Purdue Extension Does…Tomato Health!

As summer rolls on local gardeners continue to gather garden bounty for the kitchen table, with the common tomato in all its forms being the prize jewel of many gardens.  Summer diseases, however, can often cause otherwise beautiful fruit to suddenly lose their appeal as tomato diseases begin to set in.

There are many common diseases that can affect tomatoes when conditions are right, with new concerns unfortunately being found all the time.  Those diseases more common to southern Indiana are as follow:

For diseases where tomato leaves begin turning brown at the bottom and work towards the top of the plant, the most likely suspects are either early blight and Septoria leaf spot. Both diseases cause lesions that initially appear on lower leaves, and both diseases can progress rapidly from lower foliage to new growth during wet weather. Early blight lesions have target-like rings within the brown area — a bull’s-eye pattern. Septoria leaf spot causes small, chocolate brown, circular spots that are 1/10 to 1/8 inch in diameter. Both diseases attack less vigorous plants and plant parts. The fungi responsible for these diseases overwinter in infested crop residue in the garden.

Yellowing and wilting lower leaves are the first noticeable symptom of Fusarium wilt and Verticillium wilt. The wilt may affect one side of a leaf. Fusarium wilt may cause a seedling disease, whereas Verticillium wilt usually does not. Fusarium wilt is usually more severe on plants grown in light sandy soil. The fungi that cause these diseases survive for many years in the soil, even in the absence of tomato plants.

Bacterial spot and bacterial speck infections result in dark brown spots on leaves that are often smaller than those caused by early blight or Septoria leaf spot. The spots may occur on younger leaves and may occur along leaf veins where water collects. Severe infections may cause dark scab-like lesions on fruit.

Blossom-end rot is a disorder of tomato fruit that usually occurs after rapidly growing plants experience a prolonged dry spell or after a period of unusually abundant rainfall. It is not caused by a disease or other pest (that is, it is non-infectious). Blossom-end rot most often affects the first set of fruit produced. Heavy application of nitrogen fertilizer also tends to promote blossom end rot. Although the cause of this disorder is calcium deficiency within the fruit, environmental conditions can lead to blossom-end rot even when the soil has sufficient calcium. Adding calcium fertilizer after this disorder appears is unlikely to help. Symptoms occur on green or ripe fruit and appear as dry, leathery areas on the blossom end of the fruit. The leathery areas are generally concave and are usually larger than a quarter, but can be as wide as the fruit itself.

“Catfacing” is another non-infectious problem that can be recognized by the malformed tomato fruit it causes. Catfacing often occurs when the flower buds were exposed to cold. Heirloom varieties exhibit a high proportion of fruit with catfacing, so catfacing may not detract from the marketability of these varieties. Variety selection is the most practical way to limit this problem — larger varieties tend to be more prone to catfacing

To reduce or totally avoid disease challenges in your garden, always try the following steps:

1. Diagnose the Problem Correctly  – Before you can treat any disorder, you have to identify the problem correctly. For additional information on tomato challenges (including color photos for disease identification), check out the free Purdue publication “Five Steps for Healthy Garden Tomatoes” at https://www.extension.purdue. edu/extmedia/BP/BP-184-W.pdf .  You can also send a disease sample to the Purdue Plant and Pest Diagnostic Laboratory, with instructions on how to prepare and send a sample found on the lab website at:www.ppdl.purdue.edu .

2. Plant Resistant Varieties  – Whenever possible, choose varieties that have resistance to diseases. For example, tomato varieties are available that are resistant to Verticillium wilt, Fusarium wilt, and root-knot nematode — thus, the letters VFN – are often associated with tomato varieties that have such resistances. There are no other practical means of controlling these diseases except for resistant varieties. Some varieties also may have partial resistance to leaf (foliar) diseases such as early blight. Heirloom varieties will likely lack resistance to any diseases, so if you grow heirlooms closely follow the remaining suggestions listed here.

3. Practice Crop Rotation, Fall Tillage, and Sanitation – Whenever possible, do not plant tomatoes in the same place year after year. Many pathogens, such as the ones that cause early blight, survive from year to year in crop debris. Planting a crop unrelated to tomato for three or four years will allow the crop debris to break down and make it less likely for pathogens to survive. Crop rotation is particularly important for heirloom varieties since they are susceptible to a greater number of diseases.

If it is not possible to rotate to a different plot of ground each year, remove tomato plants from the garden as soon as you complete harvest. Plants that are not removed provide a winter haven for all sorts of tomato pathogens. You can compost or simply discard dead plants, but do not use composted tomato plants in tomato production.

Some residue can be expected to remain in the garden. Tilling the soil in the fall to a depth of 4 to 8 inches will bury this residue and hasten its decomposition.

Use clean stakes or cages each year. You should take plants or fruit suspected of disease far away from the production area. This cleanup should be routine with all garden vegetables and equipment. You should also destroy all weeds because they can harbor tomato pathogens until spring.

4. Maintain Plant Vigor – Healthy plants tend to resist diseases better than plants that lack water or nutrition. Tomatoes planted in well-tilled, well-drained, and properly fertilized soil will be less prone to early blight and Septoria infection. Tomatoes will grow in many different soil types, but a deep, loamy, well-drained soil is ideal. They grow best in a slightly acidic soil, pH 6.2 to 6.8. You should till the soil in spring prior to transplanting.

Soil test to apply the correct amount of needed fertilizer for optimum growth and health, or apply a complete fertilizer (i.e. 10-10-10 or 8-16-16) at 2 to 3 pounds per 100 square feet to supply the needed nitrogen, phosphorus, and potassium. Slowly add about 1 inch of water per week, being careful to avoid wetting the leaves or using overhead irrigation.

5. Use Fungicides as Needed – Regardless of the efforts to prevent disease, many tomato gardens will have sufficient foliar disease in the soil or residues to compromise yield or fruit quality. If you decide to apply fungicides, the following checklist might be helpful:

• Be safe. Before you purchase a fungicide, check the label to be sure that it will control the diseases your plants have, and that it is safe to use on tomatoes.

• Use a pressure sprayer for best results. Compared to dusting plants, mixing fungicides with water and applying them with a pressure sprayer allows much better coverage and distribution of the fungicide on the plant.  Products that contain the active ingredient chlorothalonil are preferred, but fungicides that contain copper as the active ingredient also can be effective, especially if disease pressure is low.

• Apply fungicides before disease symptoms occur or in the early stages of the disease. These applications will be more effective than applications made after the disease is well along. Begin sprays when plants approach 10 to 12 inches tall and continue spraying at 7- to 14-day intervals throughout the season, especially if disease has been severe in recent years. Providing good coverage over the entire season means that fungicide applications must be repeated.

If you would like more information on this or other garden topics, please contact Purdue Extension – Dubois County at 812-482-1782or kjeck@purdue.edu.

Kenneth J. Eck
Extension Educator, Agricultural & Natural Resources
Purdue Extension – Dubois County

Cover photo by Anda Ambrosini on Unsplash