Invasion of the Thrips
No, this is not a sneak preview of the latest low-budget horror movie from Hollywood! There is currently a panic situation in the horticulture world whereby the Western Flower Thrip (Frankliniella occidentalis) is quickly developing resistance to the available insecticides for control on roses. Rose growers, both home and commercial, have become concerned over the increasing populations of thrips in spite of regular spraying habits. Apart from the loss of the aesthetic quality of the flowers, extensive damage to foliage( (mostly deformation, stunted growth and marred petals) can also occur.
Description of Thrips
Adult thrips are about 2 mil long and usually have dark body with four wings fringed with hairs. Their small size often makes them difficult to detect in the garden.
Rose Damage Characteristics
Damage is inflicted by nymphs and adult thrips sucking the plant sap with their rasping sucking mouthparts. They mainly attack the tender young leaf tissue peduncle and flower bud. The resulting infested bloom then shows the damage as tiny holes in several rows of outer petals as the bloom attempts to open. In some cases the bloom never reaches maturity since it has been robbed of the necessary nutrients and growth regulators to develop fully to the open bloom stage.
Thrips have been noticed to display certain preference in the varieties they like to feed on. While no general trend has been established, thrips tend to attack white roses, it would seem that thrips prefer petal substance to be on the low side avoiding varieties with high starch content. The most frequently posed question by rose growers is why their white roses do not open correctly. The answer is usually the pre-feeding by thrips before the bud matures, i.e. removal of vital growth regulators by sucking adult thrips.
Life Cycle of Thrips
Populations of thrips are supported by the female depositing eggs in the tender plant tissue (bud, new upper foliage sets etc.) Quite often the female thrip will bore into the immature bud to deposit her eggs. The eggs hatch in about two to four days in summertime into tiny wingless, almost white, nymphs. These nymphs then feed and molt four times before reaching adulthood. The Process of egg to adult thrip takes about two weeks. However, great importance should be placed on a later stage of development. The Larvae move down the plant to pupate in the soil of leaf litter at the base of the rosebush. This process can last up to four days before adulthood is reached and the thrip becomes a fully winged mobile insect. Females live about 30 to 45 days , depositing up to 300 eggs.
Control of Thrips
There are a number of criteria of to be considered in developinga proper control against thrips.
1. Spraying should be directed at two focal points, the young tender and developing buds as well as the soil level of the bush. In that way, adults and developing pupae in the soil are destroyed.
2. The pesticide spraying should be repeated five daysapart to kill the next generation larvae in both soil andupper foliage areas. Remember the eggs hatch in abouttwo days.
3. Examine carefully the foliage and buds for signs of resistance to pesticide control about one day after spraying. You should observe near total kill rates. If resistance to the pesticide selected is noticed then immediately change to an another insecticide of a different chemical
1. class type-change from Orthene to Merit, to Avid. Do not mix two insecticides in the hope of control, it will only encourage resistant populations to develop.
2. At a last resort remove all infected blooms and wait for the next bloom cycle.
Like most all movie scripts, the ending to the story can be a happyone, and this potential invasion of the thrips will seem like abad dream. Don’t let this tiny destructive insect spoil your rosegarden and the appreciation it brings from friends and neighbors.
This article is from the Beverly Hills Rose Society Newsletter and was authored by Dr. Tommy Cairns.
Editor’s note: There has recently been discovered in our valley Chilli Thrips. They were named that because it was first found on pepper plants in Argentina. They have moved here from the east so be on ther watch for them. They can be a serious threat to your roses.
The Destroyers of Roses
by Dean Murakami of Sego Nursery in the San Fernando Valley is an award winning author who has been recognized by the ARS for his excellence in rose horticultural knowledge.
The chilli thrips (accepted name and spelling by Entomologists in the USA) or yellow tea thrips, Scirtothrips dorsalis Hood, an extremely invasive species of flower and vegetable thrips spreading from Asia over the last twenty years, and has now achieved global distribution by appearing in Southern California on roses. Within the last decade it has most recently been reported in the continental United States from Florida as early as 2005, Texas around 2006, and Puerto Rico (2007) and now in 2014 in the Los Angeles basin. Why should rose growers and gardeners be concerned about this latest insect?
In late 2005, Chilli Thrips were reported as significant on roses in Palm Beach County. By January 2007, the thrips had been found in more than 30 counties in Florida, and had been detected in southern Georgia. And now by 2015 California has been invaded by this destructive pest.
Chilli thrips manifest themselves by preferentially feeding on new growth near the bud, and their presence on roses results on characteristic wrinkled leaves, with distinctive brown scarring along the veins of leaves, the buds of flowers, and the calyx. For the rose exhibitor and garden beauty, these thrips destroy not only the flower bit also all the foliage.
DIFFICULT TO DETECT BY EYE
Chilli thrips have a rapid life cycle, and can develop from egg to adult in slightly less than two weeks under our Southern California climate. Unfortunately for the home gardener, their detection is difficult due to their relative small size, under a millimeter in length, i.e. 25% of the more common Wester F lower Thrip ubiquitous to California. As a rough guide, under a low power magnification the thrip body suggests a yellow coloration (hence the original name of yellow tea thrips). It is this extremely small size that evades detection by the naked eye and allows them to freely breed into large colonies causing disastrous consequences and ultimately death of the host plant.
Strong visual evidence of the presence of Chilli Thrips can be
observed by dead tissue occurring within the vein structure
of the upper developing foliage around the bud.
Image courtesy from Rick Bennett of the Desert Rose Society
Comparison of relative sizes of Chilli Thrips to the most common pest here in Southern California, the Western Flower Thrips
Like most insects, Chilli thrips are known to develop resistance to pesticides extremely quickly.
Only the insecticides :
* imidacloprid (Merit, Bayer Insect Killer)
* spinosyn (Captain Jack’s Deadbug, Conserve)
* abamectin (Avid)
have been demonstrated to be effective against these thrips as others
Western Flower Thrip