Q: I’m having an ongoing problem with Septoria leaf spot on my tomatoes. My garden is small, and I can’t move it. The last two years I have been using a heavyweight weed barrier to cover my entire garden. I cut small holes in the mat so that very little soil can get through. I use San Marzano tomatoes shipped from Oregon. I spray with Ortho Garden Disease Control and use aspirin (1 per gallon) every two weeks.
I do get huge volumes of beautiful Italian tomatoes, so in that respect I am very lucky. However, I cannot stop Septoria from eventually destroying my tomatoes from the bottom up every year. This is heartbreaking after all the care I put into my garden. Trying to “control” this problem is NOT the solution. It is an expensive, time-consuming waste of time and money. It is also very frustrating because the disease always wins.
Since my garden is so small, can I “sterilize” it in the off-season so I can kill the Septoria spores that are still in the soil? Surely there has got to be something available that can destroy these spores.
If that’s not possible, can I remove the soil and replace it with new topsoil from a nursery? This will be my last resort if it’s guaranteed to work. Do you have any advice on this approach?
I would like to eliminate this problem permanently.
A: If it helps any, I feel your pain. Septoria leaf spot is a problem I battle every year, too. That and early blight seem to be getting worse, and they’re both diseases that plague just about every tomato grower.
Home gardeners are at a big disadvantage when it comes to the best solution: rotating your crops. Farmers can move tomatoes around to stay a step ahead of disease. Most home gardens are so small that even if you don’t plant in the same exact space, it’s easy for disease spores to blow or splash 10 feet to infect the slightly relocated crops.
Septoria technically doesn’t overwinter in soil, but it can live in bits of infected plants that fall and/or get worked into the soil. It’s nearly impossible to keep all infected leaves out -- although the weed fabric is about as good as anything.
Even if you manage to avoid this route of infection, Septoria can come into a garden on already infected transplants. Weeds in the solanaceae family (jimsonweed, horsenettle, groundcherry and black nightshade) also are potential carriers of spores. There’s some suspicion that spores even get passed along on infected seed.
First, I wouldn’t recommend replacing your soil. That would be a ton of work and expense. And since this disease is so easy to bring into the garden, there’s a good chance you’d have it right back again in a year or two.
You mentioned sterilizing the soil. That’s a possibility, but I’m not aware of any products that kill off and prevent Septoria when used in the off-season. Solar sterilization most likely would kill the disease, but that’s done by over about 8 or 10 weeks in summer (especially June and July). Lightly cultivate the soil, wet it and then stretch clear plastic over the soil, held down by rocks or boards around the edges. Let the sun bake the soil for 8 or 10 weeks. That’s effective at killing off most pathogens in the soil surface.
The down side is that you wouldn’t be able to grow tomatoes that season. An alternative is to grow at least a few tomatoes in pots (in soilless mix) that season so you don’t go tomatoless. I know that going without tomatoes is totally unacceptable for real gardeners. I’d rent a plot somewhere before skipping tomatoes for even a year.
What most people do is spray the heck out of their tomatoes. Daconil (chlorothalonil) is the most effective fungicide available to home gardeners, but it’s supposed to be applied every 7 to 10 days to work best.
I’ve never gone that route, preferring to try things like the aspirin water you mentioned and maybe sulfur or neem oil (so-called “soft” pesticides). But like you, it’s just a matter of time as to how many tomatoes I’ll get before the plants die from the bottom up and stop producing.
The ultimate answer would be tomato varieties that are resistant to Septoria. Unfortunately, no one’s been able to discover or breed that variety yet.
A few other things to double-check…
1.) Don’t water over the plants. Water the ground. And try not to splash any soil up on the stems since that’s one way to start an infection from the ground. Drip irrigation under the weed fabric will eliminate splashing.
2.) Are you re-using the weed fabric? Spores can overwinter on that. Definitely toss it at the end of the season along with every last infected leaf piece you can find.
3.) Don’t compost any tomato plants. Odds are your pile won’t get hot enough to kill off any disease spores. Ditto for eggplants and potatoes, which are in the same family and also potential carriers of Septoria spores.
4.) Try picking off an infected leaves as soon as you see them. That might at least help slow down the disease’s progression.
Good luck. Wish there were a better answer here. Whoever comes up with the first Septoria-resistant tomato is going to make a lot of money.