Don’t Let Your Guard Slip When Taking On Thrips

Photo by Oscar E. Liburd

Photo by Oscar E. Liburd

There are several species of thrips that affect blueberry production in Florida. The Florida flower thrips, Frankliniella bispinosa Morgan, is the principal flower thrips that infest blueberries in Florida. The larvae and adults feed on the reproductive parts of the blueberry flower. Flower thrips are common during the spring in February and March depending on the location in Florida. The south-central counties tend to see flower thrips two to three weeks earlier than northern counties. Flower thrips have yellow fringed wings as well as punching and sucking mouth parts.

Photo by Andrew Derksen

Photo by Andrew Derksen

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Chilli Thrips

Another species of thrips that infest blueberries is the chilli thrips, Scirtothrips dorsalis Hood. Chilli thrips are native to Southeast Asia and were first reported in blueberries in Florida during summer 2008 in Hernando, Citrus, and Lake counties. Since that time, there have been sporadic outbreaks in several Central Florida counties. Chilli thrips are very small and only about ¾ the size of flower thrips. They have dark-fringed wings and dark spots across the back of the abdomen. They feed on young leaves and stems and are usually found in late spring and summer between the months of May to August. Several growers have reported high populations of Chilli thrips after the bushes are pruned.

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Species’ Specs

Thrips species complex and population are influenced by temperature, humidity, and host plants. Some common hosts influencing the population of the Florida flower thrips include Carolina geranium Geranium carolinianum L., Pusley Richardia sp., and Thistle Circium spp. Many of these plants flower just prior to or during the period of blueberry flowering. Similarly, chilli thrips have a wide host range and many plant and weed species are known reproductive hosts. Common hosts known to influence the abundance of chilli thrips include: viburnum, (Viburnum suspensum Lindl), Brazil pusley — tropical Mexican clover (Richardia brasiliensis Moq), waxweed, tarweed Cuphea spp., and sweet basil (Ocimum basilicum L.).

Photo by Oscar E. Liburd

Photo by Oscar E. Liburd

Some symptoms resulting from flower thrips injury include brown floral petals with lesions, flower abortions, small brown spots on the fruit, poor fruit set, and low yields. Alternatively, symptoms of chilli thrips infestation include leaf bronzing, shoot dieback, and leaf curling. In some cases, brown spots (mottling effect) appear on developing and ripe fruits.

There are some similarities between the life-cycle of flower and chilli thrips. Thrips tend to form hot spots (concentrated in small areas) when they first appear in a blueberry planting and then spread out to other areas. Generally, the lifecycle varies from 15 to 23 days depending on environmental conditions. There can be at least two to three generations per year. Adults feed and lay eggs that hatch in one to three days. There are two larval feeding stages that last for about six to nine days and a prepupal and pupae (non-feeding) stage that last for two to four days before emerging as adults.

→3-Step Approach To Thrips Management←

3-Step Approach To Thrips Management

1. Weekly monitoring. Thrips populations should be monitored at least once per week. Flower thrips can be monitored using white sticky traps placed within the canopy of the blueberry bushes. Growers should use at least two traps per acre, one on the border and the other in the center of the field. If individual trap catch is more than 50 thrips per week, then some type of management action is warranted. Alternatively, growers can tap blueberry flowers over a white cardboard sheet and if a grower is averaging more than two to three thrips per flower cluster (six to nine flowers) then it is advisable to use some type of management action.

Chilli thrips can be detected in the field by tapping young leaves (plant tissues) on a white board and counting the thrips that fall unto the board before they begin to walk away or by hanging white sticky traps directly inside the bush of the plant. These traps are usually changed once per week. Traps can be locally made in the absence of commercial white sticky traps by using white sticky card boards (5 x 8 inches). Chilli thrips numbers also could be accurately assessed by dipping blueberry plant tissues into alcohol. It is recommended you treat with pesticide if you are averaging more than five thrips per plant.

2. Cultural control. Thrips have a wide host range and many plant and weed species are known reproductive hosts. Therefore, eliminating alternate host and weeds (when possible) can help to suppress thrips populations.

3. Use of reduced-risk, conventional, and organic insecticides. Thrips population can be suppressed in blueberries with the use of effective reduced-risk insecticides such as Delegate (spinetoram, Dow AgroSciences) and Assail (acetamiprid, United Phosphorus Inc.). Conventional products including Malathion and Sevin (carbaryl) also are effective in reducing thrips populations.
Growers should limit the use of synthetic pyrethroids because they can destroy the natural enemies that usually regulate the thrips population. In addition, they should avoid using a product from the same class of insecticides more than two times consecutively to reduce potential for resistance build-up in thrips population.

Growers who are producing organic berries can use Entrust (spinosad, Dow AgroSciences), PyGanic (pyrethrins, MGK Co.), and neem oil (azadirachtin). Entrust was the most effective among the organic group of insecticides.
Some biological control agents that can be used for thrips control include Amblyseius swirskii (predatory mite) and Beauveria bassiana (fungus that grows naturally in the soil).

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