| In this week's Ag News . . . | Corn and soybean planting are underway, while the effects of the drought are becoming more noticeable in some areas; Bt corn may offer fewer toxins than nonBt corn; and grain elevators and USDA working to improve pest management.
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There are no experimentally derived economic thresholds for flea beetles, but the following guidelines are suggested by Iowa State University: In field corn prior to stage V5, treat when 50% of the plants have severe feeding injury and five or more beetles are found per plant; in seed corn on susceptible inbreds, treat when 10% of plants have severe feeding injury and two or more beetles are found per plant.
The March 10 Crop Watch included a discussion of expected higher populations of the flea beetles this year and cultural practices to help limit potential damge.
A list of insecticides labeled for corn flea beetle control is available.
Iowa State University also includes a discussion of the flea beetle at their Integrated Crop Management Web site.
Robert Wright
Extension Entomologist, South Central REC, Clay Center
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Russian wheat aphid populations can be very explosive, especially during warm dry weather. If conditions are optimum, infestations can double in a week, resulting in a rapid onset of economic infestations and damage. Aphid dmage will be most dramatic when the flag leaf and head are emerging. Damage (discoloration or striping) to the flag leaf will result in reduced ability of the wheat plant to produce photosynthate to supply to the filling head. Even more dramatic can be the impact of the tightly curled flag leaf as the head is trying to emerge. If the awns of the head become caught in the curled flag leaf, the head can become distorted and seed set on the resulting curved head will be reduced and seed yield reduced. Damage by the aphid can continue through the dough stage, but the severity of the damage will be lessened once the heads have emerged. After heading, economic thresholds for treatment increase dramatically, and serious damage after heading will likely occur only if conditions are dry with no rainfall, the wheat is seriously stressed, or both. Rainfall during the heading stages tends to keep aphid populations from becoming extreme.
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Control of the Russian wheat aphid can be difficult because of the secluded location of the aphids on the plant. Two treatments have been shown to be the most effective against this pest. These are Lorsban 4E-SG and DiSyston 8E. Both of these products should give good control of the aphid. Refer to use restrictions for these chemicals on the label.
Control of the Russian wheat aphid can be adversely affected by environmental conditions and the aphid population level at the time of treatment. Extremely severe infestations are more difficult to control and can rebound much more quickly.
For more on this pest, check the NU Extension publication, Russian Wheat Aphid, G89-936, available at local Extension offices.
Gary Hein
Extension Entomologist, Panhandle REC, Scottsbluff
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It is also becoming apparent that wheat curl mite populations came through the winter in very good condition as those fields which were severely affected have very high mite populations. High mite populations will have little consequence on the current disease situation since the current problem results from virus infections that began last fall. Serious wheat streak problems can be traced back to poor control of volunteer wheat in surrounding fields, early planting of winter wheat in the threatened areas or both. Growers will need to decide what to do with infected fields since severe outbreaks of wheat streak mosaic can make these fields not worth harvesting. If fields are showing serious signs of suspected wheat streak damage, it is important to verify the cause of the problem. Several other production problems can be confused with wheat streak, especially in the early stages of symptom development. Yellowing wheat can be due to poor fertility or to other diseases (e.g. root and crown rot, barley yellow dwarf).
If serious wheat streak is suspected, growers must contact their insurance agent so fields can be adjusted. If the insurance adjustor releases the field, the grower can decide future uses of the field. If it becomes apparent that the field will be lost to wheat streak and the field is released for insurance, destroy the wheat as soon as possible to preserve soil moisture. This is important whether you're planning to grow a summer crop or fallow the field until fall winter wheat planting.
Because of the likelihood of reduced soil moisture in these fields, it is advisable to use adjoining fallow fields for summer crops and saving the destroyed wheat acreage for winter wheat planting this fall.
Gary Hein
Extension Entomologist Panhandle REC, Scottsbluff
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Cowpea aphids, Aphis craccivora, have been found in alfalfa in Kansas periodically the last few years. They've also been identified in Missouri, Oklahoma, Illinois, and California alfalfa fields. Cowpea aphids have a shiny black body with white bands on the legs and range in size from 1.5-2.5 mm long. They are pear-shaped and have antennae shorter than their body. Adults may be either winged or wingless.
Dr. Phil Sloderbeck, Extension entomologist at Kansas State University, Garden City, has compiled some information on cowpea aphids at http://www.oznet.ksu.edu/dp_entm/extension/Current/CPA2.html.
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Early this spring aphid samples from Kansas were sent to Susan Halbert at the University of Florida, who determined they were the cowpea aphid. While these are not common in alfalfa, she noted that the Chinese common name for A. craccivora means "alfalfa aphid."
While treatment thresholds have not been established for Nebraska, it is thought to be similar to other aphids.
A 1990 Oklahoma report noted that: "Cowpea aphids damage alfalfa and feed on the plant [in a way] similar to the pea aphid; therefore, thresholds are likely similar. On alfalfa less than 10 inches tall, 50 aphids/stem should be used as a threshold. On alfalfa taller than 10 inches, 100 aphids/stem may be used."
A variety of insecticides are labeled for control of aphids on alfalfa in Nebraska. A list is available at http://www.ianr.unl.edu/ianr/entomol/instabls/aphids.htm.
Bob Wright
Extension Entomologist, South Central REC
The itinerary has been set for the 2000 Nebraska Weed Tour. The tour, which will begin at the Haskell Ag Lab near Concord, provides a hands-on look at University research herbicide trials. While most participants are from the agricultural chemical industry, the tour is free and open to the public. Individuals may attend all or part of it. The itinerary is:
Jeff Rawlinson
Extension Technologist, Weed Science
Growing degree day accumulations as of May 1 using a 48° base. Alfalfa weevils usually begin causing noticeable damage at 375 GDD so damage is now possible throughout the state where alfalfa is grown.
The University of Nebraska Plant and Pest Diagnostic Clinic (P&PDC) provides a one-stop center for diagnosis of plant and pest problems. The NU plant pathology, entomology, weed science, and horticulture disciplines cooperate in the unified clinic.
Samples and inquiries can be submitted to the Clinic, which will direct them to the appropriate specialist or diagnostician. Currently, Mrs. Jane Christensen is coordinating the clinic on a part-time basis while a permanent director is being sought.
Summer hours for the Clinic are 7:30 a.m. — 4:30 p.m. Monday through Friday. Mrs. Christensen is available 8 a.m. to 4 p.m. Tuesdays and Thursdays and 8 a.m. to 11 a.m. Fridays.
Samples should be sent to:
Packing and submitting samples
When submitting a sample, please include some basic information that includes:
A fresh plant or insect sample of good quality and representative of the problem will make diagnosis easier and quicker. Follow these tips on preparing and sending your sample:
Loren J. Giesler
Extension Plant Pathologist
Producers often wonder what row spacing is best for soybean and grain sorghum production. They also wonder if they should use a planter or a drill to plant these crops. Hybrid drills with planter units under a drill box and corn planters with interplant units give producers even more options for narrow row crop production. The better depth control and better seed-to-soil contact that a planter unit has to offer gives these options an advantage over conventional drills for narrow rows.
To help answer producer's questions and to evaluate different machinery management options regarding row spacing and planting method, research is being conducted at the University of Nebraska Rogers Memorial Farm, 10 miles east of Lincoln. Different planting methods and row spacings are being evaluated in a dryland no-till soybean/grain sorghum rotation. A 30-inch planter was used at half population to double seed the 15-inch planter plots to simulate a 15-inch planter. A 7.5-inch drill was used at double population with half the openers plugged to seed the 15 inch drill plots. The same population was dropped for all planting methods each year for each crop. The plots were replicated three times and harvested with a combine and weigh wagon. Research continues this year.
With the grain sorghum data (and some corn data at the same site), it appears that a 15-inch planter results in the best yield. The soybeans were the least sensitive to the different planting methods.
Other Nebraska data shows little yield advantage for narrow row soybeans in areas of good soybean production as population uniformity usually isn't the yield limiting factor; water at pod-fill is. By spreading the cost of the 15-inch planter across all three crops (and not having a drill), the machinery management decision becomes easy. By raising up and not using the interplant units, corn could be planted in 30-inch rows using the same planter.
Paul Jasa
Extension Engineer
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Planting intentions for the eight major U.S. field crops (corn, soybeans, wheat, barley, sorghum, oats, cotton, and rice) total 252.6 million acres in 2000, up about 1 million from last year's planted area. On the eve of planting decisions, farmers faced mixed price signals for major field crops-prices were up for corn, soybeans, and cotton from a year earlier, but down for winter and spring wheat.
Farmers intend to plant a record 75 million acres of soybeans and the largest cotton area (15.6 million acres) since 1995. Nationwide corn plantings are expected to expand 1 percent to 78 million acres in 2000. U.S. farmers have indicated their intention to modestly cut back the biotech share of planted acreage.
USDA Economic Research Service Report
Environmental conditions and the specific Bt maize hybrid both affect the actual reduction, but maize varieties expressing Bt throughout the plant, rather than in just specific areas, showed the most significantly lowered fumonisin levels. Mycotoxins like fumonisin, a potential cancer-causing agent often present at elevated levels in insect-damaged maize kernels, are both health and export concerns.
The model allows users to simulate, in one or two dimensions, water moving from the soil surface to groundwater. They can also use it to visualize how pesticides would be transported in different soils.
I found a mediocre wheat field which averaged about 22 stems per foot of row in eight-inch rows. The producer's options were to leave it, which would require immediate spraying for broadleaf weeds, or destroy it and plant dryland corn. The insurance would give him about seven bushels (of a twenty-seven-bushel potential) if he destroyed it now. I calculated about a 20-bushel yield, which may still be better than dryland corn this year!
In an established alfalfa field I could not get the soil probe to go into the soil deeper that 4 to 5 inches (I weigh 200 lbs with both feet on the probe!) The 0.40 of moisture over the weekend will not be enough to compensate for the extremely dry soil in this field. Alfalfa needs 6 inches of moisture to make a ton of hay per acre. We can only account for 3 to 3.50 inches of soil and precipitation for first cutting. Most fields are only 8 inches tall.
According to records from the NU High Plains Climate Center for Lancaster County we have received eight inches less rainfall than normal since July 1, 1999. I could only probe the top two feet of soil in dryland soybean and corn stubble fields that have not been tilled. I must assume that is about how far off-season moisture has penetrated. Moisture in the top two feet is estimated by hand-feel at about 70%-80% of field capacity. That would translate to 2.8 to 3.6 inches of moisture above the wilting point and only 1.4 to 1.8 inches above the point where crops would begin to experience moisture stress, (given a two-foot rootzone).
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