Heirloom Expert: Early Blight in Tomatoes

There are a few steps you can take to keep you tomatoes free from the fungal diseases of which they are prone.

tomato leaf

All tomatoes are prone to fungal diseases. Every variety reacts differently regardless of being a hybrid or heirloom.

Photo by Doug Oster

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I’ve only had a vegetable garden for five seasons and it’s done pretty well, but last year my tomatoes looked awful. The leaves started to turn yellow and then dried up and fell off. I’ve heard that heirloom tomatoes aren’t as good at fighting off diseases and pests. Is that true?

 As far as the tomatoes go, you’re not alone. I had my worst year yet for tomatoes last season. In the east, we were both blessed and cursed with lots of rain. Add cool temperatures in the spring, a quick switch to hot, humid weather and what we got was fungal issues for tomatoes. Most of my plants looked like yours and were affected by early blight.

There are many techniques to slow the fungal diseases, but as gardeners we’re slaves to the weather, especially when it comes to tomatoes. Every season offers new challenges — last year was a tough one for you and me to grow tomatoes. On the bright side, peppers flourished in my garden, hopefully something similar happened in yours.

All tomatoes are prone to fungal diseases. Every variety reacts differently, regardless of being a hybrid or heirloom. Some heirlooms will be more resistant as will certain hybrids. When choosing varieties, it’s smart to look for types that are known to be resistant, but I’m not doing it that way. Even in my worst year I pick more tomatoes than I can use, so I’m growing what I love, what I’m sent from readers, and what I’m curious to try.

Here are some things I do to keep my tomatoes free from fungal issues during a “normal” season:

  • Everyone longs for the first tomato of the season, so some plants go in before the last frost, with the protection of floating row covers. Those plants and the ones planted right after frost are most at risk. A cold, wet spring will make them struggle all season, but it’s worth the effort in case the weather cooperates. There is no better feeling than picking the first ripe tomato.
  • The trick to beating the diseases is to keep planting into summer if you’re climate will allow. Planting early varieties like ‘Sub-Arctic Plenty’ or others late in the season will usually provide disease-free foliage. In my zone 6 garden, I plant up to July 4th. The tomatoes love the warm soil and quickly catch up to the plants put in the garden early on. Even though the plants have the same weather from summer on, the late plantings are often unscathed.
  • I like to remove the lower leaves of the plants from any tomato plants; this makes it harder for soil-borne fungal spores to splash up and infect the plant.
  • The plants are mulched the day they are put in the ground. Even though that doesn’t allow the soil to warm up as quickly as I would like, it’s smothering those same spores.
  • Often times I’ll cover the soil with black landscape fabric a few weeks before planting to try and warm up the soil.
  • Give the plants lots of room, at least 3 feet, 5 if you have the room. Good air circulation between plants will help keep them happy.
  • Keep the plants off the ground. Grow them in cages or stake them.
  • Grow the tomatoes in good soil amended with compost. It acts as a natural fungicide.

Doug Oster, contributing editor


Doug is the Pittsburgh Post-Gazette’s Backyard Gardener (www.Post-Gazette.com/GardeningWithDoug) and co-host of The Organic Gardeners radio program on KDKA.