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Basil downy mildew11/22/2023 ![]() If the weather dries sufficiently, though, the disease will subside. ![]() But one brief rainstorm could be enough to initiate the disease, if spores are present, even in a normally dry region. Gardeners living where the humidity is always low probably won’t have problems with BDM. If the summer is hot-in the mid 90’s and above- and the nights don’t cool off very much, the relative humidity won’t rise to the critical 80-85% level required for germination. But over the past few years, BDM has struck earlier in the growing season. Most years, we can grow basil successfully for a few months before the humidity increases. So, even during comfortable daytime weather, the infection gets its start quietly, hours before the alarm clock goes off. With BDM spores on a susceptible variety, 2 or 3 hours of high humidity will get the disease growing. It’s usually around dawn, the coolest hours, that the relative humidity reaches its highest reading. Here’s how:Īs the temperature decreases through the night, the relative humidity rises. Local weather reports will indicate the relative humidity, and you might be surprised by how high that number is at dawn, even during “nice” weather.Īlthough you might not have had rain or high humidity during the daytime, your basil can still become infected. Microscopic BDM spores on the leaves need relative humidity above 80% or 85% for only a few hours in order to germinate. ![]() Why? Because humidity causes the problem in the first place! The first thing to do is to discard the clear plastic wrap around the plant. The local grocery store had full sweet basil in small pots, so I bought one. I picked the good green tips, and kept them indoors in a glass of water until they went into tomato-basil salads. ![]() We’ve had a very rainy spring and summer so far (2020), and this plant started showing signs of distress by mid June. It had been growing in a large pot with a tomato, so I cut the basil at soil level and threw it in the trash. The leaves became yellow overall, and black spots showed up. The condition worsened, as it infected more leaves and more stems. The plant looked fine one day, and the next morning it looked like this! After a stretch of high humidity or rain, the symptoms became readily apparent. BDM targets only basil.Īs you can see in the photo, above, formerly healthy green leaves developed yellow patches bordered by the main veins. You need not worry that Peronospora belbahrii will infect other plants in your garden. But there’s more to it than just growing them in pots, as you’ll read later. The plants grown in the garden, however, almost always have succumbed to BDM. I’ve successfully grown it in pots every year since the disease was first identified in the United States. Once the disease has reached your plants, you might think it’s all over.īut it isn’t! By managing it differently than you normally do, you can have beautiful basil once again. This water mold has been seen in more than 44 of these United States, and in just about every country where this herb is grown. Well, join the club! For over a decade, we’ve been dealing with spotty ugly basil, infected by that awful disease known as basil downy mildew. And it used to be so easy to grow! Now their leaves develop black spots every summer, and they’re yellow between the veins. From Anchorage to Adelaide, readers at The Farm In My Yard clearly have problems with this herb. Gardeners throughout the world are having issues with basil. It just doesn’t look quite right, which prompts the question, And don’t forget the basil!īut you’ve noticed how basil has struggled the past few years despite all the suggestions offered by the garden center. ![]() What could be more refreshing than a garden salad harvested from your own back yard? We love our tomatoes, cucumbers, green onions, ripe sweet peppers, and the ‘Tango’ celery added to mixed greens. ![]()
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