There is nothing like a freshly picked tomato.

It seems like it takes forever before the first fruits are ready. Then it always seems like something happens to the fruit or plant to limit the number of fruit. Some common issues with growing them include the lack of fruit set, black bottom on the fruit, and spots on the leaves.

Blossom drop resulting in the lack of fruit set is currently the most common problem. Low or high night temperatures is one cause of blossom drop. Most tomato varieties will not set fruit unless the night temperature is between 55 and 75 degrees F for at least part of the night. Beating rains, sudden periods of cool weather, hot and drying winds, and excessive applications of nitrogen fertilizer interfere with fruit set.

Once fruit set, blossom end rot is usually the first problem found on the fruit. It begins as a small, water-soaked spot on the blossom end, which is located on the bottom of the fruit. The spot becomes flattened or sunken. Later, secondary fungi may invade the affected area, resulting in further decay of the fruit. Usually, the first fruits to ripen are affected.

Blossom end rot occurs when environmental conditions prevent the distribution of calcium to the fruit. Environmental conditions such as low soil moisture, hot and dry wind, heavy applications of nitrogen fertilizer, and fluctuations in soil moisture contribute to the development of blossom end rot. Under environmental stress conditions, calcium moves to the leaves with the water inside the plant and bypasses the fruit. Without calcium, the tissue at the blossom end of the tomato breaks down.

To manage blossom end rot, maintain an even moisture supply by watering plants as needed and mulching the plants with straw to conserve soil moisture. At this time, applications of calcium to the soil or foliage do not prevent or cure the disorder. Blossom end rot is not caused by a lack of calcium in many cases but by poor distribution of calcium in the plant.

Early blight is one common disease on tomato plants that is caused by the fungus Alternaria solani. The fungus generally causes small, irregular, brown, dead spots on the older leaves of the plant first. As the spots enlarge, they usually show ridged, concentric rings in a target pattern. These spots are typically surrounded by a yellowed area. During periods of high temperatures and humidity, the fungus can spread.

Septoria leaf spot occurs on tomato leaves too. Septoria leaf spot is caused by the fungus Septoria lycopersici. The infections usually start on the older leaves of the plants near the ground. At first, spots on the leaves appear water-soaked and are often scattered thickly over the leaf.

These spots become roughly circular and have gray centers surrounded by dark margins. The spots are smaller and more numerous than those of early blight. The numerous spots on the leaves eventually cause the entire leaf to turn yellow, then brown, and wither. This disease is favored by moderate temperature and rainfall.

Both early blight and septoria leaf spot spread by spores produced by the fungi. They often occur on the same leaves. The spores are carried by the wind or by raindrops splashing the spores onto the leaves. The spores germinate on the leaf surface and infect the leaf tissue if the temperature and moisture conditions are just right for the fungi.

To manage early blight and septoria leaf spot, cultural practices can be used. Good air movement around the plants helps dry off the leaves quickly, which discourages disease development. Caging or staking plants helps increase air circulation around the plants. Also, rotate the location of the tomatoes in the garden each year to help prevent a buildup of diseases against them in one location. Picking off the leaves when you see the spots of early blight as they first appear may help reduce its spread.

Fungicides can be used to help manage these diseases. It is best to apply them before the plant is infected. A fungicide containing the active ingredient mancozeb can be used during the early season before fruit harvest starts, and chlorothalonil can be used during the season while picking fruit. Good coverage with the fungicide on both sides of the leaves is important in order to protect from more infections by early blight and septoria leaf spot.

Apply the fungicide according to the label directions, making sure the product is labeled for use on tomato plants. Follow label directions on how often to apply the fungicide, which may be weekly, and the number of days you should wait after spraying before you can harvest the fruit. The fungicide needs to be applied several times, possibly weekly, during the season to protect the new foliage.

For more information about growing tomatoes, contact the Daviess County Cooperative Extension Service at 270-685-8480.

Annette’s Tip

The spotted winged drosophila (SWD) was captured in traps locally last week, which tells us the pest is in the area. This fruit-fly like insect is a pest of raspberries, blackberries and blueberries. It is recommended to refrigerate berries immediately after picking. This will stop or slow down the development of the insect if present. Freezing berries will kill the SWD in the fruit. Placing netting with openings of less than 1 mm over the crop to exclude the insect is also suggested. More management information can be found at https://entomology.ca.uky.edu/ef231.

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