Sunday, February 2, 2014

Lemongrass Rust

Lemongrass is commonly grown by backyard gardeners as an ornamental plant. It is popular in Thai cooking and other Asian dishes.  Leaves can also be dried for herbal tea. The lemon-scented oil is used as a fragrance.

Unfortunately, lemongrass is susceptible to a fungal infection known as rust disease.  The environmental conditions that favor this disease are high rainfall, high humidity and warm temperatures.  

The disease initially begins as tiny yellow spots on the leaves. They merge together developing streaked patterns of brownish, purple lesions running up and down the leaf.  Both upper and lower surfaces of the leaf are infected. Wind and rain spread the spores.

The good news is that, normally, the disease is not fatal, but defoliation, poor yields and reduction in oil can occur. Diseased plants are safe to use in cooking recipes.

Here’s what to do:
·        Keep plants growing vigorously with adequate fertilizer.
·        Avoid planting large numbers of plants together.
·        Try growing plants under cover to protect their leaves from        rainfall.
·        Thin out diseased leaves and destroy the material.

Although the University of Hawaii has not evaluated this fungicide, Trilogy (neem oil) is the only registered material in Hawaii for use against this disease on lemongrass.