An outside view of a flour mill

Flour Mill

Facility Type: Hal Ross Wheat Flour Mill

Location: Kansas State University (KSU), Manhattan, KS

Objective: Comparison of efficacy and levels of sanitation on application of Heat, Sulfuryl Flouride (SF) and Methyl Bromide (MB) to control Stored Product Insects (SPIs) in three separate applications over two years (2009-10)

Equipment Used: Direct-fired, make-up air gas heaters using Propane as fuel, industrial strength fans for airflow management, high temperature fabric ductwork and real-time wireless temperature monitoring system to monitor and manipulate temperatures for effective disinfestation.

Heater models used: (2) THP-4500 (4.5 Million BTUs/hr, MBTUs/hr), (1) THP-1400 (1.4.MBTUs/hr)

Process: The Hal Ross flour mill on the KSU campus in Manhattan, KS was heat treated and chemically fumigated (Methyl Bromide and Sulfuryl Flouride) on three occasions (2009-10) with stated objectives. In order to gauge the effectiveness of MB, SF, and heat, a bioassay box with 12 compartments was used.

Eggs, young larvae, old larvae, pupae, and adults of the red flour beetle, along with a temperature sensor, were placed into separate compartments in the bioassay box. In these boxes, two levels of sanitation were simulated: dusting of flour (good sanitation) and 2-cm-deep flour (poor sanitation). Each compartment held 50 individual beetles at a particular life stage.  Boxes were placed in 25 locations in the mill across all five floors. Eleven boxes were placed on the floor, while the remaining 14 were placed inside different pieces of equipment.

Forced air, direct fired heaters were used for heat treatment of the mill. Positive pressurization of heated space eliminated the need for sealing the facility unlike chemical fumigation. An array of high temperature duct was laid out on the basis of layout of individual floors for effective heat distribution. Industrial strength fans were positioned on all levels of the mill for effective air-flow management and to minimize the occurrence of hot or cold spots.

Since the study involved comparison with SF and MB, the duration of heat treatment was restricted to 24 hours. The twenty four hour duration included the time to reach minimum temperatures (122°F) lethal to SPIs and this time ranged from 11 hours (first treatment) to 8 hours (third treatment).

Summary of Outcome:

Mortality of eggs was <100% with all three treatments; however, differences in egg mortality among the three pest management treatments were not significant. The only significant difference among treatments was evident with adults, large larvae, and small larvae, in compartments filled with 2 cm deep flour (poor sanitation). The lower mortality at from 90 to 96% in poor sanitation (2 cm deep flour) simulations point out the importance of cleaning the facility so that the flour does not act as an insulator resulting in survival of life stages of insects.

All three treatments performed well against red flour beetle life stages. With SF, egg survival was evident in a majority of the compartments with dusting and 2 cm deep flour for the very first treatment, because the mill temperatures were below 27 degrees C (80 degrees F).  The survival observed with heat treatment for all stages was primarily on the first floor of the Hal Ross floor mill. The first flour has large covered roll stands (product zones), which retarded air movement, and this lack of proper air circulation resulted in less than 100% mortality for all stages.

Like SF, with heat, the very first treatment was less effective than the subsequent two treatments. For the second and third heat treatments, the hatch on the roof was opened, and this permitted satisfactory air movement and improved insect kill. Although MB was the most effective of the three treatments against all life stages of the red flour beetle, results suggest that heat is a viable MB alternative for the future.

Acknowledgements: We thank the Grain Science & Industry Department, Kansas State University, Manhattan, KS for the research collaboration & Dr. Subramanyam Bhadriraju for leading this project. This research project that was supported by funds from EPA-Region VII and by the Propane Research and Education Council, Washington, D. C. We are also grateful to USDA, Agricultural Research Service, Center for Grain and Animal Health Research, Manhattan, KS for scientific evaluation and assessment of indirect efficacy of heat.

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