If you plan to ship plants outside of the Federal Fire Ant Quarantine, you must comply with Federal regulations (7 CRF §301.81-11 (2010)). Compliance involves the exclusion of fire ants by treating the growing media with an approved insecticide. This is outlined in detail in the Fire Ant: Quarantine Treatments for Nursery Stock, Grass Sod and Related Materials. (There are special provisions for greenhouse-grown products and fruiting containerized crops.) Most growers choose to utilize the incorporation of bifenthrin into the potting mix. For adequate control and compliance, the proper amount of bifenthrin must be used. Certification periods correlate to specific rates, ranging from 6 months to a continuous certification using from 10 ppm to 25 ppm, depending on the desired certification period (Table 1). The rate will change based on the bulk density of the potting mix (Table 2). What is the bulk density? Bulk density is simply the weight of a known volume of a material. For our purposes, we can think of that as how much your bark mix weighs dry in pounds per cubic yard.
Follow these steps to determine bulk density using our ounces over fluid ounces method.
- Collect a representative sample and mix it with 3 to 5 other samples from different areas around the bark pile. This is a composite sample.
- Pull a 32 fl. oz. sample (Figure 1) from the composite sample, then weigh and record the weight in ounces. (Figure 2).
- Oven dry on low heat or air dry. Periodically weigh the sample and keep drying until the sample stops losing weight. It will dry quicker if you spread it out on a baking sheet (Figure 3). When the sample weight stabilizes, record the weight in ounces. This is the dry weight.
- Take the dry weight, and divide by the original volume (32 fl. oz.). Now you have oz./fl. oz. Multiply that number by 1615.8 to get pounds per cubic yard. This is your bulk density. Your bulk density should be between 300 and 500 lbs. per cubic yard.
- Now, look at your bifenthrin product label. Match the bulk density to the desired concentration to provide you with the pounds of product to add per cubic yard of mix.
* Remember that ounces (oz.) is a weight and fluid ounces (fl. oz.) is a volume.
Here’s an example. About 3 quarts of bark was dried in a flat pan with a fan over for several days. The bark was turned over several times a day to speed drying. A known volume was established by pouring 80 fl. oz. of water into a bowl and marking the water line. The empty bowl was weighed (5 oz.) and bark filled to the marked water line. The combined weight of the bowl and bark was 30 oz. The weight of the bowl was deducted from the total weight, so the dry bark sample weighed 25 oz. We incorporated our weight into the oz. over fluid ounce method. (25 oz. ÷ 80 fl. oz. = 0.3125 oz./fl. oz. Next we used our conversion to get the bulk density (0.3125 oz./fl. oz. x 1615.8 = 504.9 lbs./yd3). Using 500 lbs./ yd3 we determined that 6.25 lbs. of bifenthrin product would provide us with the continuous rate (Table 2).
Table 1. Quarantine Treatments for Nursery Stock, Grass Sod, and Related Materials
|Insecticide*||Dose rate (ppm)||Certification period|
Table 2. Amount of granular Bifenthrin 0.2% formulation to add to 1 cubic yard of media based on dose rate and bulk density of potting media.
Information for both tables from Imported Fire Ant: Quarantine Treatments for Nursery Stock, Grass Sod and Related Material- APHIS 81-25-001 (2019)
If you do not want to calculate the bulk density yourself, you can send a quart sample to the Soil, Forage and Water Testing Laboratory at Auburn University. The cost will be between $6.00 and $8.00. Use a routine soil analysis form and write in that you would like “Bulk Density Only.”
For more information, contact the Commercial Horticulture team.