- Additional Plants: native plants
- Pest Management: chemical control, economic threshold, field monitoring/scouting, integrated pest management
Stock Seed Farm has been producing seed from warm season native grasses for 48 years. It is a family operation that grows 34 different varieties of grasses and wildflowers on 1500 acres. Stock Seed Farms is recognized as a leader in production and marketing of native plant material throughout the United States. It has been responsible for the introduction of several grasses and wildflowers into the commercial market. Seed producers throughout the Midwest follow the production practices developed by Stock Seed Farms.
PROJECT DESCRIPTION AND RESULTS
Seed of Big Bluestem, a native prairie grass, is in demand for use as pastures conservation and erosion control, Conservation Reserve Program, wildlife habitat and roadside seedings. The cost of these seeds is generally high because of insufficient supply caused by poor seed yields and poor quality seed.
It had been suspected for many years that the poor seed yields and poor quality might be due to damage inflected during the pollination and seed formation by a minute fly maggot. Dr. Ray Gagne of the National Museum Washington D.C. has identified this multiple generation midge as Stendiplosis wattsii Gagne or Bluestem Midge. In our initial studies, we observed seed yield reduction of 50% in 2001 and 75% in 2002.
Also present in the fields of Big Bluestem are numerous species of beneficial and innocuous insects. Most of these have never been identified, named or studied.
The economic questions that need answers are whether the midge can be reduced as a problem without severely harming the natural fauna. Secondly, will control of the midge give us increased seed production. Thirdly, will the increase in seed production justify the increase cost of control and in the end, will this give us a more economical supply of high quality seed.
To answer the economic questions, we felt that we needed to find a safe economic insecticide that could be applied once to give adequate control for increase seed yield. We selected a pyrethroid insecticide called Warrior, made by Syngenta. Warrior was chosen because it is labeled for midge control in other crops, its low impact on the environment, it is safe to apply, has some residual control and it is available. Syngenta was also willing to provide product at no cost for testing. The next question we need answered is “When is the best time to apply the Warrior to give us the best control of the Bluestem Midge.”
The project team consisted of five members:
- David Stock, President, Stock Seed Farms, Project leader
- Earle Raun, PhD, Pest Management Co., Entomologist for the project
- Rod Fritz, General Manager, Stock Seed Farms, Assisted in management of project
- Mike Fritz, Field Technician, Stock Seed Farms, Assisted Dr. Raun in collection and interpretation of data
- Jim Rice, Production Manager, Stock Seed Farms, Field trials
The goals of the project were to determine the life cycle of the generations of the Bluestem Midge including the (a) emergence of the over wintering (diapause) generation, (b) the number of generations during the summer, (c) being to establish their relationship to flowering of the Bluestem grass in order to (d) time insecticide application(s). Measure the effect of the spray on the other fauna in the treated plots. And determine what improvement in seed production resulted from controlling the Midge with a one spray program.
Cone traps were built and placed in Bluestem fields. Each week a clear plastic sheet, coated with tangle foot was placed in the collection jar on the top of the trap. Midges emerging from their over wintering sites thus would be caught. The tangle foot sheets were taken into the laboratory once a week. The trapped insects were examined under a microscope and their numbers recorded (table 1).
As Bluestem seed heads began to form, twenty of these were randomly collected each week to form a bouquet. Each bouquet was covered with a clear plastic bag and observed twice daily for emergence of insects. When insects were seen they were immobilized by placing the entire bouquet in refrigeration for about 5 minutes. Using a small camel’s hair brush, the insects were then removed into alcohol in a watch glass. Under magnification the insects could be identified and sorted into vials of alcohols, counted and the numbers recorded. Table 2 provides the number of midges emerging on a weekly basis.
To attempt control measures, 3 oz of warrior insecticide in 25 gallons of water were applied to one acre plots, using a ground applicator. In order to determine the most efficacious timing, plots received one treatment each at approximately weekly intervals, determined by weather conditions.
To measure the results of insecticide treatment, random collections of about one quart of seed heads were made from each quadrant of each 1 acre treated plot and its companion untreated plots. These collections, made at harvest time, were taken to the laboratory where florets were examined microscopically. Included in table 3 are the number of florets examined for each plot and treatment dates, as well as the fate of each floret. Damages to seeds in that category could not be separated. Some were obviously diseased, some fed on by insects, and some the result of dry weather or other causes.
These studies have resulted in tentative conclusions as follows:
1) In East Central Nebraska the Bluestem Midge, Stenodiplosis wattsii Gagne, breaks diapauses in mid to late June. Midge flies mate and oviposit on the first florets of the warm season grass species. Maggots hatching from the eggs feed in developing seed of these grasses. They pupate and emerge as adult flies in 14 to 16 days. Generations continue, with the 4th generation of females laying eggs, which hatch into the over wintering (diapauses) generation.
2) Pollination of Big Bluestem began about the 15th of July, peaked the 4th of August, and was essentially over by the 20th of August. One application of Warrior insecticide was most effective at the mid-August applications during both 2002 and 2003, with 66% and 55% good seed respectively. This compares with 25% and 32% good seed in untreated plots, an improvement of approximately 250% and 170% in those two years.
3) Sticky boards placed in both treated and untreated plots two days after the chemical treatment were left in place for a week. They were then examined under the microscope for numbers of insects caught in the Tanglefoot. There were only minor differences in the number of trapped insects between the treated and untreated plots indicating little effect of the chemical on most fauna in the field.
Table 1. Adult Midges Emerging from Diapause Traps on a Weekly Basis in 2003
Date, Males, Females, Total
6/17, 0, 0, 0
6/24, 124, 30, 154
7/1, 41, 21, 62
7/8, 57, 27, 84
7/15, 14, 4, 18
Table 2. Summer Generation Midge Adults Emerging from 20 Bagged Bluestem Seed Panicles Weekly in 2003
Date, Males, Females, Total
7/15-21, 0, 0, 0
7/22-28, 11, 2, 13
7/29-8/4, 1, 4, 5
8/5-11, 5, 16, 21
8/19-25, 3, 11, 14
8/26-9/1, 27, 40, 67
9/2-8, 10, 22, 32
9/9-15, 1, 7, 8
9/16-21, 1, 1, 2
Table 3. Effect of Timing of Single Applications of Warrior Insecticide on Seed Production in Big Bluestem Grass to Control the Seed Midge.
Treatment date, Florets examined, Damaged seed (%), Good seed (%)
None, 393, 75.3, 24.7
8/2, 427, 36.7, 63.3
8/9, 447, 34.2, 65.7
8/20, 482, 51.0, 49.0
9/5, 451, 63.1, 35.3
None, 433, 67.2, 32.7
8/5, 516, 55.4, 44.6
8/13, 517, 50.5, 49.5
8/20, 533, 45.9, 55.2
8/29, 570, 69.5, 30.5
Dr. Ray Gagne, National Museum, Washington DC. Provided positive identification of the insect problem.
Dr. Bret Ratcliffe, University of Nebraska Museum, Lincoln, NE. Placed specimens collected into reference collection for future use.
Dr. Rob Mitchell, University of Nebraska, Department of Agronomy, Lincoln, NE. provided field consultation regarding crop growth stages.
Robert Kacvinsky, representative, Syngenta Chemical Co., Lincoln, NE. Provided insecticide for tests.
The data has given us the information we need to determine the life cycle of the Bluestem Midge. This data would indicate that an application of insecticide would need to be applied from the first of August to the 15th of August for best control. It has also given us confidence that we are not having a large impact on the natural fauna in the treatment area.
We are not satisfied with using a calendar date to determine treatment. The data from the last two years could have been influenced by the drought. Would a normal year or a wet year change the dates for best treatment? Research needs to be done that will determine the time of treatment based on plant growth stage. We have already started that work. Dr. Rob Mitchell, USDA-ARS, has been helpful in educating us in determining the different plant growth stages of Big Bluestem. Once we are familiar with that, then another series of tests should be done based on plant growth stage.
The yield increase would indicate that it is economical to make at least one treatment. At an estimated application cost of $20.00 per acre, and an increase in seed yield of 50 pounds per acre, one could expect a $100 return for a $20 investment.
We have several obstacles before this could be a recommended practice. The first is that this has not been tested on a large scale. We feel that large scale testing is the next step to determine if we can duplicate the same results. The second problem and the biggest is the lack of labeling for use on warm season native grasses. An application for IR-4 has been made and there is interest by the regional EPA committee for permission but a timetable for review has not been set.
As we become more familiar with the bluestem midge, we would hope there might be opportunities for control by change in cultural practices or biological control.
Entomologists from Iowa, Missouri, Kansas and Nebraska visited the project as it was being started, in the fall of 2002.
Two Doctoral students, one from France and from Florida visited the project in the summer of 2003.
Presentation will be given at the Nebraska Seed Improvement Conference on January 27, 2004 in Kearney Nebraska. This is the annual conference of the members of the Nebraska Crop Improvement Association (NCIA) and the Nebraska Seed Trade Association (NSTA).