Wednesday, May 28th, 2008...1:19 pm

Diseased Marigolds

                                              Alternaria

TheGardenLady received this question from Helen.

I just put in marigolds next to my tomatoes, as companion plants. I think I’ve overwatered them and it’s been rainy in Ithaca this year…White spots are forming on them. I don’t have a digital camera handy, or I’d show you what they look like. My daughter says they have the chicken pox! Do I dig them up and replace them with new ones or do I just try to dry them out? I worry if they stay, that they are diseased and will just get worse-maybe attracting pests… What’s your advice?

Not seeing your marigold plants TheGardenLady thinks you have diseased marigold plants. Heavy rains and winds can carry a disease called alternaria to ornamental plants. See here.

Even though TheGardenLady has not seen the marigold plant and the problem, TheGardenLady would pull out the sick looking marigolds which are cheap to replace. The reason for this suggestion is because you might get a similar fungus, a fungus in the same genus, on your tomato plants and this alternaria or Tomato Early Blight damages the tomato plants and fruits. See here.

If it is alternaria, the fungus gets into the soil and can remain in the soil for a few years which means you will have to be careful what you plant in that location. Scientists are working on creating alternaria resistant plants. You can put plastic sheeting around the tomato plants so that the fungus can not get from the soil to the tomato fruit.

Tomatoes are known for having numerous problems (see here), so TheGardenLady suggests that you should vigorously watch your tomato plants to see if they remain healthy.

You tried to do something interesting by doing companion planting, but because you now have a specific problem due to excessive rains, you will have to rethink what you will plant in that site.

TheGardenLady highly recommends visiting your local Master Gardener Office or extension office and taking the infected plants to the office to be sure that you do indeed have alternaria. The people in these offices will ID the problem more accurately than an email can and you will learn what you should do. They keep abreast of your local problems and can advise you specifically.

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