Richard Bogren | 5/23/2016 2:36:16 PM
By Dan Gill
LSU AgCenter Horticulturist
One of the special joys of gardening this time of year is harvesting vine-ripened tomatoes from backyard gardens. While tomato harvest typically extends into July, high temperatures, diseases and insect problems, like stink bugs, often reduce the quality of tomatoes harvested then. The best tomatoes are harvested in May and June.
Tomatoes seem to have more than their share of problems, but most of us end up getting a decent crop anyway. Some problems, however, are especially tragic. These are the problems that can destroy plants before you get your harvest.
Bacterial wilt is certainly one of these. Once they get into the tomato plant from the soil or insects, bacteria multiply rapidly, moving into the vascular system and clogging up the vessels. This prevents the plant from moving water from the roots into the upper plant. The tomato plant suddenly wilts, and watering will not revive it.
There are no treatments for bacterial wilt. Infected plants should be quickly removed and disposed of. Future plantings should be made in a different location.
Various viruses also attack tomatoes. Viruses frequently cause the foliage, particularly the new growth, to be twisted and deformed. You may see mottling of yellow, light green and dark green in the leaves, which is a symptom called mosaic.
There are no treatments for virus-infected plants. Infected plants should be immediately removed and discarded to reduce the chances the disease will be spread by insects to plants that are still healthy. Choose virus-resistant cultivars if they’re available when you purchase transplants.
Blossom end rot is another common problem of the fruit. This is a physiological disease caused by a calcium imbalance in the fruit – not a pathogenic organism. Affected tomato fruit have a round, dark brown, dry, sunken area at the bottom of the fruit right around where the blossom fell off.
Plants subjected to wide fluctuations in soil moisture are prone to this problem. Plants in containers are especially vulnerable because the soil in the pots dries out so fast. Excessive phosphorous can interfere with calcium uptake, so be cautious about using fertilizers high in phosphorus – the middle number in the analysis. A calcium deficiency in the soil will cause blossom end rot, but have your soil tested before adding lime to the soil.
To deal with a current problem, treating plants with a product labeled to control blossom end rot in tomatoes may help. These products, available at local nurseries and garden centers, contain calcium in a rapidly available form and are sprayed onto the plants.
Caterpillars are active right now. Tomato fruit worms often chew round holes in the top of the fruit. During summer, these wounds can quickly become infected with fungi, leading to rotting fruit. Fruit cracks around the stem can also lead to rotting. Inspect your tomatoes frequently, and any that show a crack or hole should be harvested, rinsed, dried and allowed to ripen on the kitchen counter indoors.
The tomato hornworm is a large, green caterpillar with a red horn on its rear. It is a voracious leaf feeder. Once this caterpillar gets large, it can almost strip a plant of leaves in a few days. Control caterpillars with weekly applications of the organic insecticides Bt or spinosad. Permethrin and carbaryl are popular conventional insecticides for caterpillar control.
Fungal diseases are active now. A wide variety of diseases attack tomato foliage. With recent rains, early blight, late blight and various fungal leaf spot diseases have been showing up. When it comes to disease control, early intervention is critical. If you wait until almost all of the foliage is infected, spraying at that point will do little good.
To manage diseases, spray preventatively or at the very first sign of symptoms. Then continue to spray regularly to maintain protection. Neem oil and copper fungicides are good options for organic gardeners. Chlorothalonil controls a wide variety of fungal diseases that attack the leaves and fruit.
Speaking of fruit, buckeye rot is a fungal disease active now that attacks the fruit. Look for brownish, discolored areas on sides or toward the bottom of the fruit. The lowest fruit are the most vulnerable. Keep plants mulched to prevent the fungus from splashing from the soil to the fruit. Promptly remove and dispose of any infected fruit. Spray plants regularly with chlorothalonil if the severity of the situation warrants it.
A dropped flower is like a broken promise. Once a tomato plant is developing about as many fruit as it can handle, however, it will tend to drop most or all of the flowers it continues to produce. Higher temperatures in the 90s this month will also encourage blossom drop. That’s why it is important to plant tomatoes early.
By mid-to-late summer, intense heat and growing pest populations take a heavy toll on tomatoes. When the crop finishes and plants are looking poorly, usually sometime in July or early August, we pull them up.
In August you can plant new tomato transplants for a fall crop. That is one of the perks of gardening in a climate like ours with a long summer growing season.
Tomato bacterial wilt. Photo by Dan Gill
Tomato fruit split. Photo by Dan Gill
Tomato blossom end rot. Photo by Dan Gill
Tomato fruit worm damage. Photo by Dan Gill