Miller Magazine Issue 109 / January 2019

80 ARTICLE MILLER / JANUARY 2019 The times of preparation, treatment and aeration must be declared. The dosage and type of fumigant are declared and correlated with the label. The sealing is described. All doors must be locked, carry a label and have extra locks to avoid the chance of personnel entering with their own keys. The aeration process must be described and even the dea- ctivation of used fumigant. A release procedure and signing are also required. Resistance management Most countries in the world have issues with insects showing some level of resistance to phosphine. If resistance is detected, then a higher dosage is required in combinati- on with longer exposure. The fumigator needs to search for resistance by collecting insects and putting them in the test. There are five tests that are commonly used [1]: • The molecular test using PCR and molecular markers • The FAO test using 30ppm for 20 hours. • The Nayak et al 2013 modified test using 6 hours of exposure. • The Dose response test using 3 days at a range of con- centrations. • The Detia Degesh Kit using 3000ppm for 9-12 minutes The last test can be performed on site by fumigators. Fumigation protocol There are very few phosphine fumigation protocols inter- nationally accepted. 1. According to the Australian GRDC standard [3] the con- centration of phosphine must remain above 200ppm for 10 days or above 300ppm for 7 days. 2. According to Coresta Guide No2 [4] the concentration of phosphine must remain above 200ppm for 4 days when the product temperature is >20C or above 300ppm for 6 days when the product temperature (T) is 16C>T>20C. The Coresta is actually focusing on the insect Lasioderma sericor- ne of Tobacco but recent research showed that it has excel- lent results on most stored product insects. 3. The COFP standard (by the USDA) [5] requires the con- centration of phosphine to remain above 300ppm for 6 days when the product temperature (T) is 16C>T>20C, or above 300ppm for 4 days when the product temperature is >20C. The common thing between all protocols is that the fu- migator needs to measure the concentration continuously as well as the product temperature. The general idea is that Fu- migation is not recommended below 16C and the minimum duration is 4 days plus the time to reach the concentration. So no phosphine fumigation can last less than 5 days. Silo tightness If a silo/bunker/warehouse/container/stack is not airtight, the phosphine gas will escape. When the gas escapes, we face two serious problems: it may threaten the life of people and animals nearby and the treatment may fail. For both rea- sons we need airtight assets. To determine the level of tightness there is an Australian standard for pressure testing issued by GRDC and revised in 2014. The bottom-line of the standard is that the “Half-life Pressure Test” time must be over 3 minutes. How do we me- asure that? We increase the pressure in the asset to 25mmHg and measure the time needed to drop to 12mmHg. This is the “Half-life Time” and it must be longer than 3 minutes. If we cannot reach this level of tightness, we must be pre- pared to deal with leakages. We must be prepared to add gas and also to deal with the risks of escaping gas. Recirculation Most professionals know that phosphine (molecular wei- ght: 33,9 g/mol) is a bit heavier than air (molecular weight: 28.9 g/mol). That means the phosphine gas would go down pulled by gravity. But this is not happening. The reason is that the phosphine gas is moving together with the air. In the gra- in we usually have air movement caused by the differences of the temperature during the day. Unless we use recirculation of phosphine (j-system) we cannot guarantee that phosphine will reach all areas of grain mass and that it will create an equilibrium. What happens without recircu- lation is shown on the next graph and it allows insect survival. Photo 1: Studies (in SCI Journals) on resistance globally 1996-2016 [1] Photo 3: phosphine concentration by time through 2 sensors. Significant fluctuation caused by the lack of j-system. Monitoring shown on Centaur. ag platform Photo 2: Air flow due to temperature differences (natural convection currents)