1. Sooty molds in wheat 1 2. Barley yellow dwarf infections this year 2 3. Sericea lespedeza control 3 4. Plant analysis for soybeans 4

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1 Number 198 June 26, Sooty molds in wheat 1 2. Barley yellow dwarf infections this year 2 3. Sericea lespedeza control 3 4. Plant analysis for soybeans 4 1. Sooty molds in wheat The rainfall in late May and the first half of June triggered numerous reports from eastern and central Kansas of sooty molds on wheat. Symptoms of sooty mold include a dark olive green or black fungal growth on the heads of mature wheat. The small patches of mold are randomly distributed on the glumes, chaff and awns, and are very superficial. The fungi that cause sooty molds are very common. These fungi specialize in decomposition of plant debris and are often among the first to colonize dead tissues of mature plants. Sooty mold on wheat. Photo by Erick DeWolf, K-State Research and Extension Plant Pathologist. 1

2 In most situations sooty molds are considered to be a cosmetic problem and will not result in any reduction in yield. However, if wet weather persists the fungi can begin to colonize the kernels, resulting in small dark lesions known as black point. No management of sooty molds is possible or needed. Fields with large amounts of sooty molds will make harvest operations a dirty job, because the black spores are disturbed and blown into the air by the combines. Individuals with severe mold allergies should take precautions to minimize exposure to the dust and spores generated during harvest. Interestingly, the distribution of the sooty molds can provide some insights into other production problems that were previously unidentified. For example, when sooty mold is found in patches within a field, it suggests that these plants matured earlier and have weathered longer than the other areas of the field. Clearly, many things can cause wheat to mature early, including standing water, dry soil conditions, fertility problems, or diseases such as barley yellow dwarf and takeall. In many situations the plants that matured early will have smaller kernels. In most cases, however, the sooty mold was not responsible for the reductions in grain fill, but is simply an indicator of other, earlier problems. -- Erick DeWolf, Extension Plant Pathologist dewolf1@ksu.edu 2. Barley yellow dwarf infections this year One of the most common disease problems in Kansas this year was barley yellow dwarf. Some questions have arisen about this, such as: * Why was barley yellow dwarf so widespread when there weren t many oat-bird cherry aphids or greenbugs reported? This is a good question, but I don t think anyone has any answers. The only explanation is that the aphids and greenbugs had to have been present throughout the Central Plains, just at low population levels. Those are the two primary vectors of barley yellow dwarf on wheat. It doesn t take a very high population of aphids to introduce and spread the virus. * Is there a new variant of the barley yellow dwarf virus that is more virulent? There is no indication of that. In our variety screening for barley yellow dwarf reactions of wheat, the varieties have reacted this year the same as they have in previous years. There are eight known strains of the barley yellow dwarf virus, but only two that infect wheat in Kansas. Those two are known as the PAV and RPV strains. Of those two, the PAV is more prevalent, but it doesn t make much difference. Both strains cause similar symptoms and yield reductions in wheat. The strains of the barley yellow dwarf virus that infect wild grasses such as big bluestem are different than the strains that infect wheat. Each strain of barley yellow dwarf virus is vectored by specific species of aphids. The PAV and RPV strains that infect wheat are vectored by the oat-bird cherry 2

3 aphid and greenbug. Other strains, that infect other grasses, are vectored by different aphid species. * Did the barley yellow dwarf infections this year occur mostly in the fall or spring? All I can say for sure is that the barley yellow dwarf infections at our variety screening trials near Manhattan were fall infections. We maintain clean plots for comparison purposes in both the fall and spring. Where we used an insecticide seed treatment in the fall and sprayed for aphids and greenbugs every 2-3 weeks in the fall, there was a big difference between the treated and untreated plots in the level of barley yellow dwarf infection. Where we waited until late winter and early spring to spray for aphids and greenbugs every two weeks, there was very little difference between the untreated and treated plots in the level of barley yellow dwarf infection. * If the infected plants show yellowing symptoms but are not stunted, will there still be any yield loss? It s possible, but the level of yield loss will probably not be as great as where the plants were stunted. When barley yellow dwarf causes both yellowing or purpling (the nature of the discoloration depends on variety) and stunting, yield losses can be as much as percent or more. When the disease causes yellowing or purpling but with little or no stunting, yield losses will usually be limited to about 15 percent or less. * Which varieties have the best resistance ratings to barley yellow dwarf? We screen varieties based on the visual symptoms. We also have a test nearby with a smaller number of varieties in which we take yield data. In our tests, the level of visual symptoms corresponds closely to the level of yield reduction. The varieties with the best visual ratings against barley yellow dwarf are: 2137, 2174, Coker 9663, Duster, Endurance, Everest, Intrada, McCormick, Overland, Overley, Pioneer 25R47, Roane, Sturdy 2K, T441, Truman, and Winterhawk. Some of those are soft red winter wheat varieties. -- Bill Bockus, Plant Pathologist bockus@ksu.edu 3. Sericea lespedeza control Sericea lespedeza continues to be a major concern on rangeland, pasture, and some CRP acres in Kansas. There are no known biological controls that can be effectively used on sericea lespedeza. However, grazing with goats can suppress sericea lespedeza stands and produce a saleable product. It takes 4 to 5 goats per acre (of sericea) to graze the plant heavily enough to eliminate seed production. Mowing in mid- to late-july will eventually reduce stands of sericea lespedeza to some extent. Sericea has not been eliminated, however, even after several years of mowing. Herbicides applied at the correct time and under favorable environmental conditions can significantly reduce sericea lespedeza. 3

4 Remedy Ultra (triclopyr) and PastureGard (triclopyr + fluroxypyr) can provide effective control when applied during June and into early July when the sericea plants are in a vegetative growth stage. Broadcast applications of Remedy Ultra at 1 to 1.5 pints/acre and PastureGard at 2 pints/acre should be applied in spray volumes of 10 to 20 gallons/acre. Products containing metsulfuron, such as Escort XP and Cimarron Plus, are generally more effective in the late summer when sericea lespedeza is actively blooming. Recommended rates are 0.5 oz/acre of Escort XP and oz/acre Cimarron Plus. For spot application, mix 1 fl oz PastureGard per gallon of water, use a 1% solution of Remedy Ultra in water, or 0.3 grams Escort XP per gallon of water. Aerial applications of these products should be done with a minimum spray volume of 3 gallons per acre. Higher rates, e.g. 5 gallons per acre, will generally be more effective. Sericea lespedeza is a state-wide noxious weed in Kansas and therefore needs to be controlled. Sericea lespedeza has a tremendous seed bank that helps reestablish stands. Herbicide treatments will need to be repeated every 2 to 4 years to keep this invasive species in check. Initial treatments should reduce dense stands to the point where spot treatment can be used in future years. Left untreated, sericea lespedeza will dominate a site, greatly reducing forage production and species diversity. -- Walt Fick, Rangeland Management Specialist whfick@ksu.edu 4. Plant analysis for soybeans Plant analysis is an excellent quality control tool for soybean growers. There are two primary ways plant analysis can be used: as a routine monitoring tool to ensure nutrient levels are adequate in the plant, and as a diagnostic tool to help explain some of the variability in soybean growth and appearance we see in fields. Keep in mind, however, that any plant stress (drought, soil compaction, cyst nematodes, etc) can have a serious impact on nutrient uptake and the nutrient concentrations found in soybeans. Sampling under stress conditions for monitoring purposes can give misleading results, and is not recommended. Monitoring to ensure adequate plant nutrition For monitoring purposes, collect sets of the 3 upper, fully developed trifoliate leaflets, less the petiole, at random from the field at flowering to initial pod set (growth stages R2-R3). The top, fully developed leaves are generally the dark green leaves visible at the top of the canopy, which are attached at the second or third node down from the top of the stem. Sampling later, once seed development begins, will give lower nutrient contents as soybean plants begin to translocate nutrients from leaves to the developing seed very quickly. The sampled leaves should be allowed to wilt over night to remove excess moisture, placed in a paper bag or mailing envelope, and shipped to a lab for analysis. Do not place the leaves in a 4

5 plastic bag or other tightly sealed container, as they will begin to rot and decompose during transport, and the sample won t be usable. The data returned from the lab will be reported as the concentration of nutrient elements, or potentially toxic elements in the plants. Units reported will normally be in percent for the primary and secondary nutrients (N, P, K, Ca, Mg, and S) and ppm, or parts per million, for the micronutrients (Zn, Cu, Fe, Mn, B, Mo, and Al). Most labs/agronomists compare plant nutrient concentrations to published sufficiency ranges. A sufficiency range is simply the range of concentrations normally found in healthy, productive plants during surveys. It can be thought of as the range of values optimum for plant growth. The medical profession uses a similar range of normal values to evaluate blood work. The sufficiency ranges change with plant age (generally being higher in young plants), vary between plant parts, and can differ between cultivars. So a value slightly below the sufficiency range does not always mean the plant is deficient in that nutrient, but it is an indication that the nutrient is relatively low. Values on the low end of the sufficient range are common in extremely high-yielding crops. However, if that nutrient is significantly below the sufficiency range, then one should ask some serious questions about the availability and supply of that nutrient. Levels above the sufficiency range can also indicate problems. High values might indicate over fertilization and luxury consumption of nutrients. Plants will also sometimes try to compensate for a shortage of one nutrient by loading up on another. This occurs at times with nutrients such as iron, zinc and manganese. In some situations very high levels of a required nutrient can lead to toxicity. Manganese is an example of an essential nutrient which can be toxic when present in excess. Diagnosing field problems Plant analysis is an excellent diagnostic tool to help understand some of the variation seen in the field. When using plant analysis to diagnose field problems, try to take comparison samples from both good/normal areas of the field, and problem spots. Collect soil samples from the same good and bad areas, and don't wait for flowering to sample soybeans. Early in the season collect whole plants from different places in your sampling areas. Later in the season, collect sets of top, fully developed leaves. Handle samples the same as those for monitoring, allowing them to wilt to remove excess moisture and avoiding mailing in plastic bags. The following table gives the range of nutrient content considered to be normal or sufficient for top fully developed soybean leaves at flowering. Keep in mind that these are the ranges normally found in healthy, productive soybeans. 5

6 Nutrient Content Considered Normal or Sufficient for Soybeans Growth Stage Nutrient Units Top, fully developed leaves at flowering Nitrogen % Phosphorus % Potassium % Calcium % Magnesium % Sulfur % Copper ppm Iron ppm Manganese ppm Zinc ppm Boron ppm Molybdenum ppm Aluminum ppm <200 In summary, plant analysis is a good tool to monitor the effectiveness of your fertilizer and lime program, and a very effective diagnostic tool. Consider adding this to your toolbox. -- Dave Mengel, Soil Fertility Specialist dmengel@ksu.edu 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, swatson@ksu.edu, or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader jshroyer@ksu.edu 6