Number 259 August 20, 2010

Transcription

1 Number 259 August 20, Downy brome control in wheat 1 2. Wheat seeding tips for good stand establishment 2 3. Stalk rots in grain sorghum 4 4. Clarification on herbicide-resistant sorghum lines 7 5. Comparative Vegetation Condition Report: August Downy brome control in wheat Downy brome is one of the most significant cheatgrass problems in wheat in areas of Kansas west of I-35. Cheat and Japanese brome are the other two cheatgrasses that infest wheat in Kansas. Of the three cheatgrass species, downy brome is often the most difficult to manage. One reason for this is that herbicides labeled for use in wheat are more effective on cheat and Japanese brome than on downy brome. Another possible reason is that downy brome tends to mature earlier and set seed lower in the wheat canopy than cheat or Japanese brome, and thus, more seed may remain in wheat fields after harvest. Finally, downy brome is more abundant in ditches and other non-cropland areas than cheat or Japanese brome, and tends to creep into fields from those areas. The best way to control downy brome is with crop rotation. This is true for all cheatgrass species and other grassy weeds, such as feral rye, Italian ryegrass, and jointed goatgrass. Downy brome seed generally does not remain viable in the soil for more than two to three years. Most of the seed will germinate within one year, but where populations are heavy in a given field, there can be significant emergence even after two years. Where downy brome has been a serious problem, it s best to keep the field out of wheat for at least two years. During the period when the field is out of wheat, it s important to make sure the downy brome is killed before it sets seed. Glyphosate and fall applications of atrazine are effective in controlling downy brome after a summer row crop. Tillage can also be used, where appropriate, to control downy brome. Again, it is important to till the plants before they set seed. Most of the cheatgrass herbicides on the market can do a fairly good job of controlling light to moderate infestations of downy brome if applied as a postemerge treatment in the fall. The 1

2 exception would be Finesse Grass & Broadleaf, which is not very effective for downy brome control. None of the cheatgrass herbicides seem to provide good control of heavy populations of downy brome. Olympus, Olympus Flex, Maverick, PowerFlex, and Beyond (Clearfield wheat only) should be applied after wheat begins to tiller and when the weeds and crop are actively growing. Research at K-State indicates that even winter time treatments can provide control if applied when plants are actively growing and if mild temperatures persist several days before and after treatment. Later applications in the spring generally are less effective than fall treatments, and have increased potential for crop injury. PowerFlex has provided slightly better control of downy brome in the spring than the other cheatgrass herbicides. There are no confirmed cases yet of ALS-resistant downy brome populations in Kansas. However, ALS-resistant cheat and Japanese brome have been confirmed and resistant downy brome could be present as well. -- Dallas Peterson, Weed Management Specialist 2. Wheat seeding tips for good stand establishment Getting a good stand of wheat during the optimum time in the fall is an important first step in getting good yields. Often, problems with plant growth and development later in the year can be traced back to poor emergence or inadequate root growth and tiller development in the fall and early winter. There are a few important steps producers can take to improve their chances of getting a good stand of wheat: * Proper tractor speed. It is best to use a tractor speed of between 5 and 6 miles per hour in most cases when drilling wheat. If higher speeds are used, the openers will tend to ride up in the soil every now and then, similar to the effect of a speedboat pulling a water skier. At slow speeds, the water skier sinks into the water a bit; but once the boat picks up speed the water skier lifts up onto the surface of the water. The same principle applied to a tractor pulling a grain drill. * Proper, uniform seeding depth. The ideal planting depth for wheat in most cases is about 1.5 inches. When planting early into very warm soils, it is especially important not to plant too deeply since coleoptile lengths are shorter than normal under warm conditions. On the other extreme, producers should also be especially careful not to plant too deeply when planting later than the recommended time into very cool soils. Getting a uniform seeding depth is also important. Where producers are planting into fields with heavy residue, or where there is uneven distribution of chaff from the previous crop, uneven planting depth can be a serious problem. In those situations, it is common to end up with poor stand establishment in areas of the field where the drill opener rode up over the residue or chaff, and was unable to penetrate the soil to the same depth as in other areas of the field. 2

3 * Firm seedbed. One of the most common problems in wheat stand establishment is planting into loose, fluffy soils. This problem tends to occur most often where soils have been tilled repeatedly during the summer. When seeds are planted into loose soils, rains in the fall will settle the soil and leave the crowns of the seedlings too close to the soil surface. Having a good closing system behind the drill openers, with adequate down pressure, should help. * Plant during the optimum time. In general, wheat should be planted somewhere around the Hessian fly-free date. There may be good reasons to plant some wheat before the fly-free date, such as planting for pasture or time pressures from having considerable acreage to plant. But stand establishment and ultimate grain yields are usually best when wheat is planted after the flyfree date and before deadlines set by crop insurance. Planting more than three weeks after the fly-free date can be risky. Late-planted wheat often does not develop an adequate root system before winter, and forms fewer productive fall tillers. When planting late, seeding rates should be increased by 25 to 50 percent (up to a maximum of 120 lbs/acre) to help ensure an adequate stand and compensate for the lack of tillering. * Adequate soil fertility. In general, producers should apply at least part of their nitrogen needs before or at planting time to get the plants off to a strong start. If the soil is low or very low in phosphorus or potassium, these nutrients should be applied at planting time as well so that the plants benefit early in their development. * Using a seed treatment. Fungicide seed treatments may help with stand establishment in certain situations. For seed production fields, a systemic seed treatment is highly recommended to help keep seedborne pathogens such as bunt and loose smut out of seed stocks. In addition, seed treatments sometimes improve stands. Due to the high value of the seed produced, even small yield increases can justify the use of seed treatments. For grain production fields, seed treatment economics are less certain. Conditions favoring use of standard seed treatments in grain production fields include: 1) high yield potential field, 2) seed saved from field with loose smut, bunt, or Fusarium head blight last year, 3) expensive seed, 4) low planting rates, 5) planting under poor germination conditions, especially very early or late planting, or 6) poor quality or old seed. If planting that late or into heavy residue, it s probably a good idea to use a fungicide seed treatment, even on seed that has high test weight and good germination. Insecticide seed treatments may be needed for control of soil insects. Under certain conditions, producers may want to use the higher rates of insecticide seed treatments for fall control or suppression of greenbugs and Hessian fly. * Make adjustments for planting into row crop stubble. When planting wheat into grain sorghum stubble, producers will need an extra 30 lbs N per acre over their normal N rate. When planting wheat into soybean stubble, producers should not reduce their N rates since the N credit from soybeans doesn t take effect until the following spring. If the wheat is being planted no-till after row crop harvest, N rates should be increased by 20 lbs N per acre over the normal N rate. Seeding rates should be increased when planting wheat late after row crop harvest. It s best to use a seeding rate of 90 to 120 lbs per acre in central and eastern Kansas, and 75 to 100 lbs per acre in western Kansas. When planting more than three week s after the Hessian fly-free date, producers should use a seeding rate of 120 lbs per acre. -- Jim Shroyer, State Extension Agronomy Leader jshroyer@ksu.edu 3

4 3. Stalk rots in grain sorghum Some fields of grain sorghum and corn in Kansas have developed stalk rot problems this summer. Stalk rot is the most prevalent disease of both sorghum and corn in Kansas. Annual losses are difficult to determine, because unless lodging occurs, the disease goes mostly unnoticed. The best estimates are that at least 5 percent of the sorghum and corn crops are lost each year to stalk rot. The incidence of stalk rot in individual fields may reach 90 to 100 percent with yield losses of 50 percent. The most obvious losses occur when plants lodge, however recent advances in harvesting equipment have helped a great deal in recovering grain from lodged fields. More important may be the yield losses that go unnoticed. In sorghum, these losses are caused by reduced head size, poor filling of grain, and early head lodging as plants mature early. In grain sorghum, the two most common types of stalk rot are charcoal rot and Fusarium stalk rot. Although caused by many different organisms, the symptoms of the various stalk rots are somewhat similar. Symptoms generally appear several weeks after pollination when the plant appears to prematurely ripen. The leaves become dry, taking on a grayish-green appearance similar to frost injury. The stalk usually dies a few weeks later. Diseased stalks can be easily crushed when squeezed between the thumb and finger and are more susceptible to lodging during wind or rainstorms. The most characteristic symptom of stalk rot is the shredding of the internal tissue in the lowest internodes of the stalk, which can be observed when the stalk is split. This shredded tissue may be tan colored (Fusarium stalk rots); red or salmon, (Fusarium and Gibberrella stalk rots); or grayish-black (charcoal rot). Charcoal rot Hot, droughty weather with soil temperatures in the range of 90 degrees or more are ideal for the development of charcoal rot. Drought does not cause the problem, but it weakens the plants defenses to the disease. Charcoal rot is usually less severe if drought stress is reduced. While it is difficult to separate the effects of charcoal rot from simple drought stress, a good rule of thumb is that plants infected with charcoal rot will die about two weeks earlier from dry weather than plants that do not have charcoal rot. Grain fill that would have occurred during this period is the amount of yield loss that can be attributed to charcoal rot. The plants will die prematurely. When stalks are split, the typical shredded appearance in the lower stalk associated with all stalk rots will be present. Additionally, there will be a gray to black discoloration of the inner stalk caused by numerous sclerotia (small, black reproductive structures of the fungus) forming on the vascular bundles and decaying tissue. 4

5 Closeup of charcoal rot in grain sorghum. Photo by Doug Jardine, K-State Research and Extension. Lodging from charcoal rot in grain sorghum. Photo courtesy of the University of Missouri. 5

6 Fusarium stalk rot Fusarium root and stalk rot is generally found in the same areas where charcoal rot develops. The pith of Fusarium stalk rot infected plants will have a shredded appearance and is typically tan in color, but in some hybrids the pith in the lower stalk may be pink to red in color. Plants may die prematurely or lodge. Fusarium stalk rot is favored by dry conditions early in the season, which decreases nutrient solubility, making the nutrients unavailable to the plant. Later in the season, following pollination, warm (82 to 86 degrees), wet weather can leach remaining nutrients from the soil resulting in late-season nitrogen stress and an increase in stalk rot. Fusarium stalk rot in grain sorghum. Photos by Jim Shroyer, K-State Research and Extension. General considerations Stalk rot is a stress-related disease. Any stress on a crop can increase both the incidence and severity of stalk rot. Research has indicated that when the carbohydrates used to fill the grain 6

7 become unavailable due to nutrient shortage, drought stress, leaf loss from insects, hail, disease or reduced sunlight, the plant uses nitrogen and carbohydrate reserves stored in the stalk to complete grain fill. This loss of nitrogen and carbohydrate reserves weakens stalk tissues and results in increased stalk rot susceptibility. Early maturing hybrids are generally more susceptible than full-season hybrids. Other than irrigation or rain, there is little that can be done to prevent stalk rot by late summer. No hybrid has complete immunity to the stalk rotting pathogens. When choosing a hybrid, a grower should select a hybrid that is not only a high yielder, but one that has good standability and stay-green characteristics. This will help assure that if stalk rot does occur, losses due to lodging will be minimal. A balanced nutrition program based on soil tests should be used. Overall fertility levels should be adjusted to fit the hybrid, plant population, soil type, environmental conditions and management program. An excess as well as a shortage of nitrogen can lead to increased stalk rot problems. Producers can check their sorghum for stalk rots by squeezing the lower stem with their thumb and fingers. If the stalks crush easily, they are probably infected with one of the stalk rot organisms and may lodge at any time. Check 100 plants across the field to determine the percent of affected plants. If the percentage of stalk-rot-infected plants is high, sorghum should be harvested as soon as possible, even if it hasn t dried down adequately in the field. If the stalks are firm, the plants will probably be able to stand just fine in the field for several more weeks if necessary. Rotation with nonsusceptible crops, such as small grains and alfalfa will reduce the severity of stalk rot but will not eliminate it. A good insect control program is a must in limiting losses to stalk rot. Pathogens may enter stalks or roots through wounds created by insects. Hail damage will generally increase the amount of stalk rot damage. For more information, see Stalk Rots of Corn and Sorghum, K-State publication L-741, at: -- Doug Jardine, Extension Plant Pathology jardine@ksu.edu 4. Clarification on herbicide-resistant sorghum lines In e-update No. 157, August 6, 2010, we had an article on the two new lines of herbicideresistant sorghum nearing the market. I need to make two clarifications to that article. First, the new traits, originally developed by K-State, were licensed to DuPont Crop Protection, not DuPont. Secondly, the herbicide that will be used on the ALS-resistant sorghum will be named Zest, not Zeal. -- Curtis Thompson, Weed Management Specialist cthompso@ksu.edu 7

8 5. Comparative Vegetation Condition Report: August 3 17 K-State s Ecology and Agriculture Spatial Analysis Laboratory (EASAL) produces weekly Vegetation Condition Report maps. The most recent VCR maps from EASAL are below: 8

9 Map 1. The Vegetation Condition Report for August 3 17, from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that the unfavorable conditions in west central Kansas have expanded northeast into Rooks County. Map 2. The Vegetation Condition Report for August 3 17, from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that compared to the previous period, there has been a rapid deterioration in vegetative condition. This is very noticeable in a band running northeast from Meade County in the southwest to Nemaha County in the northeast. 9

10 Map 3. The U.S. Corn Belt comparison to the 21-year average also shows evidence of the hot dry weather over the period. The eastern regions of the Corn Belt show the most pronounced departure from average conditions. Map 4. The U.S. Corn Belt condition in early-august compared to late-july shows that the overall vegetation condition has declined during this period. This is very visible in Kentucky and Ohio. 10

11 Map 5. During this period, much of the mainland U.S. is showing an overall pattern that is greener than the 21-year average for the period. Notable exceptions are upper New England, southern Pennsylvania, and Maryland, where drought conditions prevail. -- Mary Knapp, State Climatologist -- Kevin Price, Agronomy and Geography, Remote Sensing, Natural Resources, GIS -- Nan An, Graduate Research Assistant, Ecology & Agriculture Spatial Analysis Laboratory (EASAL) 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 11