Crop & Pest Report - All
Insecticide Control of Sunflower Head Insects
I’ve updated this article on timing of insecticide application for management of sunflower head insects from an old issue of the 2013 Crop & Pest Report. Chemical treatment is directed at the larval stage of the banded sunflower moth (BSM) and sunflower moth, which is the actual damaging stage. But, insecticides should be targeted at the adult red sunflower seed weevils to prevent egg laying.
Once the decision to treat has been made, it is critical to time the spray application correctly to get effective management of sunflower head insects. The best sunflower plant stage to treat is usually the R5.1 growth stage, or when pollen shed is just beginning on the outer rim of the sunflower head. This is the time when most BSM eggs have hatched. Eggs hatch into larvae in about 5-8 days, and larvae mature through 5 growth stages in about 2 weeks. Young larvae feed on the bracts, pollen and disk flower for the first half of its development before tunneling into the seed.
Larvae can be found on sunflower heads from mid-July through mid-September. So, insecticide treatments need to be timed before 12-15 days after BSM egg hatch depending on temperatures. At this time, BSM larvae are beginning to feed on the disk flowers and are exposed on the head, and are susceptible to the insecticide treatment. For RSSW, adult weevils are feeding on pollen and laying eggs into the developing seed at this time (early flowering).
On older flowering plants (after R5.7) where the seeds have started developing, larvae of BSM and RSSW will be feeding inside the seeds and will be protected from the insecticide. By then, much of the feeding damage has already occurred. Application at an earlier growth stage is rarely justified (before flowering), but may be warranted if monitoring reveals earlier than normal egg-laying activity of banded sunflower moth or the presence of numerous RSSW adults in heads.
The banded sunflower moth, red sunflower seed weevil and the lygus bug have all impacted quality of confection sunflowers in past seasons. It is recommended that sunflowers grown for these markets be treated a minimum of two times, once at early flowering and again 5 to 7 days later. With this type of program, a window of protection should be provided to minimize impact from all three of these seed-damaging insect pests.
Please see the 2015 ND Field Crop Insect Management Guide for insecticides registered in sunflower.
If you need to spray flowering sunflowers, remember to PROTECT BEES by notifying bee keepers before an insecticide application and spraying in late evening. A NDSU YouTube video is available on Protect Bees from Pesticide Poisoning.
Always read, follow, and understand the label in regards to pollinator protection.
Red Sunflower Seed Weevil Threshold for 2015
Red sunflower seed weevil (RSSW) adults are emerging now and will fly to the nearest flowering sunflowers. The USDA NASS reports that 25% of the sunflowers were blooming in North Dakota (USDA NASS News Release – July 27, 2015). I have received one field report of adult weevils near Dickinson in SW, ND. Please send me your reports of locality and numbers if you find them. Weevils are small (2.5 to 3.1 mm long) and reddish-orange.
Scout for adult seed weevils in 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.
For RSSW, insecticide treatment is directed at the adult stage. The 2015 economic threshold for RSSW is calculated at 4-5 weevils per head for oilseed sunflowers and only 1 weevil per head for confection sunflowers. Please see Tables 1 and 2 (next page) for details on RSSW thresholds based on market price and plant populations at $8 or $10 insecticide cost per acre.
Sunflower Insect Traps
Pheromone traps run by the IPM Survey scouts showed high numbers of banded sunflower moths located in southwest and central North Dakota and increasing numbers of sunflower moths in north central and northeast North Dakota (see maps).
Soybean Aphids - IPM Scouting Update
Eighty-eight fields were scouted by the IPM Scouts for soybean aphids last week. The IPM scouts in North Dakota and Minnesota found soybean aphids in 60% of the soybean fields surveyed. Percentage of plants infested with soybean aphids ranged from 0 to 100% with an average of 43% of plants infested. The average number of soybean aphids per plant ranged from 1 to 225, and has not increased much from last week’s scouting report. It looks like the severe thunderstorms have had a negative impact on soybean aphid populations in some areas. For example, soybean aphids in our research plot at Casselton decreased after last Thursday’s night thunderstorm and is below the E.T. Scouting is important all the way through the R5 (beginning seed). At the R6( full seed) and later stages, research trials throughout the north central states have not demonstrated a yield benefit to treating soybeans for soybean aphid. The USDA NASS reports that 86% of the soybeans were blooming (R1), and 51% setting pods in North Dakota (USDA NASS News Release – July 27, 2015).
Good Bug Corner-Monarch Butterfly
This week’s Good Bug Corner featured insects are the Monarch butterfly in the insect family Nymphalidae. These beautiful butterflies are important pollinators, and well known for their 6,000 miles roundtrip migration from their overwintering home in Mexico to summer homes in North America. The butterfly feeds on nectar from flowers while the caterpillar feeds exclusively on the milkweed plant. Populations of the Monarch butterfly have significantly decline over the past years, and 2013-2014 recorded the lowest number of Monarch butterflies ever observed during migration. Some of the threats to the Monarch butterfly are: habitat destruction of overwintering and resting sites, such as urban sprawl reducing crucial habitat of flowering fields; pesticides including insecticides that are used to control field crop insects and herbicides that kill milkweed and other wild flowering plant species; and adverse climate conditions which impact its development and survival. There is a nationwide effort to protect and increase populations of the Monarch butterfly and other pollinators through enhancing or restoring 7 million acres of land for pollinator over the next 5 years. Planting a butterfly garden is a good way to help conserve the Monarch butterfly. See the NDSU Extension fact sheet on Butterfly Gardening.
Soybean Aphids - Scouting Critical
Some “hotspots” soybean fields are at economic threshold (E.T. = average of 250 aphids per plant, 80% of the plants infested, and increasing populations) and will be or have been sprayed with insecticide for soybean aphid control. These fields are located near the Red River Valley area (see maps). We also are just starting to see soybean aphids in other outlier areas – Pembina and Rolette in NE, and Wells and Benson Counties in Central North Dakota. Ninety three fields were scouted by the IPM Scouts for soybean aphids last week. The IPM scouts in North Dakota and Minnesota found soybean aphids in 55% of the soybean fields surveyed. Percentage of plants infested with soybean aphids ranged from 0 to 100% with an average of 51% of plants infested, an increase from last week’s average of 39%. The average number of soybean aphids per plant ranged from 1 to 225. Our high count last week was only an average of 67 aphids per plant, so aphid populations are increasing. We are and will continue to get migratory winged aphids from neighboring states through the fall, so scouting is the best way to find and identify any fields above E.T. Scouting also is very important as the soybeans are in the susceptible reproductive stages. The USDA NASS reports that 71% of the soybeans were blooming (R1), and 23% setting pods in North Dakota (USDA NASS News Release – July 20, 2015).
The next 7 days will remind everyone that late July is climatologically the warmest period of the year. Much of the rest of this month will be dominated by an upper-level wind flow sometimes referenced as an “Omega” (Ω) pattern. There will be a trough (dip) in the jetstream along both the west and east coasts of the United States. That will create a ridge of high pressure in the Great Plains from Texas to Canada. If you examine Figure 1 you can somewhat imagine the jetstream looking like the greek letter Omega.
This shift from periodic days of cooler air over the past week to consistently warm and humid weather started yesterday (Wednesday) and is expected to continue through at least Monday. The upper-level wind will be from the west or southwest, but the near surface flow will frequently be from the south advecting Gulf of Mexico moisture into the region, meaning humid conditions are expected through early next week with above average temperatures. This will bring bountiful growing degree units to the area, but also have the potential to add disease risk with high relative humidity levels on several occasions. That will be particularly true in the eastern part of North Dakota into northwestern Minnesota.
With dew points at least in the 60s with some periods perhaps even as high as the lower 70s, any thunderstorms that do develop would have the potential to drop heavy rainfall in localized areas. There appears to be two time frames for thunderstorm development during this forecast period. One will be later today (Thursday) into Friday morning, and again early next week (later Monday into Tuesday). Although specifics for early next week are lacking, the storms that do develop today into tonight will probably have some localized severe weather potential as well as that risk for heavy downpours. The thunderstorms early next week will be associated with a brief cooling period that is expected to last only one or two days.
Projected Growing Degree Days (GDDs), base 34°, 44° and 50° for the period July 23 through July 29, 2015 are presented in Figure 2 and the number of hours expected to be at or above 85% can be found in Figure 3.
Assistant State Climatologist/Meteorologist
(701-231-8209) Twitter: @darylritchison
Crops overall are looking great. Rainfall has slowed down with most NDAWN stations in the region reporting between 0.2 and 0.5 inches of rain over the past week. Some disease is present across the region with downy mildew in sunflower and multiple diseases including tan spot, Fusarium head blight, and ergot being reported in wheat. Corn in the area is looking relatively good, especially with recent temperatures in the upper 80s.
There have been reports of crop injury from improper sprayer cleanout. Be sure to clean nozzles, screens and filters, more information on proper cleanout can be found in the NDSU weed control guide on page 70 section A8.
Area Extension Specialist/Cropping Systems
Scab is showing up in the wheat and barley fields in our region. Much of the stripe rust has gone into the black teliospore stage; however at the LREC, we still have some yellow-orange pustules present in our small grains. Also, a few leaf rust pustules can be found sporadically on these plants. Stripe rust causes the flag leaf to dry -own rapidly (see photo).
Corn growth has been excellent in last few weeks. Corn is starting to tassel in the southern and valley parts of my region. Meanwhile, we have water-affected soybean fields which can be found in high rainfall areas. These fields look chlorotic and are developing slowly. Outside these areas, we have a lush late-July soybean crop coming along.
We finished up our on-station and off-station field days on Tuesday. Thanks for all the support for our research and extension programs!
Area Extension Specialist/Agronomy