Regional Gardening Reports :: National Gardening Association

In the Garden:
Lower South
May, 2009
Regional Report

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Birds may appreciate your luscious tomato harvest as much as you do. Netting can help protect the fruit from any overzealous winged marauders.

Tomato Problem Solver

Gardeners love tomatoes. In fact it is almost an obsession with us. I was just out in the garden yesterday enjoying some of the early harvest of a few 'Juliette' tomatoes and checking on the progress of several other varieties I am growing this year.

Tomatoes are one of the top three things that make the phones ring at the local County Extension Office (trees and turf are the other two). Despite our love affair with tomatoes they do have their share of ailments. Here are a few of the more common things we run into as tomato growers and some possible solutions to them.

Failure to Set Fruit
Causes of failure to set blooms include: nights are too cool, days and nights are too warm, excessive nitrogen levels early in the life of the plant, and lack of wind to shake the flowers. Tomatoes pollinate themselves when the flowers are shaken a bit, causing pollen to fall from the male flower parts onto the female flower parts.

Consider these possibilities. Temperatures are not in our control but we do need to plant and the proper time for our area so the plants can set fruit when temperatures are right. Here in the South our large-fruited tomatoes have a fairly short productive window. Small-fruited types tend to set fruit better in the heat. We should cut back on fertilizer until the first fruit sets and then we can give the plants a boost of nutrients. If your plants are growing in a very protected area such as a greenhouse, shaking the bushes just a little each day can assist in pollination.

It is also important to plant varieties suited to your area. Some of the great heirlooms such as Brandywine take a long time from planting to harvest. In our Lower South climate they are usually just starting to set fruit when the really hot weather arrives and thus are not as productive as they would be in another part of the country.

Blossom End Rot
When the bottom of a tomato (opposite the stem end) turns black, the problem is most likely blossom end rot (BER). It is caused by a lack of calcium to the tip of the fruit. When the cells in tip of the tomato lack calcium during growth, they die and the black decay you see follows. You may have adequate calcium in the soil but still get BER due to soil moisture fluctuations (from wet to dry). I have noticed that BER is worse on the first tomatoes of the season and tends to not affect later fruit as much.

If you haven't had a soil test in the past few years, it would be a good idea to have one done to make sure your calcium levels are adequate. Your County Extension Office can assist you in having your soil tested.

BER is best prevented by keeping soil moisture evenly moist. If your soil is sandy and prone to moisture fluctuations, adding compost prior to planting may help. Garden centers sell a BER spray (contains calcium). This must be applied starting when tomatoes are about marble-sized in order to prevent BER on the fruit.

Stink Bugs
The hard, white to yellow spots on the surface of a tomato are caused by insects with piercing, sucking mouthparts feeding on the fruit as it nears maturity. Insect culprits include stink bugs and their "cousins," the leaf-footed plant bugs. When these same pests feed on small, newly formed fruit, it causes dimples in the fruit known as "catfacing".

When the weather warms these pests often show up to spoil the show. There are sprays to control them but you need to be diligent and start early in their life cycle. Veteran gardeners learn to recognize their egg clusters which look rather like a grouping of tiny fat whiskey barrels to me! The newly hatched stink bugs are tiny, rounded versions of the shield-shaped adults, while yound leaf-footed bugs are usually orange with long black legs. These pests are more susceptible to lower toxicity spray options when they are young. Plus the young ones lack the wings to fly away. Spray in early morning when the bugs are more sluggish.

Wilting Plants
Tomatoes often wilt during the day and recover in the evening when the sun goes down and the roots can catch up and replenish the water supply. This is normal in the hot Lower South climate.

Wilting tomatoes that do not recover in the evening may be showing signs of wilt diseases of the root system or nematode damage to the roots. You can examine the roots and stem for the diagnosis.

Dig up a declining plant and look for swollen areas on the roots (nematodes). Then split the stem lengthwise and look for a brown streak between the green "outer bark" and the cream colored stem interior (wilt diseases). The solution to both is to select varieties with a VFN after their name.

Sometimes we see plants with a VFN showing these symptoms. This is usually due to a mislabeled plant (not the variety you thought you were getting), or a strain of the disease that overcomes the plant's resistance. Now you will see for example V, F1, F2, N plants indicating they are resistant to two strains of the fusarium fungus.

Finally, too much rain can cause wilting if the soil does not drain adequately. Waterlogged soil prevents oxygen from getting to the root system and can result in root loss and subsequent wilting.

Leaves Curling
If it is the older leaves that are curling, there is not a concern. Tomatoes often do this as summer temperatures rise. Some varieties are more prone to this than others and high fertility levels increase the condition. It does not hurt the plants is any way.

If you are seeing a twisting of new leaves and growing shoots it may be a sign of virus infection or herbicide injury. Viruses can be spread to healthy tomato plants by sap feeding insects like aphids.

Herbicide injury can occur from drift from lawn applications, use of a sprayer on the tomatoes that had previously been used to apply a herbicide, use of grass clippings or hay as a mulch from herbicide-treated lawns or pastures, or even use of manure from cattle that grazed on treated pastures. Neither virus nor herbicide damage is treatable. Infected plants should be removed and discarded.

Foliage Yellowing
Nitrogen deficiency can cause yellowing in older leaves. The solution to this is simply to start feeding them with a complete fertilizer product. Temporary dry soil conditions, especially in a sandy soil, can cause the symptoms you describe. Although the plants recover with watering the older leaves may then turn yellow and die.

Another possibility would be nematodes, stressing the plants by debilitating the root system. If the plants continue to decline, pull up a plant and examine the roots. If nematodes are present they would show up as swollen areas on the roots . There is no cure for nematodes but you can plant resistant varieties in the future.

Foliage diseases caused by fungal leaf spots and blights will typically be accompanied by yellowing, especially on older leaves. Avoid wetting the foliage when possible, mulch the soil surface, and remove affected lower leaves promptly. Sprays for fungal diseases are available as a last resort.

Fruit Splitting and Cracking
Tomato fruit splitting is usually due to fluctuating moisture conditions. As a tomato goes through a slightly dry time, the cells keep dividing even though the moisture supply is limited. When a good rain or irrigation follows those cells swell up rapidly. The skin cannot expand fast enough and splits. The best remedy is to keep moisture levels fairly even, especially as the fruit nears ripening.

Some varieties are prone to cracks that appear near the stem end. These cracks may run in semi circles around the point where the stem attaches or they may be short, deep cracks in the shoulder of the fruit oriented more in a stem-to-blossom direction. This is not something that you can control and in my experience is more variety-specific. It generally doesn't ruin the tomatoes like the fruit splitting from moisture fluctuations does.

Spider Mites
These pests love hot weather. The cause tiny specks of white on the foliage which gives a general bleached-out look, and may also cause bronzing of the foliage and curling under of growth. In severe infestations there is a fine webbing seen under the foliage and shoots.

Mites are easily kept in control by an occasional blast of water directed upward from beneath the foliage. Try to wet the lower leaf surfaces as you spray and this will really set them back, preventing an outbreak if done every week or so. Insecticidal soap is an effective spray for mites but you must have good coverage of the lower leaf surfaces for it to be effective.

Here in Texas our state bird is the mockingbird. I love their beautiful songs. I love the fact that they eat insects. I despise their interest in my tomato fruits! Bird netting or a well trained cat are about the only ways I know to prevent damage, short of resorting to ballistic measures (which are frowned upon by neighbors and the local police department)! Some gardeners feel that providing a supply of water nearby will minimize damage from birds.

The above tomato problems are certainly not all the things we gardeners can encounter but I've already run long on this article and this list should be a good start for helping you identify, prevent, and remedy the most common challenges to growing a bountiful harvest of tomatoes!

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