Tomatoes and Blights

You can definitely feel autumn in the air.  Mornings are crisp and cool, but not so cool that you can't be outside in your shirtsleeves  - or pajamas.  :)  The days are warm, but not too warm; and the nights are just perfection.  I love this time of year - as long as I don't think about what's right around the corner.

Fall is a busy time in the gardens.  The vegetable and fruit gardens are putting on their last hurrah.  One picking of tomatoes yielded 14 quarts of crushed tomatoes, 10 quarts of spaghetti sauce, 12 pints of garlic-basil-tomato sauce, 15 pints of salsa and 12 quarts of tomato soup.  Plus about 60 pounds of tomatoes given to friends and family.  I really hope next spring when I am too tender-hearted to throw away those extra tomato seedlings, someone reminds me of this season's excesses!

This over-achieving production is in spite of having some problems with tomato blight.  It appears that there may be a variety of blights attacking my tomato plants this year.  That's one of the dangers of a wet growing season, and of growing tomato varieties that aren't resistant to the various tomato diseases.  I am pretty attached to my Sheyenne and Cannonball tomatoes that were developed by North Dakota State University specifically for success in our North Dakota soils and growing conditions, so I am willing to take the risk on blights.  My brother, who was one of the recipients of some of the excess this year, said these tomatoes made the best tasting salsa he's ever had.  I happen to agree with him - they are firm, meaty tomatoes with a rich, tomato taste.  People who choose to grow heirloom varieties of tomatoes feel the same way about their tomatoes - the benefits of those varieties make them worth the extra trouble and the risk of blights. 

Early blight (internet photo)

Early blight is caused by the fungus Alternaria solani.  It comes from the soil and starts attacking the lower leaves of the tomato plant.  The first indication is usually some large, irregular brown spots which appear on the leaves and may have lighter, yellow spots in the center.  Eventually the entire leaf withers, dies and falls from the plant.  The fungus also infects the fruits, causing dry, leathery sunken spots near the stem end.   The dying off of the leaves makes the tomatoes prone to sunburn because they lack the protective foliage cover.   If this blight occurs early enough in the season, it can decrease the vigor of the plant and diminish production for the year.  (As you can see above, that was not a problem with my tomatoes this year.)

Septoria leaf blight, caused by the fungus Septoria lycopersici, occurs later in the growing season.  It makes its initial appearance as small yellowish-tan blotches on the leaves, with a dark halo around them.  They are smaller than the spots of early blight and are more regularly shaped.  They may have dark spots in the center of the lesions, called "fruiting bodies".  Infected leaves generally drop from the plant, again leaving the tomatoes susceptible to sunburn and rotting.  Spots may also appear on the stems and the blossoms, interfering with fruit production.

Late blight is caused by the pathogen Phytophthora infestans, which is classified as a "water mold".  This pathogen attacks both tomatoes and potatoes.  In fact, its greatest claim to fame is the Irish potato famine during the 1840's.  It makes its appearance on tomatoes as regular or irregular oily looking spots.  A distinctive difference between late blight and other blights is that while early and Septoria blight attack the lower, older foliage first, late blight attacks the plant from the top down, affecting the youngest foliage first.  Late blight also more readily attacks the fruit, causing dark, mushy lesions, which may be more pronounced at the stem end of the tomato, but eventually cover the entire tomato.  The rotting tomato emits a distinctive, foul odor.  I've found that while you can trim out affected spots on tomatoes affected by other blights, tomatoes affected by late blight often have a nasty taste throughout the entire tomato.

As with all fungal infections, prevention is the best cure.  Good air circulation goes a long ways toward preventing fungal and mold diseases.  Remember those little seedlings I couldn't bear to throw away?  Well, at Wiese Acres, I have a limit to the space in my vegetable garden.  So, my tomatoes ended up a little more crowded than they should have been this year.  Strike one for my tomato plants.  Then, my tomato foliage went crazy and I didn't take time to properly prune the plants to keep them from completely overfilling the tomato cages.  Strike two.  Then, we had days and days of rain and even when it wasn't raining, we had cool, damp, gloomy weather.  Strike three!  And I had blights. 

Once any blight appears, if it is not extensive, you can gain some control by pinching off the affected  leaves and destroying them, then spraying the plant with a fungicide to prevent or at least slow further infection.  Chlorothalonil or mancozeb are effective against the blights, or for an organic solution, copper based sprays may provide some control.  Fungicides are more preventive than curative, so it's best to spray before any symptoms occur.  I'm a sort of "just in time" gardener, though, so it usually doesn't occur to me to spray fungicides before I have fungal infections. 

It will be critical to clean all the infected foliage off the garden and destroy it.  This debris definitely doesn't belong in the compost pile.  It will either be bagged and taken to the landfill, or it will be burned.  Next year, I will need to be careful to not plant any plants in the nightshade family (tomatoes, potatoes, eggplant, peppers) in the same area, as the spores of the fungus can overwinter in the soil.  I'll need to make sure that I don't overcrowd things next year, and if I irrigate, ideally, it can be done with a drip system.  If overhead irrigation is my only choice, it will need to be done early in the day when the leaves won't stay wet for extended periods.  I'll also check the nutrients in my soil.  Blights are much more likely to attack plants that are less vigorous and proper fertilization is one way to foster good, healthy plants.  I'll also place some mulch around the base of the plants as the mulch may stop any spores that may still be in the soil from splashing up onto the foliage and setting up housekeeping.

On a positive note, I did not have any blossom end rot.  I save my egg shells for several months leading up to planting time, crush them, and sprinkle a handfull in the bottom of the planting hole.  This supplies needed calcium for the tomato plants.  In addition to having the calcium available to them, though, they need to have even, consistent moisture to allow the calcium to be absorbed into the plant and fed to the tomatoes.  One or the other alone may not prevent blossom end rot, but the two together is just about a guaranteed prevention.

So, I've learned a few things to not do with tomatoes this year.  As I think about my aching feet and look at my reddish tinged hands, I can't help but think that throwing away those extra seedlings might just be the most important lesson, though.