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When I started working at Gardener's Supply in the 1990s, my Vermont backyard was pretty green—with grass. Today, there's just a tiny bit of the original lawn left. Most of the available space has given way to trees, shrubs, perennials, annuals and stonework. Watch a slideshow of my garden in Burlington, VT.
In addition to my work at Gardener's Supply, I work in the gardening division at Church Hill Landscapes. In that role, I maintain dozens of gardens and learn a lot in the process. I believe that all gardening is good gardening.
Late blight, a disease that strikes tomatoes and potatoes, can quickly ruin an entire crop — and infect other plants as well. It is critical that gardeners understand that late blight is not like other tomato and potato diseases. Many other diseases affect these crops in home gardens, but most of them only affect leaves or cause limited damage to fruit, and while they may reduce the harvest, they generally don't cause a total loss. In the last few years, late blight has become a major threat to both home gardeners and commercial growers. It's important for gardeners to be aware of this disease so they can act quickly.
Furthermore, because most pathogens are not readily dispersed by wind, their effects are localized. Late blight, on the other hand, kills plants outright, and it is highly contagious. Its occurrence in your garden can affect other gardens and farms due to the wind-dispersed spores.
The fungus, (Phytophthora infestans), that causes late blight is aptly named: phytophthora in Latin means "plant destroyer." Infected plant tissue dies. Outbreaks spread quickly under favorable conditions (cool, wet weather) because the pathogen can produce huge numbers of wind-dispersed spores. Once a plant is infected, it must be destroyed.
The USA Blight web site tracks the occurance of late blight in real time. Check the site regularly during the growing season. When late blight is detected in your region, consider a weekly prevetative spray.
Cornell plant pathologist Meg McGrath suggests using Actinovate (which contains the beneficial bacteria Streptomyces lydicus) as a preventative spray, and adding a copper-based product when late blight is present.
Remember that while these sprays can help reduce the likelihood of infection, you still need to monitor plants closely.
Unfortunately, there's no silver bullet for control. The key is to plant wisely, be prepared, be alert and learn to distinguish late blight from other common diseases.
Make sure you know what late blight looks like. Draught stress and two other diseases look similar but unlikely to kill your plant. The images at right can help you distinguish them.
If treated plants show signs of continuing infection or if unsprayed plants succumb to late blight, take action immediately:
If left unattended, the disease will spread quickly from your plants to those of your neighbors and local farmers. Please, garden responsibly!
Last updated: 2/27/19
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