I was watering my tomato plants yesterday, and one of them has some sort of strange growth. I’m thinking miniature alien egg sacs, but am hoping I’m wrong! What is it? How do I get rid of it? Will it spread to my other tomatoes?
It’s hard to say, but it looks like they might be Adventitious Roots.
Tomato hornworm eggs?
Third picture down is a hornworm egg. They look like adventitious roots to me.
So assuming these are adventitious roots, do I need to worry about them?
We had a very rainy June - could that be the cause?
Definitely adventitious roots. Tomato plants, when first planted as ‘starters from greenhouses or wherever’, are often planted with most of the already present stalk buried under the soil. This is so the plant can form/grow even more roots and be stronger overall, even though it sounds counterproductive to the ‘naive’. Moisture can help stimulate the growths, iirc, like putting a willow branch within a glass of water to grow cuttings, etc. If a tomato branch bends down to the ground and stays there a while, chances are you will see roots form where it touches (not a bad thing).
Nothing to worry about, imho.
Is there an authoritative and useful site that can give me advice on growing tomatoes in pots and the common tomato maladies? Most of the ones I’ve found through searches often have contradictory advice.
The one i’ve been relying on so far is http://www.growbetterveggies.com/
Can you dopers suggest better sources?
I’d be interested in that, too. The only part of my yard that gets enough sun for tomatoes is the deck, so I started growing them in pots last year. Had a bunch of blight on them, though - I don’t know what I did wrong, so I’m hoping it doesn’t happen again this year.
Mine seem to be doing really well on the deck but one of them is starting to develop yellowing leaves. The other one is unaffected even though they’re both in the same kind of soil and receive the same water/fertilizer regimens. However they are different types of tomato.
I’ve done research and received a host of conflicting advice on what the cause might be. Trying to break the deadlock here.
This (pdf) has always helped me when in doubt. I know that the OSU extension site has great info on most things horticultural. Not sure of the ‘home’ URL, but here is a listing for tomatoes. Well, on that last link, just click the ‘home’ link and start digging 
(not meant as pun, sorry)
There is also great help at forums.gardenweb.com, ime. VERY broad of scope.
ETA - first link is for diseases - not implying your 'maters are diseased. Sorry about that.
For those of you looking for authoritative web sites, check your state or county Extension service.
Oops. I see Ionizer has beaten me to the punch, although he or she is promoting the wrong OSU. 
I do quite agree with you, fwiw. A son’s wife is an entomologist there, so I gotta push things that way now and then, ya know… I’m more of a Tx A&M guy. Take that as you will, of course.
I am having a great 'mater year so far with me having so much that four neighbors are getting a sackful of 'em every other day - along with several cucurbit types (and around two hundred watermelons on-vine currently! Too numerous to count anyways). Just tonight, I ate seven sweet corn (Peaches and Cream) cobs standing in garden - damn those are good! Don’t even need to cook 'em they are so tender.
Good luck with those 'maters!