Crop & Pest Report - All
Get Ready To Scout for Red Sunflower Seed Weevils
Red sunflower seed weevil (RSSW) adults will be emerging soon and will fly to the nearest flowering sunflowers. However, I have not received any field reports of adult weevils in sunflowers yet. So, please send me your reports of locality and numbers when you start finding them. Weevils are small (2.5 to 3.1 mm long) and reddish-orange. Peak emergence will occur later in early August this year. The 2013 National Sunflower Association Sunflower Survey indicated that 60% of field surveyed in North Dakota had RSSW damage with an average of 5.7% of the seeds damaged.
Scout for adult seed weevils on the early blooming sunflower fields when the yellow ray petals are just beginning to show. A NDSU YouTube video is available on Scouting for Red Sunflower Seed Weevil in Sunflowers. Counts should continue until the economic threshold level has been reached or most plants have reached 70% pollen shed. At 70% pollen shed, plants are no longer susceptible for egg laying or significant damage. When sampling, use the X pattern and begin counting at least 70 to 100 feet into the field to avoid field margin effects. Count the number of weevils on five plants at each site for a total of 25 plants. Assuming the field is at threshold, we recommend that treatment be considered when three out of 10 plants are just beginning to shed pollen.
If you need to spray flowering sunflowers, remember to PROTECT BEES by notifying bee keepers before an insecticides application and spraying in late evening. A NDSU YouTube video is available on Protect Bees from Pesticide Poisoning.
What is the Economic Threshold (E.T.) for RSSW in oilseed sunflowers in 2014?
Oilseed Sunflower: The E.T. can be calculated using the following formula:
Threshold (weevils per head) =
Cost of Insecticide Treatment
(Market Price x 21.5) x (0.000022 x Plant Population + 0.18)
Assuming a plant population of 20,000 per acre and a market price of 19 cents per lb., the E.T would be at 4-5 weevils per head if treatment costs were $8 to $10 per acre, respectively. Other examples of threshold calculation when the cost of insecticides is $8.00 and $10.00 per acre are listed in Tables 1 &2.
Banded Sunflower Moth and Sunflower Moth Trap Update
Sunflower moth continues to be trapped at low, sub-economic levels in the IPM scouts’ pheromone traps. Using the pheromone traps, an average of 28 moths per trap per week is considered economic. IPM scouts are detecting increasing numbers of banded sunflower moths in pheromone traps, especially in the more northern regions of North Dakota. Sunflower crop development is in the R1 to R3 crop stages in surveyed fields of North Dakota. Sunflower should be scouted for banded sunflower moth eggs or adult moths when most of the plants in the field are at plant stage R3 (distinct bud elongated ¾ inch above the nearest leaf, yellow ray petals not visible). See last week’s issue 12 of Crop & Pest Report July24, 2014 for more information.
The IPM Crop Scouts surveyed 92 soybean fields last week and soybean aphids were observed in only 9% of the fields surveyed. Soybean aphids continue to be detected at low densities ranging from 0 to 16 aphids per plant; however, incidence (% of plants infested in field) increased. The high was 86% incidence in three of the positive fields. Surveyed field were in the V5 to R3 (beginning pod) crop stages. With moderate temperatures (high 70sF to low 80sF), conditions are optimal for aphid reproduction and populations can double in only 3 days in the field. So, continue to scout for soybean aphids through the R5 (beginning seed) crop stage.
Beneficial insects that eat soybean aphids also have been increasing. Ladybeetles, syrphid fly larvae and lacewing larvae have been observed in fields infested with soybean aphids. Remember to avoid early insecticide applications, since insecticides kill beneficial predators and parasites.
Insect Control in Confection Sunflowers
Control of seed-infesting insect pests is important for confection sunflowers and dehulled oilseed sunflowers since they are grown under contract with very low tolerance levels of insect seed damage. This often requires at least one or two well-timed insecticide application depending on insect populations. Red sunflower seed weevils, banded sunflower moths and Lygus bugs are three major insect pests that impact the quality of confection sunflowers in North Dakota. Lygus bug, which causes kernel brown spot, is only a problem on confection and dehulled oilseed sunflowers. Adult Lygus bugs are about ¼ inch in length, and pale green, or brown with a distinctive triangular marking on its back. Nymphs are small, green, and move rapidly around plants when disturbed. The 2013 National Sunflower Association Sunflower Survey found that 46% of fields surveyed in North Dakota had brown spot with an average of 4.3% of the seeds damaged with brown spot. Lygus bugs have piercing-sucking mouthparts that inject saliva to digest the developing sunflower kernel and then suck the fluids into their stomach. This feeding injury causes the brown to black spot on the sunflower kernel resulting from tissue death at that feeding site, and causes an unpleasant taste.
The economic thresholds for these pests in confection sunflowers and dehulled oilseed sunflowers are:
Red sunflower seed weevil = 1 to 2 weevils per plant
Lygus bug = 1 Lygus bug (adult or nymph) per 9 heads
Banded sunflower moth = none, assume 1-2 insecticide sprays during flowering
Insecticide efficacy trials in confection sunflowers were conducted to evaluate the efficacy of different insecticides at three different timings (early = R5.1, late – 7 days after R5.1, and both timings) for control of the Lygus bug (Lygus species) and banded sunflower moth (Cochylis hospes) in North Dakota. Treatments included: esfenvalerate (pyrethroid, Asana 0.66 EC) at 8 fl oz/acre; zeta-cypermethrin (pyrethroid, Mustang Max 0.8 EC) at 2.8 fl oz/acre; and chlorpyrifos (organophosphate, Lorsban 4 EC) at 16 fl oz/acre. Results (Fig. 1) found that the best Lygus bug control was achieved using a dual application – early + late flowering. The pyrethroid group of insecticides had lower percentage of damaged seeds for Lygus bugs than the organophosphate group. For banded sunflower moth, all three insecticides provide adequate control at either the early application or the dual (early + late) application, but not the late application. The best time to treat confection sunflowers is once at early flowering and again 5 to 7 days later when insect pest populations are above thresholds. With this type of program, a 14 day window of protection should minimize seed damage from insect pests. Although there were significant yield differences, these differences were most likely caused by other factors, since insect pressures were generally low. [Note: Lygus bug is not listed on the Asana XL or Mustang Max 0.8 EC labels under sunflower. Mention of any products is not an endorsement by NDSU or the author.]
Consult the ND Field Crop Insect Management Guide 2014, E-1143, NDSU Extension Service, for a list of insecticides registered for sunflower insect control.
Weather/Crop Phenology Maps
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