University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article
line

WATCH FOR THESE TOMATO PROBLEMS
 
Dr. Leonard Perry, Extension Professor
University of Vermont

If your tomato plants and fruits aren’t looking as healthy as they should, perhaps with leaf spots or diseased fruits, they may have one of several diseases.
           
The disease that flared up a few years ago in the Northeast, destroying many home and commercial tomato plantings, was late blight—the same fungal disease as gets on potatoes and caused the famous Irish potato famine in the mid-1800s.  If you had tomatoes with this, you may recall the nickel-sized or larger spots, olive-green to brown, on leaves.  Sometimes the border of these spots is slightly yellow or appears water-soaked.  Soon, brown to black lesions grow on stems with brown spots on fruit. 
           
Late blight is often around but conditions aren’t prime for it to spread and get out of control.  If it is present, sprays are available but must be applied early in the season.  Once leaves are over about 10 percent affected, sprays do little good so plants should be destroyed.  Before doing this, make sure you have this disease, checking with either the state Agriculture department specialists or those at the Plant Diagnostic clinic at your state university (www.nephd.org).  If late blight has been present, you may try growing the resistant ‘Legend’ (a red slicing type) and ‘Juliet’ (a red plum cluster type and All-America Selections winner) among others.  Since it needs living material to overwinter, don’t save over tomato plants and definitely not potato tubers in the ground.
           
Much more common on tomatoes (and potatoes) is early blight, another but different fungal disease.  It causes leaf spots, stem lesions, and fruit rots.  The name is deceiving as it more often develops not early but rather on mature leaves.  It usually progress up the plant, starting first with older leaves near the base.  Spots may have concentric rings, giving a target or “bulls-eye” appearance.  Stem lesions often are sunken with lighter centers. On older fruits, the dark and leathery sunken spots are often on the end attaching to the stem.
           
Rotating other crops for a couple years in the same spot, particularly small grain cover crops, corn, or legumes can help in control.  Some cultivars (cultivated varieties) have resistance to early blight (sometimes seen as Alternaria blight).  Keeping up with weeding and fertility, especially nitrogen and phosphorus, and watering early in the day so leaves dry quickly, all can help in avoiding early blight.  Sprays are available and ideally should be started early in the season.
           
Septoria leaf spot, another fungal disease, occurs under similar conditions as early blight and has similar controls.  Its spots are often gray or tan, with darker margins, and have dark pimple-like structures in the center that are fairly easily seen.  These dark fungal structures are absent from early blight lesions, nor do the spots have the target-like appearance.
           
If the fruits rot on the ends opposite the stems, this is likely the common blossom end rot.  It is actually not caused by a disease, but by the growing conditions--  uneven watering and a calcium deficiency.  Especially if it is hot and dry, and then followed by heavy rain or watering, this rot can develop as the plant can’t absorb enough calcium.  Other factors to try and avoid through culture include low potassium or calcium levels, excess magnesium or nitrogen causing rapid plant growth, root damage, or high relative humidity.  Balanced watering and fertility, and perhaps calcium sprays to foliage, should keep this under control on tomatoes, as well as on squash and peppers.

Verticillium wilt fungi are in the soil, and if present can cause plants to wilt, beginning with lower leaves.  Lesions on leaves have a V-shape, widest on the leaf margin.  Leaves die, and eventually the whole plant can die.  As there aren’t easy controls for this, crop rotation should be practiced, and controlling weeds as many host this disease.  There are many cultivars with resistance to this disease.
           
Anthracnose is a fungal disease of green, but especially of ripening, fruit.  Small, slightly sunken and watersoaked spots appear, that grow larger and become dark in the centers.  As it spreads in the fruit it causes a softening decay.  To avoid this disease, grow plants on well-drained soils, keep up with weeding, avoid excessive overhead watering, and rotate crops yearly.  If present, you may need to resort to sprays.

Visit the Cornell University Vegetable MD Online for more information and photos on these and other problems of tomatoes, as well as of other vegetables (vegetablemdonline.ppath.cornell.edu). It’s always good to check with professionals, such as at local full service garden stores or plant clinics, to make sure your plants have a particular disease before treating it.  Cultural controls and rotating crops, as mentioned, go a long ways to future prevention.  Also make sure you check when ordering seeds or buying plants in the future that they have resistance to some of the more common diseases.  These are indicated by letters in catalogs, such as for Fusarium (F) or tomato mosaic virus (TMV), and can be found in keys there to these code letters.
 

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