Integrated Pest & Crop Management Newsletter University of Missouri-Columbia Vol. 16, No. 3 Article 1 of 7 March 17, 2006 Roundup Ready Alfalfa: Is it worth it for you? By Kevin Bradley and Robert Kallenbach As the time for spring establishment of alfalfa nears, growers in Missouri and throughout the U.S. have a new option to consider - Roundup Ready Alfalfa. Since its introduction in 2005, we have received a lot of questions about the utility of Roundup Ready alfalfa in Missouri. In this article, we give our opinions on the advantages and disadvantages of this new technology. First, we’ll start with the bad news. The technology fee alone will cost Missouri growers an additional $2.50 per pound of seed planted. Another way of looking at this is an additional $125.00 per bag of alfalfa seed purchased, or total seed costs per acre somewhere on the order of $80.00 to $150.00 per acre (depending on alfalfa variety and seeding rate). In our opinion, another potential disadvantage is that this is the first genetically-modified perennial crop that is designed to be sprayed with the same herbicide in the same location throughout the life of the stand. This places tremendous selection pressure on the weeds in these environments, which could result in some of these weeds developing resistance to glyphosate. We have already seen glyphosate-resistant weeds appear in annual Roundup Ready crops that are planted without rotation. Granted, most alfalfa producers will probably not need to spray on an annual basis, but how many times will a producer spray glyphosate during the alfalfa’s lifetime? How long will a Roundup Ready alfalfa crop persist? We don’t have an answer for these questions now, but Roundup Ready alfalfa systems will likely last longer and could be sprayed much more than our conventional systems, for many of the reasons that will be discussed below. One of the clear advantages of this technology, however, is in the control of troublesome broadleaf weeds like curly dock, musk, bull, and Canada thistle, horsenettle, and dandelion. Of these, curly dock is especially troublesome in established alfalfa stands. In many areas, curly dock infestations are the reason that alfalfa stands are eliminated after only 3 or 4 years of establishment. Although we have not been able to conduct research to address this issue yet, it seems clear that we will be able to prolong the life of a stand through the use of the Roundup Ready technology. Another advantage that we see with the Roundup Ready technology is with spring establishment. Often, spring-established alfalfa is more difficult from a weed management standpoint. This is because many summer annual weeds emerge throughout April and May into newly seeded stands that have little to no canopy. To complicate this issue further, only a few conventional herbicide options are available for application on these newly seeded stands. Table 1. Influence of herbicides and seeding rate on crabgrass control in RR alfalfa. | Alfalfa Seeding Rate (lbs/acre) | Herbicide Program | Rate Product/ Acre | 4 | 8 | 12 | 16 | | | ----- % Crabgrass Control ---- | ____________________|_____________________|_______|_______|________|________| Eptam (PPI) | 4.5 pts | 50 | 63 | 75 | 86 | Butyrac + Poast Plus| 2 qts + 1.5 pts | 83 | 83 | 89 | 92 | Raptor | 5 fl ozs | 53 | 58 | 84 | 90 | Roundup WeatherMax | 22 fl ozs | 98 | 99 | 98 | 99 | _____________________________________________________________________________ This was the rationale behind two research trials that we conducted with Roundup Ready alfalfa in 2005. In these trials, we compared the weed control achieved with a standard glyphosate program (Roundup WeatherMax at 22 fl ozs/A) to that received with conventional programs that have been utilized by growers for a number of years. In these experiments we also evaluated the effect of alfalfa seeding rate on the level of weed control achieved. Our thinking was that with highpriced seed, growers might be tempted to reduce seeding rates. For years, we have used higher-than-necessary seeding rates so that new alfalfa stands can compete with weeds. With Roundup Ready alfalfa, weed control would be less difficult and the need for high-seeding rates to out-compete weeds in the early establishment phase would not be as critical. As illustrated in Table 1, we observed increasing levels of large crabgrass control with corresponding increases in alfalfa seeding rate with the conventional herbicide programs, but not with glyphosate. Regardless of seeding rate, the glyphosate program provided essentially complete large crabgrass control. We observed a similar response with both giant foxtail and common lambsquarters (data not shown). After one year of research, these results confirm what many have suspected from the beginning; that the flexibility and broad-spectrum weed activity that we have observed with glyphosate in other Roundup Ready systems seems to apply to Roundup Ready alfalfa as well. However, one of the big questions that each grower will have to answer for themselves is, "Is it worth it?" As shown in Table 1, our results indicate that we can achieve good crabgrass control with many of our conventional herbicide programs. We observed a similar response with both common lambsquarters and giant foxtail (depending on the conventional treatment). Weed control may not be as high for conventional programs as with glyphosate, but producers will have to determine whether or not this is good enough. In other words, is the difference in weed control that you will achieve with a glyphosate program be enough to justify the cost of the technology compared to a conventional program? This question becomes more difficult to answer as the number of different weed species increases, and as you incorporate other factors into the decision-making process. Kevin Bradley 573-882-4039 Robert Kallenbach 573-882-2801 ********************************************************** Check Winter Wheat Fields for Virus Diseases By Laura Sweets This is the time of the year when symptoms of wheat spindle streak mosaic, wheat soilborne mosaic and barley yellow dwarf may be quite evident in winter wheat fields. So far only a few questions on wheat have come in and most of those have been related to poor stands due to dry conditions. Both wheat spindle streak mosaic and wheat soilborne mosaic tend to be more severe when wet conditions occur after planting in the fall or in the late winter/early spring months. Most of the state was dry last fall and has been dry until the weekend of March 11-12, so wheat spindle streak and wheat soilborne might not be expected to be widespread or severe this spring. The mild conditions for much of the winter might have allowed some aphids to survive in wheat fields meaning that early season barley yellow dwarf is possible. Although there are no rescue treatments for wheat virus diseases, it is still a good idea to scout fields for plants showing virus symptoms and to send in samples to identify the virus or combination of viruses that are present so that proper preventative management measures can be used the next time wheat is planted in that field. Descriptions of the wheat virus diseases most likely to occur on winter wheat in Missouri are given in the following paragraphs. Symptoms of wheat spindle streak mosaic appear in early spring as yellow-green streaks or dashes on the dark green background of the leaves. These lesions usually run parallel to the leaf veins and tend to be tapered at the ends giving the lesions a spindle shaped appearance. Foliage symptoms are most obvious when air temperatures are about 50 degrees F. As temperatures warm-up, foliage symptoms of wheat spindle streak mosaic tend to fade. Plants may be slightly stunted and have fewer tillers than normal. Wheat spindle streak mosaic tends to be more prevalent in lower, wetter areas of a field. The virus which causes this disease is soilborne and is spread by the soil fungus Polymyxa graminis. Wet falls tend to favor outbreaks of wheat spindle streak mosaic the following spring. Wheat soilborne mosaic causes light green to yellow green to bright yellow mosaic patterns in leaf tissues. Symptoms are most evident on early spring growth, and warmer temperatures later in the season slow disease development. Symptoms of wheat soilborne mosaic are not always particularly distinctive and might occur as a more general yellowing similar to that caused by nitrogen deficiency. Infected plants may be stunted. This disease may be more severe in low lying, wet areas of a field. The soilborne wheat mosaic virus survives in the soil and is spread by the soil fungus Polymyxa graminis. Again, wet falls tend to favor outbreaks of wheat soilborne mosaic the following spring. Barley yellow dwarf is an extremely widespread virus disease of cereals. Symptoms include leaf discoloration ranging from a light green or yellowing of leaf tissue to a red or purple discoloration of leaf tissue. Discoloration tends to be from the leaf tip down and the leaf margin in towards the center of the leaf. Plants may be stunted or may have a rigid, upright growth form. Symptoms are most pronounced when temperatures are in the range of 50-65 degrees F. The barley yellow dwarf virus persists in small grains, corn and perennial and annual weed grasses. More than twenty species of aphids can transmit the barley yellow dwarf virus. Symptoms may be more severe and yield losses higher if plants are infected in the fall or early in the spring. Infections developing in late spring or summer, may cause discoloration of upper leaves but little stunting of plants or yield loss. The other virus disease likely to occur on winter wheat in Missouri is wheat streak mosaic, but symptoms of this disease are not usually evident until later in the season when air temperatures increase. Wheat streak mosaic causes a light green to yellow green mottling and streaking of leaves. Symptoms may vary with variety, virus strain, stage of wheat growth when plants are infected and environmental conditions. Plants may be stunted. As temperatures increase later in the spring, yellowing of leaf tissue and stunting of plants may become more obvious. The wheat streak mosaic virus is spread by the wheat curl mite. Symptoms are frequently found along the edges of fields where the mite vector first entered the field. Both the wheat streak mosaic virus and the wheat curl mite survive in susceptible crop and weed hosts. Thus, the destruction of volunteer wheat and weed control are important management options for wheat streak mosaic. A management program for virus diseases of wheat should include the following steps: **Plant good quality seed of resistant varieties. **Avoid planting too early in the fall to minimize opportunity for insect vectors to transmit viruses to young plants. **Destroy volunteer wheat and control weed grasses. **Maintain good plant vigor with adequate fertility. Laura Sweets Ag Ext.-Plant Sciences 573-884-7307 ********************************************************** Take Action Now to Manage Soybean Cyst Nematode By Allen Wrather Here is the situation: Soybean cyst nematode (SCN) is the worst pest of soybeans in the United States, and the situation isn’t getting any better. Yield suppression due to this nematode in the United States during 2004 was valued at about $820 million. However, these losses can be reduced by planting soybean varieties that have some resistance to SCN and by rotating soybean with corn, grain sorghum, cotton and certain other crops. Unfortunately, selecting varieties with resistance to SCN in a field can be complicated. The following is a brief explanation of how to select SCN resistant soybean varieties. Some high yielding SCN resistant varieties of soybeans are available, but most are only resistant to one or two races of this nematode. Currently, SCN races 1, 2, 3, 4, 5, 6, 9, 10, and 14 were present in Missouri. Most companies use the wild type soybean numbered 88788 (resistant to SCN race 3 and 14) and/or the wild type soybean named Peking (resistant to SCN races 1, 3, and 4) as SCN resistant parents for developing varieties. In 1988, soybean cyst nematode in most Missouri fields could not attack varieties developed from these parents. However, in 1998, SCN in 54% of Missouri fields could attack varieties developed from these parents. Most companies still use these two parents for developing SCN resistant varieties, but some are now using other parents for developing SCN resistant varieties. If you planted an SCN resistant variety in 2005 and SCN damaged it, you should rotate the field to another crop for 2006. The next time you plant soybean in this field, select a variety that got its resistance to SCN from a different parent than the variety that was damaged in 2005. Information about soybean variety resistance to SCN is available at the University of Missouri Variety Testing web site, http://agebb.missouri.edu/cropperf/vartest. At this site, you should click on "2005 Soybean Results" and then in the next window click on "Characteristics of Varieties". Here you will find lists of varieties tested during 2005 and the source of SCN resistance used to develop each variety. Crop rotation is useful for SCN control because the numbers of this nematode in the soil decline during years when corn, grain sorghum, or cotton is grown. The number of years a non host crop should be planted before planting soybean again will depend on the population of SCN in the soil. The first step toward protecting soybean against SCN is to test the soil for the presence of SCN. Soybean growers should take soil samples and have them tested for SCN, and, if it is present, take steps to protect their crop against this pest. The SCN Coalition says this another way, "Take the Test. Beat the Pest." Information about taking and submitting soil samples for SCN analysis can be obtained from University of Missouri Extension Regional Agronomists or at the University of Missouri web site http://soilplantlab.missouri.edu/nematode. Much of the research to develop SCN resistant varieties and information about the benefits of crop rotation for SCN management were funded by the Missouri soybean check off managed by the Missouri Soybean Merchandising Council. For more information about SCN management contact your University of Missouri Extension Regional Agronomists, read, Soybean Cyst Nematode: Diagnosis and Management, http://muextension.missouri.edu/explore/agguides/crops/g04450.htm, or read, Soybean Cyst Nematode Management Guide, http://planthealth.info/scnguide/. Following these suggested procedures will give soybean growers a better chance of producing a profitable soybean crop in 2006. Allen Wrather, Professor University of Missouri-Delta Center **************************************************************** Influence of Fall and Spring Herbicide Applications on Soil Temperature and Moisture at Corn Planting: 1st Year Results By Nick Monnig and Kevin Bradley There are many different opinions that exist on the utility of fall herbicide applications and on what effect they may or may not have on soil conditions at the time of corn planting. Some claim that fall herbicide applications can lead to increased soil temperatures at the time of spring planting. Others contend that applying a herbicide in the fall to eliminate winter annual weeds allows the soil to dry out faster in the spring. In the fall of 2004, we established two field experiments in central and northwest Missouri to investigate the effects of fall or early spring herbicide applications on soil temperature and moisture. In both experiments herbicide applications were made in the fall, 45, 30, and 7 days prior to corn planting. Each timing consisted of the following four treatments: 1.1 lb Princep 90DF plus 1 pt 2,4-D ester per acre, + oz Basis plus 1 pt 2,4-D ester per acre, 22 fl ozs Roundup Original Max plus 1 pt 2,4-D ester per acre, and an untreated control. Soil temperature thermometers were placed at a two inch depth to record soil temperature every day from March 1 to May 3. Soil moisture readings were recorded every two weeks at a 4 + inch depth beginning in early March and continuing until two weeks after planting. Based on the first year of soil temperature results from these locations, very few differences in soil temperature were observed between any of the treatments at each of the four application timings. Additionally, the treatment differences that were present were somewhat variable between the four timings. The only consistent difference between treatments spanned over a period of ten days from March 28 to April 6, which is significant as this is the time period when many producers have begun corn planting in Missouri. During this ten-day time frame, the untreated plots ranged from two to three degrees Fahrenheit higher in soil temperature than any of the herbicide treated plots, regardless of the specific application timing. This result was certainly not what we expected, but we will be collecting a second year of data from more trials this year to see if we can draw any specific conclusions pertaining to the effects of fall and early spring herbicide applications on soil temperature at planting. Similarly, few differences in soil moisture were observed between any of the four treatments or timings. Herbicide applications in the fall did not decrease soil moisture at the time of corn planting. However, at the Northwest location soil moisture readings two weeks after planting revealed significantly less soil moisture in the untreated plots than in plots treated with a herbicide (Figure 1). The untreated plots had approximately 10 percent less volumetric water content than any of the herbicide treated plots. We attribute this response to the presence of dense stands of winter annual weeds in the untreated compared to the herbicide-treated plots, which served to "wick" significant amounts of moisture from these plots. This response has been observed more consistently in our research with fall herbicide applications on soybeans (article coming in next IPCM newsletter), but our results in corn thus far have been quite variable. One factor that is likely to have a major impact on this response is the amount of rainfall received at these locations throughout the winter and early spring. Last year, both of these locations received significant amounts of rainfall in the winter and early spring months, resulting in relatively high soil volumetric water content throughout the spring. This year, we have been especially dry throughout the month of February and on into the first part of March. If there are differences in soil moisture due to the removal of winter annual weeds with fall or spring herbicide applications, we feel that we are more likely to detect these differences during a dry year such as the one we are currently experiencing. Overall, after one year of data our field studies have not proven that fall herbicide applications either increase soil temperature or decrease soil moisture at corn planting, as some have speculated. At this time we can only conclude that our data indicate that the removal of these winter annual weeds with fall or spring herbicide applications will have only a minor impact on the soil conditions that exist at corn planting. We will continue to investigate all of these factors in trials that were initiated in the fall of 2005. Kevin Bradley 573-882-4039 Nick Monnig 573-882-6536 ******************************************************* Soil Temperature Reports Aid Planting Decisions By John Lory Soil temperature is one of the primary factors controlling seed germination. Corn germinates when soil temperatures exceed 50 degrees F, soybean germinates when soil temperatures exceed 50 to 55 degrees and sorghum requires soil temperatures above 60 degrees for germination. The University of Missouri maintains a network of automated weather stations throughout the state. Twenty two of the weather stations report soil temperature at two inches below a bare soil surface. Five of these locations also measure two-inch soil temperature under a ground cover of soybean or corn stubble. Missouri soil temperature data is easily accessed over the internet at the web site ,http://agebb.missouri.edu/weather/stations/index.htm". At this site there is a link to a page summarizing the previous day’s high and low soil temperature at the 22 locations reporting two-inch soil temperature. This Web site also has links to 11 weather stations around Missouri that provide live reports of current weather conditions including two-inch soil temperature. Soil temperature is also a component of the University of Missouri’s Horizon Point Custom Weather system that sends site-specific weather reports directly to your e-mail. The Horizon Point e-mail report will include a graph of the average daily two-inch soil temperature for the past two weeks at the weather station closest to you and the long-term average soil temperature for that location (see the example figure below). This e-mail report will allow you to track trends in soil temperature and determine if current soil temperatures are above or below average. You can sign up for the Horizon Point Custom Weather system at http://agebb.missouri.edu/ horizonpoint/ or by contacting Nick Jaskolski at 573-884-6311 or at HorizonPoint@missouri.edu. John Lory Division of Plant Science and Commercial Agriculture Program ************************************************************************* Efficient Spraying Saves More than Energy By Bill Casady Spraying should account for very little energy used on the farm. At about two tenths of a gallon per acre, spraying is not an energy-intensive field operation. However, poorly managed spraying can lead to re-sprays making spraying not only energyintensive, but economically very inefficient as well. There are several potential pitfalls to efficient application of crop protection materials, but the good news is that they can all be managed. Nearly as costly as a re-spray are the inefficiencies resulting from overlap, poor calibration and offtarget placement. Round these out with poor spray distribution or nozzle selection and there is potentially a lot of room for improvement. With little or no calibration, it is estimated that as few as 5 percent of spray events are within the plus or minus 5 percent of target rates considered reasonable accuracy. The surprising statistics from some research show that crop protection materials are often over-applied by more than 20 percent due to overlapping and poorly calibrated sprayers. An herbicide program with a projected material cost of $20 per acre may cost as much as an extra $4 per acre for the waste created by overlap. Similarly, a $50 program might cost an additional $10 per acre. Improving accuracy can save a potential $10,000 over a thousand acres. A simple sprayer calibration can make huge differences, and it might even be worth investing in a light-bar for guiding sprayers through the field. The least expensive improvement is proper calibration, and the cost of calibration is almost free, and the returns are enormous. Calibration may very well be the best investment you ever make. The perfect time to calibrate is while the sprayer is still clean at the beginning of the season. Start with a new set of nozzles if you covered a lot of acres last season and follow the calibration procedures found in MU publication G1270 (http://muextension.missouri.edu/xplor/agguides/agengin/g01270.htm). The chances are very high that without further calibration throughout the season that misapplication beyond the 5 percent margin is very likely. As nozzles wear, their output trends higher. Consider a re-calibration whenever you do a thorough sprayer cleanup. It doesn’t need to require more than about twenty minutes. If that single re-calibration saves 5 percent on say the last 500 acres sprayed at $25 per acre then that twenty minutes worth of work would come in at about $1,875 per hour. Realistically, the actual savings for that twenty minute exercise are $625 and remember that any money saved is, as always, completely tax free. Please follow safe practices for limiting exposure whenever mixing, loading or applying crop protection materials. See MU publication G1917 for details (http://muextension.missouri.edu/explore/agguides/agengin/g01917.htm). Bill Casady (573) 882-4370 ********************************************************************* Weather Data for the Week Ending March 14, 2006 By Pat Guinan -------------------------------------------------------------------------------- | Monthly | Growing Weekly Temperature (deg. F) |Precip (in.)|Degree Days^ -----------------------------|------------|------------ Ext- Ext- Depart| Depart|Accum Deprt Avg.Avg. reme reme from |Mar 1- from |since from Station County Max.Min. High Low Mean avg. |Mar 14 avg. |Apr 1 avg ------------------------------------------------------|------------|------------ Corning Atchison 55 33 62 20 44 +7 | 0.61 -0.31| * * St. Joseph Buchanan 57 35 76 24 46 +7 | 1.35 +0.49| * * Brunswick Chariton 64 38 76 26 49 +9 | 1.23 +0.29| * * Albany Gentry 55 32 67 21 44 +6 | 0.64 -0.39| * * Auxvasse Audrain 66 39 80 26 51 +11 | 3.50 +2.37| * * Columbia Boone 66 40 78 26 52 +10 | 2.47 +1.28| * * Sanborn Field Boone 67 42 78 28 53 +11 | 1.99 +0.78| * * Novelty Knox 63 36 77 24 48 +9 | 1.67 +0.66| * * Linneus Linn 61 35 75 24 47 +9 | 2.59 +1.74| * * Monroe City Monroe 64 38 78 26 49 -8 | 2.15 +1.13| * * Versailles Morgan 68 42 82 27 54 +11 | 1.85 +0.61| * * Green Ridge Pettis 66 40 76 25 52 +12 | 1.66 +0.52| * * Lamar Barton 70 42 81 23 54 +10 | 1.07 -0.46| * * Cook Station Crawford 69 43 79 27 56 +12 | 3.60 +2.28| * * Alley Spring Shannon 69 40 80 27 56 +13 | 4.10 +2.74| * * Round Spring Shannon 69 41 81 28 55 +12 | 4.04 +2.68| * * Delta Cape | | Girardeau 66 45 76 33 58 +13 | 7.04 +5.56| * * Cardwell Dunklin 71 49 81 36 61 +14 | 2.36 +0.27| * * Clarkton Dunklin 70 48 79 33 60 +14 | 3.23 +1.70| * * Glennonville Dunklin 70 49 79 35 60 +14 | 3.02 +1.54| * * Charleston Mississippi 69 48 80 33 60 +15 | 3.77 +2.17| * * Portageville- | | Delta Center Pemiscot 70 50 81 35 61 +15 | 2.53 +0.69| * * Portageville- | | Lee Farm Pemiscot 71 50 82 37 62 +16 | 2.30 +0.46| * * Steele Pemiscot 72 50 81 36 62 +16 | 2.71 +0.62| * * -------------------------------------------------------------------------------- * Complete data not available for report ^Growing degree days are calculated by subtracting a 50 degree (Fahrenheit) base temperature from the average daily temperature. Thus, if the average temperature for the day is 75 degrees, then 25 growing degree days will have been accumulated. -------------------------------------------------------------------------------- Pat Guinan, Commercial Agriculture Program (573) 882-5908