Following are some things I recommend in my classes. I like to use non-toxic and easy-to-use solutions to pests.
Borage planted with tomatoes repels worms
Marigolds planted with tomatoes repels root knot nematodes
Nasturtiums and tansy are reported to deter squash bugs
Some have luck with planting icicle radishes around the squash plants to deter those pesky squash bugs.
Plant lots of rosemary for mosquito control; also yarrow, lavender and mint.
If tomato plants are turning yellow, it may mean lack of magnesium. Dissolve 2 TB epsom salts in a gallon of water, put in a hand sprayer and spray the leaves (top and bottom) of tomatoes – peppers, too. About a week later, if the tomatoes are still not responding, mix the same amount and use to water the tomatoes/peppers.
To repel pests eating plants (e.g., basil, sage, peppers), boil red pepper flakes in water. Strain into a spray bottle and add about 1-2 tsp of dish soap (preferably 7th Generation or Ivory Soap). Shake and spray on the plant leaves.
For fire ants, boil orange peels in water with some whole cloves. Strain into a jar and add the same amount of water. Pour on the mound. May have to repeat after about a week. It makes the ants go away.