Soybeans that had emerged at the time of a hailstorm will have been damaged. This brings up the question of whether the soybeans can recover, how much potential yield loss may have occurred, and whether it would be worth replanting some fields. The first two articles in this Agronomy e-Update will address these issues.
Assessing the effect of hail on soybean is not a simple matter. The method of assessment depends on the stage of growth at the time of the hail and must incorporate estimates of node damage, leaf loss, and stand loss.
The figures below were generated from data used by the crop insurance industry to estimate potential yield loss from percent stand reduction at different original populations, percent of nodes cut off or broken, and percent leaf loss (Soybean Loss Adjustment Standards Handbook, USDA-FCIC-25440, 06-1999).
* Vegetative growth (VE, VC, V1 to VN)
Damage to nodes and leaves: Soybeans can tolerate quite a bit of hail damage to nodes at early stages of growth. If the plants have a leaf or two remaining, or even just the cotyledon leaves, after a hailstorm, they can branch extensively from axillary buds and compensate quite well. In the vegetative stages, more than 50% of the nodes must be cut off or broken before resulting in a yield reduction of more than 10%. Put another way, even if up to half the nodes are cut off or broken,yield loss will be only 10% or less -- if the soybean has not flowered.
Pre-flower stand loss: If the hail was severe enough to break the stem below the cotyledons, the plant will die. In that case, producers need to evaluate the extent of stand loss to estimate the potential effect on yield. The yield loss will normally be less than 10% as long as the remaining population is more than 60-90,000 plants per acre, depending on the yield environment. In environments with medium to low yield potential, 50,000 to 60,000 plants per acre often will maximize yield. In higher-yielding environments, 80,000 to 100,000 plants per acre can maximize yield. We'd like to have more plants than that, but often don't see much of a yield response to the higher populations, especially in stressful years. In general, a 50% stand reduction can be expected to result in a 20 to 25% yield loss.
As long as hail damage causes only 25 to 30% stand loss or less, it’s probably best to leave the stand alone and not replant. More yield will likely be lost by replanting than by leaving it alone.
* Flowering and pod set (R1 to R6)
Damage to nodes and leaves: Indeterminate varieties will grow and flower over a 3 to 4 week period. As a result, a hailstorm that causes significant loss of leaves, flowers, and early pods during the first 2 weeks or so of this period of flowering will not necessarily cause much yield loss. Unless the weather is very hot after the hailstorm, more flowers will form and set pods. If the hail occurs toward the end of that 4-week window, however, or if there is heat stress after the hailstorm, a significant loss of flowers and pods from hail damage can dramatically reduce yields. For indeterminate varieties at any level of leaf loss, yield losses are maximized when damage occurs at R5, and are less at earlier and later stages.
Loss of leaf area causes greater yield losses over more stages of development for determinate varieties than for indeterminate varieties. The flowering period is more compressed for determinate varieties, so they have less opportunity to compensate for loss of leaves, flowers, and pods. Yield losses of up to 10% can result from significant leaf loss in the later vegetative stages. Determinate varieties have 3% to 17% greater yield losses than indeterminate varieties from damage that occurs in the early reproductive stages (R2 to R3), depending on the extent of leaf loss. Yield losses are greatest from damage at R4 to R5.5.
Stand loss: If hail breaks the stems of plants and causes plant death in the R1 to R6 reproductive stages of growth, the remaining plants will normally have only limited ability to branch out and compensate.
* Pod fill through maturity (R6.5 and later)
Plants cannot compensate through either additional flowering or new branch development after R6.5. Therefore, the way to estimate yields at these stages is to make a direct seed count. Hail damage to leaves at these stages will have little or no effect on seed development or yields.
-- Kraig Roozeboom, Crop Production and Cropping Systems Specialist
2. Replanting soybeans late: Variety selection, seeding rate, and row spacing
Where soybean stands have been devastated by hailstorms, drowning, or some other factor, producers may be thinking about replanting. With later-than-optimal planting dates, should producers make any changes in management strategies? Should a shorter-season variety be substituted as we move into late-June planting dates?
The following is adapted from the variety selection section of the Soybean Production Handbook, C-449:
As planting is delayed, the situation begins to resemble double-crop soybean production. The soybean crop following wheat is usually planted 2 to 6 weeks later than the optimum date for highest yields. Since planting is delayed, often until the end of June or early July, one is temptedto switch to a shorter-season variety to ensure the crop will mature before frost.
While planting a variety that is too late in maturity will increase the likelihood of frost damage, switching to a substantially earlier maturing variety should be resisted. This is for two reasons.
* First, early-maturing varieties planted late in the season will usually have limited vegetative development, short stature, and low yield potential.
* Second, any given variety will have fewer days to flowering, pod development, and maturity when planted late compared to earlier planting dates.
As planting dates get later into June, the day length has begun or will soon begin to shorten and nights will start getting longer. This causes plant development to speed up. Consequently, there is not a one-for-one relationship between the number of days difference in planting dates and the number of days delay in maturity. As a general rule, for every three days delay in planting, maturity is delayed by only one day.
Since soybean development is hastened in later plantings, the highest yields in a late-planted or double-cropped system are often achieved by using the same variety or one only slightly shorter in maturity as what is used in full-season production.
Other management practices can be affected by late planting, however. Because late planting shortens the period for vegetative growth and reduces canopy development, increasing the seeding rate alone or in combination with narrow row spacing can help the crop compensate by providing the opportunity to produce more pods in the canopy.
Seeding rates can be increased by 30% to 50% in high-rainfall environments if planting is delayed until late June or July. Although past research has demonstrated no consistent benefit for narrow row spacing (less than 30 inches) in Kansas, narrow rows may have an advantage in late plantings in the eastern half of the state.
-- Kraig Roozeboom, Crop Production and Cropping Systems Specialist
-- Bill Schapaugh, Soybean Breeder
3. Comparison of summer annual forage options
Producers often overlook summer annual forages as a potential crop, either for full-season production or as a doublecrop. These crops have good potential in either situation. The various types of summer annual forages each have their own strengths, weaknesses, and production requirements. The following chart lists some of the main factors to consider.
Summer Annual Forages: Production Characteristics
Forage Sorghum / Sudangrass / Sorghum-sudangrass hybrids / Hybrid Pearl Millet / Foxtail Millet / Finger MilletStrengths
Yield,
better quality with brown midrib (BMR) hybrids, better yield with photo-period sensitive (PS) hybrids / Rapid regrowth (leave 6-8 inches of stubble), small stems, extensive tillering / Yield, regrowth, better quality with brown midrib (BMR) hybrids / Rapid regrowth, quality, greenbug resistant, extremely low potential for prussic acid toxicity, drought resistant, high leaf:stem ratio / Short growing season/late planting, no prussic acid toxicity, drought resistant, can plant in August for emergency forage / Forage quality, numerous tillers, lower water requirement
Forage Sorghum / Sudangrass / Sorghum-sudangrass hybrids / Hybrid Pearl Millet / Foxtail Millet / Finger Millet
Weaknesses
Limited regrowth, no grain yield with PS hybrids, BMR trait may result in more lodging with delayed harvest, potential for nitrate and prussic acid toxicity, susceptible to chinch bugs / Yield, potential for nitrate and prussic acid toxicity / Potential for nitrate and prussic acid toxicity, susceptibility to chinch bugs / Sensitive to overgrazing (maintain 8-inch stubble), potential for nitrate toxicity, susceptibility to chinch bugs / Quality, palatability, yield, shallow rooted, uproots easily when grazed, awns can injure livestock (sore mouth) / Small seed, yield, sensitive to wet soils, requires more growing season and rainfall than foxtail millet, susceptible to Helminthosporium diseases (leaf spots, seedling blight, head blight)
Forage Sorghum / Sudangrass / Sorghum-sudangrass hybrids / Hybrid Pearl Millet / Foxtail Millet / Finger Millet
Uses
Silage – harvest at mid to late dough / Grazing, hay – harvest before heading to maximize quality / Grazing, hay – harvest before heading to maximize quality / Grazing, hay – harvest before heading to maximize quality, cut whenever growth reaches 40 to 50 in. / Grazing, hay –harvest before heading to maximize quality and to avoid livestock injury from awns / Grazing, hay –harvest before heading to maximize quality
Forage Sorghum / Sudangrass / Sorghum-sudangrass hybrids / Hybrid Pearl Millet / Foxtail Millet / Finger Millet
Planting date
Northwest:
May 15 – June 10
Southeast:
May 1-15; June 5-25
Rest of state:
May 15 – June 20 / Northwest:
May 15 – July 1
Rest of state:
May 20 – July 10 / Northwest:
May 15 – July 1
Rest of state:
May 20 – July 10 / June 1 – July 1
(does not tolerate cold, wet soils) / June 1 – July 1
(does not tolerate cold, wet soils) / June 1 – July 1
(does not tolerate cold, wet soils)
Seed Depth (depending on soil type and moisture conditions)
1 to 1½ inches / 1 to 1½ inches / 1 to 1½ inches / ¾ to 1 inch / ¾ to 1 inch / ½ to 1 inch
Seeding Rates (assumes 65% to 70% emergence)
Narrow rows:
10-20 pounds/acre
Wide rows:
4-6 pounds/acre or similar to grain sorghum if seeds/acre / Narrow rows (pounds/acre):
West: 10-15
Central: 12-20
East: 20-30
Irrigated: 30 / Narrow rows (pounds/acre):
West: 10-15
Central: 12-20
East: 20-30
Irrigated: 30 / Narrow rows:
West: 5-15
Central: 10-20
East: 10-20
Irrigated: 10-20
Wide rows:
10 pounds/acre / Narrow rows:
15-30 pounds/acre
(lower rates in dry environments, higher rates with more rainfall or irrigation) / Narrow rows:
10-15 pounds/acre
(lower rates in dry environments, higher rates with more rainfall or irrigation)
Fertility:
• Nutrient requirements are similar to grain sorghum. Fertilize according to soil test recommendations.
• Nitrogen application rates are calculated usinga base rate of 30 to 40 lbs/acre N (Central and West), or 40 to 50 lbs/acre N (East) for each expected ton of dry matter production, minus adjustments for previous crop, manure and profile N soil test.
• To minimize nitrate accumulation potential, base nitrogen (N) application rates on a profile N soil test if following a legume, a poor-yielding crop, or where manure has been applied. Maximum N rates should not exceed 120 lbs/acre.
• Split N applications provide better nutrient distribution and reduce potential for nitrate or prussic acid toxicity. Apply half before planting and half after first cutting, or four weeks after start of grazing.
• Apply phosphorus either preplant or banded at seeding because it does not move appreciably in the soil.
• Apply lime if the soil pH is 6.0 or less in the eastern third of the state, or less than 5.5 in other areas.
Weed control:
• Rapidly growing summer annual forages are competitive with weeds that emerge after seeding.
• Can use cultivation to control weeds if row spacing is adequate.
• Few herbicides are labeled for weed control in most summer annual forages.
• Atrazine may be either soil-applied or applied postemerge on forage sorghum hybrids.
• Concep-treated seed must be planted when chloracetamide herbicides (e.g. Dual II Magnum) are used. Be sure to read and follow the label.
• Other herbicides are brand specific and should not be applied unless specifically approved on the label.
Insect pests:
• Greenbugs can damage sorghums and sudangrasses, but hybrid pearl millet is highly resistant.
• Chinch bugs are often a problem in central and eastern Kansas, particularly during dry seasons or if the summer annual is planted into wheat stubble. Heavy infestations or destructive insects may necessitate spraying with an approved insecticide. Follow label directions carefully when applying insecticides.
-- Kraig Roozeboom, Crop Production and Cropping Systems Specialist
-- Dave Mengel, Soil Fertility Specialist
-- Curtis Thompson, Weed Management Specialist
4. Wheat streak mosaic potential on fields of hail damageded-out wheat
Many acres of wheat have been hail damaged by hail in Kansas this year. Producers should be aware that hail damageded-out wheat can easily lead to problems this fall with volunteer wheat and wheat streak mosaic.
Where wheat has suffered hail damage, many of the kernels will shatter and eventually emerge as volunteer wheat. Shattering may continue to occur right up through harvest. Depending on the stage of maturity at the time of the hail damage, the shattered kernels may begin emerging any time from just prior to wheat harvest to as much as a month or longer after harvest. Wheat seed has a post-harvest dormancy requirement, which is slightly different for each variety. If the wheat was near maturity at the time of the hail, the kernels may germinate within 2 to 6 weeks of shattering. If the wheat was in the soft dough stage or earlier, it may take even longer for the shattered kernels to germinate.
In either case, the shattered kernels will create an early source of volunteer wheat, and a perfect “green bridge” for wheat curl mites. These insects need green plant tissue to thrive. They begin to migrate off wheat as it dries down, at or near harvest time. If they can’t find new green plants to live on, the curl mites will eventually die out. Volunteer wheat also leads to Hessian fly problems.
If there are young stands of volunteer wheat present shortly after harvest time, which is possible on hail damageded-out fields, the curl mites will move onto these plants, live through the summer, and then move onto fields of planted wheat this fall.
It is important that volunteer wheat be controlled completely. This is especially true on fields where volunteer wheat emerges early and is present at or shortly after harvest time. That is the most potentially threatening scenario for wheat streak mosaic infections to occur on planted wheat in the fall. Producers should closely monitor hailed-out damaged fields during the summer, and make sure all volunteer wheat is completely dead at least two weeks before planting wheat this fall.
-- Jim Shroyer, ExtensionAgronomyState Leader
-- Erick DeWolf, Extension Plant Pathologist
These e-Updates are a regular weekly item from K-State Extension Agronomy and Steve Watson, Agronomy e-Update Editor. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Steve Watson, 785-532-7105 , or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader 785-532-0397
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