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If the soil is dry and it is necessary to plant deeper, the soil temperature at the deeper depth may not be 60-65° F, the minimum preferred soil temperature for grain sorghum. When the calendar suggests it is time to seed grain sorghum if soil moisture permits, it usually is best to plant. Many old timers have suggested that seed does not grow in the bag. Emergence will also take longer and seed and seedling losses are greater. The longer a seedling takes to emerge, the greater the possibility of stand loss to crusting, disease, insects, and rodents. With heavy residue cover, it will help to leave a narrow band exposed over the row to let the sun hit and warm the soil surface.
Seeding too shallow or too deep also increases the possibility of injury from preemergence herbicides. With little soil cover and a small amount of precipitation, the herbicide may be moved into the seed area. Creating a depression when seeding or using furrow openers can be a problem if rainfall concentrates the herbicides in the seed area. Deep planting weakens the seedling and provides more time to imbibe the herbicide.
Bob Klein
Extension Cropping Systems Specialist, West Central REC
Earlier this month a cold front spewing rain, sleet, and ice moved through western Nebraska, just as fields of winter wheat appeared to be in good condition and entering the jointing stage. With temperatures ranging from 19° F to the low 20s for more than 24 hours, serious damage might have resulted. While there may be damage in some areas, generally the wheat looks great, reported Drew Lyon, Extension Dryland Cropping Systems specialist at the West Central REC in North Platte.
"It's amazing. Much to my surprise I haven't seen any damage from that coldsnap."
Often it may take several days for damage to become apparent, however any significant damage would likely be visible by now, given the recent warmer temperatures.
"Wheat, for the most part, is looking pretty good. Wheat that was planted late or wheat planted back into summer crop stubble is not looking as good though due to a lack of available moisture," Lyon said.
While researchers are not sure why there wasn't significant frost damage, a fortunate combination of factors may have worked to the advantage of local wheat producers.
Not surprisingly, the recorded temperatures for April 15 at six Panhandle sites at 5 feet above the ground and four inches below the soil surface differed greatly. While the difference may not be unusual, the amount of difference provides insight into the plant's microclimate. (See table.)
The degree of injury to wheat from spring freezes is influenced by the:
Not surprisingly, prolonged exposure to freezing causes much more injury than brief exposure to the same temperature. Generally it had been thought that temperatures below 20-25° F for a minimum of two hours would cause freeze injury at this growth stage. As the table indicates air temperatures were easily in the low 20s for 24 hours; however soil temperatures were significantly warmer having not yet cooled from the preceding balmy weather. Soil temperatures at 4 inches below the surface ranged from the upper 30s to sometimes, even the upper 40s. The growing point, often still wrapped in leaves and only an inch or less above the soil surface, would have been somewhat protected and in a microclimate somewhere between the two temperature extremes. In addition the rain and sleet would have helped insulate the wheat plant. Relative humidity readings ranged from the mid 70s to the upper 90s. Wind speeds ranged from 5 mph to more than 10 mph.
Where plants were already reacting to a lack of soil moisture, the severity of freeze injury may have been reduced. Drought stress tends to harden plants to cold and decreases their water content and potential for injury. Other factors also affect plant injury from one field to the next. These include differences in elevation and topography of the field.
These same low temperatures now would likely cause much more significant damage since the plants are at a later growth stage. If you suspect freeze injury in your field, split the stem lengthwise with a sharp knife. A normal, uninjured growing point is bright yellow-green and turgid; freeze injury causes it to become white or brown and water-soaked in appearance. This injury can occur even in plants that appear normal because the growing point is more sensitive to cold than other plant parts.
For more information on spring freeze injury, read the NU Cooperative Extension publication, EC94-132, Freeze Injury to Nebraska Wheat, available from your local Cooperative Extension Office.
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Five wheat viruses commonly occur in Nebraska: soilborne wheat mosaic, wheat streak mosaic, high plains, barley yellow dwarf and wheat spindle streak. Telling one from the other in the field can sometimes be a challenge, especially when multiple infections by more than one virus are present in the same plant. This chart (below) can help with field diagnosis, but remember a laboratory analysis of infected plants is the only sure method of identifying a specific virus disease.
Common associations of more than one virus in a field are spindle streak/soilborne mosaic, barley yellow dwarf/wheat streak mosaic and wheat streak mosaic/high plains. The most lethal of these combinations is wheat streak mosaic/high plains which can reduce yields to almost nothing. With the aphid-vectored barley yellow dwarf and the curl mite-vectored wheat streak mosaic and high plains, the incidence and severity of these diseases is directly associated with the distribution of the aphid or mite vectors.
Virus diseases in wheat can be controlled through cultural practices such as proper planting time and destruction of volunteer wheat and grassy weed hosts, and through the use of more tolerant or less susceptible varieties.
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John Watkins
Extension Plant Pathologist
Historically, sorghum growers have had few herbicide choices; however, several manufacturers have recognized the lack of weed management options in sorghum and are adding some options.
Connect 20 WSP
Connect is a new postemergence herbicide from Aventis for broadleaf control in sorghum. Connect is a 20% by weight wettable powder formulation of bromoxynil. This is the same active ingredient found in Buctril. Sorghum growers will benefit from Connect because it allows a variety of tank mix options. Also, Connect will provide quick burndown of many broadleaf weeds with less leaf burn than Buctril.
Connect may have quite an impact in corn as well.
For corn growers, using Buctril for broadleaf control and Accent for grass was all but impossible since Accent requires adding crop oil, too hot for the Buctril on corn. Connect allows the use of crop oil with reduced injury risk, making it viable tank mix partner.Paramount
Paramount, from BASF, was labeled last year for postemergence grass control over sorghum. Paramount also provides good control of field bindweed. Paramount is a 75 DG formulation of quinclorac. At 5.3 oz/a, Paramount can be applied over sorghum from emergence to 12 inches for around $24/a. For adequate weed control, crop oil is required. Paramount found good use last year with sorghum growers as postemergence grass control was difficult to achieve before Paramount.
Outlook
Outlook is also from BASF and is a 6lb/gal liquid formulation of dimethenamid, the active ingredient found in Frontier. Outlook contains a more active isomer of dimethenamid with use rates of 10 — 21 oz/a, depending on soil type. Rates are approximately 55% of the Frontier rates with similar activity. Safened seed is required with Frontier or Outlook.
AIM (label pending)
Aim is a formulation of carfentrazone from FMC for broadleaf control. Although Aim will do well on many broadleaf species including Redroot pigweed, Black nightshade, and Common lambsquarters, it really shines with velvetleaf control. With a low use rate of 0.33 oz/a at a cost of around $4/a, Aim fits the bill for velvetleaf control in sorghum fields. Because Aim is a cell membrane disrupter, some leaf burn is typical following an application.
Ally + 2,4-D (label pending)
A section 18 is being sought for Ally + 2,4-D over grain sorghum. The addition of Ally can offer increased control of kochia, Common lambsquarters, and ragweed. Ally is currently labeled in wheat for broadleaf control with some limited grass activity. Crop safety will be similar to that of 2,4-D alone. Look for the section 18 possibly in late May early June.
Jeff Rawlinson
Extension Technologist
Alex Martin
Extension Weed Specialist
With the unseasonably warm weather for much of our spring, many growers observed alfalfa stands breaking dormancy and greening quite early this year. For some, green up came too early and did not provide growers with enough time to control problem weeds, especially mustards.
Now that alfalfa stands across the state are well into green up, herbicide selections are severely limited. In many stands, mustards including shepherdspurse and pennycress are very prominent. Herbicides such as Lexone/Sencor, Roundup Ultra, Velpar, Zorial, and Karmex are no longer an option once the alfalfa has broken dormancy, due to potential injury. Although a few herbicides may be useful to control winter annuals after established alfalfa stands break winter dormancy, their activity on more mature winter annuals can be quite reduced.
Butyrac (2,4-DB) is a growth regulator that is converted to 2,4-D within the plant. Butyrac has fair activity on many annual broadleaf weeds at 1-3 qt/A. The effect of Butyrac on mature mustards will be very limited. Butyrac should not be used when temperatures are expected to fall below 50° F for three days after application.
Poast will have good activity on most annual grasses at 1.5-2 pt/A but will not control over-wintered downy brome. Be aware of a 30-day harvest restriction.
Pursuit can be used at 2 oz/A with good activity on pennycress, and other winter annuals. As mustards mature, the efficacy of Pursuit will be limited.
Select will provide excellent con-trol of downy brome at 6-8 oz/A.
In fields where this control will not be effective enough, growers will need to wait until fall. Once the alfalfa stand has gone dormant, winter annuals can be more easily controlled with treatments such as Roundup Ultra, Lexone/Sencor, Velpar, Zorial, Gramoxone Extra, and or Karmex.
The best advice for producers at this time is to assess the quality of the stand and weed growth stage, control what weed species they can this late in the season and throughout the summer, and regain control of winter annuals once the stand has gone dormant in the fall.
Jeff Rawlinson
Extension Technologist
Alex Martin
Extension Weed Specialist
Monday, June 19
1 p.m., Concord, Haskell Ag Lab
Tuesday, June 20
9 a.m., Lincoln, Havelock Research Farm
3 p.m., Clay Center, South Central Research and Extension Center
Wednesday, June 21
9 a.m., North Platte, West Central Research and Extension Center
3 p.m. (MDT), Sidney, High Plains Agricultural Laboratory
Thursday, June 22
8:30 a.m. (MDT), Scottsbluff, Panhandle Research and Extension Center
Jeff Rawlinson
Extension Technologist
Alex Martin
Extension Weed Specialist
Spring planting activities were underway in many areas of the State, according to the Nebraska Agricultural Statistics Service April 24 report.
Precipitation fell over most of the state last week with the largest accumulations in the Panhandle. Corn planting occurred where surface moisture conditions permitted and soil temperatures were warm enough. Last week's moisture should help pastures and alfalfa crops, but additional moisture will be needed.
The winter wheat crop rated is rated 6% very poor, 12% poor, 30% fair, 49% good, and 3% excellent. As of Sunday (April 23), 32% of the crop had jointed, well ahead of last year at 23% and the five-year average at 12%. Additional moisture continued to be needed in the Panhandle and other wheat producing areas to ensure plant growth and development.
Oat planting was virtually complete at 98%, well ahead of 83% last year and 65% for the five-year average.
Corn planting progressed to 12% seeded. This was ahead of 6% last year and the average. Reports indicated that 1% of the fields had emerged, ahead of last year and average.
Nebraska Agricultural Statistics Service
Growing degree day accumulations as of April 24 using a 48° base. Alfalfa weevils usually begin causing noticeable damage at 375 GDD.
We continue to monitor alfalfa for weevil and army cutworms, although some of the latter have reached maturity. One producer installed drip irrigation on alfalfa on four pivot corners this spring. Wheat continues to look either very good or very bad, the latter due to poor germination last fall and very thin stands.
Alfalfa fields are very dry as expected. One alfalfa producer is irrigating his fields.
Planting is going well as the ground is very mellow. Once the weather allows there will be a lot of corn and soybeans planted in a very short time here. Soil temperatures are favorable for corn and most of the planters are adjusted for the dry conditions.
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