May 18, 2001
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Bean leaf beetles moving into fields; expect to see relatively high numbers Get a grip on postemergent weed control in corn
Alfalfa weevil activity Deep soil moisture recharging well Using the NU Plant and Pest Diagnostic Clinic Tips for collecting and sending plant and pest samples
New herbicide registrations and label changes West Central REC
Open House June 8 The many faces of glyphosate Field updates Ag News -- Roy Frederick discusses the outlook for corn production and the markets; NU researchers discuss surprising findings with heifer replacement studies; also, USDA ARS research updates on reintroducing native soil fungi, using satellites and planes to scan cornfields, and the discovery of two new corn viruses.
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Cold winters are a major mortality factor for many insects, including the bean leaf beetle. So, did the cold temperatures we had this winter kill enough beetles so they won't be a problem this spring? Well, probably not. The prolonged snow cover probably insulated overwintering beetles from some of the extreme temperatures, and because we had such high populations last year, we expect to see relatively high numbers of beetles this spring. In fact, farmers are beginning to notice beetles as they plant and early-planted soybean fields are currently being colonized by over-wintered beetles.
Bean leaf beetles have two generations a year in Nebraska; however, since they over-winter as adults, three periods of beetle activity are seen in the growing season: overwintering colonizers, F1 generation (offspring of the colonizers, the true first generation) and the F2 generation.
Bean leaf beetles over-winter as adults in protected sites such as grassy field edges, leaf litter, and crop residue. They become active fairly early in the year and often can be found in alfalfa prior to soybean emergence. As soybeans emerge, the beetles quickly move to the seedling plants, feeding on cotyledons and expanding leaf tissue. These over-wintered beetles, called colonizers, mate and begin laying eggs.
Females live about forty days and lay from 125 to 250 eggs. After egg-laying is complete the colonizing population dwindles as the beetles die. A new generation of beetles (F1) will begin to emerge in late June to early July. The F1 beetles mate and produce a second generation of beetles (F2) that begin to emerge in mid August and feed on leaf and pod tissues. The pod-feeding F2 beetles are most likely to cause economic damage.
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Bean leaf beetles vary in color, but are usually reddish to yellowish-tan. They are about 1/4-inch long and commonly have two black spots and a black border on the outside of each wing cover. These spots may be missing, but in all cases there is a small black triangle at the base of the wings near the thorax.
Because they move to soybean fields so soon after seedling emergence, early-planted fields will usually have more beetles and suffer the most injury. This has become more of a problem in recent years because planting dates seem to be getting earlier each year. Although the defoliation caused by the beetles can appear to be quite severe, research in Nebraska and elsewhere has shown that it usually does not result in economic damage. Soybean plants have the capacity to compensate for a large amount of early tissue loss, so it takes a considerable amount of beetle feeding to impact yield.
Generally, unless insect populations are large enough to cause more than 50% to 60% defoliation, it is unlikely that treatment would be economically justified. This point is illustrated by the economic thresholds for bean leaf beetle on seedling soybean given in Tables 1 and 2. For example, if the value of soybeans is $5/bushel and the management costs are $6/acre, it takes three beetles per soybean seedling (stage VC) before treatment is justified. It is rare to see beetle numbers this high.
Be aware that these thresholds are for defoliation of beans at VC - V1. If beetles enter the field right at or during seedling emergence, the thresholds will likely be lower because the beetles do not have leaf tissue to eat and will feed on the growing point, stem, and cotyledons. We do not have a good research base for bean leaf beetle injury to newly emerging soybean, but the thresholds are probably about 1.5 beetles lower than the VC thresholds.
Remember that early-planted soybeans are the most susceptible. If economic thresholds are reached, many insecticides are available for bean leaf beetle control. All will do an adequate job if applied according to label directions.
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Another reason some producers treat bean leaf beetle on seedling soybeans is to reduce the pod damaging F2 generation that emerges in August. UNL Extension does not recommend this practice. There are many environmental factors that can impact beetle populations throughout the growing season, making it impractical to use spring beetle numbers to accurately predict if beetle populations will reach economically damaging levels in August.
Regular scouting and use of the appropriate economic thresholds are the best ways to manage late season bean leaf beetle in soybean. Recent findings by Wai-ki (Frankie) Lam and Larry Pedigo of the Iowa State University Department of Entomology, are providing additional late-season bean leaf beetle management tools for soybean producers. Although the researchers found that there is not a tight correlation between spring colonizing beetles and the F2 population, they found the F1 and F2 populations are highly correlated. They are developing economic thresholds for late season damage based on F1 beetle counts. If F1 beetle numbers reach an economic threshold, the producer can schedule to treat the F2 generation. This will allow some flexibility for the producer. We will provide information on F1 and F2 bean leaf beetle sampling and thresholds later this summer.
Tom Hunt
Extension
Entomologist, NEREC
Haskell Ag Lab, Concord
Keith Jarvi
Extension Assistant
Integrated Pest Management, NEREC, Norfolk
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Obviously some herbicides provide better control on some weeds than on others. Choose a herbicide that will provide the control you desire. Second, consider crop safety and application timing of the herbicide. For example, Basis Gold will have good activity on many grass and broadleaf weeds but it should not be applied to corn over 12 inches. All herbicides carry some type of timing restriction and pushing those limits can easily result in crop injury or reduced weed control.
Often, efficacy is influenced by the rate used. Choose a herbicide that will allow you to use the required rate for different weed sizes. For example, 24 oz/a of Roundup Ultra will do well on most velvetleaf plants in the 1-3 inch stage; however, if you are dealing with 4- to 8-inch weeds, you will need to increase that rate to 1 qt/a. Caution should be used when increasing most herbicide rates because this can increase the possibility of crop injury.
Finally, follow label recommendations where additives are concerned. Many labels will suggest adding crop oil or AMS to enhance herbicide uptake or movement into the plant cell. Most postemergence herbicides will call for an additive of some sort to enhance activity. As always, read and follow label recommendations and restrictions for maximum herbicide efficacy and crop safety.
Brady Kappler
Weed Science Educator
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Alfalfa weevil activity seems to be light, at least in southern and eastern Nebraska. Early reports of alfalfa weevil seem to have been isolated incidents. Alfalfa is in the the bud stage and beyond in southern Nebraska and progressing rapidly in the north. If weevils are near or above threshold levels, it is probably better to take an early cutting rather than use an insecticide.
Keith Jarvi
Extension Assistant
Integrated Pest Management, NEREC, Norfolk
Deep soil moisture recharging well;
recent rains eliminate precipitation deficits dating back a year
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Abundant precipitation has fallen across the entire state of Nebraska during the last six weeks. So much rain has fallen that precipitation deficits from last year's drought have been eliminated. All climate districts within the state are showing a surplus for the last six weeks, year to date, September to date, and one year records.
Soil moisture reserves have shown a positive response to the abundant moisture. All active soil moisture monitoring sites within the High Plains Regional Climate Center Automated Weather Data Network indicate deep soil moisture recharge. During the last 14 days, we have seen an increase in stored moisture at 100 cm.
The latest storm event May 3-6 dropped three to seven inches of rainfall across eastern Nebraska, with one- to three-inch totals common across western Nebraska. Even with the heavy rainfall, flooding reports were minimal. The most significant flooding occurred on the Missouri and Platte rivers. The minimal amount of flooding reported with such a heavy precipitation event indicates that more rainfall was captured by soils than ran off into streams.
What has become apparent with the recent stretch of inclement weather is that we are experiencing a significant increase in severe weather. We have seen temperatures swing from much above normal to much below normal over short times. The conflict between air masses has resulted in favorable precipitation. For the time being, it doesn't appear that the pattern will change. Nebraskans should expect roller coaster weather with periods of three to five days of above normal temperatures followed by five to seven days of below normal temperatures. Interspersed between these temperature swings will be the chance for thunderstorm activity and associated heavy rain.
Hopefully, planting delays will be minimal. There has been enough time between precipitation events that soils have been able to dry out adequately to allow for normal tillage and planting operations. Above normal temperatures have aided the drying process and helped minimize cool soil temperatures which may develop after significant precipitation events.
We have been fortunate compared to Iowa, Minnesota, and Wisconsin where substantial precipitation has resulted in significant planting delays. In southern Illinois, Indiana, and Ohio abnormally dry conditions have resulted in poor corn emergence and virtually halted soybean planting. It really is too early to tell, but perhaps the eastern Corn Belt is going to experience problems similar to those which occurred in the western Corn Belt last year.
Al Dutcher
State Agricultural Meteorologist
If you have plant or insect problems, remember that the NU Cooperative Extension Plant and Pest Diagnostic Clinic offers a variety of services. These include identification of plant diseases, insects, horticultural plants, weeds and herbicide injury. The charge for services is the same as last year: - $10 for a standard sample. This includes all samples that can be diagnosed with only visual and/or microscopic examination. Culturing for pathogen identification costs an additional $10. This fee helps cover the cost of media and the time to identify the causal agent.
Additional charges may include:
Follow the tips, below, for collecting and sending samples to the Plant and Pest Diagnostic Clinic to ensure samples arrive in good condition for an accurate diagnosis. When you have a plant or pest problem, first consult with your local Cooperative Extension educator who can often help with a diagnosis. They also have copies of the specimen identification form used when submitting samples to the Clinic. The forms and samples should be sent to:
Jennifer Chaky
Coordinator, Plant and Pest Diagnostic Clinic
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Several new herbicides have received registrations and labels have been changed for several other products, as described in the following:
Valor
Valor is a new pre-emergence and pre-plant burn-down compound from Valent for small-seeded broadleaf control in soybeans without significant rotational concerns. Product availability will be limited in 2001; however, a small amount will be sold in Nebraska, Minnesota, and South Dakota. The product also will be available for demonstration sites in those states.
Harmony GT
The EPA has approved a Harmony GT supplemental label for corn and soybeans. The "GT Burndown" label allows burndown/pre-emergence applications in fields to be planted to corn or soybeans
Liberty and Liberty ATZ
The EPA recently approved label revisions for Liberty and Liberty ATZ herbicides. Two important changes were:
Liberty ATZ
The lowest recommended use rate is now 40 fluid ounces/acre (2.5 pints/acre). Restrictions were revised by removing "Do not add any surfactants or crop oils". Under the spray additives section, the statement, "Do not add any surfactants or crop oils," was removed and the statement "Liberty ATZ Herbicide is formulated to provide optimum herbicidal performance. Use of additional surfactants or crop oils will not enhance weed control" was added. The cultivation statement was replaced with: "To maximize weed control, no cultivation should occur in the period from five days before . . ."
Liberty
The statement "Do not add any surfactants or crop oils" was removed from restrictions. Under spray additives the statement "Do not add any surfactants or crop oils" was removed and "Liberty Herbicide is formulated to provide optimum herbicidal performance. Use of additional surfactants or crop oils will not enhance weed control" was added. The lowest recommended use rate for weeds in corn/soybeans is now 24 fl. oz./acre. Also, the section for "Sequential Applications with Liberty Herbicide" (allowed 20 fl. oz./acre followed by a second treatment of 20 fl. oz./acre) was removed. The cultivation statement [was replaced ] with the following: "To maximize weed control, no cultivation should occur between the period from five days before an application to five days after an application of Liberty Herbicide." Removed the statement "Position drop nozzles over the row centers". Changed rate from "16 to 34 fluid ounces" to "24 to 34 fluid ounces".
Spartan
Spartan has once again received a Section 18 label for sunflowers in Nebraska. This label allows for application rates ranging from 2 to 5.33 oz, depending on soil type. Spartan provides good control of kochia as well as pigweed and nightshade. It does have burndown activity and can be applied from 30 days before planting to three days after planting.
Brady Kappler
Extension Educator, Weed Science
The University of Nebraska West Central Research and Extension Center will be hosting an open house Friday, June 8, from 1 to 4 p.m. It will be held in conjunction with NebraskalandDays June 8-19.
"West Central REC has strong ties with the North Platte community and west central Nebraska dating back almost 100 years. We thought the open house would be a great way to highlight our research and extension activities for the public," said Gary Hergert, REC director. Displays and field plots will showcase more than 25 species of penstemonculture and winter wheat variety tests.
West Central's horticulture staff and Lincoln County Master Gardeners will be available to answer questions. The North Platte Veterinary Diagnostic Lab and the Nebraska Plains Higher Education Center will showcase their activities and services. In addition, exhibits will feature soils, entomology, animal science, weed science, range and forage, irrigation and forestry departments from West Central.
For more information contact T.L. Meyer, communications associate at the West Central REC, at (308) 532-3611, Ext. 150.
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These days it seems that many herbicides are changing names or formulation or manufacturers. This makes it difficult for everyone keep up with just what is what. Lately new glyphosate products have led the pack with new names and distributors.
Below is a table listing many of the new glyphosate products available and registered for use in Nebraska on Roundup Ready corn and soybeans . The table lists the product's name, distributor, formulation, acid equivalent, and whether surfactants are required, may be added, or are not needed.
This is not an all inclusive list, but a representative table of available products. Remember that glyphosate herbicides respond positively to the addition of AMS, especially in hard water.
Brady Kappler
Extension Weed Science Educator
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Nebraska Agricultural Statistics Service: Winter wheat rated 2% very poor, 9% poor, 31% fair, 51% good, and 7% excellent. Lower condition ratings were noted in the Panhandle and southeast Nebraska. Comments from the southern Panhandle indicated fields were either good or poor, with some fields having been adjusted and released by crop insurance. Sixty percent of the crop had jointed, compared to 86% last year and 64% for the five-year average.
Corn planting moved ahead to 76%, with the largest gains in the western two-thirds of the state. This continued well behind the 92% pace of last year but was near the 77% average. Thirty percent had emerged, compared with 53% last year and 24% average.
Soybeans planting moved ahead to 18% complete, behind 54% last year and 23% average. Five percent of the crop had emerged, compared to 14% last year and 4% average. Sorghum planting made limited progress with 6% planted as of Sunday. A year ago, 19% had been planted and 11% is the average.
Sorghum planting made limited progress with 6% planted as of Sunday. A year ago, 19% had been planted and 11% is the average.
Oat planting was nearing completion at 92%. Planting was complete at this time last year with 99% average. Seventy-one percent of the crop was emerged, behind 97% last year and a 89% average.
Sugar beet planting progressed to 91% complete The first fields of alfalfa were being cut, although less than 1% was harvested statewide. Conditions rated 2% very poor, 5% poor, 24% fair, 51% good and 18% excellent, well above year ago levels. Pasture and range conditions showed improvement again last week and rated 3% very poor, 10% poor, 31% fair, 50% good, and 6% excellent. Most producers had moved cattle to pastures, with hay supplies very short.
Kansas Department of Agriculture Plant Disease Report (May 14): Stripe rust of wheat can be found across much of the state. Some levels required treatment in southwest Kansas. Cephalosporium stripe and Strawbreaker of wheat were reported last week. Both diseases can be described as out of the ordinary in Kansas production.
The overall low level of disease in the crop continued to be the major finding of recent survey activities. Tan spot and speckled leaf blotch were found in most fields in central and south-central Kansas. Severity levels were consistently low with infected leaf areas of less than 5%. No infection of the flag leaf was noted from either disease and most infection was limited to lower leaves. Trace levels of leaf rust were found in a few fields in north central and northeast Kansas. Fields were in flag to early head stage.
Stripe rust, which was favored by cool temperatures of a few weeks ago, had moderate levels in southwest Kansas. Incidences were high with some infection of the flag leaf (5-10% severity). Ford, Gray, and Edwards counties had fields with these significant levels. Bob Bowden, KSU extension specialist, reported limited fungicide applications in the southwest to curb the disease in susceptible varieties. Other reports of stripe rust were made across much of south central, central, and northeast Kansas. Incidences and severities were trace to low in fields from the Oklahoma to the Nebraska borders.
Predicted hot weather of this next week will stop any more infection of stripe rust and likely effect adversely most fungal foliar diseases. Wheat streak mosaic has had a few reports in central Kansas with high incidences related to infected volunteer wheat in the fall. Crazy top or downy mildew also was reported in a few fields in central Kansas.
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