Certified GKH Gardening Expert
This could be due to one of a few different things. The first thing that comes to mind, is an over-watering issue, which would lead to infections with these symptoms. This can be remedied with wettable sulfur, since it is not too far along.
They second thing that could have happened, would be the pH of the soil being off, and usually too high. This is if you know for a fact that overwatering was not the issue. If this is the case, then the pH being off would cause the appearance of deficiencies. Dolomitic lime will help in this case. As would a small amount of wettable sulfur, or iron sulfate.
The last and probably least likely in this situation would be an actual Iron, magnesium, and calcium deficiencies. Fortunately, my remedies, as described, will correct these issues anyway.