I am happy to say that I have only to contend with two persistent tomato plant pests: slugs and tunneling creatures. However, there are many more and I will discuss them here.
Slugs (and sometimes snails) are a major challenge in my Pacific Northwest tomato sauce garden. Planting marigolds and basil around the tomato plants helps to distract them, however I do not appreciate that they can decimate my basil.
The main problem with tunneling creatures is that their activity can disturb tomato plant roots beneath the surface of the soil to the point that plants will die from lack of water and nutrients. However, there are some that will eat the roots as well.
The best way I've found to deal with this is to line the beds with 1/4-inch hardware cloth on the sides and bottom about 2 feet down. Make sure the sides and bottom are connected with wire.
These critters eat holes in my tomato plant leaves. They make some of the leaves a bit ragged, but so far no major damage beyond that. Mostly they chew the lower leaves and so I just remove the ratty-looking ones. One year I purchased an egg case of Praying Mantis, hoping that they would eat the potato beetles. I did not see a noticeable reduction in potato beetles but it was fun to see fully grown praying mantis hanging out in my garden!
One organic option is to fill a water bottle with water and then apply a sticky solution such as Tangle Trap, available at garden stores, to the outside of the bottle. Set it in your garden and as the bottle warms up, it attracts the flea beetles and they get stuck to the bottle.
These are microscopic unsegmented eelworms that live in soil, mostly in Gulf Coast areas with sandy soil. They cause stunting, wilting, yellowing and possible death to tomato plants. Additionally, knots or lumps appear on the roots. Avoid by selecting resistant varieties denoted with the initial "N."
To avoid this pest, it would be best to rotate the location each year for tomato planting to confuse the pest. Also, treat the soil after a tomato-year by planting marigolds in that bed. Till marigold plants into the soil once they are at least 3 months old.
These are 3-1/2 to 4-inch pale green caterpillars that feed on leaves and stems of tomato plants. They blend in really well with the plant so you may see their droppings first which are dark green or black. Pick them off unless they have white projections coming out of their bodies. These projections are actually braconid wasp cocoons. The larvae of the wasp feeds on the hornworms so it's good to let them alone to continue to infect more hornworms.
These are about 1-1/2 inches long and green or brown with a light yellow line along the body. These appear from late spring into early summer. Check undersides of leaves for eggs. If not removed, these will hatch into larvae that will eat your tomatoes.
French marigolds planted with tomatoes are said to help deter whitefly.
For aphids, spray a dish soap/water solution on them every week.
Foliar-spraying once a month with compost tea has eliminated both aphids and blight issues in my tomato sauce garden. Click here for information on compost tea.
Common Problems Solved. April 2007. Organic Gardening Magazine.
8 Cagey Culprits. May/June 2003. Organic Gardening Magazine.
The Complete Book of Vegetables, herbs and Fruit. The Definitive Sourcebook for Growing, Harvesting and Cooking. M. Biggs, J. McVicar, B. Flowerdew. 2004 Edition. Kyle Cathie Limited.