“I am very fond of the Spring-flowering colchicums, but unfortunately slugs are also, and those greedy gastropods and I have a race for who can see the flower-buds first. If I win I go out after dark with an acetylene lamp and a hatpin and spear the little army of slugs making for a tea-party at the sign of the Colchicum.”
Edward Augustus Bowles My Garden in Spring (1914)
Clearly last summer’s drought stressed some plants more than we realised at the time. Thrips. We have thrip infestations on plants which do not normally suffer. Plants show the damage as silvering on the leaves. It is common in many rhododendrons but bay trees and photinia are also prone to infestations, along with other plants. You can’t turn the silver leaves green again. Turn over the leaf and you will see rusty looking spots behind. This is the residue of the thread-like thrips which suck the chlorophyll out of the foliage. The damage is done.
Prevention is better than a cure. A strong, healthy plant with plenty of air movement around it and good light levels is better able to withstand attack. There are systemic insecticides you can use which the plant absorbs into its system, killing the thrips from the inside out but you have to wait until the critters are active again – usually late November. The bands sold that you wrap around the trunk of the tree will either be soaked in systemic insecticide or in Neem oil. We have never tried Neem and are surprised if it works as a systemic, but others say it does.
Contact insecticides don’t work unless you can saturate the underside of every single leaf so most organic remedies won’t work. The fresh spring growth will hide a multitude of sins and we are hoping that the thrippy plants will look fine again. Some varieties are much worse affected and generally we choose to remove those and replace with better performing varieties because we do not want to have to use systemic insecticides just to keep plants healthy.
First published in the Waikato Times and reprinted here with their permission.