How to Spray When Mantids Are in the Garden

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Mantid egg casing on a tree.

Q. Well they are back and so the battle begins.  I’m just starting to see a stinkbug or 2 and a few leaves on my squash has eggs on them.  I know just how fast those hungry buggers can suck the life out of cukes, squash, melons or whatever sounds good to them. 

This year I bought some praying mantis eggs/nest.  It’s impossible to see when they hatch and leave home so I just thought they died.  Imagine my surprise to now be finding baby mantis’s in my front and back yard....on the very same plants the squash bugs are hitting. 

So here’s my question.  To spray for the bugs or hope the praying mantis’ will feast on the squash bug buffet? 

Thoughts, ideas or opinions?  All are very much appreciated!
-Sue

A. Sue, that’s a really good question and it is one of the major difficulties we face when we try to manage our garden and fruit trees organically or as organically as possible. You have introduced an insect predator into your garden to help keep some of the "bad bugs" under control rather than to use pesticides. It is one of the cornerstones of integrated pest management or IPM. We should also be realistic about what praying mantis can and cannot do. They are not focusing on "bad guys" to help you, they are just looking for a meal. Their meals include "good bugs" and "bad bugs".

This idea works great with some pesticides approved for organic production and it does not work well for others. For instance if we use a pesticide allowed in organic production that targets a certain pest while not harming others it can work fine. An example is using Bt that kills only the larva or worms of moths and butterflies but we want to protect the praying mantis. It is totally safe for the praying mantis since it targets only the worms or larva of moths and butterflies. However, if we are realistic, it also kills the larva of butterflies which are not plant pests for our gardens.

However, if we use insecticidal soap, which is also recommended in organic production, and apply it to our vegetables or fruit trees, we are applying it is an "indiscriminate killer"; it will kill any insect on contact, squash bugs, leaf footed plant bugs, aphids, honeybees as well as praying mantis. 

When we choose to use an "indiscriminate killers" but want to keep beneficials, like praying mantis, from getting harmed, then we must direct the spray on the insects we want to kill and avoid spraying the ones we do not want to harm. This requires a lot of plant inspection on your part; looking for, identifying and targeting the "bad bugs" with the spray. 

Focusing on the use of beneficial insects as your primary method of controlling "bad bugs" limits your ability to use pesticides. You must either not use pesticides or select pesticides which will not harm the beneficial insects or direct any pesticide sprays so that they come in contact only with "bad bugs".

Another approach is to use these indiscriminate killers, such as insecticidal soaps, to keep bad insects under control and realize you will have "collateral damage". The "collateral damage" which occurs is the killing of good bugs and bad bugs with the hope that the good bugs will recover after the spraying is over. 

You also select "organic" pesticides that do as little damage to the general insect population as possible. This type of spray program limits the use of beneficial insects for any long-term control. It is really a "spray and pray" program.

Enjoy your praying mantids. They will migrate to other parts of your landscape as well as your neighbors. Visit and inspect your garden and fruit trees often. Use plants sprays when "bad bugs" are getting out of control and target your sprays on these "bad bugs".