405 Extension Agronomy eupdate 05/24/2013 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, 785-532- 7105 swatson@ksu.edu, Jim Shroyer, Crop Production Specialist 785-532-0397 jshroyer@ksu.edu, or Curtis Thompson, Extension Agronomy State Leader and Weed Management Specialist 785-532-3444 cthompso@ksu.edu.
eupdate Table of Contents 05/24/2013 Issue 405 1. Early applications of foliar fungicides to corn: Are they a good idea?... 3 2. Diagnosing early season growth problems in corn... 5 3. Comparative Vegetation Condition Report: May 7 20... 13 2
1. Early applications of foliar fungicides to corn: Are they a good idea? Recently, there has been interest in making early season fungicide applications to corn at the V4 to V8 stages of development. This concept has been promoted mostly by fungicide manufacturers and custom applicators. There is little question that fungicide applications made at the traditional time, VT R1 (tasseling through brown silk), will usually have a much greater effect on corn yield than an application at V4 to V8 assuming disease pressure is heavy enough to justify a fungicide application at all! Early fungicide applications can be done at comparatively little cost, especially if they are combined with a postemergence herbicide application. So the question is whether producers would get enough of a yield increase from an early application of fungicide to justify the low cost and potential disease resistance risk. Corn producers looking at this option would probably be thinking about using it as a supplement to a VT/R1 application, not a replacement. To address the question of fungicide timing in corn, we have to start by looking at what is going on with corn plants at various stages of growth. Kernel row number determination of the uppermost ear begins shortly after the ear shoot is initiated (V5 to V6) and continues through at least V8. Anything from about V5 to V12 that severely limits photosynthesis, such as loss of leaf tissue, can result in fewer kernel rows or, more likely, fewer kernels per row. Although such early stress can be important, it will have much less potential to reduce yield than the same level of stress that occurs shortly before to shortly after pollination. Shortly before silking (one-two weeks) is a critical period for the determination of the potential kernel number per ear. During the two-week period shortly after silking, it is also important to minimize the potential impact of any stress (drought, nutrient deficiency, pest problems) on the kernel abortion process, which affects the final kernel number. This is why the VT/R1 application can be important if disease pressure is heavy enough. It might also seem to make some sense to apply a fungicide to help protect the plants from stress at V4 to V8, and for the period of time after that during which the fungicide will have residual activity. But what diseases might be present at these early stages of growth? The most common early season diseases on corn in Kansas at that time would be anthracnose leaf blight and possibly common rust. Anthracnose leaf blight is most commonly found in continuous corn fields under no-till or strip-till residue management systems. The disease infects corn most often in the seedling stage, prior to V5, so a fungicide application made at V5 will usually be too late to help control anthracnose leaf blight. Contrary to popular thinking, controlling anthracnose leaf blight will not help reduce the incidence of anthracnose stalk rot since the pathogen overwinters in corn residue. Anthracnose stalk rot typically occurs later in the season, since the stalk rot pathogen is caused by an infection through the roots, not the leaves. 3
Common rust has not been shown to cause any yield loss in field corn, and like anthracnose stalk rot, generally infects the plants after the V5 stage of development. The disease that is responsible for most of the yield loss to corn in Kansas gray leaf spot typically occurs later in the season. Wouldn t the early fungicide applications provide residual control of later disease infections? Fungicides do have some residual activity (about 21 days for strobilurins and 14 days for triazoles), and would protect the leaves on which they were applied against any early infections. But since fungicides are not translocated from one leaf to another, an application made at V4 to V8 would not protect leaves emerging later, when protection against gray leaf spot may be most needed. The bottom line is that an early season application of fungicide to corn would primarily be used to help control anthracnose leaf blight, but would have limited effect on other diseases. Chemical companies typically promote the use of their products as stress reducers, even in the absence of disease. While there is data to suggest that certain fungicides can reduce plant stress, the question is does this result in economic yield increases? Data from company trials is often different than data from university trials. University data for 2012 from 10 Corn Belt universities plus Ontario, Canada was recently combined. In 65 observations, the average response of a V5/V6 application of fungicide compared to a non-treated control was actually a reduction of 1.1 bushel per acre. There were 243 observations for fungicides applied between VT and R2, the university recommended time. The average yield response compared to a non-treated control at this stage was an increase of 4.9 bushels per acre. The range of yield increases for this timing was 0 bushels in Nebraska to a high of 15 bushels in New York. There were 35 observations where a V5 application was followed by a VT/R1 application. The net result was a 3-bushel-per-acre increase. Only in Ohio did a V5 + VT application out yield the VT application alone. Another, and probably more important, factor to consider is the potential for overuse of strobiluron and triazole fungicides to result in the development of resistant strains of disease pathogens. This has already occurred with the frogeye leaf spot pathogen in soybeans in the central Mississippi River basin. Judicious use of fungicides will help decrease the risk of resistance development in Kansas, both on corn and soybeans. -- Doug Jardine, Extension Plant Pathology jardine@ksu.edu -- Ignacio Ciampitti, Crop Production and Cropping Systems Specialist ciampitti@ksu.edu 4
2. Diagnosing early season growth problems in corn What are the most common causes of poor seedling growth in corn? There can be several possible causes. If the plants emerged in good fashion, but the seedlings have problems maintaining adequate growth and development or leaf color, there may be several possible reasons. A few of the most likely causes include: Compacted soil or waterlogging. Wet soils and unusually cool temperatures can inhibit root growth especially, slowing plant development. This can cause yellowed, wilting plants due to poor root growth, drowning, or a seedling blight infection. Seedling blight is often characterized by stem tissue near ground level that is discolored or water-soaked in appearance. Also, planting in wet soil can compact the seed furrow, inhibiting root growth. A shallow compaction layer can slow early root growth, resulting in stunted, nutrient deficient plants. Figure 1. Sidewall and seed zone compaction in heavy clay soil. Photo by Stu Duncan, K-State Research and Extension. Early-season lodging. This is usually associated with hot, dry weather during V1 to V6, which prevents adequate development and penetration of nodal roots. Plants can survive for a time on just the seminal root system, but they will have little mechanical support. Reasons for poor nodal root development and an elevated crown include sidewall compaction, erosion after emergence but before nodal root development, and sinking of the seedbed due to pounding rains. Often a good soaking rain is enough to allow nodal roots to establish and plants can recover. Inter-row cultivation can be used to push soil against plants with exposed crowns. 5
6
Figures 2 and 3. Corn seedling lodging caused by shallow planting and poor nodal root development (plant on left). Photos by Doug Shoup, K-State Research and Extension. White grubs or wireworms. These soil insects may be eating the roots, which will cause the plants to wilt. Black cutworms. These insects, which can be found in the soil or on the surface, cause window paning of the leaves on young plants. Cutworms may also cut off seedling plants at the soil surface. Flea beetles. These tiny leaf-chewing insects can cause scratches on leaves. Eventually, the leaves may shrivel, turn gray, and die. Plants are more susceptible to flea beetle injury when temperatures are cold and seedling growth is slow. Seedling plants are often able to recover from flea beetle injury because the growing point remains below ground level until the fifth leaf emerges. Chilling injury (cold weather crown rot). When this occurs, plants are stunted and may display nutrient deficiency symptoms. Root development is usually normal, but the crown will have dark brown or black discoloration, which can be seen by splitting the stem. This kind of injury is associated with unusually cool temperatures from emergence to V4 not freezing, but close to it. Symptoms are similar to Stewart s Wilt, so check for flea beetle feeding, which is the vector for this disease. 7
Figure 4. Cold weather crown injury. Plant in center is healthy. Photo by Doug Jardine, K-State Research and Extension. Freezing temperatures. A freeze that occurs after emergence can cause leaves to first appear watersoaked, then turn white within a few days. A freeze can kill leaves. Plants will recover from this if the freeze occurs before the fifth leaf emerges because the growing point is still 8
underground. Plant roots are undamaged by a freeze. If the weather warms back up sufficiently after the freeze injury occurs, chances of plant survival are increased. If it stays unusually cool and wet, crown rot can occur. In rare cases, such as the Easter freeze of 2007, temperatures can get low enough to damage the crowns below the soil and kill the plants. Figure 5. Corn after a hard freeze caused 25% stand loss in this case. Photo by Stu Duncan, K-State Research and Extension. Free ammonia from an anhydrous ammonia application. This can injure roots and kill germinating seed if the ammonia was applied too shallowly (especially in coarser soils), too close to the time of planting, or if dry soil conditions slowed the conversion of ammonia to ammonium. One way to minimize damage is to apply the ammonia at a 10 to 15 degree angle from the direction of planting. If injury occurs then it is more randomly distributed, reducing the multi-plant skips, and allowing the unaffected plants to compensate. Ammonia injury can also occur when sidedressing anhydrous ammonia under dry soil conditions. Root injury can occur if the plants get too big or the knives run too close to the row. Ammonia injury resulting from poor soil sealing can cause leaves to appear watersoaked or have dead margins. Roots may appear sheared off, or burned off. Plants will normally recover from this injury, but yields can be reduced. Putting a urea-based N fertilizer in contact with the seed. Urea will hydrolyze into ammonia and injure the seedling. 9
Figure 6. Seedlings damaged after starter fertilizer containing urea-n was placed in direct seed contact. Photo by Dorivar Ruiz Diaz, K-State Research and Extension. Nitrogen (N) deficiency. This does not usually occur until a later stage of growth in conventional tillage systems. But in no-till corn, especially in high residue situations, N deficiency is common where producers haven t applied nitrogen as a starter, or broadcast a significant amount of N prior to or at planting. In early planting in very cold soils where no N was applied close to the seed as a starter, seedlings may be N deficient in conventional-till also. Nitrogen deficient corn seedlings will be spindly, with pale yellow-green foliage. As the plants grow, the lower leaves will fire, with yellowing starting from the tip of the leaf and progressing back toward the stalk. Phosphorus deficiency. This can result in stunted growth and reddish-purple leaves early in the growing season. Phosphorus deficiency is often enhanced by cool, wet growing conditions. Some hybrids can naturally develop a reddish-purple coloration early in the season regardless of plant phosphorus status. A soil fertility test is one of the most definitive tools used to confirm this situation. Potassium deficiency. Potassium deficiency is first seen as yellowing and necrosis of the leaf margins. Potassium is a mobile nutrient and tends to appear in the lower, older leaves first. Symptoms usually appear sometime after emergence, close to the V5 to V6 growth stages. Cold and compacted soils can generate potassium deficiency due to poor root growth. 10
Figure 7. Potassium deficiency on corn in cold soils. The edges of the leaves are chlorotic. Photo by Stu Duncan, K-State Research and Extension. Iron deficiency. This can cause upper leaves to be pale green to yellow between the veins. Iron chlorosis is most likely to occur in the western half of Kansas where erosion or leveling has exposed highly calcareous subsoil, low in organic matter. Sulfur deficiency. This can result in stunted plants having pale green or yellowish leaves, with no distinct pattern on the leaves. With sulfur deficiency, yellowing is most pronounced in younger, rather than older, leaves. Herbicide injury. This is not as common now as in the past, but can still occur. Corn is very susceptible to injury from carryover from ALS-inhibiting herbicides which may have been applied to a previous crop. Carryover depends on soil ph, soil texture, application rates, rainfall, and other factors listed on the herbicide labels. Symptoms include stunting, chlorosis, reddening, and an overall sickly appearance. Corn will not grow out of this type of injury. Figure 8. ALS herbicide carryover injury to corn. Photo by Stu Duncan, K-State Research and Extension. 11
For more details on these and other potential problems, see the newly revised Diagnosing Corn Production Problems in Kansas, K-State publication S-54, at: http://www.ksre.ksu.edu/bookstore/pubs/s54.pdf Also, see Corn Production Handbook, K-State publication C-560, at: http://www.ksre.ksu.edu/bookstore/pubs/c560.pdf -- Ignacio Ciampitti, Cropping Systems and Crop Production Specialist ciampitti@ksu.edu -- Dorivar Ruiz Diaz, Nutrient Management Specialist ruizdiaz@ksu.edu -- Jeff Whitworth, Extension Entomology jwhitwor@ksu.edu -- Doug Jardine, Extension Plant Pathology jardine@ksu.edu -- Stu Duncan, Northeast Area Crops and Soils Specialist sduncan@ksu.edu -- Doug Shoup, Southeast Area Crops and Soils Specialist dshoup@ksu.edu 12
3. Comparative Vegetation Condition Report: May 7 20 K-State s Ecology and Agriculture Spatial Analysis Laboratory (EASAL) produces weekly Vegetation Condition Report maps. These maps can be a valuable tool for making crop selection and marketing decisions. Two short videos of Dr. Kevin Price explaining the development of these maps can be viewed on YouTube at: http://www.youtube.com/watch?v=crp3y5niggw http://www.youtube.com/watch?v=tudok94efxc The objective of these reports is to provide users with a means of assessing the relative condition of crops and grassland. The maps can be used to assess current plant growth rates, as well as comparisons to the previous year and relative to the 24-year average. The report is used by individual farmers and ranchers, the commodities market, and political leaders for assessing factors such as production potential and drought impact across their state. NOTE TO READERS: The maps below represent a subset of the maps available from the EASAL group. If you d like digital copies of the entire map series please contact Kevin Price at kpprice@ksu.edu and we can place you on our email list to receive the entire dataset each week as they are produced. The maps are normally first available on Wednesday of each week, unless there is a delay in the posting of the data by EROS Data Center where we obtain the raw data used to make the maps. These maps are provided for free as a service of the Department of Agronomy and K-State Research and Extension. The maps in this issue of the newsletter show the current state of photosynthetic activity in Kansas, the Corn Belt, and the continental U.S., with comments from Mary Knapp, state climatologist: 13
Figure 1. The Vegetation Condition Report for Kansas for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that for the first time this season, snow is not an issue. Vegetative activity is relatively high in the East Central and Southeastern Divisions. Moisture has been higher in these areas and temperatures have been favorable. In the western divisions, while temperatures have been closer to normal, continuing drought conditions have hampered plant development. 14
Figure 2. Compared to the previous year at this time for Kansas, the current Vegetation Condition Report for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that photosynthetic activity in the Flint Hills has been much lower. Cool temperatures have delayed plant development. Last year, most vegetation was 4 to 6 week in advance of average production. This year, plant development is closer to 2 weeks behind average. In the western divisions, dry conditions rather than cooler temperatures have had a greater impact. 15
Figure 3. Compared to the 24-year average at this time for Kansas, this year s Vegetation Condition Report for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows only a small portion of the state has close to average photosynthetic activity. The South Central and the Southeastern Divisions show the greatest increase in biomass production. These areas have had favorable moisture and temperatures. The Southeastern Division averaged 2.00 inches of precipitation last week, which is 149 percent of normal. 16
Figure 4. The Vegetation Condition Report for the Corn Belt for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that photosynthetic activity is greatest in the southern portions of the region. Productivity in the area from Illinois to central Pennsylvania has been reduced due to delays in spring planting. In the first part of this two-week period cool soil temperatures slowed activity, while saturated soils slowed planting in the second part of the period. In the Northern Plains, cold soil temperatures continue to slow activity. 17
Figure 5. The comparison to last year in the Corn Belt for the period May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows only southern Illinois has a widespread area of greater plant productivity. Last year, most of the region was well above long-term average production, with warm temperatures and little snow cover accelerating production at that time. 18
Figure 6. Compared to the 24-year average at this time for the Corn Belt, this year s Vegetation Condition Report for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that the eastern portion is close to long-term average productivity, while the western and northern regions are below normal. In Ohio, by the end of this two-week period, only 16 percent of the corn had emerged, compared to an average of 52 percent emerged. 19
Figure 7. The Vegetation Condition Report for the U.S. for May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that Southeast and the Pacific Northwest have the greatest levels of photosynthetic activity. There are some areas of reduced biomass production along the central Mississippi river basin due to spring flooding. Additional areas of reduced activity can be seen in the central Corn Belt, where cool, wet soils have delayed spring planting. 20
Figure 8. The U.S. comparison to last year at this time for the period May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that the Northern Plains and New England have much lower photosynthetic activity. Cool soil temperatures are the major drivers in this delay, although drought continues to influence the southern portions of the region. Large areas of extreme to exceptional drought continue from Nebraska through Texas. 21
Figure 9. The U.S. comparison to the 24-year average for the period May 7 20 from K-State s Ecology and Agriculture Spatial Analysis Laboratory shows that the Plains continues to lag in production. Across the north, the main driver is cool soil temperatures. Across the Southern Plains, drought continues to be a significant factor. The area of exceptional drought is centered along the Oklahoma/Texas Panhandle, and extends north to western Nebraska and west into southern Colorado and eastern New Mexico. -- Mary Knapp, State Climatologist mknapp@ksu.edu -- Kevin Price, Agronomy and Geography, Remote Sensing, Natural Resources, GIS kpprice@ksu.edu -- Nan An, Graduate Research Assistant, Ecology & Agriculture Spatial Analysis Laboratory (EASAL) nanan@ksu.edu 22