Plant diseases or blights in a hydroponics garden are much less frequent than in a dirt garden because there is no dirt to grow bacteria. Not to mention the fact that many plant diseases travel to the plant from the surrounding soil. Plant disease cannot occur without a host plant, a pathogen, and favorable environmental conditions.
Plants can be more susceptible to disease if weakened by environmental conditions such as too much shade, high humidity and crowded conditions. They are also more susceptible when weakened by nutrient deficiency or toxicity (too many nutrients) and poor pH.
There will always be some trouble with disease, just watch for it and take care of it immediately. Unfortunately, many disease cures involve the use of harsh chemicals which you really do not want on your plants. A hydroponics garden can easily collect such chemicals in the nutrient solution with indiscriminant use and get into the plant cells – not something you want.