Two diseases that attack tomatoes early in the growing season around blossom set are Early Blight and Septoria.  Both start on lower leaves of the plant and result in leaf spots that may eventually kill the leaf. Defoliation of the plant is harmful and also leads to sunscalded fruit.  Disease development is favored by warm temperatures, abundant rainfall and high humidity.  We’ve had perfect conditions for both diseases, and I am seeing them on some of your tomatoes.  Mulching, caging, no overhead watering and good air flow are helpful to reduce disease pressures. To learn more about these early tomato diseases, here are articles from K-State Research and Extension, University of Minnesota, and Missouri Botanical Garden.

https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Early%20Blight%20of%20Tomatoes.pdf

https://extension.umn.edu/diseases/early-blight-tomato

​http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/septoria-leaf-spot-of-tomato.aspx

Harlequin bugs are orangeish-red and black mottled insects that can do a lot of damage on cole crops, tomatoes and potatoes when in high numbers.  They feed on the plant sap, causing stippling of leaves and distortions in the heads of cabbage and brussels sprouts.  Their eggs are very interesting.  They lay a group of 6 barrel shaped black and white eggs on the underside of leaves.   Here are some links from University of Maryland Extension and K-State Research and Extension.

https://extension.umd.edu/hgic/topics/harlequin-bug-vegetables
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https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Harlequin%20Bug.pdf

Aphids attack a multitude of plants in all stages of plant growth.  They are small, pear shaped and come in a variety of colors.  They are recognized by the 2 tubelike structures at the end of their body called cornicles.  Aphids feed by using their mouthparts to suck plant juices out of leaves and fruit.  They secrete a sticky substance called honeydew that ants love.  Sometimes ants farm aphids, moving them around.  Generally, natural enemies of aphids keep them in check.  However, if you have sprayed an indiscriminate insecticide, the lady beetles, syrphid fly larvae, aphid lions and small wasp parasites known as braconids will also be killed and an aphid population can increase exponentially.   A strong stream of water will knock most aphids off the plant and in doing so break off the mouthparts so they can’t eat anymore.  For more information on aphids, here is a link from K-State Research and Extension.
 
https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Aphids.pdf
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The Colorado potato beetle is generally found on potatoes, tomatoes, eggplant and other solanaceous family plants.  Adults become active in May and lay eggs on the underneath side of leaves.  Damage to crops when populations are high, especially in the 2 week time frame of potato flowering, can be significant.  If you have a few plants, the best thing to do is scout them closely and handpick any eggs or insects.  For more information about Colorado Potato Beetles, here are links from K-State Research and Extension and University of Minnesota Extension.
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https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Colorado%20Potato%20beetle.pdf

https://extension.umn.edu/yard-and-garden-insects/colorado-potato-beetles

If you grow any cole crops—cabbage, broccoli, cauliflower or kale—you know that little green worms can wreak havoc on your plants.  Early scouting and control are key to managing the pest.  If you see the brown or white butterly flying around your plants, they are looking for places to lay eggs and you will have worms eating your cruciferous vegetables soon.  Here are links from K-State Research and Extension with detailed information about the cabbage looper and imported cabbageworm.

https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Cabbage%20Looper.pdf

https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Imported%20Cabbageworm.pdf