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Tomato Blight
Without a lot of further ados, let me give you my take on blight.
Three Kinds
Unfortunately, there are three kinds of tomato blight" that youre 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. Youll get fruit if you have this problem.
Blight Two
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 youll get fruit but the yield will be reduced.
Least Common
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 wont 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 youve got the problem solved and the next years 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 hybrid cultivars.
What Can Be Done
So if you have the problem now, what can you do?
Generally if youve already seen the problem, theres 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 youve 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 (Ive 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
Ive 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 be water-splashed.
No Work When Plants Are Wet
If the dew is on the plants, youve 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 anything can.
Rotate
While Ive written this advice before, Im 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 theres 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 the problem.
Don't Compost Blight
If you have plant debris and youve 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).
Do you have a question about Tomato Blight?
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