Silica may confer some internal sap-sucking pest resistance to some plants by strengthening cell walls.

But, I don't know which plants this works better for or what forms of silica are best? Soluble forms like monosilicic acid [Si(OH)4] are clearly absorbable, but what about insoluble forms too? What about silica/silicon dioxide (SiO2) (diatomaceous earth) or calcium silicate (Ca2SiO4)? Do those still work, if even to a lesser degree?

Here is a link that might be useful: Calsil

That's helpful. Thanks

How do I prevent them come back?

==>>> you dont ... and they may never come back ...

you treat.. for a CURRENT and EXISTING problem ... and then.. ONLY .. if they are a threat to teh tree.. and a little cosmetic damage.. is usually not a threat to a tree ...

and never treat on a future potential problem.. that would be akin to polluting.. since there is nothing there that argues in favor of hard core chems ...

and without even seeing the tree ... let me guess.. the worms did no apparent current damage.. so they didnt need to be treated last year either ...

its just not needed.. and a waste of money ...

keep in mid.. its a tree.. not a child.. it doesnt need inoculations.. education.. college etc... nor will it ever need to be fed ... keep that clear in your mind... its not a child ... its a tree .. [unless a soil test indicates something is missing from the soil itself ...]

ken

Nonetheless, I have been cutting the branches off since early May when the worms were just babies.

You are probably doing more damage to the tree than the caterpillars are.

Stop cutting branches off your tree. If the worms are numerous, spray the tree with a strong stream of water from your garden hose to knock them off.

Usually that is all you need to do.