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Agronomist notebook: Leaf miner, a farmer’s worst nightmare

Saturday October 26 2019

Philomon Endong'a displays tomatoes he grows in his venture in Mosop, Nakuru County.

Philomon Endong'a displays tomatoes he grows in his venture in Mosop, Nakuru County. Farmers are encouraged to buy and use certified seeds that are resistant to tomato diseases. Research is ongoing to identify resistant varieties and their development. PHOTO | JOHN NJOROGE | NMG 

ANN MACHARIA
By ANN MACHARIA
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Tomato is one of the many vegetables grown in large quantities in Kajiado County. Others are sukuma wiki and cabbage.

The environment is conducive to the growth of the vegetables since the region is hot. For years, farmers have had challenges with Tuta absoluta, or tomato leaf miner.

The problem grows worse during the warm weather as it is the time the multiplication rate increases. It is a common virus disease affecting tomatoes, beans, pepper, and mimics the symptoms of moisture stress. The disease also results in stunted growth.

Most farmers are aware of the pest and are doing all they can to control and eliminate it as they struggle to increase production. Unfortunately, the disease spreads very fast.

Farmers have aired their grief on social media, posting images of diseased vegetables and lamenting of making huge losses.

One farmer said he lost more than 60 per cent of his tomato crop to the pest. Once the pest invades a farm, the plants wilt. A farmer might think the crops are wilting due to high temperatures or lack of water. The tomato plant’s leaves curl and turn purple.

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One may quickly rule the condition to be as a result of phosphorus deficiency. As the leaves curl, they become thick and stiff.

Some fruits fail to develop while others become deformed. Some fruits ripen prematurely. Young plants quickly die after infection.

SPREAD FOR LONG DISTANCES

To tell if the wilting is as a result of the pest and not high temperature or lack of water, soak the soil around the plant in the evening. Check the state of the plant the following morning. If it has not revived, then the plant has the top curl virus.

The disease is spread by the beet leafhopper, a tiny wedge-shaped insect that varies in colour from pale green to brown.
The virus is most prevalent when temperatures are warm and populations of leafhoppers are most significant. The virus and the beet leafhopper have many hosts. The pest can quickly spread for long distances.

The beet leafhopper acquires the virus from infected plants and weeds such as mustards. The plants begin to show the symptoms seven days after they are infected.

Farmers are encouraged to buy certified seeds that are resistant to the disease. Research is ongoing to identify resistant varieties and their development.

Since infected plants do not recover, they should be removed from the farm and destroyed. The diseased plants should be placed in bags and incinerated.

Beet leafhoppers do not easily attack tomatoes in greenhouses and shade nets as they prefer feeding in sunny spots. For this reason, providing shade to tomatoes and peppers discourages leafhoppers from landing on the plants.

Soils should be kept evenly moist. This can be achieved by applying mulch to reduce the evaporation rate. Since the pest is attracted to widely spaced crops, one should minimise spacing.

The farmer can also intercrop to control the levels of the curly top virus. There are no pesticides for controlling the virus. However, spraying with neem oil will keep the pest at bay.