BACTERIAL SOFT ROT (Xanthomonas campestris pv. vesicatoria) ON CHILLI LEAVES

Perhaps this disease is less common being spotted in Malaysia, but it spread very fast during outbreak especially on intermittent of rainy and hot days. Usually the pathogens attack on the immature plant, causing defoliation.

Water-soaked soft rotting on the leaves margins, lesions became opaque like scalded by insects or dropped off.

Early symptoms showed with multiple greasy grey spots.



There is no BACTERICIDES in the current market. The only treatment available is using the copper based fungicides like tribasic copper sulphate (Cuproxat) with 1.5-2ml/L of water or copper hydroxide (Parasol) with 0.5-1g/L of water. Copper will disrupt the enzyme activity in the bacterial cells with exchange of magnesium and calcium ion, in turn accumulation causes cell ruptures.

Sanitizer e.g.SPOREKILL is highly recommended to add into spraying programme with copper fungicide to sterilize the leaves surfaces. It enhances the performance of fungicides with one time job killing the bacteria and other pathogens, while fungicides will play the residual role on the latter part.

 

One of the most concerning issue among farmers are copper fungicides are not safe and cause plants yellowing. However, with the careful steps followed, plants are usually safe from phytotoxicity. There are 3 precautious steps need to take note that pH, moisture and type of copper will determine how much of copper ion will be released on the leaves. Excessive of copper ion released if using ACIDIC water.

 

Second, copper deposited on leaves once applied and gradually release the copper when there is moisture like morning dew or raining. Too much of moisture like raining will release high concentration of copper.

 

Third, using fixed copper like copper hydroxide and tribasic copper sulphate instead of copper sulphate pentahydrate, which is less soluble and prolong the protection on the leaves. Solubility of copper: copper sulphate pentahydrate > copper hydroxide > tribasic copper sulphate. Hence, tribasic copper sulphate is recommended, it release 50% of the copper ion for shock treatment while another 50% will stay on plant surface to provide protection.

 

To be noted that copper fungicides are mainly play the protection function. During the disease outbreak, it is too LATE to be applied and treatment became limited. BRING THE RAINCOAT BEFORE IT RAINS.