Question
QUESTION: "Bayer Advanced" (a liquid pesticide) has been recommended for treatment of bark beetles in my two coast redwoods which have been in my front yard for 28 years and stand 75' tall.  Do you think "Bayer Advanced" will help???

ANSWER: I assume you are going to use Bayer Advanced as a preventive--in that case it should prevent the attack of bark beetle and other insects that would feed on the bark and foliage of redwood. The product is a systemic insecticide meaning the plant will take up the insecticide into its system and if an insect bores or eats the plant part the insect would be killed.  

Assuming you have no signs of bark beetle attack this product should prevent attack. If there are signs of attack I would recommend that the trunk be sprayed with a product called Merit. Merit is in the Bayer product but spraying the trunk will get the product to the bark surface killing any beetles present. Of course this will take a pressure sprayer that can reach the full extent of the trunk--that is why the Bayer Advanced is recommended for most homeowner situations.

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QUESTION: My two Coast Redwoods do show evidence of beetle boring i.e. a couple of 1" dia. dead branches riddled with holes and lots of frass in the bark at eye level!  I had an arborist come by (he took one of the branches with him) and he felt Bayer might not help because they say pour the diluted pesticide around the trunk (1oz. per 1" of circumference) when the feeder roots extend 15-20' away from the trunks; in addition, my trees are each 75" in circumference.  That's a $100 investment that might be an excersize in futility because everything I read says that once the eggs are laid it's too late.  The arborist did state the beetles will not kill the trees because of the distasteful tannin in the wood.  I think I'll start looking for a lumber mill that will take the trees down for the wood!!  I wouldn't recommend Redwoods to anybody.

Answer
What I would do is spray the trunk with Merit or Onyx insecticide as far up the tree as you can. May take a pressure sprayer to reach but most of the attack seems to be on  the lower limbs and trunk  so a pump up sprayer can reach 20 feet or more. These beetle attack trees that are under stress so I would recommend that you fertilize the trees with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter and water in good.

The trees also like water so during times of no rain water the tree with 1 inch of water (place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop.) Do this once a week if it does not rain.
 
I would not give up on the tree just yet as long as it has green foliage I would not think about cutting it down.