There's nothing in the world like a vine ripened tomato that you grew yourself. If you have ever had a vegetable garden chances are you had atleast one tomato plant. The smell that a tomato plant leaves on your hands is unforgettable. I prefer the heirloom varieties with their endless colors, shapes and flavors. If I could grow only one variety I would have to go with cherokee purple, my all time favorite heirloom variety. I also highly recomend a few others but I'll put that list at the bottom of this blog...  this blog is about blight identification and prevention.

There are three major types of blight that can mess with your tomatoes. Septoria leaf spot, early blight and late blight. All are fungal diseases spread by spores, which require moisture to infect a plant. Septoria leaf spot or septoria blight ussually appears on the lower leaves after the first fruit set. Fruit is rarely infected. Leaf loss reduces fruit yield and quality and exposed fruit are susceptible to sunscald. Blight is spread by splashing water and working with plants that are wet. It will overwinter on tomato and weed refuse.

Early blight appears on the lower leaves, ussually after a heavy fruit set. The spots are dark brown to black. Concentric rings form in the spot and create a bulls eye. The leaf around each target turns yellow and then drops. This nasty fungus can even infect stems and create stem cankers. Occasionally attacks fruit producing large sunken black target spots on the stem end of the fruit. Infected fruits drop before they mature. Overwinters on old tomato vines and weeds in the nightshade family.

Late blight, caused by a fungal-like organism occurs in moist weather with cool nights and warm days. Dark green to nearly black wet spots begin spreading in from the leaf edge. In wet weather the spots may have a downy, white growth on the lower leaf surface near the outer portion of the spot. Spots also develop on the fruits. At first, the spots are grey-green and water-soaked, but they soon enlarge and turn dark brown and firm, with a rough surface. When conditions are right, the disease will progress pretty quickly.

It is difficult to save a tomato plant once it has been infected with blight - even if you spot it early and remove the infected leaves. And one infected plant is all it takes to ruin your whole crop of tomatoes (and potatoes), so here is some advice, based on the research I have been doing lately.

Blight loves cool, damp conditions and cloudy days. (UV rays kill the spores carried by the wind.) So water your plants in the morning and do it at ground level, not from above. Inspect your plants at least once a week. More often if the weather is cool and wet. If you find late blight in your garden, let your local garden extension service and your neighborhood gardeners know. Act quickly.

If you are forced to remove your plants, do it on a bright sunny day to kill off the spores that may blow around. Late blight shows up on other plants, almost always unnoticed: potato, hairy nightshade, bittersweet nightshade, tomatillos and petunias! If you wait until late blight shows up to use a fungicide, it will be too late. It has to be done as a   preventative measure and I am not recommending that just yet, since fungicides can actually lead to other diseases. Once you begin spraying, the treatments must be regular and thorough. Use chlorathalonil or copper-based products and follow the directions carefully. Consider planting potato and tomato varieties that have shown some resistence to late blight, such as such as ‘Allegany', ‘Elba' or ‘Kennebec' potatoes and 'Black Plum,' 'Matt's Wild Cherry,' 'Yellow Currant' and 'Yellow Pear' tomatoes.

Some of my suggestions for fungicides that may be effective in preventing and controlling blight.

-- SERANADE -- Organic Control For Disease, Insects and Weeds. This is is the HOT new product of the year in the organic world. It is NOT a chemical but instead contains a patented strain of Bacillus subtilis (a bacteria) which is an ecologically safe control used by organic growers (OMRI-listed) to control a broad range of diseases, including anthracnose, downey mildew, early blight, late blight, leaf spot disease, powdery mildew, and much more.

-- An old organic solution is to spray your plants with a solution of baking soda. There are lots of formulas floating around. Here's one:
1 T. baking soda
1 T. dormant oil 
1/2 t. insecticidal soap or dish soap (to serve as a surfactant)
1 gallon of water

Mix together. Spray with a hand-sprayer or pump-up sprayer. Be sure to spray undersides of leaves too.

-- COPPER-FUNGICIDES -- Copper products are the "big gun" in the organic world and some organic people use them. However, they are technically considered an Inorganic Fungicide and are used as a broad-spectrum foliar fungicide. They are somewhat effective but are not as effective as chlorothanlonil. I don't like using them as copper can also be toxic to fish and can cause a whole host of symptons/irritations to the person putting the copper products in their garden.

1.  KOCIDE: Its active chemical ingredient is cupric hydroxide.

-- Over-the-Counter General Use Products Containing Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) 

1.  GARDEN DISEASE CONTROL by Ortho -- the replacement for Daconil I think, generally available wherever gardening supplies are sold. Costs roughly $15.00 a pint.

2.  BRAVO--available in several formulations, containing from about 30% to about 80% chlorothalonil--more of a commercially-oriented product for agricultural users and forest service. If you buy Bravo be sure to get the 30% one. That is the concentration the government rates as safe for use in vegetable gardens.

3.  FUNG-ONIL by Bonide--essentially the same as Ortho Garden Disease Control

All of these are generally considered safe for use in the chemical world, but they break down into compounds that are toxic to fish and mammals. They are very effective though, and to be honest, they are more effective than anything we organic gardeners use. That doesn't mean I would use it. If used, protect eyes and skin as it may irritate them. Generally the MOST EFFECTIVE product available for treating blights. All these products use chlorothalonil from the same manufacturer so they are all pretty much the same, although one might be 27% active ingredient and another one might be 29%. They may have different inert ingredients.

Before you begin spraying for any of the blights listed above I would recomend being absolutely positive that what you are dealing with is in fact blight. Yellowing of the leaves can mean several different things including but not limited to...

too much water
too little water
zinc deficiency
iron deficiency
potassium deficiency
calcium deficiency
root-knot nematodes (only in sandy soil)
tobacco mosaic virus
aphids
tomatoes grown too close to the roots of a black walnut tree, or the use of a home-made mulch containing shredded black walnut tree leaves or wood

If the leaves are yellowing AND wilting it could be verticillium wilt or fusarian wilt, although I really have not seen them much at all in my years of growing tomatoes.

Peace

Chris Condello

I also want to include my list of favorite heirloom tomato varieties...

1. Cherokee Purple

2. Garden Peach

3. Gold Medal

4. Striped German

5. Black Krim

My favorite cherry tomato is Sun Gold with out a doubt...