Bacterial spot in tomato fruit and its management

It is caused by the bacterium Xanthomonas campestris pv. vesicatoria. Bacterial spot develops on seedlings and mature plants. On seedlings, infections may cause severe defoliation. On older plants, infections appear as water-soaked areas. Leaf spots turn from yellow or light green to black or dark brown.

Older spots are black, slightly raised, superficial, and measure up to 0.3 inch (7.5 mm) in diameter. Larger leaf blotches may also occur, especially on the margins of leaves. Symptoms on immature fruit are at first slightly sunken and surrounded by a water-soaked halo, which soon disappears. Fruit spots enlarge, turn brown, and become scabby.

Management of bacterial specks:

The two diseases have similar control measures. Once they have already set in, there is currently no known cure. The best is to try and manage the diseases' aggressiveness to just salvage some harvests. Here are a few control measures that can be undertaken;

• Avoid/minimize working on the crops when the leaves are wet as this may only spread the disease to unaffected plants or parts. The spores can be spread through hands and clothing of pickers, cultivation and pruning equipments.

• Periodic disinfecting of the pruning tools while working on the tomato plants can help. Bleachers (such as Jik) and alcohol (70%) can be used. These can be wiped or sprayed on the pruning tools  

• Avoid overhead and sprinkler irrigation methods; embrace drip and furrow irrigation which do not make the leaves wet. This is because the diseases are favored by warm, wet and humid conditions.

• Use only certified seeds free from infections. In case of infected seeds, use hot water to treat

• Regular and routine use of copper-based fungicides helps prevent the bacteria spores from germinating, thus acting as a preventative measure. It may also help in suppressing the diseases once already set in though it may not help much. Sulphur may also be used, but should not be applied at the flowering stage as it causes flower abortion. 

Here are some copper formulations that can be used:

• Copper Oxychloride (green copper) e.g 

       Green Cop® 500WP https://www.agropests.co.ke/products?s=green%20cop

       Isacop https://www.agropests.co.ke/products?s=isacop

• Copper hydroxide (blue copper) e.g Funguran https://www.agropests.co.ke/products?s=funguran , 

        Vitra https://www.agropests.co.ke/products?s=vitra  

• Copper sulphate pentahydrate eg Mastercop https://www.agropests.co.ke/products?s=mastercop 

• Resistance has been observed in copper use, but this can be enhanced by tank-mixing them with Mancozeb e.g Milthane Super https://www.agropests.co.ke/products?s=milthane