First, some relevant information: I am growing Yukon Gold potatoes. I am in hardiness zone 6b. The weather over the last month has been dryer than normal for the area I am in (Northeastern US). I have four potato plants, all near each other. In my shared garden I don't think anybody else has potato plants.
About a week ago I saw some leaves curling on one of my potato plants. The leaves weren't dry; in fact, they felt kind of spongy. This happened after I had buried the plant for a second time in dirt. The plant is now buried about 12 inches up from where the original dirt level was, when the potato first sprouted.
Then yesterday I noticed some black spots appearing on a few leaves, and some of the newer leaves having large black spots and more curling. See pictures below. Text of question continues after pictures.
My largest plant is the one with the most spots, while one of the other plants is starting to show similar symptoms, and my other two plants are showing no symptoms. What kind of disease is this? From my Google results my best guess is leaf curl or early blight, but I am not sure which one.
What should I do to treat my plants? Or are they goners? Is it worth pulling out the two infected plants to try and save the two healthy (so far) ones?
Also possibly relevant: I saw two species of bugs I haven't seen in my garden before on my potato plant today. One was a red/orange kind of beetle, about a half inch long, which I was unable to get a good picture of. The other is shown in the picture below.