Plant Disease and Insects

This week’s blog is about plant disease and insects.

It does not matter what kind of crop you are growing, you always have to look out for plant diseases and insects to avoid crop damage. There are three factors and conditions necessary for diseases in plants: host plant, disease causing organism or pathogen must be present and a favourable environment for disease organism to develop. If one of the factors is not present, the disease has no change to develop.

An example of a disease related to lavender is the Alfa Mosaic virus. For viruses in general, it is important to know that it can decrease the production of chlorophyll and the cells my either grow and divide rapidly or may grow very slowly and be unable to divide. Viruses are often transmitted by a living factor like insects, fungi, nematodes or mites, but also by non-living factors like mechanical means like rubbing. Symptoms can be lack of chlorophyll formation in green organs or stunting or other growth inhibition (Watts, 2017)

Insects and humans, due to touching, mostly spread the Alfa Mosaic virus. Is not very difficult to notice on the plant.  The leaves will turn yellow and then curl up, mostly into contorted shapes (Julian, 2009). If you notice these symptoms on your lavender plants, make sure you take the plant away from healthy ones, to avoid contamination.

Another common disease is the Lavender Shab Disease – Pheomopis lavandula. It is a fungus which kills the stems of the lavender. Fungi are microscopic organisms which reproduce through dispersal of spores. It often causes stem rust and powdery mildews. Many symptoms are similar to drought and nutrient deficiency’s, so it is important to investigate properly. Symptoms can be, off-coloured plant, wilting and dieback, leafspots, or the roots have brownish streaks.

Signs of Pheomopis lavandula are that the leaves will start to wilt, even though there has been no drought. This disease was the reason for an epidemic around 40 years ago, causing many commercial lavender growers to close. It is important to look out for small black shapes called pycnidia, emerging from the bark. The best is, to burn the affected plants (Julian, 2009).