Biologicals and chemicals — can they be used together, and what to watch for

The biologicals used in the field, such as fungi and bacteria that control pests and diseases, are real living organisms, not stable chemicals. This difference changes how they must be used.

Usually not mixable with fungicides

If the biological you are using is a fungus, mixing it with a fungicide kills what you just bought while it is still in the tank. This sounds obvious, but it happens very often, because farmers want to get everything done in one spraying.

If you need to use both, leave several days between them, and read the biological's label to see what interval it specifies.

Sunlight and heat are the enemy

The organisms in biologicals can be killed by ultraviolet light and heat, so spraying in strong sun is a waste. The right time is late afternoon or evening, when humidity is high and the sun has gone.

Store them correctly

Many biologicals must be kept somewhere cool and have a much shorter shelf life than chemicals. A product left in a very hot shed for several months may have no live, working organisms left at all, even though it looks exactly the same from the outside.

The mixing water matters too

Tap water with residual chlorine can kill the microorganisms in a biological. If you have to use tap water, draw it and let it stand first so the chlorine can evaporate.

Why they are worth the extra work

Biologicals have no residue problem, so they can be used closer to harvest, and they are an important tool for reducing the number of chemical applications, which directly slows resistance.

Using both together according to a plan, rather than choosing one or the other, is the approach that works in practice on most farms. But the order has to be right, and that depends on the crop, the pests found and the time of season, so plan it with our staff from the start of the season rather than deciding on the spot. Important note This article explains general safety principles. It is not a recommendation to use any particular chemical. Mixing rates, the crops a product may be used on and the waiting periods required differ by product and change with government notifications. Always treat the product label as the authority, and consult an agricultural specialist or our staff before deciding to use it.