The Three Kinds of Tomato Blight You'll See in the Home Garden
Just when you think you've escaped tomato blight - it's that time of
year and when you think you're about to get a great harvest of
tomatoes, the proverbial compost hits the can.
Without a lot of further ado's, let me give you my take on blight.
Unfortunately, there are three kinds of "tomato blight" that you're
likely to see in your garden at this time of year.
The first one and most common is "Septoria leaf spot".
This particular problem appears roughly around the end of July and
starts out as small round black or brown rotting marks on the lowest
leaves. It works its way up the plant to hit all the leaves but it
starts from the bottom first. You'll get fruit if you have this
Early Tomato Blight
The second most regularly seen tomato blight is Early Blight.
It usually appears about the same time as the Septoria but it has
concentric target-shaped marks. In other works, the spots on the leaves
look like targets with circles within circles. This tomato blight
spreads all over the plant and you'll get fruit but the yield will be
The least common of these tomato blights is the Late Blight.
It appears later than the first two and the first symptoms are a watery
type of lesion on the lower leaves. If you get this one, you won't have
to ask what you have because the elapsed time from the time you first
see it to the time the plant wilts and dies is about a week. If your
tomato plants simply shrivel up and die with big brown spots on the
leaves – and it seems to happen almost overnight – your plants are
suffering from Late Blight.
The interesting thing about the tomato blight problem is that they
are not regular.
There are a multitude of causes and seasonal
variations and you think you've got the problem solved and the next
year's weather will come back, change, and create the problem all over
again. I do note that the older tomatoes – the heirloom varieties – do
tend to be more susceptible to tomato blight problems than the newer
Late blight- when the entire plant looks like this in about two days. Fast! And the tomatoes go mushy
What Can Be Done
So if you have the problem now, what can you do?
Generally if you've already seen the problem, there's not a lot you can
do. A preventative spray of lime-sulphur or Bordeaux mix will slow down
the spread of Septoria and Early Blight but the real key is in the
prevention of the problem
Next spring, mulch your tomatoes. Mulching will reduce the stress on
the plant but more importantly it will prevent "splash-back" from the
ground to lower leaves during rainstorms.
If you've ever noticed the lower leaves on tomato plants tend to be
dirt splashed, it is because rain or overhead irrigation tends to
splash dirt up. This dirt can contain the spores for blight and it is
this inoculation that we want to avoid.
Install drip irrigation or use individual watering bottles (I've
written about them before) with pinholes in the tops to water each
plant. The trick is to prevent the splashing while ensuring the plant
has enough water.
No Evening Watering
Do not water in the evening. We want our leaves to be dry going into
the evening. Damp leaves and dark conditions are ideal for spore
starting and keeping those leaves dry is the way to keep them healthy.
Crowding Is A Problem
I've said this before but too many folks try to crowd tomatoes
together. You really do need to space them apart. I find that staking
the plants and giving them at least two square feet each is the best
way to keep those leaves dry. I also prune off the lower leaves once
the plant has set that bottom cluster of fruit. This lets the air and
sunlight into the fruit and it also removes those lower leaves that can
No Work When Plants Are Wet
If the dew is on the plants, you've just watered, or it has just
finished raining, do not work around the plants. Your hands and
activities around the plant can spread the problems as quickly as
While I've written this advice before, I'm about to do so again. Do not
plant any crop in the same place more than one year. Planting in the
same spot from year to year is simply an invitation to problems. They
build up in the soil and there's little you can do to prevent them
using your tomatoes as a food source. And I don't care how small your
garden is, you have to move those tomatoes from year to year if you
want to avoid this problem.
Other Plants Affected
Also do not plant peppers, potatoes or eggplant in that garden region
as they will act as alternate hosts and be just as quickly wiped out by
Don't Compost Blight
If you have plant debris and you've had a problem, do not compost this
material. The average home composter is not working at a high enough
temperature to knock back the overwintering spores so the best thing
you can do is bag up the dead leaves and stems and send them to the
dump or municipal composting facility where the compost temperatures
are high enough.
If you do see a branch with a problem, prune it out immediately. Do not
let is sit on the plant to infect all other parts of the plant and
reduce your yield. Similarly, remove weeds from around your tomato
plants. They reduce air circulation, scavenge nutrients your plants
need and can act as a host for tomato blight.
Select Disease Resistant Plants
If you have a problem with tomato blight, then do plant modern
cultivars with disease resistance. Look for letters after the name of
the plant in seed labels that might say "V" for verticillium resistant,
or "F" for fusarium resistant. While not specifically blight resistant,
they do have better overall resistance to tomato blight problems than
those without those initials.
In the case of the tomato blight, the cure rests in good gardening
techniques rather than any kind of magic spray (organic or otherwise).
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Can You Eat Tomatoes from Blighted Plants?
The reality is that if your plant is hit with late blight, you won't be able to harvest a good tomato. The fruit rots almost as fast as the leaves do.
If the leaves are just spotted and marked with early blight or other disease, then yes you can eat the fruit.
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