Late Blight Found on the Farm


We are very sad to report that late blight (Phytophthora infestans) has struck some of our outdoor tomato fields in Montague.  This disease is the most dreaded disease that exists for tomato and potato growers. We saw it first on our farm in 2009, weeks earlier in the season, where it caused massive crop loss and severely impacted us financially. It is the disease that caused the Irish Potato famine in the 1800’s.  It has been increasingly found in Massachusetts and the Northeast in general over the past few years.

The early spread of the disease in 2009 was due to infected plants sold by big box stores. This year the disease traveled north by natural dispersal, though faster than in other years. Usually we don’t see much of late blight here – if it arrives at all, it comes after our plants have mostly died back from the common and omnipresent septoria leaf spot and early blight (these are much slower moving diseases).

The rainy and humid weather that we have been having the last week or so creates perfect conditions for this disease to thrive (while it has been a relief of the drought).  The disease spores travel very easily on wind, clothes, hands and farm machinery, so plant pathology experts at Umass have been alerting growers to be on the look out for this disease as it came up the Atlantic states.  Many organic farms in the valley are finding it in their fields. All tomato fields in Massachusetts are at high risk for getting infected by this disease.  Potatoes are also in danger, though there are no confirmed infections of potatoes to date in the state. The disease spreads with devastating speed and can kill healthy tomato plants within one week of initial infection.

This is what our tomato fields should look like:

field crops




2009 tomato field with late blight




Meanwhile Umass extension recommends that we spray all of our still uninfected tomato and potato fields with a copper material at least once per week until the crops ripen.  This is fixed copper and is the only material that certified organic growers can use that has a chance of slowing the spread of the disease.  Even though it is a naturally occurring metal and is allowed for use in organic farming, it is a material that can irritate the eyes and skin of the person applying it.  For this reason you may see us driving around the farm on the spraying tractor wearing a mask and goggles as a safety precaution.  There is a possibility that you will see some of the green residue of this spray on the tomato fruits, and if you do you should wash the fruits before eating.  Copper in this form has a very low toxicity to humans and animals, but it is important to wash it off the fruit.
We don’t like having to rely on a spray to fight this disease, but we see no other alternative.  Our tomato crop is at very high risk and even with the spray we might lose most of the tomato crop.

Here is a close up of an infected plant, showing affected stems and browned leaves:
Close up of plants and tomatoes with late blight

Here is a close up of tomatoes in which the fungus is living and sending out spores:
Late Blight on Tomato Fruit


At its worst, late blight could cause us to lose a massive amount of tomatoes, meaning that shareholders would not get as many tomatoes for the season as we had hoped.  However, if the copper can prevent the fungus from inoculating and infecting the leaves and fruits on our later season plantings, we might still get a crop. We do expect it to impact the farm financially, as tomatoes are a big part of our business, as ingredients in our shares, through bulk orders to our members, in retail sales and in offerings to our wholesale restaurant and store customers.

Compared to the losses of 2009, we are doing much better, as we had dead fields by the end of July in 2009. We have some separated fields in Montague that are not showing signs of infection yet. We also have a section of heirloom tomatoes for the Tomato Festival in Granby that are not infected yet.

Our tomato plants this year in Montague were looking loaded with fruits, one of the best-looking crops we’ve seen – and we hope that we will still be able to harvest a portion of these before the disease progresses. Since we plant so many acres of tomatoes, we have high hopes that even in the event of a major loss, we will still be able to provide tomatoes to our members for weeks.  We will just have to wait and see.  We can also protect our later season tomato plants in hopes of those turning out healthy.  Dry weather with little rain is also helpful in preventing the spread of the disease. Though we don’t want too much of that either!