April 16, 2014 in Soybean Disease Management
The 2014 small grains fungicide efficacy ratings are now available. To access, click on the following link:
Fungicide use is common in small grains and can be a useful tool to protect yields from yield robbing diseases under the appropriate conditions. In Del-Ma, our most common yield impacting diseases include powdery mildew, leaf blotch complex (Septoria and Stagonospora leaf blotch), tan spot, and rusts. Often, fungicides applied to a susceptible variety when diseases approach the flag leaf will give you the most consistent yield protection. This is because the flag leaf provides the lions share of carbohydrates for grain fill. Recommended timings for protection of the flag leaf is between Feekes 8 and 10.
In times where wheat prices remain high, many people are experimenting with split fungicide applications. In these programs a fungicide is applied around green-up or jointing with an herbicide, and often a cheap triazole is used. This early application is then followed by a second fungicide application at the Feekes 8-10 timing. Others may apply a more expensive fungicide at a reduced rate (for example, 3 oz when 6 oz is the lowest labeled rate) and come back with a full rate fungicide application later in the season. The idea behind the early treatments is to keep the developing plant clean until the flag leaf emerges, thereby increasing yield potential. Remember that fungicides give you roughly 14 days of full protection and another 7 days of partial protection, so green-up or jointing applications will not protect the plant from late season diseases. Additional drawbacks include the additional cost of the fungicide and the additional exposure of the pathogen population to a particular fungicide mode of action. Increased exposure to a particular mode of action increases the risk of resistance development in some fungal pathogens. The use of reduced fungicide rates (below label rate) further increases resistance risk. Powdery mildew is a great example of a pathogen that can easily develop fungicide resistance.
Split applications such as those described have proven useful in some states, particularly in areas where spring wheat is planted or where foliar diseases come in hard and early in the season. However, in many situations early applications may not be needed. Often, foliar diseases in Del-Ma do not arrive until later in the season. Thus, a single spray at Feekes 8-10 may be all that is needed in many disease favorable growing seasons. The exception is powdery mildew, which has caused significant levels of disease on susceptible varieties in disease favorable years. If you know your variety has a chink in its powdery mildew armor, then an early season application may provide some benefit.
There is no easy answer with fungicide use in Del-Ma wheat. The impact of a disease on yield is dependent on the variety, the environment, and the pathogen. The best way to make informed spray decisions is to know your variety, pay attention to the weather, and scout your fields. If you have the time I suggest scouting your small grains every 1-2 weeks to help you determine if or when a fungicide should be used on your fields.
Many growers are interested in learning more about GMO’s. GMO Answers is a platform that can be used to access information on this topic. The “Ask a Question” feature allows you to pose your questions and concerns about GMO’s and have them answered by someone with a background in the field.
Click the following link to visit the site:
The following information comes from the site, and pertains to where support is generated:
“GMO Answers is funded by the members of The Council for Biotechnology Information, which includes BASF, Bayer CropScience, Dow AgroSciences, DuPont, Monsanto Company and Syngenta. Our members are dedicated to the responsible development and application of plant biotechnology.
Supporting partners are organizations, companies and others who are committed to the five core principles of GMO Answers and have added their support to this initiative. To date those partners include The American Farm Bureau Federation, American Seed Trade Association, American Soybean Association, National Association of Wheat Growers, National Corn Growers Association, National Cotton Council, South Dakota Agri-Business Association”
Soybean Cyst Nematode (SCN) is considered the most significant yield-limiting pest of soybeans in the United States. Often the effects of this organism go unnoticed and growers may not realize how much yield they are losing due to this nematode. SCN is a sneaky little devil.
Unfortunately our tools for managing plant parasitic nematodes are limited due to a dearth of effective new products. Rotations to non-hosts can help reduce populations and seed treatments might provide benefit in some cases. However, resistance to SCN is still the best, most effective, and most economical means to minimize the effects of SCN on soybean.
Greg Tylka, a nematologist at Iowa State, is one of the foremost experts on SCN. He recently published a report of his most recent screening results. The take home message? Although the results were variable as a result of environment, amount of SCN, and SCN HG-Type (think of this as the nematode team affecting a field), the use of SCN resistant varieties increased yields 5-50% over susceptible varieties. Nematode reproduction was also greatly reduced in resistant varieties in comparison to susceptible varieties. These data support what we already know in Delaware-plant SCN resistant varieties to maximize yields and profits. Resistant varieties are currently our best tool for SCN management and should continue to be used in SCN infested fields.
Reference: Tylka, G. (2014). Trial Results Show Dual Benefits of SCN Resistance. Integrated Crop Management News. Paper 9.
Take a minute to catch the new videos on soybean rust management and updates by following this link:
Although soybean rust has not had the devastating impact initially predicted, it still remains a viable threat to soybean production. One of the major successes of plant pathology was the response to this emerging threat. The collaborative effort between plant pathologists across states was and is a reason that the impact of this disease thusfar has been marginal. SBR has never impacted us in the Midatlantic. I expect someday we will see it, so it is important to stay up to date with the most recent information on disease management.
Rusts are fungal pathogens with complex life cycles. After infecting a susceptible host, a rust pathogen produces a organ that functions as a straw, draining the plant of carbon and other vital nutrients. This is different from other fungal pathogens such as Fusarium, which can survive on decaying residue and produce toxins that kill plant tissues. Rusts produce fluffy orange to red colored pustules on leaves, each of which can produce thousands of small spores capable of traveling great distances on air currents. When rusts reach plants at critical stages of growth, significant reductions in yield can occur.
In wheat we see leaf, stem, and stripe rusts (above). In corn we see common rust and occasionally southern rust. In soybean the concern is obviously soybean rust, which has yet to impact soybean production in DelMar. These pathogens require living hosts to survive and reproduce. Thus, they do not overwinter in DelMar and instead blow in from southern regions. The cold temperatures we have experienced this winter are not unique to DelMar and have extended into the south. This is likely to have pushed the rusts further away from DelMar, which may impact their ability to spread northward in significant amounts during the field season. At least, that would be the standard assumption.
Despite the colder than usual temperatures, researchers in the south have found that surprisingly, some rusts are still hanging on. For example, in Louisiana, which has experienced temperatures in the teens with heavy rains, researchers have been actively shouting for soybean rust. They have found pustules of the fungus on old, deteriorating kudzu leaves. At first glance, the spores appeared to be dead, but further tests revealed that between 5-40% of these spores were still viable. This just goes to show that we always need to be vigilant when it comes to plant diseases. Plant pathogens are tricky, and not nearly as straightforward as many believe them to be.
Scouting fields for plant diseases is a simple way to maximize profits and yields over time. Scouting allows growers to assess stand losses early and replant as needed, determine what diseases are active and their potential to damage the crop at key growth stages, obtain historical data on common disease issues in fields, determine if fields require an early harvest, make timely fungicide applications or avoid applying fungicides unnecessarily. The following are some techniques to scout small grains for diseases and some common diseases that you may see in your fields.
To scout small grains first estimate the size of your field. A good rule of thumb I use is to scout 1-2 sites per acre of field. Ensure that each site you choose in a field is chosen AT RANDOM, that is, without bias. A protocol for randomly choosing sites in a field can be found by following this link: http://www2.ca.uky.edu/entomology/entfacts/entfactpdf/ef113.pdf. At each site you will scout a circular area 10-15 feet in diameter. Within each circular area note any issues with stand, health, etc. Select 25-50 plants at each site and assess for disease. A 10x hand lens is often required to visualize signs (the pathogen, its parts, or products) of most plant disease causing agents. The entire plant should be assessed. Fields should be scouted approximately every 2 weeks until harvest and perhaps more if the weather is wet and humid.
Diseases that may start to develop or show symptoms early (jointing and later) include viruses, powdery mildew, leaf blotches, and root rots.
Diseases that tend to show up around flag leaf include rusts and the occasional smut
Diseases that tend to occur around flowering include Fusarium head blight, Stagonospora glume blotch, and eyespot.
Keep in mind that many plant diseases cannot be positively identified without the help of a plant diagnostic lab. Improperly diagnosed diseases can result in severe crop losses or unnecessary pesticide applications. If you have diseased plants and need help with disease identification send samples (placed in plastic bags with a piece of moist paper towel) to the University of Delaware Plant Diagnostic Clinic located at Townsend hall in Newark, Delaware. Your local county agent can assist you in submitting samples to the clinic.
Scouting takes time and effort, as well as attention to detail. However, this effort pays in the long run with increased yields and profit.
How much yield loss can result from diseases in corn? A new publication is available that summarizes data from the United States and Canada in 2012. The publication is a result of a group extension effort between several plant pathologists in the USA and Canada. Click on the link below to access the article:
Soybean cyst nematode (SCN) is a major pest of soybeans and other legumes. This pest has been an issue for Delaware growers for many years and continues to spread to other regions. Figure 1 shows the most recent SCN distribution map for the United States. Compare this with the distribution in 2008 (Figure 2). This map was constructed by the SCN working group.
aFigure 1. SCN distribution as of January 2014.
We have experienced exceptionally cold temperatures in Delaware this Winter. The main issue most growers are concerned with at this point is the impact on wheat or barley stands, particularly in late planted fields. What about the impacts of these temperatures on field crop diseases?
It is difficult to say for certain what impact these temperatures will have on field crop diseases. However, I speculate that it likely will negatively impact several pathogens that we saw during the rainy 2013 growing season, especially those that prefer warmer temperatures. In particular, the deep cold throughout the region will likely push the rusts further south, which may impact when initial infections occur on our crops. Frogeye leaf spot, which prefers warmer temperatures may also be negatively impacted. The cold temperatures may also impact overwintering potential of late blight in potatoes that may originate from cull piles or weeds. This does not mean that we will not have issues with these diseases in 2014, but the primary inoculum for some pathogens may be negatively affected.