1. Preplant and preemerge herbicide programs for grain sorghum 1 2. Manure application on no-till fields 2 3. Effect of stripe rust on winter wheat 3

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1 Number 28 April 13, Preplant and preemerge herbicide programs for grain sorghum 1 2. Manure application on no-till fields 2 3. Effect of stripe rust on winter wheat 3 1. Preplant and preemerge herbicide programs for grain sorghum Almost all sorghum in Kansas is planted late enough in spring that a preplant burndown is required. By the time most sorghum is planted, summer annual grasses, large-seeded broadleaf weeds like velvetleaf and sunflower, and sometimes some pigweeds, may be seen even in fields that had atrazine the previous fall. These fields should be treated with a preplant burndown of glyphosate and 2,4-D, tankmixed with a residual grass-andpigweed herbicide, 1 to 2 weeks ahead of planting. This gives the 2,4-D time to decompose, and the residual herbicide time to get activated by a rain. Some additional atrazine may be added to the spring burndown, depending on whether and how much was applied in fall. Atrazine will help control henbit when added to a spring burndown treatment of glyphosate. Getting good grass control is critically important in grain sorghum. Three residual, grassand-pigweed herbicides are registered for use in grain sorghum: S-metolachlor, alachlor, and dimethenamid-p. All require the use of Concep-treated sorghum seed. They have the same mode of action, and provide similar control at appropriate rates. If these herbicides are soil-incorporated preplant, they must be kept shallow. A properly adjusted field cultivator with a leveling harrow usually provides the best incorporation. An advantage of mechanical incorporation is that less precipitation is required for herbicide activation, so performance in drier weather is better. On the other hand, if a lot of rain follows application, performance will be better with surface (preemerge) applications. The per-acre cost of these three herbicides is relatively high, and some producers may be tempted to reduce rates to keep expenses down. This can work well where there is a history of excellent grass weed management, together with a stale-seedbed technique

2 using a preplant burndown under no-till. Remember, though, that there s little you can do in grain sorghum if a flush of grass seedlings develops in the crop. Full rates of atrazine/acetamide premix products (such as Bicep Magnum, Lariat, or Guardsman Max) usually give good season-long control of most grasses and smallseeded broadleaf weeds, such as pigweeds, if they are activated by a half-inch or more of rainfall. However, these products do not give adequate control of large-seeded broadleaf weeds, such as velvetleaf, common sunflower, and common cocklebur. Nor do they control shattercane. They also do not control devilsclaw, puncturevine, or late-emerging kochia. Where grass pressure is heavy, it is a good idea to apply about one-half to two-thirds of the atrazine/acetamide premix product with the burndown, about two weeks before planting. The remainder of the residual herbicide should then be applied as a preemerge treatment. To keep costs down, some sorghum producers use a higher rate of atrazine plus crop oil concentrate for early postemerge grass control. However, chances of satisfactory control are not good unless grass pressure is very low. This is, however, very effective on emerged broadleaf weed seedlings as long as they are not triazine resistant. -- Dave Regehr, Weed Management Specialist dregehr@ksu.edu 2. Manure application on no-till fields No-till poses something of a dilemma for those who want to apply manure to their fields. Best management practices for manure applications call for incorporating the material into the soil, and there are applicators that can inject the manure into the soil without creating too much disturbance. But conventional surface applications of manure can pose a problem for no-till producers, since it is not possible to incorporate it after application. Although surface application of manure, without incorporation, does raise some concerns, that does not mean manure cannot be used on no-till fields. Actually, most of the sound application practices used for manure application on conventional-till fields still apply. Correct application rate and uniform spreading are still necessary to derive maximum benefits. The major concerns from application of manure to no-till fields would be the potential for: (1) manure to move off-site in surface water runoff, (2) odor problems, and (3) ammonium-nitrogen volatilization loss. All of these potential problems are minimized by incorporation.

3 To minimize the runoff potential, manure should not be applied when runoff potential is the greatest. This would include months with the most intense precipitation events and on snow-covered or frozen ground. Application on steeply sloping land and near surface water sources without vegetative filter strips also should be avoided. Little can be done to minimize ammonium-nitrogen volatilization from surface applications of manure. Ammonium-nitrogen volatilization is slower in cooler temperatures, but without incorporation or precipitation to move ammonium into the soil within a couple days, ammonium-nitrogen loss will be substantial regardless of air temperature. Most feedlot manure contains little ammonium-nitrogen, however, so losses from that source are of little concern. To manage objectionable odors from surface-applied manure, the manure should not be applied close to residences, or when prevailing winds are blowing toward residences. There are few other options. If the manure is from a facility that is under regulations for land application of manure, the nutrient management regulations must be followed for rate and method of application. -- Dave Whitney, Soil Fertility Specialist, Dan Devlin, Environmental Quality Specialist ddevlin@ksu.edu 3. Effect of stripe rust on winter wheat Stripe rust has become one of the most feared leaf diseases on wheat in Kansas. The first significant stripe rust infestation in many years occurred during the spring of 2001 followed by infestations in 2003 and These infestations have affected wheat in western Kansas during each of these 3 years. Stripe rust is a different rust organism than leaf rust. Stripe rust has historically been most prevalent in the Pacific Northwest. This cool-season rust, best adapted to temperatures less than 65 o F, will attack the wheat crop much earlier in the season than leaf rust. Because of the early infection potentially stripe rust could be more devastating to wheat than leaf rust. Currently, the thought is that stripe rust spores are blown into the area from the south each year and do not overwinter in Kansas. There are two ways to fight stripe rust: resistant varieties and fungicides. Fungicide applications on wheat do not assure increased grain yields and profits even when rust is present. Timing of the rust infection relative to wheat development (earlier the infestation the greater the impact), environmental conditions during the rust spore showers and infection (moist and cool is best for stripe rust while moist and warm is best for leaf rust), and timing of the fungicide application (most importantly protecting the flag leaf) all interact affecting the impact of the rust on wheat yield.

4 Tests were conducted in southwest Kansas in 2004/05 to evaluate the impact of fungicide applications on wheat variety yield and test weight. Several wheat varieties were planted in Comanche County by Paul Rickabaugh, in Stevens County by Gary Gold, and in Clark County by the farmer cooperator Mark Luckie during fall of Tilt at 4 fl oz/a was applied at the flag leaf stage in Comanche County and Quilt at 14 fl oz/a was applied at the flag leaf stage in Clark County on April 27, Quadris at 6.2 fl oz/a and Tilt at 4 fl oz/a was applied at the flag leaf stage in Stevens Co. during the first week of May Varieties were not replicated. Each location was treated as a replication. Thus, statistically, only fungicide treated vs. not treated averaged over varieties can be compared and varieties averaged over fungicide treatments can be compared. At these locations, all varieties had some level of stripe rust infection during the spring of The stripe rust resistance bred into our current wheat varieties is temperature sensitive and is expressed at warmer temperatures. It is most likely that the cold temperatures experienced in April of 2005 led to the stripe rust infestation even on the stripe rust resistant wheat varieties. With the warming temperatures in May, stripe rust did not advance on these resistant varieties. Averaged over wheat varieties, fungicide application increased wheat yield 9 bu/a and test weight 0.6 lb/bu. This more than paid for the fungicide applications. Tam 111, which has stripe rust resistant, was the top yielding variety and had one of the highest test weights of the varieties evaluated. Tam 111 is very susceptible to leaf rust, however. Lakin, 2137, and Above, all susceptible to stripe rust, were among the lowest yielding varieties. Fungicide application on these three varieties increased test weight about 1.4 lb/bu. Return to fungicide application would be greatest on susceptible wheat varieties. Varieties, grouped by stripe rust reaction Wheat variety response to fungicide, 2005 Clark, Comanche, and Stevens Co. Yield (bu/acre) Test weight (lbs/bu) Fungicide No fungicide Fungicide No fungicide Resistant Intermediate Susceptible A similar variety response test was conducted in Ford County in 2001, another year of heavy stripe rust infection. That year, the average yield of treated wheat was 48 bu/acre, while the untreated wheat averaged 29 bu/acre. In 2004/05, there were also three separate fungicide trials at the Southwest Research- Extension Center at Garden City. These trials tested various fungicides (Headline, Quilt, and Tilt) on three varieties: Jagger (resistant to stripe rust); Stanton (intermediate to stripe rust); and Thunderbolt (intermediate to stripe rust).

5 In this test, fungicide application on Jagger wheat did not affect grain yield, moisture, or test weight. A very low level of stripe rust was present on Jagger, with only 4% of the flag leaf being affected when not treated with a fungicide. All fungicide treatments performed similar on stripe rust when applied at flag leaf emergence or after. Leaf rust destroyed about 9% of the flag leaf when left untreated. An early application of Headline (at Feekes 4-5, or early jointing) did not provide the same level of protection as the fungicide treatments applied at flag leaf emergence or after. Stanton wheat has an intermediate response to stripe rust; however, initial infestation on the lower leaves in this test was very heavy, likely because of the very cool weather in April. Fungicide application on Stanton wheat did not statistically increase grain yield or test weight, although Headline, Tilt, and Quilt treated wheat tended to have higher yield (39 in the untreated compared to in the treated). All test weights were excellent regardless of treatment. When left untreated, stripe rust destroyed approximately 33% of the flag leaves on Stanton. Fungicide treated Stanton had less stripe rust infestation. No differences were observed among the fungicides evaluated. As temperatures warmed up in May, the progression or spread of stripe rust on Stanton stopped. If weather had remained cooler allowing stripe rust to progress and completely destroy the flag leaf results could have been much different. Thunderbolt wheat has an intermediate response to stripe rust. Thunderbolt was heavily infested in this test during April when temperatures were very cool. Stripe rust did not move onto the flag leaf as expected with only 6% of the flag leaf being destroyed on the untreated Thunderbolt. Fungicides had no effect on grain yields, and wheat response to fungicides was similar regardless of fungicide used. Fungicide application was not profitable on Thunderbolt in this test. Wheat yield potential and wheat variety susceptibility to stripe rust must be considered before fungicide applications are made. The value of the wheat crop will also impact whether fungicides should be applied. Where quality is essential to maintain high value, such as wheat produced for seed, fungicide applications may be especially beneficial. There is variable response of wheat to fungicides when infested with stripe rust. There are no guarantees fungicide applications will be profitable. However, the 2001 test suggests that stripe rust can be very devastating -- more devastating than leaf rust. Stripe rust has to be taken very seriously. Wheat variety selection remains one of the most important management decisions a producer can make to manage stripe rust. -- Curtis Thompson, Southwest Area Crops and Soil Specialist cthompso@ksu.edu These e-updates are a regular weekly item from K-State Extension Agronomy. 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

6 this weekly update, contact Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader