Having late blight arrive in my gardens in 2009 was like adding insult to injury.
We managed to miss the early round of blight as we grow all our own seedlings. It did arrive on the wind however, and around July 18th I had decisions to make. Basically I decided I was NOT going to lose my tomato crop. That meant getting an NOP approved copper fungicide formulation – Champ WG. And we bought two new hand-held sprayers.
The information for the average gardener was incomplete and conflicting – far too little to guide a sensible approach. The most prevalent advice was “It’s terminal. Kill all your plants.”
Here’s what I did instead.
I got informed. I read all the references I had about tomato diseases. The most cogent information came from The Compendium of Tomato Diseases (Jones, Jones, Stall and Zitter, APS Press) and from Cornell’s extensive information site. Bruce Watt at the UMaine labs was also very helpful.
I started monitoring twice every day AND trained the young folks who work for me to SEE the difference between early and late blights.
When it arrived we attacked it systematically and frequently.
We pruned extensively and followed each pruning with a copper spray (a total of 5 times at the recommended 5-10 day interval). We do not have professional equipment and so we could not get full coverage of the LEAVES. However, it turns out that it was enough to stay ahead of much of the infection AND THE SPRAY ACTUALLY PROTECTED THE FRUIT.
We stayed at least one step ahead of the infection, and as a result I have a fabulous tomato crop. The learning curve resulted in some real observations that anyone can use.
Know what you’re looking for, monitor frequently and GET IT IMMEDIATELY. DON’T DOUBT IT... ACT! Clip off every infected leaf and stem. Over and over again. Take all infected material to the dump – NOT the compost pile.
Early blight shows up as drying and dying leaves AT THE BOTTOM OF THE PLANT.
EB can be managed culturally, and if managed should not result in significant loss of crop.
Late blight usually starts at the top of the plant or on the WINDWARD SIDE. As the earliest infection arrives on warm southerly winds, the south/southeast side of the garden should be monitored carefully. Later in the season the wind can also bring it from your neighbors garden, from any direction.
Early in the season late blight infection shows as roundish lesions on leaves, and uniquely will CROSS THE CENTER VEIN OF THE LEAF. Later blotches appear on stems, and still later, hard crusty lesions form on fruits.
In the mean time, the fruit can be protected from spore contact with an anti-fungal spray.
Look for stem lesions and cut below the lesion. LOOK at the cut stem: if there is discoloration in the pith of the stem, cut again lower. When the pith is a clear green you’ve gotten it (for the moment!)
Understand that the fruit is infected by spore contact, not systemically. Spray set fruit to protect it. While pruning the first time we cut open several fruits on heavily infected plants and found them to be just fine... thus connecting the dots. Protecting the fruit is the goal. Harvest fruit early – just beginning to ripen and WASH FRUITS WITH SOAP AND WATER to remove the copper and clean them so they can continue to ripen without further spore contact. There are protocols recommended by many experts. But many of these are farm sized solutions. The small scale family gardener is another matter. We have the privilege of a walk through the garden and daily attending to our plants. Consistent observation and action will see you through most problems. We need to look ahead to next year and stay informed about managing a healthy garden. Buy locally grown seedlings, use certified disease free seed potatoes, and pull out ALL volunteers in 2010.
Here’s the text of the doc I’ve been passing out at Farmers Market and the Common Ground Country Fair.
HOW TO PREVENT LATE BLIGHT IN 2010
This has been a really tough gardening season – no news to anyone!
With cool temps and over 20” of rain, the scene was set for disease. When big box stores sold plants pre-infected with late blight, the conditions were just right. As a result, the blight popped up all over New England and as far south as Maryland - all at once. There was a fast spread and only pockets of gardens were spared. As many of you know, lots of folks lost their tomato and potato crops.
Phytophthora infestans affects both potato and tomato plants. The blight strain in Maine this year is the same as the blight that caused the Irish Potato Famine. Late blight is a systemic infection. When it reaches maturity it releases wind borne spores. The spores can travel as far as 30 miles. This fall garden clean up is essential. Tomato plants need to be removed from the garden and taken to the dump. The blight will not live over the winter unless there is live tissue. For this reason it is not wise to compost potentially infected plants. In 2010 buy your tomato starts from a local garden center or from folks you know. Locally grown cannot be pre-infected.
POTATOES WILL BE THE 2010 PROBLEM
Potatoes will live over the winter in your garden. "The one you missed" will come back next spring as a volunteer, and could potentially infect your garden (and your neighbors’) again.
ALL 2010 POTATO VOLUNTEERS SHOULD BE DESTROYED.
Careful potato harvesting this fall will help prevent continuing infection. Cut off all potato foliage, both dry and green, and take it to the dump. Leave the spuds in the ground for a good two weeks. Removing the foliage means you will not dig your potatoes and drag them through potentially infected foliage.
DIG AS COMPLETELY AS POSSIBLE.
Put your crop out in a single layer, in a warm, dark, and dry area to cure. If any potatoes are infected they will show it at this point rather than by infecting your entire crop in storage. In 2010 do not use saved potatoes as planting stock. Buy new, certified disease free planting stock. Folks selling seed potatoes should be able to show that their seed is certified.
References: http://www.nofasummerconference.org/lateblight.html
