I got an email notice yesterday that Late Blight, which rapidly kills tomatoes and potatoes (among other plants), was discovered 200 miles away from me.

Why should you care and what should you do?

You may recall that late blight is what caused the potato famine. It rapidly spreads through a region by spreading spores, quickly killing affected plants in its path. Once infected, you cannot save the plant and what you need to do is remove the plant, get it off site (meaning trash), and clean up any fallen debris. End of story, end of tomato season for you.

Now before people run screaming for the hills, let’s put this in a bit of perspective:

• I am NOT telling you to run out and buy stuff or start spraying your plants. I definitely AM suggesting you prepare.
• Late blight occurs every year. Some years more problematic/common, some years less.
• Late blight typically spreads (on the US eastern seaboard) from south and west to northeast. You may recall that Maine is sometimes called “the tailpipe of the nation” because all the auto pollution from south and west travels along prevailing winds in this direction. Spores follow the same wind patterns.
• This advance warning system allows you to get ready, which is what you should do now.

Again, once infected, you cannot save your plants. This is why the advance system was set up – so you can be prepared and take action in advance of the problem showing up at your door.

Late blight (P. infestans) is a fungal disease. (Technically it is a water mold, but most people outside a lab refer to it as a fungus, so do I.)

When the spores land on your potato or tomato plant leaves, the fungus grows and kills the plant. The fungus prefers moist, humid weather. If the leaves of your plants are wet, that is prime growing conditions.

You may have heard me say (a few thousand times) that using a sprinkler in a vegetable garden is bad for a number of reasons, including because it creates prime fungal growth conditions. This is what I’m talking about.

What can you do?

1. Stop using overhead watering, because this creates prime fungal growth conditions.
2. Find an appropriate fungicide and start applying it prophylactically.

I’m not going to provide a list of fungicides at the moment but I will tell you two things:

1. I prefer to use Serenade, which can be used on tomatoes and potatoes for late blight but also on a number of other plants for various fungal and disease issues. Due to both the pandemic and a gazillion new gardeners buying everything garden related they can get their hands on, the price has jumped from $20 to $60 this year.
2. While copper is considered effective, it is possible to overuse and cause long-term soil problems. For most gardeners, that isn’t an issue, as long as you follow the label.
3. ALWAYS READ THE LABEL and follow the instructions there. Honestly, it is frightening how often I see people using all sorts of things without reading and following the label. Just because something is OMRI (organic certifying agency) approved does not mean it is safe under all circumstances.
4. Next year, you can choose late blight resistant varieties. Please note the “resistant” in that sentence. As far as I know, none are guaranteed to survive P. infestans, but some will do better than others. Some common resistant varieties include: Mountain Magic (F1), Plum Regal (F1), Defiant PhR (F1), Mountain Merit (F1),  Iron Lady (F1), Jasper (F1),  Red Pearl (F1),  Legend,  Matt’s Wild Cherry,  Wapsipinicon Peach, Lemon Drop,  Pruden’s Purple

So, what should you do right now? Sign up for the email alerts, do some research on preventative fungicides including reading the labels so you know how to use them if necessary, set up your irrigation so it waters the soil, not the leaves.

Do you need to start spraying right now? I’m not planning to spray yet – 200 miles is still far away. I am, however, keeping an eye on the weather (high humidity? rain?) and the late blight map.