In just the last month a new pest has appeared on roses. It’s damage includes distorted and elongated foliage, scarred flower buds, and brown, angular spots on the new growth of the roses. The culprit has been identified: chilli thrips.
Previously a pest of tropical and semitropical areas of Texas, Florida and the Caribbean,
the 'chilli thrips’ distorting and disfiguring damage can be mistaken for other conditions. Herbicide damage, micro-nutrient deficiency, even excessive aphid infestation can lead to damage that looks much like these tiny, almost impossible to see pests.
|Chilli thrips damage|
The pests are small, and may have come in on the remnants of hurricane Dolores, which broke up over Southern California this last July (the thrips were first discovered in mid-August of this year). At 2 millimeters long, they’re not much larger than a grain of sand. This makes them incredibly mobile as they can be swept up into the atmosphere on strong winds and deposited hundreds if not thousands of miles away. They are thought to have originated in the Caribbean, an area prone to massive hurricanes that can travel from the far eastern Atlantic Ocean all the way over across Mexico into the Pacific. It’s as if they were living in an international airport for wind distributed insects.
Besides taking them to their destination, the hurricane also created the perfect conditions for their survival. The warm rains and overcast sunlight combined to create loads of soft, easily infested foliage on the roses that are the ideal conditions for this pest which feeds mostly on new growth.
So how can you take care of this? There is a possibility that the insects might not make it through the winter. They are tropical pests and may not have the ability or the strategy (hiding in leaf buds of nearby host plants that can keep them alive through the winter) to make it through one of our average winters. However this is an El Nino year and that means that winter temperatures might not dip low enough to kill of this pest. There is also the possibility that insect predators like insectivorous mites and others could start to find them tasty and effect control that way. For those experiencing infestations of this mite in greenhouses and areas where they are established there is a predacious mite that you can purchase to control it.
If you are facing an infestation it is recommended that you remove all infested foliage from your plants, bag it where you cut it, and dump it in a landfill. Composting the foliage can lead to a greater level of infestation in yours and your neighbors yard as the tiny little pests slough off of the infested foliage as you are carrying it to your compost pile.
There are pesticide strategies as well. Spraying fine horticultural oils like Monterey Horticultural Oil and alternating those sprays with products containing Spinosad can help bring damage to roses down to manageable levels.
Is this just a fluke due to El Nino? No, probably not. Los Angeles County entomologist Gevork Arakelian says the new pest introduction rate has increased to about two new pests a month. This may be due to the El Nino conditions making it possible for pests established to the south of us to head northward, and also the lack of funding for agricultural interdiction programs designed to keep pests from arriving here via our ports, airports and borders.