Bill -
My understanding is the chemicals that have been used over the years to combat nematodes are very toxic and have been banned. The climates of San Francisco and coastal Northern California are "ground zero" for nematode infestation.
DT
The nematode problem has gotten worse in the SF/Monterey area over the recent past due to a combination of causes:
a) The nematodes have gradually developed resistance to Nemacure over generations of repeated exposure. [The nematodes' life cycle is four months, so in thirty years they've had nearly 100 generations for evolution to favor those resistant to the pesticide.] Unless you don't believe in evolution, in which case, it must be
b) The greens are more stressed out generally because they are being maintained to a more difficult standard, so they are more susceptible to nematode damage.
It's probably a combination of both.
I don't know whether the same nematodes live up in the Pacific NW that do in Monterey and SF. [I believe there are many different subspecies.] In SF, the "solution" has been to remove the nematodes physically by rebuilding the greens, and then hope someone comes up with a better control for nematodes before the poa takes over again and the little buggers come back. Some were hopeful they could keep poa out of the greens indefinitely with other chemicals, but it appears to be a losing battle. And it's a losing battle whether they have bentgrass greens or fescue.