Not fruit fly's that ruin the fruit. They must mean because that Guava is so prolific,that uneaten ,unpicked fruit become food for the harmless fruit fly we have. Its the type they grow in HS science classes.

Hmmm... Do you grow Feijoa Stan? Hayward is a cooler climate than a few miles inland, but we are close so we should be able to compare pests. :-)

I found info online that backs up what I heard, but I'm still unclear on if it's a current problem in my area. I better just call my county ext master gardener program.

Here's some info for others interested:

News (probably not as reliable as contacting the local county ext master garden program): https://www.google.com/amp/s/www.nbcbayarea.com/news/local/Guava-Fruit-Flies-Threaten-Californias-Fruit-Industry-215622061.html%3famp=y

UC info on quarantine (current? Not sure): https://www.cdfa.ca.gov/plant/medfly/docs/regs/3406-TXT-medfly.pdf

UC info on all sorts of fruit flies: https://www.cdfa.ca.gov/plant/PDEP/treatment/index.html

The links, above, re med fly and CDFA is regulatory info which is used when an infestation is detected.

Verify the potential for problems with such invasive insects with the Master Gardeners at your county's Extension Service office.

More than likely, you'll only be faced with nuisance fruit flies.. Easy remedy is to collect and discard over-ripe and fallen fruits http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/PESTS/fruitflies.html

I have Pineapple and yellow lemon guava. Fruit flies have never been a problem. The real problem?...... my children. They get to them before I can

In Central Florida near the East Coast we have a big problem with fruit flies both the Caribbean variety and the standard fruit fly. I have a home orchard with two guava trees. One is a Ruby Supreme guava and the other a Barbie Pink guava. The Ruby Supreme was under incessant attack by the fruit flies. Nothing I tried including spraying or using traps with apple cider vinegar and dish soap could eradicate them. Actually, the latter seemed to be effective against the Caribbean fruit fly but not against the standard fruit fly. To make a long story short I uprooted and destroyed the Ruby Supreme guava tree. It was painful because I love guavas but it's just too much trouble dealing with those pesky critters. The Barbie Pink guava is still in my orchard but I have noticed the fruit flies attacking it. So I removed all the fruit and threw them away. I will most likely destroy that tree also later this winter or maybe repot it into a half whiskey barrel planter. It might make a good gift for my sister if/when she buys her own home. Or if I could get a greenhouse installed in my yard then I could isolate the tree from the flies. I also have the feijoa selliowana (aka the pineapple guava) tree in my garden. The 5 of them are in pots and I had thought about making a hedge out of them. They don't seem to tolerate the blistering summer heat of Florida so they need to be in shady spot during the late afternoon hours. I am not sure if the fruit fly can attack the pineapple guava because it seems they have a much thicker peel than the ordinary guavas. A thick peel is the best line of defense against fruit flies I hear. I was hoping someone on this forum could confirm if they are resistant to fruit flies or not. But it has to be a report from someone who lives in an area that is prone to that sort of infestation.