I use between 2/3rds and 3/4 of a cup of food grade DE for every gallon of spray I am making. I mix it first in a separate jug and then pour it through a strainer into my sprayer then add the other ingredients and extra water to make the amount I am looking for.
I don't see why you can't add Spinosad without any problems. I add Permethrin and Dawn and if I need to use a copper spray at the time I am using it I will add that and have had no problems.
I find spraying much easier than dusting and just as if not more effective but then I am applying it to a lot of plants. If it is a bit windy which it always seems to be this time of year dusting can be challenging to say the least. I do use it in my duster when I don't have many plants to treat and don't want to mix up a small batch for spraying.
Bill
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