With the problems a lot of gardeners across the country have had with the wetter and cooler than normal summer, adding diseased tomatoes on top of that could be the straw that breaks many backs.
Late Blight at Red Fire Farm
Late blight, an infection of tomato and potato plants caused by Phytophthora infestans, gained infamy as the cause of the Irish potato famine. Now, it is rearing its head in one of the worst outbreaks in North America, mostly on the east coast, due to large retailers sourcing possibly infected tomato seedlings from a single nursery, Bonnie Plants, which has since recalled $1 million worth of plants. (C&EN requested comment from Bonnie Plants, and if the company gets back, this post will be updated.)
Such threats to crop production have led to myriad methods by which a grower can determine when to preventatively spray a chemical to protect his or her crops from any number of insects, fungi, or bacteria. For example, a Beaumont Period (during which the temperature is not less than 68 degrees Fahrenheit and the humidity is not less than 75% for 46 of 48 consecutive hours) encourages P. infestans proliferation, and if such a period occurs or is predicted to occur, fungicide application is recommended.
Some fungicides that act against P. infestans include mandipropamid, a chemical whose probable method of action is blocking phospholipid biosynthesis and cell wall deposition, and copper fungicides--used by organic growers--which come in various formulations, including mixtures with copper sulfate or copper hydroxide, and have multiple targets in cells, most likely denaturation of proteins. Late blight is such a problem that companies are continually developing new products to combat the infection--last year, BASF came out with Initium, which is billed as a new class of chemical for use against P. infestans and is pending regulatory approval in South America and Europe.
The home grower can use forecasting and treatment tactics to avoid diseases on crops, but such proactive (and possibly unnecessary) treatments may be more costly, as sprays are done earlier and more frequently than would be done with reactive treatment. But waiting until a disease rears its montrous visage may mean having to rip up, bag, and throw away rows and rows of well-loved plants. A spokesperson of the Maryland Cooperative Extension says that once you have late blight, that's it--the only thing to do is off the plant and toss it in the trash.
Late Blight on Tomatoes at Red Fire Farm
Some home gardeners hope to avoid pulling up plants by spraying copper fungicides. Treatment like this might possibly work on a home-grown scale, but Granby, Mass.-based Red Fire Farm's Sarah Ingraham says her organic farm's tomatoes were not so lucky. Last week, they first noticed signs of late blight on 1/4 of all of their tomato plants--a full two acres, the worst-infected of which were ripped up and thrown away. They are now spraying the remaining plants with NuCop 50 WP, a copper fungicide that contains copper hydroxide.
Ingraham says the farm has never had such an outbreak of late blight, and because the farm starts its tomato plants from seed, the source of the fungus may have been local home growers who bought the mass-distributed infected plants (P. infestans sporangia can travel miles on the wind). To prevent disease, Red Fire Farm alternates rows of tomatoes with smaller plants, such as peppers, for better air circulation (which decreases humidity and prevents rows of plants from touching and spreading innoculum); rotates crops to prevent disease-causing microbes from building up to high concentrations in one area; and mulches to prevent inoculum from the soil getting to the plants during watering or rain--only when a dire situation arises does the farm use certified-organic chemical treatment. "In wet years, tomatoes face a lot of diseases anyway," Ingraham says. But don't worry about not having tomatoes this year; "there are other good things out there to buy from local farms," she says.
Above photos by Sarah Ingraham/Red Fire Farm