The Battle of the Blight

There is a moment in every garden season where I feel downright discouraged and defeated in my efforts.  That moment is when I realize that Early Blight has taken hold of my tomato plants.  Every year, I try so hard to be diligent in my watering, staking, and pruning, and every year those hopes sink when I see those tell-tale spots and yellowing leaves at the bottoms of my tomato plants.

Early Blight is a fungal condition, and here in Minnesota, it is almost inevitable due to our warm and humid growing conditions. The spores reside primarily in the soil, and most often it is spread to tomato plants when soil particles splash up onto the low-hanging leaves during rain or watering.  Once the spores settle in on the leaves, they spread up the plant, leaving behind leaves covered in dark spots that will eventually yellow, and then turn brown and dry up completely.  The spores spread by contact (soil to leaf, leaf to leaf, leaf to human hand to leaf, etc.), and high humidity or persistent wet conditions will speed up the progression of Early Blight.

Of course preventing Early Blight in the first place is the most ideal scenario, but if it does show up, it can be controlled rather easily with a little work and diligence.

Here's a run down of some strategies I'm using for battling Early Blight in my garden this year (all of these strategies can be used both as preventative measures and as control measures if Early Blight is already present):

• Mulch: The best way to battle blight is to put a barrier between the spores (in the soil) and the plant.  I had every intention of getting this task accomplished much earlier in the season (in hopes of avoiding Early Blight all together), but with the devastating spring planting delays for farmers in the area, my brother just couldn't get away from the farm to deliver my straw bales last month.  But, better late than never!  I spent the past few evenings at the community garden laying down a nice 3-4 inch layer of mulch around the tomato plants (I put down a layer of newspaper first, to keep the weeds from popping up through the mulch, which also acts as an additional barrier).  Bonus benefit: this is going to make a huge difference in retaining moisture for the plants as well!

• Create a Healthy Splash Zone: The bottom 8-10 inches of the plant is what I like to call the "splash zone."  This is where soil particles and Early Blight spores are most likely to splash up and onto the leaves of the plant.  From early on (as soon as transplants start to take off), I remove any leaves that touch or come close to the ground to create a space barrier between the ground and first set of leaves on the tomato plant (see photo above).  It isn't always going to be foolproof (Minnesota's "tropical" downpours can really move dirt high on the plants), but it is a good way to make sure that leaves are not in direct contact with the soil for prolonged periods of time. Good staking and plant supports will go a long way to help keep plants off the ground as well.  

• Careful Watering:  Whenever possible, I water in the morning.  This allows leaves that might get a little wet to dry out quickly.  Leaves that remain damp for extended periods of time (i.e. heavy dew in the evening or late in the day watering) will give the spores more time to fester and spread.  Also, whenever possible, avoid drenching the entire plant by watering directly at the base of the plant (another way the deep watering is paying off year).  I learned this lesson the hard way the year we reseeded our backyard and had a sprinkler hitting the garden every evening--that was by far the worst (and most out of control) case of Early Blight I've dealt with.  I've also learned to avoid using any kind of nozzle attachment on my hose when watering the tomatoes, as they tend to send the water out with more force than a plain hose with a moderate flow (more force = more splash).  A soaker hose would work well for this purpose, too.  

• Take Care of the General Health of the Plants: I like to think of Early Blight as the equivalent of the common cold.  It's sometimes hard to avoid, and once you get it, there's no easy "cure," but the better your overall heath, the less it's going to knock you down.  The same goes for tomatoes. If tomato plants are suffering from a nutritional deficiency (nitrogen deficiencies are mentioned most frequently), they will be more susceptible to Early Blight.  Healthy plants will have stronger defenses against blight and other ailments, so keeping an eye out for signs of nutritional deficiencies is crucial.  

The above strategies are your best bet to prevent and control Early Blight, but if the blight is already present and making quick progress through the tomato plants, there are also a number of options for treatment:

• Remove Blighted Leaves with Care:  As I stated earlier, in Minnesota it's usually not a matter of if Early Blight will show up, but when.  In a normal year, we get a good number of heavy rains, lots of humidity, and warm temperatures, which are the trifecta for an outbreak of Early Blight.  Once tomato leaves show signs of blight, promptly remove them from the plant to prevent (or at least slow) the spores from spreading.  Tomato plants tolerate pruning well, and you can safely remove up to 30% of the plant's foliage without ill effects.  Always tend to unaffected areas of the plant first before handling blighted foliage and scrub your hands (and clippers) down really well after handling each plant to avoid contamination.  Blighted tomato foliage should be destroyed rather than composted, to avoid reintroducing the spores to the garden the following year.  

• Commercial Fungicides: Garden centers typically carry both organic and chemical fungicides that can be used to prevent or control Early Blight.  These products are foliar sprays that need to be applied directly to the leaves (soaking both sides) about once a week, and then re-applied if it rains in between treatments.  I have tried them in the past (and I will admit I did pick up a bottle of organic fungicide last week out of desperation to keep the blight at bay until I could get the mulch down and do a more thorough job of cleaning up the plants), but I haven't found them to be a terribly practical solution, especially if you have a lot of tomato plants (all those plastic spray bottles start to add up fast, especially if it rains every couple of days).  I'm also extremely cautious of using these products when fruit has already set on the plants.  That said, if you are so inclined, it can be a useful tool to regain the upper hand when combined with the strategies above.  Results will vary, depending on the active ingredients in the spray, growing conditions, and severity of the blight outbreak. 

• Homemade Treatments: A quick Google search will produce a number of homemade treatment options.  Last year I tried using cornmeal to prevent Early Blight by both sprinkling cornmeal around the base of the plant and by brewing a "cornmeal tea" to spray on blighted leaves, but I didn't notice that it made much of a difference (it might be the method or it might be the application; I'm not sure).  I've also come across a number of recipes for compost tea fortified with baking soda or apple cider vinegar.  I have yet to test drive that treatment myself, but it's definitely something I'm keeping in the back of my mind in case all of the strategies I've already employed fail to control the blight.  And then just this morning, a very wise and experienced gardener and friend (and regular blog reader--Hi Rori!) suggested that I try mixing up a solution of hydrogen peroxide to spray on the plants.  She recommends a peroxide to water ratio of 1 to 4 for new tender plants and a stronger 1 to 1 ratio for more established plants.  And since Rori has has never steered me wrong, I'm definitely going to give it a try! 

It has been my experience that, as long as a good effort is made to control it, the presence of Early Blight does not have a significant impact on the tomatoes themselves. Plants that have been severely pruned to control the spread of blight will look a little sad at first (here's where that disheartened feeling will creep in), but indeterminate varieties will almost certainly out-pace the blight and go on to produce a good crop of tomatoes if you make every effort to keep them healthy.  Constant control of the blight will likely be necessary (unless you are lucky enough to stop it completely), but unlike Late Blight (which is what more commonly comes to mind when someone talks about Tomato Blight or Potato Blight), Early Blight is not typically a fatal condition.  And that should leave you feeling triumphant, when all is said and done! 

As long as we're on the topic, there are also a few things to keep in mind for the end of the season: 

• Garden Clean Up: After a bout with Early Blight, the end of season clean up takes on a lot of importance. I always take care to make sure that every last leaf is removed from the garden, as even a small amount of debris can keep the spores active. 

• Crop Rotation: It is also a good idea to try to rotate your tomatoes to a different location where the spores would have been less active the year before.  This should be done for at least a year (three years is the common--but sometimes less practical for small space gardeners--recommendation), but if that's not possible, you'll want to be sure to take as many preemptive measures as possible the coming year. 

• Hardware Clean Up: When I pull out my plant supports (tomato cages, wooden and bamboo stakes, etc.) in the spring, I give them a quick wipe down with a bleach solution and let them dry completely in the sun before returning them to the garden. 

It's also worth noting that out of the eleven varieties I'm growing, two appear to be much less susceptible to Early Blight than the rest.  While all the other plants around them have a good number of leaves with signs of blight, the San Marzano and Yellow Pear tomatoes had little to no signs of Early Blight.  That is certainly something I will be taking into consideration when planning next year's garden! And maybe by then I'll have mastered the art of prevention and have no Early Blight at all! (a gardener can dream, right?)

I'd love to hear from you on this subject!  What are your best strategies for battling Early Blight?  Have you tried any of the homemade treatments?