I have a Parks Whopper tomato plant. It was doing fine but as soon as the tomatoes were ready to ripen, I noticed brown spots at the bottom of the tomato and brown spots on the leaves, which turned yellow and then started dying off towards the stem. The tomato plant is only 2 months old.
Brown Spot on Tomato and Leaves
Certified GKH Gardening Expert
The markings on the tomato appear to be the work of some type of sucking insect.
Yellowing leaves on tomato plants can be due to several reasons, including pests.
Inspect the plants more carefully for any other signs or evidence to help you pinpoint the cause.
Most infestations can be treated with Neem Oil. Neem Oil is organic and safe for people, pets and bees.
Here are some links with more information.