Last year, area farmers took a blow from the pervasive appearance of late blight (Phytophthora infestans) on tomato crops. A water mold that ran amok in last year’s cool, damp summer, the blight remains famous for its historical reasons: it was responsible for the crop losses that caused the Great Potato Famine in Ireland in 1845-1847. And last year, it devastated the tomato harvest.
Dave felt the blow: his total harvest of heirloom tomatoes was easily halved, thanks to the damage to plants and fruits caused by this disease. This year, we know we face the threat again, since the blight inoculum remains in the soil.
As you might have noticed above, the same disease can affect both potatoes and tomatoes — both are nightshades, of the genus Solanum — and since eggplant is also a nightshade, I wonder about that as well. Dave practices crop rotation faithfully this year, avoiding the placement of tomatoes in the same areas as the previous year, but since potatoes are another large crop on the farm, there is bound to be some overlap of Solanum species.
So when we heard that late blight had been confirmed both in Pennsylvania and Michigan, Dave decided it would be sensible to take precautions. There are a few sprays and such that are approved for use on certified organic crops, and the prime candidate used as a preventive against blight is copper hydroxide. The Ohio Ecological Food and Farm Association (OEFFA), the group that certifies Dave’s farm as organic, approved the use of this substance, so Dave called in an order for it, receiving it the very next day.
As with other sprays, copper hydroxide must be handled with care (it is mildly corrosive) and must be applied on a dry and not windy day. Dave pulled out one of his sprayers, mixed up a batch, and applied the preventive to two plots of tomatoes, leaving a light turquoise mottling on the leaves and early fruit.
Along with the spraying regimen — every 7 to 10 days, or after rain — we will keep our eyes open for potentially diseased foliage, fruit, and plants and remove them from the field as quickly as possible, adding them to the burn pile since they are not compostable. We’re using that same vigilance on the potatoes and eggplant, too, and I find in my own gardens I am eyeing the plants warily for suspicious spots.
Everyone connected with agriculture — farmers, researchers, and others who have a keen interest in the subject — are paying attention to blight this year, given last year’s destruction and this year’s wet start to the season. Cornell University — excellent resource for all matters agricultural — has a great fact sheet about blight that will answer many questions. USpest.org has a regularly updated map showing where late blight conditions are favorable or confirmed. There’s nothing showing in our area yet, but we know it’s there, waiting.
Here’s hoping we’ll be ready for it.