All this wet weather is causing issues with many plants, especially the annuals. Root systems aren't able to function in anaerobic soils which cause a variety of issues, including poor growth and reduced nutrient uptake.
Leaf diseases have never been higher. Nearly all leaf diseases require moisture to allow the organisms to multiply, and with rain every other day, this has been an ideal year. Disease control in years such as this becomes almost impossible. You can start with using plants that are naturally resistant to disease organisms. Secondly, if you understand the disease, you can help the plant by reducing the opportunities for the disease to flourish. For instance, all diseases require three things: the disease organism, a susceptible plant and the correct environment. Alter any one of those and the disease can't complete its life cycle. So to reduce fungal diseases of tomatoes, know that they survive in the soil for several years. So therefore eliminate the possibility of those organisms coming into contact with the tomato leaf. Move the tomatoes each year, mulch the soil as soon as the plants go in the ground, sterilize the cages (as the disease can overwinter there as well).
If only the rains could help with Japanese beetle control we'd have much less to complain about! The Japanese beetles have been out for several weeks now, feeding on a variety of plants. There are over 250 different plants they can attack, but favor some more than others: linden, brambles, roses, grapes, apples, etc. Once the beetles have moved in, it becomes a constant battle.
The first beetles to arrive at a preferred crop will send out the invitation to others to attend, so reducing those first beetles helps alleviate future populations somewhat. There are several methods to help control the injury. Exclusion using a mesh cloth can help protect small plants. Row covers, bridal veil or something similar that has small enough holes to prohibit the beetles from entering needs to be secure to the ground. But for most plants, a pesticide will be required. Sevin is an excellent choice. For organic growers compounds containing neem (Azadirect, Neemix) or pyrethrum (Pyganic) have a short but effective impact on Japanese beetles with some mortality, some knockdown off the crop and some repellent activity. But don't expect the level of control obtained with Sevin. Remember with any pesticide, rainfall washes off the product (an inch of rain can remove most of the pesticide). Sevin can provide about a weeks' worth of protection. Expect less with the organic products.