Answer: I can't say for sure, but it could be thrips. These tiny insects cause silvery brown streaks and spots on the leaves. You can deter thrips by spreading diatomaceous earth under the plants and on the undersides of the leaves. You might also try planting thrip-resistant varieties such as 'Super Red 77', 'Multikeeper', 'Albion', and 'Hilton'. These are available from Stokes Seeds, 800-396-9238, web site http://www.stokeseeds.com
There are other possible causes, including various diseases. Look closely at the damage. If there are water-soaked or sunken areas, it's more like a disease problem.
Q&A Library Searching Tips