* What is a reasonable yield response expectation from applying a foliar fungicide? * How can chances of profitable fungicide use by maximized?

Transcription

1 Number 184 April 3, Wheat fungicide management decisions 1 2. Timing of prescribed burns on warm-season grazinglands 5 3. Physical damage to wheat from sleet 6 4. Evaluating freeze injury in south central Kansas 8 1. Wheat fungicide management decisions It can be difficult at times to know whether it will be worth it to apply a foliar fungicide to wheat. There have been more than 165 wheat fungicide trials in Kansas from to attempt to answer the following questions: * What is a reasonable yield response expectation from applying a foliar fungicide? * How can chances of profitable fungicide use by maximized? These trials have occurred under almost every imaginable weather condition and disease pressure situation, and with many different varieties. Overall, the average yield response to fungicides has been about 10 percent. 1

2 The disease resistance characteristics of a variety have a significant effect on whether the variety will respond to fungicides. There are several leaf diseases that can infect wheat in Kansas and potentially reduce yields: leaf rust, stripe rust, tan spot, powdery mildew, and speckled leaf blotch. No variety is either completely resistant or entirely susceptible to all of these diseases. Since it can be difficult to know which diseases will be the most significant in any given year, I have summarized the disease reaction of the most commonly tested varieties in the recent K- State fungicide tests and divided them into three basic categories. Category 1 includes the varieties most susceptible to leaf diseases overall, while Category 3 varieties have the best overall resistance to the complex of leaf diseases in Kansas. Some may find it unusual that Jagger is in the best category (considering its susceptibility to leaf rust), but this variety does have good resistance to stripe rust, tan spot, and speckled leaf blotch. How did these different varieties respond to foliar fungicides in 2008 tests? There were three locations in which all of these varieties were tested: Republic, Reno, and Sumner counties. In these tests, Quilt was applied at 14 oz/acre at early heading. 2

3 3

4 The overall yield response from fungicide use in 2008 was greatest in Sumner County, where disease pressure was greatest, and least in Republic County, where disease pressure was light. Were the yield responses large enough to be profitable, assuming the cost of fungicide and application at $25 per acre? If so, which varieties were most likely to yield a profitable response? An analysis shows that the profitability varied, depending on the overall disease resistance level of the variety. Fungicides were most likely to pay off when applied to the most susceptible varieties (Category 1, Jagalene and PostRock). With more disease resistant varieties, fungicides had a positive net return only when wheat prices are at $8 per bushel. 4

5 In summary: * It is important to pay attention to local and regional scouting reports on disease occurrence and weather forecasts. * The greatest return for fungicides will likely be on varieties susceptible to multiple diseases. * Varieties with resistance to multiple diseases can still provide positive return to fungicide use, but only under heavy disease pressure. This analysis takes into account only grain yield, not test weight or seed size. Tests have shown that fungicides often increase those factors as well, which are especially important for seed producers. -- Erick DeWolf, Extension Plant Pathology dewolf1@ksu.edu 2. Timing of prescribed burns on warm-season grazinglands The time to burn native warm-season grasses depends upon the producer s goals. Increased livestock gains and brush control are normally enhanced by burning in the mid- to late-spring when the native grasses have an average of ½ to 2 inches of new growth. This usually occurs by mid- to late-april in the Flint Hills region, and early-may in northwest Kansas. Ideal dates may be shifted as much as 10 days earlier or later, depending on temperatures. Ideally, the soil profile should have adequate water at the time of burning and the surface should be damp. Other reasons for burning include improved livestock distribution, wildlife habitat enhancement, maintenance of CRP stands, and conservation of native plant communities. Timing for these purposes is more flexible and can be done earlier. Timing of the prescribed burn will affect species composition on grazed rangeland. Big bluestem, indiangrass, and switchgrass basal cover increase when the range is burned in late spring compared to unburned sites. The basal cover of little bluestem is normally maintained by late-spring burning. In the tallgrass prairie area, late spring burning will generally maintain sideoats grama and buffalograss, but increase the basal cover of blue grama. Kentucky bluegrass seems to be decreased by burning at any time of the year. On grazed tallgrass rangeland early burning reduces forage yield. There is no difference in forage yield between a late-spring burn and unburned range. Long-term research at the Konza Prairie Natural Research Area near Manhattan has shown that annual burning on ungrazed prairie in late spring over many years does not reduce overall forage yields. Repeated annual burning does result in a gradual decline in the percentage of broadleaf forbs and cool-season grasses (in a warm-season grassland), and an increase in the percentage cover of warm-season grasses. When annually burned rangelands are grazed, this shift is not as pronounced and a greater mix of various grasses and forbs is maintained. 5

6 With no burning over the long term, the cover of woody plants increases by about one percent per year initially, but then accelerates such that prairie grasses and forbs can be completely displaced by 100 percent tree and shrub cover in less than 40 years. The effect of burning on undesirable woody plants and forbs will vary, depending on the growth habit. In general, plants are more easily killed by burning when their growing points are aboveground, are unable to resprout from belowground, and their food reserves are at the lowest point. Burning readily kills eastern red cedar, especially when it is less than 5 feet in height. It does not have buds that can resprout, so when this plant is defoliated, it dies. Larger cedar trees will not be killed by fire and must be cut at ground level to be controlled. Buckbrush (coral berry) or sand plum must be burned in late spring for 2 to 3 consecutive years for effective control. During late spring, these plants are actively growing and fire destroys the topgrowth. Regrowth is slow since its food reserves are low. Successive burns prevent buildup of food reserves and eventually kill the plant. Western ragweed and western ironweed are perennial forbs, which can also be reduced with 2 or 3 consecutive late-spring burns. Smooth sumac has a life cycle similar to warm-season grasses in that it doesn t reach the lowest point in its food reserves until late May or June. Burning in late spring will kill the topgrowth, but results in an increase in the number of stems that resprout from belowground buds. The net result is that smooth sumac will actually spread more rapidly as a result of late-spring burning. -- Walt Fick, Rangeland and Pasture Management Specialist whfick@ksu.edu 3. Physical damage to wheat from sleet Some unusual symptoms were found on wheat in parts of southern Kansas after the recent sleet storms and heavy snows. There appeared to be webs on the wheat. These webs quickly dissolved when touched or disturbed by wind. 6

7 "Webs" on a blend of Jagalene and OK Bullet wheat in Barber County, March 28, Photo by Kelly Hrencher, Barber County producer. The problem in this case was a disintegration of the outer leaf surface layer from a hard, driving sleet and possible small hail storm immediately preceding the heavy snow that fell on March 28. The sleet and small hail physically damaged the outer coating of the leaves, and a web of cellulosic fibers and plant cell materials more or less exploded across the upper canopy. Leaf damage from the sleet and small hail at this stage of growth will likely have little effect on final yields. There are more leaves to come -- including the flag leaf, which is the most important leaf in terms of grain yield. The more important concern would be where the young developing heads were 3-4 inches above the ground when exposed to the physical damage from the sleet. It is possible, though by no means certain, that heads at this stage to be severely damaged by hard sleet or hail. By next week, it should be possible to determine if the heads are still alive. If the head is watersoaked and off-color at that time, and new leaves coming from the whorl are yellow, that head is damaged. Where heads are damaged, new tillers may start growing soon. In that case, the ultimate yield potential will depend on weather conditions through the remainder of the spring, but yields will probably be reduced to some extent. -- Jim Shroyer, Extension Agronomy State Leader jshroyer@ksu.edu 7

8 4. Evaluating freeze injury in south central Kansas Temperatures dipped into the mid-20 s in much of Kansas on the weekend of March That s right in the range where it is cold enough to have caused some damage to wheat in the jointing stage. Fortunately, there was enough snow cover to protect the heads in most cases. The ice, sleet, and other kinds of moisture that preceded the snow and hard freeze seems to have caused some damage to leaves and upper stems, especially where the leaves were exposed above the snow layer. Leaves were burned back and watersoaked in many fields. This kind of damage was especially noticeable on wheat planted very late (late October or early November) since that wheat did not develop much over the dry winter and early spring. There has also been some physical damage to the leaves and stems from the hard sleet storm that preceded the snow (see article No. 3 above). The real question now is whether any heads were damaged, either by the freeze or by physical injury from frozen precipitation. An examination of plants in the Harper-Kingman-Sedgwick- Sumner county areas on April 2 would indicate that in most cases the heads were not damaged. Wheat looked bad immediately after the freeze and snow, but the damage was largely cosmetic and the wheat will recover with warm weather. However, it is possible that some heads were damaged or killed. If new leaves emerging from the whorl are yellow, that indicates that the head was killed. In those cases, new tillers will likely begin growing shortly. This field in Harper County had some damage to the leaves from the freeze and sleet/snow storm on March 28, This photo, taken on April 2, shows the effect of planting date. The wheat on the left was planted in early October. The wheat on the right was planted at the end of October, and was poorly developed at the time of the freeze. Photos by Jim Shroyer. 8

9 A close-up of cosmetic leaf damage on late-planted wheat, from the right side of the field in the photo above. Older leaves are damaged by the freeze and sleet. But six days after the freeze, newer green leaves had begun to grow. All heads examined were undamaged. There are also areas in south central Kansas where the wheat was laid over after the March 28 freeze and snow. This could indicate damage to the lower stem or it could just be a temporary lodging due to heavy ice or snow. Where this occurred, the wheat should be monitored for recovery. If the wheat returns to its erect position, the lower stem may not have been damaged and the tiller would remain healthy. If the remains bent over, that means the lower stem was probably severely damaged and the tiller will not recover. Again, though, new tillers may have time to compensate for this. In some cases, split stems have been reported. -- Jim Shroyer, Extension Agronomy State Leader jshroyer@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 9