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Try This Technique: Preventive Pruning for Tomato Early Blight

7/3/2008 1:08:26 PM

Tags: tomato diseases, growing tomatoes, early blight prevention, organic disease control, pruning

Several seasons back, Jeff McCormack, Ph.D., founder of Garden Medicinals and Culinaries and Southern Exposure Seed Exchange, shared a tomato pruning method with me that delays the onset of early blight, and reduces the number of leaves lost in the course of the season.

Extension publications often suggest pruning tomatoes to prevent disease by improving air and light penetration. Jeff's method concentrates pruning at the base of the plant by removing leaves that eventually will be lost to early blight anyway. When the lowest leaves are removed just as the first leaf spots appear, you also remove millions of spores. And, because the bases of pruned plants dry quickly, the spread of the disease is slowed because early blight fungi need damp leaves in order to germinate and grow.

What's Early Blight?

The most common leaf-spot disease of tomato, early blight (Alternaria solani) fungi cause leaf spots to form on tomato leaves. Inside irregularly-shaped dry patches (which often have yellow margins), look for small dark rings. These are the fruiting colonies.  The grayish powder inside the dark rings are the spores, which splash or blow onto new leaves to form new spots. When spots become numerous, entire leaves wither to brown.

Commercially-grown tomatoes are often sprayed weekly with fungicides to suppress early blight. Organic growers sometimes use copper fungicides, which are often effective, but frequent use may harm earthworms. A few resistant varieties have been developed, but some failed to perform well in field trials, and others fall short in terms of flavor and texture.

Preventive Pruning

With big indeterminate varieties, prune or nip out all leaves that hang within 1 foot of the ground. If you see numerous lesions on the pruned leaves, you can go higher, to 18 inches. See the before and after photos below.

With stocky indeterminate varieties, trim out most of the leaves that touch the ground, but don't get carried away. If the plants have already set a heavy load of fruit, I also trim off some of the newest blossom clusters to keep the fruit:leaf ratio high. See the before and after photos below.

In addition to pruning, drip irrigation discourages early blight because the plants can be watered without wetting the leaves. Mulch after the plants are pruned to retain soil moisture.

Tomato Early Blight 

 

Early blight starts with a few small lesions, but quickly spreads in damp summer weather. Eventually, the lower halves of infected plants wither to brown.

 

 

 

 

Tomato Before Blight 

 

Before: Vigorous indeterminate tomatoes usually begin to show early blight symptoms just as they load up with green fruits.

 

 

 

 

Tomato After Blight 

 

After: Pruning off low leaves eliminates the damp environment early blight needs to spread, which reduces the number of leaves lost later in the season.

 

 

 

 

Ida Gold before early blight 

 

Before: Stocky determinate varieties that grow close to the ground are often hit hard by early blight just as the fruits begin to ripen.

 

 

 

 

Ida Gold After Blight 

 

After: When pruning determinates, take only the leaves that touch the ground. You can also prune off a few blossom clusters to help keep the leaf:fruit ratio high, which insures good flavor.

 

 

 


Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on .

Photos by Barbara Pleasant



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Post a comment below.

 

bashmacs
7/2/2013 10:48:23 AM

do I really have to wait until plants are dry – in the midst of a very rainy week here in NC, and just noticing early blight – would like to go ahead and start pruning. on plants with blight, fruit is not showing yet, but flowering is in process. thanks!


bashmacs
7/2/2013 10:48:14 AM

do I really have to wait until plants are dry – in the midst of a very rainy week here in NC, and just noticing early blight – would like to go ahead and start pruning. on plants with blight, fruit is not showing yet, but flowering is in process. thanks!


Lori Hirshfield
4/22/2012 8:43:10 PM
For crop rotation, how far away do I need to be from the previous site that is infected with early blight if creating a new separate garden area?

Rita J
8/28/2011 2:39:27 PM
What about Bordeaux mixture? Slaked lime, copper sulfate, water, mix well and spray on the plants. I have used it this year. So far so good.

Carey Clark
6/8/2011 12:39:50 AM
Does early blight seem worse this year? I have never had blight this early in the year. Any suggestions

Barbara Pleasant_3
6/3/2011 9:53:04 AM
Joan, it sounds like the problem is environmental stress, which can't be sprayed away. Install a cloth wind shield to tame the wind (piece of cloth stapled to stakes). If the sun is very hot you can even cover the plants with boxes for a couple of days. Right after transplanting tomatoes need to root, root, root, so focus your efforts on helping that happen. Good luck!

joan bradley
6/2/2011 9:10:47 PM
I have noticed after 2 days being planted and a day of heavy wind withered or blighted leaves which I have removed. Should I be spraying plants or could I use soap suds on the leaves?

Barbara Pleasant_3
7/15/2010 6:46:05 AM
Sherry, you are right in that you can do more harm than good by fussing with your plants when the foliage is wet. But as long as you work when the tomato foliage is very dry, you will benefit your plants by removing zillions of spores as you clip off affected leaves. This may pay off big should you get a prolonged spell of wet weather, which can cause early blight to spread upward into the foliage very quickly. Dry weather, on the other hand, seriously suppresses this disease.

sherry_20
7/9/2010 7:26:10 AM
does anyone know if i'd be wasting my time removing dis eased leaves/branches at the bottom once the early blight is in progress? or am i spreading it further just fooling around?

Muyatwa
1/14/2010 1:08:15 AM
My tomatoes have developed early blight what chemical should i use to cure them?

temba pilime
7/25/2008 2:08:56 AM
effects of pruning tomatoes

Laura_1
7/19/2008 1:39:57 PM
Your plants are probably drooping due to heat stress. Many plants do this during hot days, and they recover at night. In my garden, it's the peppers that are affected the most. Check your tomato plants a few hours after the sun sets or very, very early in the morning - chances are they'll recover on their own. Excessive watering won't help!

Debbie_2
7/18/2008 12:57:33 PM
Thanks for the advise but I was wondering if you could tell me why my top leaves are wilting everyday even though they are getting enough water. I have them in containers and it is only one of the plants and that one is very tall. They containers are huge so I can't figure it out. Thanks! Debbie

Debbie_2
7/18/2008 12:53:09 PM
I have a question.....my tomato was doing great and it is probably five feet tall now. I water the heck out of it but the top leaves still droop!!! really bad!!! The plant next to it which isn't as tall is doing fine with less water. I have them in big containers. I check the soil of the larger one with drooping leaves and it is moist. So why are my top leaves hanging their heads? Thanks, Debbie

Don_1
7/10/2008 9:48:25 PM
WOW! I was just seeing this spot on my Brandywine and wondered if good old Mother Earth News would know anything about it and it's on the front page. I will be pruning in the morning. Thanks for rocking my socks off always.







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