Six Tips for Dealing with Tomato Blight

July 19th, 2010

At this time of year, there are three kinds of “tomato blight” that you’re likely to see in your garden.

Blight One: Septoria Leaf Spot

Septoria Leaf Spot is the most common blight, and it 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 will still get fruit if you have this problem.

Blight Two: Early Blight

Early Blight is the second most regularly seen tomato blight. It usually appears about the same time as the Septoria but it has concentric target-shaped marks, the spots on the leaves look like targets with circles within circles. This tomato blight spreads all over the plant and you will still get fruit but the crop will be reduced.

Blight Three: Late Blight

Late Blight is the least common of these tomato blights. It appears later than the previous two and the first symptoms you will see are watery type lesions 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 overnight, your plants are suffering from Late Blight.

What Can Be Done

Generally if you’ve already seen the problem, there’s not a lot you can do. A preventative organic spray of Lime-Sulphur or Serenade mix will slow down the spread of Septoria and Early Blight but the real key is in the prevention of the problem. The cure rests in good gardening techniques rather than any kind of magic spray.

Mulch
Mulching will reduce the stress on the plant and it will prevent “splash-back” from the ground to lower leaves during rainstorms. The lower leaves on tomato plants tend to be dirt splashed because rain or irrigation tends to splash dirt up. This dirt can contain the spores for blight.

Rotate Crop
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. Spores build up in the soil and there’s little you can do to prevent them from using your tomatoes as a food source.

Don’t Water At Night
Do not water in the evening. You want your leaves to be dry going into the evening. Damp leaves & dark conditions are ideal for spore starting and keeping those leaves dry is the way to keep them healthy.

Do Not Crowd
You really do need to space tomato plants apart. Staking the plants and giving them at least two square feet each is the best way to keep the leaves dry. Also prune off the lower leaves. This lets the air and sunlight into the fruit and it also reduces watersplash.

Don’t Compost
The average composter does not get hot enough to kill the overwintering spores so the best thing you can do is bag up the waste.
If you see a branch with a problem, prune it out immediately. Do not let it sit on the plant to infect all other parts of the plant. Also, pull out any weeds from around your plants – they reduce air circulation, suck up nutrients and can act as a host for tomato blight.

Select Disease Resistant Plants
If you have a problem with tomato blight, plant cultivars with disease resistance. Look for letters after the name of the plant 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.

-By Maggie Oldfield Thayer Nursery

Tags: Lawn and Garden, organic gardening, Tomato Blight
POSTED IN: Lawn and Garden, Problem Solvers, Tomato Blight, Vegetables  |  10 COMMENTS »