County Farm Centre. Winter survival of Nitrogen-fixing bacteria- This past winter is unlikely

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1 : Your April issue Click on title to go directly to that article: Winter survival of Nitrogen-fixing bacteria Monitoring Evaluating Black Cutworm your winter moth arrival wheat survival with Pheromone traps Dealing with soil compaction Check Alfalfa stands for winter survival Alfalfa winter injury evaluation & management Corn rootworm survival prospects Management of Canada fleabane in soybeans South winds bring Black Cutworm April 2015 Winter survival of Nitrogen-fixing bacteria- This past winter is unlikely to have affected survival of nodulating bacteria in the soil. Bradyrhizobium japonicum is the nitrogen-fixing bacteria specific to soybeans. Other species colonize roots of different legumes. These bacteria infect roots, taking on a mutually beneficial relationship with the host plant to help convert atmospheric nitrogen into ammonium compounds that are needed by the host. Good news! In general, the cold soil conditions of this winter are unlikely to greatly reduce survival of nitrogen-fixing bacteria. While these bacteria prefer temperatures between 5 and 26 degrees Celsius, normal winter cold temperatures generally have little effect unless soils are also extremely dry. Conversely, high soil temperatures, like those experienced in 2012, have been shown to adversely affect Bradyrhizobium survival. Environmental conditions that negatively impact Bradyrhizobium bacteria populations include the following: Low ph (acid soils) High temperatures Extremely dry or extremely wet soil conditions Low organic matter Certain crop protection products (limited data) It has become clear that some strains of Bradyrhizobium japonicum are more persistent in the soil than other strains. In order to be certain that the best strains of nitrogen-fixing bacteria are available to colonize soybean roots, it is recommended that soybean seed be inoculated frequently, particularly if stressful environmental conditions exist in any field. Photo shows healthy soybean root nodules sliced open to show colour GROWMARK, Inc. The information provided in this letter is general in nature and specific information should be obtained by review of product labels and consultation with the manufacturer. Such information can be materially affected by inaccurate data or assumptions, varying circumstances, known or unknown risks and uncertainties, and many other factors which are beyond the control of GROWMARK, Inc. and results can vary widely. The user will not rely on any information provided herein and GROWMARK, Inc. will not be liable for any reliance on that information. The FS and FS Agronomy logos are trademarks of GROWMARK, Inc. and all trademarks contained herein are the intellectual property of their respective owners.

2 Evaluating your winter wheat survival - Monitor wheat stands regularly as the stands green up so you can effectively manage apparent concerns. Wheat stand establishment last fall (2014) was late in a number of cases, and observations indicated that some stands were patchy or thin. Watch these marginal stands as soils warm. Wheat has a remarkable ability to produce a serviceable crop, even when it doesn t get off to a very good start. However, stands that fail to thicken up will not produce well and may host heavy weed growth. Winter wheat requires a period of vernalization in order for it to successfully produce heads. Vernalization is an interval of cool temperatures that occurs after fall seeding while the wheat is actively growing. This process actually can proceed even when there has been little or no aboveground evidence of growth. So, for this current crop, just watch how the wheat stand greens up over the next couple weeks and make notes on stand density and tiller count. Plant Population and Productivity Healthy wheat stands usually have between 30 and 35 plants per square foot. Uniform stands having 20 to 25 plants per square foot will often produce acceptable results, especially if numerous tillers are formed. Plant stands of less than 15 plants per square foot may still yield at 75% of a normal crop, but weeds can be a major problem. Be aware that late germinating wheat is less likely to have good tiller development, so any injury to the main stem will have a proportionately greater impact on yield. To count wheat plants in drilled rows Examine the following row lengths and sample at multiple places in the field: for 6 inch rows examine 24 inches of row; 7 inch rows 20 inches of row; 7 ½ inch rows 19 inches of row; 8 inch rows 18 inches of row; 10 inch rows 14 inches of row; 15 inch rows 10 inches of row. Seeding depth and winter survival Shallow or uneven seeding depth is the factor most often associated with poor stand establishment and poor winter survival. Wheat should be planted in a firm seedbed at a depth between ½ and 1½ inches. Wheat that is planted too shallow tends to be more subject to winter heaving or cold injury. When evaluating wheat survival this spring, be sure to confirm seeding depth, especially in areas where the stand may not be as dense as desired. Snow and ice Snow cover on wheat can be very positive if it simply serves as a blanket that insulates against sharp temperature swings. In this way, snow can protect against frost heaving and against injury from bitter cold. However, if snow packs into a dense layer or just becomes too deep, especially under drifts, it will sometimes smother the wheat or foster mold growth. Ice is almost invariably hard on wheat, particularly where dense sheets form. Wheat will smother under an ice sheet that remains for several days. However, if sunlight penetrates the ice layer and results in formation of air pockets, wheat will sometimes tolerate ice sheeting. Note where the last remaining snow drifts exist and be sure to include these areas in your spring wheat scouting.

3 Dealing with soil compaction -Harvest weather conditions last fall resulted in field ruts and soil compaction. What are the different types of soil compaction we encounter? The form of compaction that we are probably most familiar with is the plow layer. This develops with equipment traffic and use of certain implements, such as the large disk. A well-defined layer develops just below the depth of tillage. Plow layer can be detected with a soil probe, tile rod, or compaction probe. This layer interferes with water infiltration and root penetration. Consequences include wet-soil symptoms or diseases early in the season as water becomes trapped above the compaction layer, followed by drought symptoms later on as the soil surface dries and roots have difficulty penetrating through the compaction layer. Look for a distinctive platy or blocky structure of the soil layer between six and eight inches deep. Deep compaction is the general compaction that develops below the eight to ten inch depth in the soil. This compaction is usually caused by heavy equipment loads on moist soils. The compaction radiates downward from the point of tire contact with the soil and can sometimes be detected twenty inches deep or more. Note that, while saturated soils may be badly rutted by equipment tires, the compaction in these wet soils is often cushioned or dispersed by water-filled pore spaces. It is the moist, but not saturated soils, which are most subject to deep compaction. The principle consequence of deep compaction is that crops will approach their yield potential only under ideal seasonal moisture conditions. Look for field growth patterns that follow traffic patterns and tire tracks, even those caused years earlier, but lack evidence of surface compaction. Correction of deep compaction can take many years and often includes deep ripping under dry soil conditions, as well as planting and maintaining alfalfa or other deep-rooted forage crop for several years. Surface compaction develops when repeated tillage destroys soil structure in the top inches of the soil profile and/or heavy rainfall causes soil particles to settle together into a dense layer. Surface compaction also readily develops in no-till when traffic occurs before soil dries adequately. This general compaction squeezes the pore spaces, reducing oxygen levels in the soil and limiting root growth. Surface compaction may or may not include soil crusting, and it need not be as dense as the plow layer to cause crop problems. Consequences include poor early root development, induced nutrient deficiency symptoms, excessive surface growth of roots, and early appearance of drought symptoms during dry weather. Look for soil that appears to be lacking in pore spaces and will not easily crumble in the hands. Also look for development of blocky or platy structure and soil that fractures along only a few significant lines. Sidewall compaction is another familiar form of compaction. In wet soil, the opener disk of the planter smears the side walls of the seed slit or furrow. This creates a dense layer that roots have difficulty penetrating. In many cases, shrinkage of the drying soil causes the seed slit to pull open. The seed, itself, or seedling roots are then exposed in the slit. As the side walls of the seed slit dry, root penetration becomes almost impossible. Consequences include poor seedling growth or a root system that grows like a fan as the roots take the only available path down the slit. Field badly rutted during soybean harvest

4 Because of the limited root development, drought or nutrient deficiency symptoms may be enhanced. Look for the distinctive seed slit with smeared walls, and roots that grow in a fan shape. Check alfalfa stands for winter survival -Detect alfalfa stand problems early and formulate your plan for managing observed stand issues. Several factors may impact winter injury and survival of alfalfa stands. Older stands, varieties that lack superior winter-hardiness or disease resistance, low soil ph, low soil fertility (particularly potassium), fall cutting between Sept. 1 and Oct. 15, all can increase the likelihood of winter injury. These stresses are additive, so the more stresses a field has endured, the greater the chances of winter injury. Weather conditions that increase the chances for winter injury (including frost heaving) are primarily bitter cold with no snow cover, ice sheeting, and wide temperature fluctuations. Injury can be as obvious as dead plants and reduced stands or, perhaps less noticeable, as low tonnage or reduced forage quality. An alfalfa field that is slow to green up this spring should be examined closely for signs of winter injury. Dennis Cosgrove and Dan Undersander, forage specialists with the University of Wisconsin, developed the following guidelines for diagnosing winter injury and managing damaged stands. We have added to the guidelines. Look for the following symptoms: Frost Heaving Frost heaving has been severe in many areas in recent years. Frost heaving is elevation of the alfalfa crown above the soil surface. This occurs when frequent freezing and thawing of soils cause soil expansion and contraction that squeezes the alfalfa taproot, forcing it upward in the soil. This will often result in breakage of lateral roots. This type of damage is especially common on fine textured, water saturated soils. Asymmetrical Growth Buds for spring growth were formed last fall. If parts of an alfalfa root have been killed, only the living portion of the crown will give rise to new shoots. Uneven Green-Up and Growth If some buds on the crown have been injured while others have not, the uninjured buds will start growth early while the killed buds must be replaced with new buds before growth can begin. Crown rot symptoms in winter-injured Alfalfa Root Damage Plants should be dug up to a depth of at least four to six inches and then the taproot should be split lengthwise with a knife. Winter killed roots will have a gray, water-soaked appearance just after the soil thaws. Once water leaves the root, the tissue will turn brown, dehydrated and stringy. If the root is soft and water can easily be squeezed from it, or is brown, stringy and dehydrated, it is most likely winter killed. Also, if 50% or more of the root is blackened from root rot, the plant will most likely die during spring green up or later in the year. A healthy root should be firm and white with little evidence of root rot.

5 Alfalfa winter injury evaluation and management -Here are quick tips for evaluating and managing alfalfa stands. How to evaluate the alfalfa stand: It has proven to be preferable to use stem density per square foot, rather than plants per square foot, to evaluate the stand. If the stem density is greater than 55 stems per square foot, yield has not been limited. If the stem density is between 40 and 55, the yield potential has been limited. Stem densities of less than 40 per square foot may severely limit yield and you should consider replacing the stand. Alfalfa plants that have frost heaved will not survive long, but one or more cuttings may be salvaged, depending on extent of injury. Count affected plants as lost to the stand. Managing a winter injured alfalfa stand: Badly thinned alfalfa stand Allow plants to mature to the early, mid or full bloom growth stage will help the plants restore carbohydrates for continued production. Severely winter injured stands should be cut at full bloom. Stands with less injury could be harvested earlier depending on the extent of the injury. Increase the cutting height This is particularly important when allowing plants to flower before cutting. Cutting high can also help salvage one or more cuttings of frost heaved alfalfa, in order to avoid damage to the elevated crown. Fertilize according to crop needs Soil test and apply needed fertilizer prior to first cutting if possible. Control weeds Herbicide applications to control weed competition will help the stand by eliminating weeds that compete for moisture, light and nutrients. Avoid late fall cutting If the producer intends to keep the alfalfa stand for 2016, then he should not take a cutting after Sept. 1, 2015 to allow for the buildup of food reserves prior to winter. Corn Rootworm survival prospects winter weather was unlikely to adversely affect corn rootworm egg survival. Corn rootworms survive the winter in the egg stage at various depths in the soil. Dr. Mike Gray, while a graduate student at Iowa State University, found that female rootworm beetles laid about 21 per cent of rootworm eggs within four inches of the soil surface, about 45 per cent of the eggs were laid between four and eight inches deep in the soil, and about 34 per cent of the eggs were laid between eight and 12 inches deep in the soil. Even when worm holes or drought cracks provide convenient entry to soil depths, rootworm eggs are rarely placed as deep as 18 inches.

6 Depth of rootworm egg placement and tillage have a significant effect on rootworm egg winter survival. In the 1980s, Eric Lawson, a graduate student of Dr. Jon Tollefson at Iowa State University, was able to determine a soil temperature regression for rootworm egg survival. He calculated that -1 C (30.2 F) was the threshold temperature, with 100 negative degree days causing a significant amount of mortality of rootworm eggs. What this means is that soil temperature of -1 C (about 30 F) for 100 days, or 20 days at -5 C (about 23 F), or 10 days at -10 C (about 14 F) could cause notable mortality of rootworm eggs. Crop residue, snow cover, soil moisture, and tillage obviously have major effects on soil temperature over winter, so it can be difficult to accurately estimate how much rootworm egg mortality might have occurred. To put all this in perspective, only once since the mid-1970s was it clear that cold soil temperatures had caused heavy rootworm egg death. We anticipate that rootworm eggs laid near the soil surface could frequently perish with bitterly cold winter temperatures and little residue or snow cover. However, for eggs laid deeper than four inches, soil temperatures rarely get to lethal temperatures for a long enough time period to cause extensive death of rootworm eggs. The single factor that most likely causes rootworm death is rainfall saturation of soil when rootworm eggs are hatching or recently hatched. Soil saturation apparently affects the ability of small rootworm larvae to move through the soil and to find corn roots. For those individuals who noted declines in rootworm pressure in 2014, be aware that it can take awhile for rootworm populations to rebound. Fields to watch will be primarily corn-following-corn, especially if the 2014 corn crop was late in maturity. Late-maturing corn is very attractive to egg laying rootworm beetles, and populations could be disproportionately high in these fields. Otherwise, if you know that beetle populations were low in your area in late July and August, last year, then rootworm pressure will likely remain low for this year. Management of Canada Fleabane With the snow melting and warmer temperature among us, it is time to think about weed management plans to control Canada fleabane that may have been in the fields all winter. We all know that managing fleabane can be difficult in the spring when compared to the fall, so differing techniques may be needed to achieve the desired result. With the lack of herbicides applied last fall due to the delayed harvest, do not be surprised if fleabane is prevalent in many geographies. In no-till environments, chemical control will be the only option to mitigate this weed problem. In the fall, glyphosate + 2,4-D can effectively manage the fleabane that has emerged. However, due to bolting in the spring, the fore mentioned mixture may not provide complete control of the tallest fleabane. There are many other herbicides that may be used instead of or in conjunction with glyphosate and 2,4-D for burndown activity. Regardless of the herbicide mixture, it is necessary to obtain complete control of emerged fleabane prior to soybean emergence. Due to the prevalence of glyphosate-(group 9) and ALS-(group 2) resistant fleabane, there are limited options for control postemergence in glyphosate-resistant soybeans. Bolted Canada fleabane

7 How should Canada fleabane be managed in the spring? 1. Apply effective burndown herbicides: Make sure the plant is actively growing to ensure translocation of systemic herbicides. For contact herbicides, consider ways to increasing coverage like increasing litres per acre (GPA) or switching to nozzles that produce smaller droplets. Use the proper adjuvant system for maximum control. 2. Include residual herbicides with burndown herbicides. 3. Start clean - Do not plant into fields with emerged fleabane. Limited options once soybeans emerge will put us behind the eight ball all season long. South winds bring Black Cutworms - The recent change in weather is likely to result in black cutworm moth arrival. South winds early in the spring usually bring a few black cutworms into the area, while southerly storm systems can bring in thousands of moths. Black cutworm moths are weak migrants in their own right, but they can hover or remain suspended in the updrafts of storm fronts for many hours. As wind currents shift, or the moths tire, they sprinkle out of these weather systems. The distribution pattern of the arriving black cutworm moths is somewhat random. This is why the pheromone traps offer useful information, specific to the individual field or local area. Female black cutworm moths are selective about where they deposit their eggs. Preferred crop sites include fields that were in soybeans in the previous year, especially when chickweed, dock, or other winter annual weeds are present. Since corn is really not a preferred host, fields of emerged seedling corn are seldom targeted. (This is ironic, considering the amount of damage caused to corn each year). Wet areas of fields are also often chosen for egg laying, as long as there isn t standing water present. For more information or discussion on any of the topics in this newsletter, please contact your local FS crop specialist..