Castile soap is often available at Dollar Stores or Big Box stores. It is old fashioned bath soap. Inexpensive, usually. A Gallon Sprayer is a pump up type that you can mix chemicals or organic concoctions in and spray on your plants. Look in the garden section of a Big Box Store. They are usually around $10. They are a good tool to have if you are serious about gardening.

ZG, I see this is your first day here. Welcome to the GardenWeb. White powdery spots are probably Powdery Mildew, perhaps the most common zinnia disease. Prevention is the best cure. Powdery mildew likes to grow in a cool shady dry place. This time of year you can't do much about cool, and the days are getting shorter. Next year, plant your zinnias in those locations that get the most sun. Wet foliage does promote several zinnia diseases, but it's a myth that wet foliage promotes powdery mildew, so don't hesitate to spray your zinnias with something like GreenCure®. In the Fall, frequent sprayings are justified. You can include a photo in your message by using the [img src="URL of photo"] HTML, but use angle brackets instead of the square brackets [ ] that I just used. In order for your photo to have a URL, you need to post it on one of the photo hosting services, like PhotoBucket. For example, if I type, <img src="http://img.photobucket.com/albums/v608/MaineMan/986wides/100_4530.jpg"> The result will appear as, I used a "trick" to keep the angle brackets from taking effect in the example above. There are several other image hosting services, but PhotoBucket is a popular one, and its basic service is free. ZM

Excess moisture from any source promotes leaf diseases on zinnia and many other plants. Management is to keep leaves as dry as possible. eg: space plants to allow for good air circulation; water at ground level; if watering overhead, allow adequate time for leaves to dry before night fall. Might take a look at this from Penn State http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/zinnia-diseases Here is a link that might be useful: zinnia diseases This post was edited by jean001a on Sat, May 31, 14 at 22:22

It does look like nutrient deficiencies, which have the twin benefits of being slow and correctable. The interveinal yellowing, where the veins stay green, is more likely magnesium than iron... but the real way to tell is where it's happening. Magnesium starts at the bottom, iron starts at the top. The pictures make me guess it's the former; you could mix up a tablespoon or so of epsom salts in a spray bottle and spritz down the plants, and see whether the leaves color up again. The yellow leaves probably are nitrogen, and a light foliar feed is very unlikely to give them too much nitrogen. Spray them down with fish emulsion and see if they green up. If they do, start giving them light doses of nitrogen regularly. Clay soil can be very rich in just about everything... except nitrogen; your amendments weren't with anything that would boost that N level for any length of time, particularly if the chicken manure was old. Best of luck -- the plants should be fine once you can give them what they need. --Alison