5 August 2009

LATE BLIGHT PLAGUE

As if this gardening season hasn’t been difficult enough - what with the rain and cool temperatures , deer damage, slug damage and miscellaneous small animal damage – disaster struck today!

The Late Blight disease, which afflicts plants in the Solonaceae family (including tomatoes, eggplants, potatoes, peppers), has been in the news this season as one farmer after another in the Northeast has lost their crop of tomatoes. I haven’t heard about potatoes being infected in this region, but potatoes are traditionally very susceptible to the disease too. It will only be a matter of time, in my opinion.

As an interesting historical note of how plant pathology has affected demography, the Irish Potato Famine beginning in 1845, was caused by the Late Blight fungus. Because of the extent of potato growing in Ireland and the reliance of the people on the potato as their staple food, at that time, the devastation of the potato crop caused famine and brought about the mass migration of Irish people to America. (Of course, delving further into history tells us that the famine could have been avoided but representatives of the government – Britain essentially – blocked famine relief efforts. I’m a Brit and I’m not proud of this. My family were immigrants to England in the late 1880’s so we weren’t actually there when this was happening. We were too busy being persecuted in Eastern Europe! Phew, what a relief.)

This week, after a tomato-less summer, we finally picked a couple of luscious large tomatoes and a bowlful of cherry-sized. But, today, the dreaded disease was seen on our most advanced and previously healthy plants – loaded with large ripening tomatoes.

Sadly, we had to immediately remove the plants out of the raised bed. We harvested all the healthy, unblemished green tomatoes, and burned everything else. We made a small bonfire on a wood pallet and built up the fire with sticks and split logs, dry leaves, mulch hay etc. and fed the diseased plants and tomatoes on the top, a little at a time. Everything was burned and then we turned our attention to our tools, shoes etc. Anything that may have come in contact with the infected plant parts were washed in a light bleach solution. This is mixed with 1 part bleach and 9 parts water. Clothing went straight in the washing machine with a little bleach added to the rinse cycle.

We have have garden beds in different locations, so there are other tomato plants, peppers, eggplants and potatoes elsewhere. We do not know yet if these other areas are infected and only time will tell. A nice planting of eggplants are growing in the same bed as the diseased tomatoes and, although they look healthy now, I am pessimistic about their future. This year, we have six different varieties of potatoes growing and they have been fabulously prolific so far. If the disease takes them, we should still be able to eat some of the potato tubers themselves – if they are not rotted – but storing them through the winter will probably not be possible.

To store potatoes, they need to be dug as late as possible in the season so that the skins have time to toughen-up. If we have to dig them up soon, the skins will be thin – delicious for immediate cooking but not storing. We’re keeping our fingers crossed that this part of the garden will be spared.

Late Blight manifests first as dark, wettish spots on the leaves and then streaky dark areas on the stems. The leaf spots appear dark in the middle and have a characteristic pale green halo. If left to develop, the plants will rot and smell nasty.

Typically, the only possible solution for this disease is spraying with fungicides – which I do not do in my garden since I’m an organic grower. I am going to look into the possibility of using a copper-based solution which has anti-fungal properties. It is possible that this is an acceptable material for organic growers. More information on this to come.

To read more about Late Blight, and to see photographs of the diseased plants, visit Cornell University’s Fact Sheet web site at:
http://plantclinic.cornell.edu/FactSheets/lateblight/late.htm