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Associate Professor of Climatological Practices
Spotted Wing Drosophila Flying
Kathy Wiederholt of Carrington Research Extension Center trapped the invasive spotted wing Drosophila in cantaloupe from a compost pile in Carrington in Foster County on Monday, July 21st. A new fact sheet entitled E1715 IPM of the Spotted Wing Drosophila in North Dakota has been developed by NDSU Extension Service. The spotted wing Drosophila (SWD), Drosophila suzukii, is a small vinegar fly that was first confirmed in ND in 2013 as an invasive pest of fruits (raspberries, tart cherries, strawberries). The SWD lays its eggs in healthy, ripening fruits. Then, larvae hatch from eggs and feed on the fruit causing spoilage. Identification, life cycle, damage and pest management strategies of SWD are discussed. Additional insecticide information also is available on the extension entomology web page.
Sharpen Desiccation – MRL Update (As of July 2014)
BASF currently has an approved label for Sharpen herbicide as a harvest-aid / desiccation application for cotton, soybean, dry bean, field pea, lentil, chickpea, canola, safflower, and sunflower, however, the MRL's (Maximum Residue Levels) supporting the harvest-aid / desiccation uses have not been cleared for all countries. See the table below for an update on the MRL’s established in the various importing countries. The MRL's for Sharpen herbicide are currently approved for the US, Mexico, Japan, and Canada (except canola and safflower). However, Sharpen herbicide does not yet have MRL's approved in some crops for Korea, in the EU, and in Codex countries. Growers should confirm the MRL status with their local processor prior to making the Sharpen application. Refer to the NDDOA web site to determine if these uses are registered in ND. Refer to #4 on the back of the North Dakota Weed Guide.
In August 2014, BASF will submit another import tolerance petition to the EU to establish new MRL’s in peas, lentils and safflower to accommodate the harvest-aid / desiccation application for Sharpen. EU approval may take up to 2 years.
Extension Weed Specialist
Root Rot of Soybean Update: Rhizoctonia
Last week we wrote an article about the high levels of soybean root rots showing up in the region. Although multiple pathogens can cause root rots on soybeans, Rhizoctonia has been consistently showing up this year. Of 8 soybean root samples received in the diagnostic lab in the last two weeks, Rhizoctonia has been isolated from four of them. Similarly, many descriptions and close-up photos sent to us have been consistent with Rhizcotonia root rot: reddish lesions/cankers with distinct margins. We are not saying all the soybean root rots are caused by Rhizoctonia, but the pathogen is definitely a player this year. Plants were stressed this early summer by wet soils which favors fungal pathogens attacking the roots. Other pathogens such as Fusarium are likely also involved in the disease showing up in growers fields this year.
Rhizoctonia root rot is caused by the fungal pathogen Rhizoctonia solani. The pathogen has different ‘Anastomosis groups’ or ‘AG’, which are similar to a ‘race’ or ‘strain’. Common AG groups found on soybean in our area are AG4, AG5 and AG2-2 Depending on the AG, Rhizoctonia solani may also infect other crops, including; dry edible beans, corn and sugarbeets.
Rhizoctonia can infect, stunt and or kill seedlings, and can also damage older plants. Significant yield losses are possible when a high level of infection occurs early. Typical symptoms of Rhizoctonia root rot include sunken lesions near the soil line that are often rusty red/brown in color.
As is the case with all root rots, there are no management strategies available once the plants are up. However, if you have significant root rot damage, a fungicide seed treatment and lengthening your crop rotation may reduce the impact of Rhizoctonia root rot in the future.
For more information on Rhizoctonia root rot, visit the North Central Soybean Research Program website, click on soybean diseases, and select Rhizoctonia from the drop down menu. The site is a checkoff funded site, supported in part by North Dakota soybean growers and the North Dakota Soybean Council.
Extension Plant Pathologist
Scab (FHB) Update
During the past two weeks, I had the opportunity to visit several winter wheat production fields and winter wheat variety trials located on NDSU Extension and Research Centers. Most of the variety trials visited had noticeable levels of scab in them. However, in plots where an early flowering fungicide application was used, the incidence of scab was less. Similarly, the winter wheat production fields visited had low incidences of scab (5-10%) and most likely benefitted from an early-flowering fungicide application. Wheat and barley crops flowering during the last part of June into early July were at greatest risk for scab infection and scab symptoms (Figure 2) are most likely visible at this time.
Up until the recent rain events, the state experienced a stretch of weather conditions (dry, windy, and warm temperatures) that reduced the risk of scab development in flowering small grain crops. After the recent storm, the risk of scab has elevated for most of the state for very susceptible varieties that are flowering (Figure 3).
Extension Plant Pathology, Cereal Crops
Wheat Disease Update
The IPM survey scouts visited 124 wheat fields last week. Tan spot was detected in approximately 84% of the wheat fields (Figure 1). Other diseases detected in less frequency were bacterial leaf streak and Septoria. Spring wheat growth stages are quite variable across the state and the late planted fields should be monitored for the development of foliar diseases.
Extension Plant Pathologist, Broad-leaf Crops
We have observed many rust diseases in the last couple weeks, including; common corn rust (Figure 1), wheat leaf rust (Figure 2), wheat stripe rust, oat crown rust (Figure 3), sunflower rust, safflower rust and even rust on vetch. This article is written to help explain the rust diseases. Detailed information on specific rusts will be in future Crop and Pest Reports if rust diseases become a concern.
What is rust? Rusts are caused by a group of fungal pathogens with complex life cycles. Many have up to five different spores stages and can sexually recombine and also asexually (clonally) produce spores. In some cases, there is an ‘alternate host’ that is needed for sexual recombination (barberry for the wheat stem rust pathogen, buckthorn for oat crown rust pathogen) but in other cases that sexual recombination happens on the crop host (the sunflower rust and common bean rust pathogens). The sexual recombination phase and the abundance of clonal spores are the primary reasons that the rust pathogens are able to evolve new races and cause major epidemics when the environmental conditions are favorable.
What do rusts look like? The uredinia stage of the rust life cycle is the most common and most recognizable spore stage. For the field crop rust pathogens in North Dakota, the uredinia are small raised pustules full of dusty spores that can be rubbed off easily. The color of the pustules/spores will vary from yellow/orange to nearly black, but many are red-brown rusty colored. The black telia stage can be observed at the end of the season. Additional spore stages such as pycnia and aecia are found on the alternate host for the cereal rust pathogens. However, the dry edible bean and sunflower rust pathogens do not require an alternate host, and pycnia and aecia occur on their host crop. Typically, pycnia are raised colored bumps, while aecia are brightly colored clusters of ‘cups’.
What environmental conditions favor rust? Unlike many other fungal pathogens, rain is not necessary for infection. However, free moisture is necessary. Dew, fog and light rain all provide enough free moisture for infection to occur. Consequently, rust is often first observed near shelter belts; the shade provides a longer dew period. Similarly, it is rare to see some rusts before canopy closure because the leaves dry out quickly (common bean rust).
How do rusts spread? Rust spores are dispersed by wind. Some rust pathogens cannot survive winter in North Dakota and the disease is a result of spores dispersal from hundreds of miles away (leaf rust and stripe rust of wheat, common corn rust). Others overwinter well in North Dakota (for example, the pathogens that cause sunflower rust and common bean rust) and spores are locally dispersed.
Do rusts spread between crops? Rust pathogens are usually very specific to their host(s) or very closely related species. For example, the pathogen that causes sunflower rust (Puccinia helianthi) will only cause an infection on sunflowers and wild sunflowers, the pathogen that causes common bean rust (Uromyces appendiculatus) will only infect common bean, and the pathogen that causes leaf rust of wheat will not infect corn. Consequently, if you see rust in one crop, it will not spread to a different crop.
How can you manage rust? At this point in the season, fungicides are the only management tool available. Timing is critical, but in general, fungicides tend to be most efficacious when applied shortly after rust is observed on the upper leaves of a crop. Depending on the crop, management guidelines, forecasting models and/or action thresholds may be available.
For more information on important rust disease in North Dakota, please visit the following articles.
Extension Plant Pathologist, Broad-leaf Crops
Extension Plant Pathology, Cereal Crops
IPM Crop Scouts Detecting Downy Mildew in Sunflower
The IPM Crop Scouts have surveyed over 50 sunflower fields in the last two weeks and found downy mildew in approximately half of them. Twelve fields had incidence levels above 6%, four of which have levels in double digits. There are no management options for downy mildew at this time, but it is important to pay attention to downy mildew for management decisions in upcoming seasons. A more detailed assessment of downy mildew (including IPM crop scout data and plant pathology survey work) will be published in the Crop and Pest Report towards the end of the season.
Extension Plant Pathologist, Broad-leaf Crops
Cercospora Leaf Spot Alert
Cercospora leaf spot is the most devastating foliar disease of sugarbeet in Minnesota and North Dakota. The disease is caused by the fungal pathogen Cercospora beticola. The fungus overwinters in infected sugarbeet debris in the field. Cercospora leaf spot develops rapidly in warm, humid and wet (from rain or dew) conditions, typically after canopy closure. Day temperatures of 80-90°F and night temperatures above 60°F favor disease development. Day temperature above 93°F is unfavorable for disease development. Typical foliar symptoms are circular spots about 1/8 inch in diameter with ash gray centers and dark brown or reddish-purple borders. Under favorable conditions, the fungus may have 4 to 5 disease cycles during the season, and with each cycle there is a substantial increase in the amount of inoculum. As such, early control (at first symptoms) is necessary to effectively manage the fungus. Since the fungus damages the leaves, it reduces the photosynthetic capacity of plants and reduces yield; the disease also results in higher impurities in the juice which reduces sucrose extraction.
Research shows that application of effective fungicides at first symptoms with subsequent applications based on the presence of leaf spots and favorable environmental conditions (Daily Infection Values for two consecutive days of 7 or higher) consistently provided the most effective and economical control.
Sugarbeet fields with more susceptible varieties that closed rows the earliest and are close to shelter-belts, waterways, and those close to previously infected fields should be the first to be scouted since they would be the first to become infected.
Guidelines that will help in effective control of the disease include the following:
- The first fungicide application should be made when conditions first favor disease development or at first symptoms. If the first application is late, control will be difficult all season.
- Use the recommended rate when applying one fungicide to control Cercospora leaf spot - do not cut rates.
- Only one application of Topsin in combination with a protectant fungicide such as TPTH should be used during the season. When mixing fungicides, use at least ¾ of the labeled rate of each fungicide.
- The fungicides that were most effective in a rotation at the inoculated Foxhome, MN site in 2013, were Inspire/TPTH/Headline; Proline/TPTH/Headline; TPTH + Topsin followed by a triazole as the second application and Headline as the last application. Proline was always used with a non-ionic surfactant.
- Never use the same fungicide or fungicides with the same mode of action ‘back-to-back’.
- Avoid using fungicides of a particular class of chemistry as a stand-alone where there is known resistance to that chemistry.
- If using one fungicide application per year, do not use the same product year after year – resistance will develop.
Use of high spray pressure (100 psi) and high water volume of 15 to 20 gal/ac will result in better disease control.
Extension Sugarbeet Specialist; NDSU & U of MN
Soybean Root Nodules
With the right kind of Rhizobia bacteria, nodules may form on the soybean roots. With this symbiotic relationship between the bacteria and the soybean plant, nitrogen gas is fixed into a plant-available nitrogen form. Without the proper bacteria, the plant will not have nodules and the soybean plant will depend on soil-available nitrogen for its growth and development. Without the nodulation, the soybean plant may not be dark green and the yield may be lower than expected. Fields without a soybean history are the most likely fields to show the light green soybean plants. Even if the seed was inoculated with the right bacteria it does not guarantee that nodules will develop. If adverse conditions occurred between the time of inoculation and planting (for instance long storage of the inoculated seed under warm conditions) the bacteria may not have been viable. There can also be field conditions after seeding which inhibit nodulation, for instance saturated soils or very dry soils conditions. It is possible to have nodulation in certain parts of the field and not in the stressed areas. Dig up some plants which appear light green, with a spade (pulling them out may dislodge nodules) and wash the roots in a bucket of water. Observe if the plant has root nodules. Cut a few nodules open and look at the color. Pinkish inside color of the nodules indicates healthy nodules. If no root nodules are found in an area of the field make sure fresh soybean inoculant is used whenever soybeans are planted again in the same field.
Extension Agronomist Broadleaf Crops