Whew - lots of good info! Thanks everyone! I am starting to get an idea of how to go with this. I have spent many, many hours the last couple of days researching nematodes, and your input has helped a bunch. After reading many sites I now have a new 3 ring binder full of printouts from the best of them with highlighting and red underlines plus a bunch of bookmarked sites and computer saved documents - I'm a bit compulsive that way - I like things all organized. LOL
I find it really interesting that what works well for some won't work for others. I have come to realize that getting the species I have identified is critical. From my research it looks like the success of specific suppressive crops and methods can really depend on which one(s) you have. Most information out there seems to refer to them all as a group, or perhaps they are only referring to their most prevalent local kind, and I found only a few sites that really break it down by RKN species. The Alabama Cooperative Extension System papers on RKN were quite useful in that. Sesame has only been shown (says ACES) to work on one species - it isn't clear if the other species were included in the study. Specific marigolds have only been shown to work on certain RKN species, but it's a bit confusing. In an Alabama paper they say that the "'Petite Harmony', 'Petite Gold', and 'Goldie' supported some root-knot reproduction." while a paper from Arkansas says those varieties lowered the populations. A Florida paper says Petite Harmony is susceptible to nematodes and Goldie is resistant. Weeeellllll, shoot! The University of Florida paper goes into great detail on varieties and which of 3 of the common RKN varieties it will work on. If you have M. hapla though, you are out of luck - Florida (not surprisingly) doesn't include the Northern species in the listing. It's no wonder gardeners can't get a consensus on their effectiveness. Similar findings on other cover crops - they work or not depending on which Knot you have, and there is some contradictory stuff on others too - generally because they are talking about different species of RKN. It looks like if you use them on the wrong species, or even with the wrong timing, you could make it worse. Spiffy.
Since these guys love warmth I would imagine climate makes a huge difference in results as well. I'm a couple miles from the ocean. While it's warm enough to plant out frost sensitive things mid March it may not get summery warm here until July (tip: don't ever plan a Summer beach vacation to San Diego in May or June - you may never see the sun). We don't get above 80 degrees very often - mid 70's is a normal summer day, and mid-60's overnight. That's a vastly different climate than most parts of the country, and even the bulk of California.
You have all given me so much good info, and I have formulated my plan of attack:
Find out which species of RKN I have.
I thought I was adding enough organic material each year, but starting now, I will be adding more. This is clearly the #1 most important thing.
More manure - b54red, I wish I could get horse like I used to when I lived in the country, but I'm in the city now and it's tough to find. Gone are the days when I had friends with horses that would even help me load it like they wanted to get rid of it or something LOL
Better irrigation practices - I have been hand watering this year (usually no rain here May - Oct) as the electric on the irrigation system is on the fritz. Time to get the electrician out so things get watered properly to avoid water stress.
Set up a strict crop rotation plan, including fallow (with appropriate cover crop to see how that works for me). I found a great sample plan that includes successions and intercropping from the Texas Ag Extension. I'll mix that up with the one recommended by California, and work out a four year whole garden plan.
Totally clean beds after each crop - no more leaving root bits in the soil to decompose on their own, and no more leaving decrepit plants in to see if I can squeak more harvest out of them.
Temporarily suspend composting garden material. Not all beds are impacted, but some might be and they just aren't showing up because it's a mildly affected crop. I don't want to add materials to the compost that might be infected. Will start later by only composting plant parts that have never touched soil. If I can't add below ground stuff and can't add stuff with Powdery Mildew I don't have much I can compost at the end of summer anyway.
Clean tools when moving from bed to bed (How annoying!)
Dry Molasses - my local nurseries don't have it but I found it online. My local hydroponics store has the liquid version in great big bottles - would that be useful, or does it have to be dry? How much would I use?
Solarization is not an option since I'm too close to the coast - skip that.
Depending on my species I will give the Teracure a try.
JackE, That product looks interesting...OMRI and everything. Since it has such a short shelf life I don't think it will be appearing on nursery shelves soon, but it's promising.
Pay more attention to plants as they are pulled. Since I have been dealing with back issues for the last few years hubbie has been doing the end of season clean out when I managed to get a few things in - a girl has to have fresh tomatoes! He's a sweetie, but a gardener he is not. It's possible he can tell the difference between a dandelion and a carrot, but I wouldn't want to put money on it. It may be that I have had this for a few years and didn't realize it. Here by the coast Powdery Mildew is a real problem, and we're used to it killing off plants by the end of the season. I bet this has been building up and I thought the die off was from PM, and never realized the real cause until I pulled those tomatoes myself this week.
Plant tomatoes (and all Solanaceae) in containers this Fall and next Spring. Give the main garden a year off from tomatoes, even the beds I think are ok. I've been pretty irresponsible - I have had either tomatoes or peppers or potatoes in nearly all of the beds all at once, and with them in all beds there can't be rotation.
Include some N resistant tomato hybrids when tomatoes go back in the garden after some rotation gets the population down...sigh...they are all boring and perfect and red. No lumpy purples or streaked yellows or bi-colors or nuthin'. I think I will continue putting the heirlooms in containers for the foreseeable future to be on the safe side.
Start all my own seedlings - no more vegetable nursery stock. Since these are self contained beds with no yard soil this undoubtedly came in on a transplant.
If I left anything important out, let me know
I've been gambling with possible pest problems, and I lost. I knew better. I knew I should have been doing crop rotation, especially for tomatoes, but since I kept finding new ones to try I kept filling up the beds with them. I blew it and now it's time to pay the piper.