PlantLife Online

Answer

Blights are caused by fungi that can over winter in the soil, they are one of those things that can be managed but never fully eliminated. When a plant is infected the damaged leaves and stems should be removed immediately and burned. At the end of the season the infected plants refuse should be completely removed and burned as well, tilling the infected plant into the ground only adds to the problem. Avoid over watering, excess water and high humidity will encourage blight to spread, irrigation should be run in the morning to allow excess water to evaporate during the day. Avoid watering the foliage. Annual veggie crops should be rotated every season to prevent the spread of soil-borne pathogens. When a garden is infected with blight like the one that is affecting your tomatoes year after year, tomatoes should not be planted the following year within 50 feet of the previous years location. 

I do not recommend using a broad-spectrum insecticide especially on veggies without knowing the culprit. It maybe time to do some closer investigation. If you do not see insects feeding on your plants during the day it maybe because many insects feed at night, head out to the garden with a flashlight to find them in action. Once you determine who or what is causing the damage you can better control them. Your neighbors will just think you really like your garden. 

As for the ants they are common in all gardens and generally do not pose any threat, however if you see lines of ants heading to one particular plant they more than likely are farming aphids, follow them, check the under sides of the leaves. A strong jet of water or some soapy water will take care of the aphids. 

Grubs are larva of adult insects, without knowing what they are its hard to say if they are causing any damage.