By Doug Oster/Pittsburgh Post-Gazette
Everyone knows homegrown tomatoes are the best. Summer isn’t complete without them. But it’s been challenging the last few seasons to grow disease-free plants.
It’s no surprise that spring temperatures fluctuate from hot and humid to brisk and rainy. But two consecutive wet seasons and another moist, cool spring has gardeners worried about fungal diseases on their most precious crop. Early blight and septoria leaf spot are the first two culprits that start to appear in June and July.
The early diseases start with bottom leaves turning yellow and blotchy, eventually drying to brown and dropping off the stems. Then the disease works its way up the plant. Most times tomatoes can survive and produce fruit, but not as well as healthy plants.
The first thing gardeners can do is to give the plant everything it needs at planting time and plenty of space between plants (5 feet if possible). A planting hole filled with compost will keep the plants strong and it’s also a natural fungicide. The organic soil amendment is available in bags or by the truckload. Many gardeners make their own by composting food scraps and garden refuse.
Another line of defense is a layer of mulch, which provides a barrier between soil-borne spores and plants. Removing some lower leaves helps too; spores thrown up by splashing rain will have farther to go. Those fungal spores are always in the soil and when things are both cool and wet, they thrive.
Leaves which stay wet for a day or so invite infection.That’s why you should always water tomatoes in the morning, to give the foliage time to dry out.
Keep the plants off the ground too. Grow them in cages or up stakes. At planting time, I surround mine with a homemade cylinder of concrete reinforcing wire 5 feet tall. A tomato stake attached to the cage stops a huge tomato plant from toppling the cage in August.
One of the best ways I’ve found to avoid fungal issues is succession planting. After the first crop is planted, find space for some more plants to be added every week, all the way until July 1.
I first discovered the technique after some of my invaluable (wife’s favorite) ‘Sungold’ cherry tomato plants were crushed by a black cherry tree during a nasty mid-June thunderstorm.There were three more scraggly plants in the greenhouse that I planted on July 15. I’d never planted that late, but the plants loved the warm soil and air temperatures. By the end of the season, when my earlier crop was succumbing to fungal diseases, those plants were thriving. They all had the same weather from June 15 on, but the greenhouse plants didn’t go through the cold, wet spring that the early ones did.
When choosing plants for later plantings, go with varieties that are bred to ripen early. Cherry tomatoes, ‘Early Girl’ and patio tomatoes are all good choices. Each plant tag will be labeled with days to maturity. ‘Sungold,’ for instance, is ready in a little over 50 days from transplant. Planting it on July 1 will give the plant time to mature before frost.
Serenade is a great, easy to find organic fungicide that is effective in combating many fungal issues. It’s a biological control with targets the spores themselves and stops them from reproducing. It’s a safe alternative to chemical fungicides. Another way to deal with fungal problems is choose many different tomato varieties to grow. Each one reacts differently to diseases.
If plants contract one of the early diseases, remove the infected foliage and treat with the Serenade. They usually put on fresh growth where those yellow leaves were and should keep producing.
Crop rotation is also important; don’t plant tomatoes in the same place every year. In my garden, there’s only one place with enough sun for the plants. I add lots of compost, and then plant, mulch, cage and hope for a dry “Italian summer.”
The weather is really the most important factor in keeping tomatoes healthy. A hot, dry summer is what tomatoes love and also gives fruit the best flavor.
One of the worst things that can happen in the tomato garden is late blight, which is fatal to the plants. Several seasons ago, our gardens were decimated by an epidemic. Late blight looks very different than the earlier diseases. It turns leaves, stems and fruit black, often starting at the top of the plant. It’s airborne and relatively rare. I’ve only dealt with it three times in as many decades.
Since the spores are spread by the wind, we usually have a warning that it’s coming. That’s when plants should be treated with fungicide as a preventative measure. There are also varieties that are late blight resistant. ‘Legend,’ ‘Defiant,’ ‘Mountain Merit’ and others are bred to fight off the disease. Any infected plant must be removed and destroyed to stop the spread of late blight.
Most importantly, identify the disease before taking action, regardless of what the plants look like. Blossom end rot is another disease that turns the bottoms of tomatoes black and is sometimes mistaken for late blight. I’ve known gardeners who have pulled all their plants thinking they had late blight, when it was something else.
By the way, blossom end rot is prevented by keeping the soil evenly moist. It often affects container plants that dry out between waterings.
When the weather doesn’t cooperate, tomatoes can be a little bit of a challenge, but worth the trouble to taste warm, ripe fruit while standing in the garden this summer.