Hello Jeff,

Sorry for the slow response. Mixing composted manure into the soil before planting is a good practice to add organic matter to the soil, thus improving soil structure and slowly releasing nutrients. Good soil helps maintain good plant health, and healthy plants are less susceptible to disease. Otherwise, I don’t think the composted manure will do a lot to directly prevent plant disease from occurring.

There are several “blights” that affect cucumber and tomato. Have you had issues with foliar disease on these plants in your garden before?

Cucumbers can get foliar diseases such as powdery mildew and downy mildew, and others. Tomatoes can get foliar diseases such as early blight (common annually in MI), late blight (not a problem every year, but devastating when it is an issue), Septoria leaf spot and others.

Here are links to some relevant tip sheets:

Management of Cucurbit Downy Mildew for Gardeners from MSU Extension

Organic Management of Early Blight on Tomato from MSU Extension

Organic Management of Late Blight on Tomato from MSU Extension

A Pocket Guide to Common Disease in the Urban Garden [on vegetable diseases] from MSU

Septoria leaf spot on tomatoes: More ways to prevent spots before your eyes from MSU Extension

Early blight of tomato from U. of Minnesota Extension

Late blight of tomato and potato from U. of Minnesota Extension

Powdery mildew of cucurbits from U. of Minnesota Extension

I know it’s a lot of tip sheets, but it’s a few disease options between the two types of plants!

Management strategies are included in the tip sheets and include practices such as mulching around the plants (could be black plastic mulch or organic mulch like wood chips), watering at the base of the plants and in the morning to avoid extended periods of leaf wetness, crop rotation, and good plant spacing and staking for good air flow around the upper parts of the plants.

One very good thing to do is to try to purchase cucumber and tomato varieties with disease resistance. Not sure if it’s too late for you to do that this year, but at least something to consider in the future. Certain varieties are more susceptible to certain diseases than others. Cornell’s Vegetable MD Online website has tables with disease resistant varieties, as well as fact sheets on a number of plant diseases.

If you are considering using fungicides to help manage these foliar diseases, make sure to read and follow all label directions. The label is the law. Also, you should identify which foliar disease you have or have had before using fungicides. Look out for and try to catch disease early though (after the first few spots have developed). Fungicides should be applied preventatively.  Plus, look for a product with a recommended active ingredient which is labeled for use on the specific plant you want to use it on (i.e. tomato) and for use against the specific disease you want to prevent.

Also consider checking out our Smart Gardening for vegetables resources!

Hope that made sense, a lot of info here. Please let me know if you have further questions! I will try to answer more quickly.

Regards,

Irene