MELeaf: A Newsletter From the Horticulture Program, May 24, 2023
In this issue:
Thrips parvispinus, is a newish invasive thrips that has popped up in Florida and has been frequently covered in the trade press this spring. Florida and Maine are far apart both geographically and climatically; what do Maine growers need to know about T. parvispinus and how worried should you be?
Background
Thrips parvispinus is sometimes referred to as pepper thrips, but this is not a generally accepted common name and is somewhat misleading as the thrips feeds on a wide range of plants. For clarity, it is probably best to stick with the scientific name Thrips parvispinus.
T. parvispinus is found in many countries around the world, most of them tropical, but also some temperate regions. A pest risk assessment conducted by the Netherlands in 2019 indicated that while the risk of T. parvispinus establishment in greenhouses and other indoor culture was high, they also concluded that it was unlikely to survive the winter and the risk of establishment outdoors in the Netherlands was low. T. parvispinus has also been found surviving in several greenhouses in Ontario, Canada, but is not established in the environment there.
In the US, T. parvispinus was first found in Florida in 2020 and has been present in Hawaii since 2006. Florida has seen establishment of T. parvispinus both inside greenhouses and in outdoor plantings. The Florida Department of Agriculture and Consumer Services considers T. parvispinus a regulated pest.
Identification
Thrips parvispinus is 1 mm long and appears dark in color. The female has a light brown to yellow head and thorax, and a dark brown abdomen. Males are completely light tan to yellow. For comparison the most common thrips we see in Maine greenhouses, western flower thrips (Frankliniella occidentalis), is 1.5 mm long and generally light in color, although some adults may appear darker. Thrips species can be difficult to distinguish from each other and identification requires the use of a microscope. When in doubt, contact the Horticulture Program or the University of Maine Cooperative Extension diagnostic lab for help.
Hosts
Thrips parvispinus has a wide host range. It can feed on more than 43 species in 19 different plant families, including many ornamental and vegetable crops. In Florida, significant damage was observed in gardenia and mandevilla production. Other hosts in Florida include: Anthurium, Hoya, Ixora, Schefflera, Hibiscus, peppers and others. List of host plants
Damage
General thrips damage (including T. parvispinus damage) can be described as spotting, stippling and silvering on foliage and flowers. In addition, Thrips parvispinus sometimes feeds in buds and on young foliage causing distorted and curled foliage. Feeding damage may also cause misshapen fruit. Unlike western flower thrips, T. parvispinus is not currently known to transmit tospoviruses or any other plant viruses.
Scouting
Plants should be inspected upon arrival and inspections should be repeated regularly throughout the crop cycle. Scout for thrips by carefully inspecting all plant parts especially plants with suspicious symptoms, magnification with a hand lens or even getting a closer look with a microscope is helpful. Keep in mind that thrips may be hiding in buds and flowers. You can also monitor for thrips (and other insects too!) by tapping flowers and foliage onto a plain white sheet of paper and inspecting the paper for any dislodged insects. Placing yellow sticky cards in the greenhouse can be a useful tool to help monitor for thrips, but should be used in combination with regular scouting.
Conclusions
So how worried should you be about Thrips parvispinus? The Horticulture Program thinks it is wise to be cautious, but we don’t think it will have a catastrophic impact on Maine growers. It appears unlikely that this pest will establish in the environment in Maine. If introduced to Maine, T. parvispinus could become a problem in greenhouses and indoor plantings. It is also possible that repeated introductions during the growing season could lead to seasonal damage on outdoor crops and other plantings. Inspecting incoming plant material for pests and looking carefully for thrips, especially in shipments from Florida, and scouting crops regularly for thrips and other pests throughout the growing season, will help minimize the potential for introduction and establishment. If you do find a suspicious thrips, we would like to know; email the Horticulture Program.
Thrips of all kinds are known to be difficult to control and Thrips parvispinus is no exception. Effective bio-control options are still being explored. There are several chemicals that have worked for growers in Florida, although repeated treatments are likely necessary. University of Florida, Thrips parvispinus Update from March 2023, includes pictures of plant damage, a host list and pesticide efficacy evaluations.
More Information
Aphids - As in many years, the most common pest we’ve seen so far is aphids. Some growers have reported that they have struggled to keep aphid populations down this spring and control has taken repeated pesticide applications.
Weather - While the weather in the last couple of weeks has taken a sunnier turn, we did have a stretch of nearly constant cloudy and rainy weather for most of the state in late April and early May. Inspectors did not observe an increase in botrytis, edema, shoreflies, fungus gnats or other damp weather concerns. Growers have been doing a great job of managing water and humidity this spring! We did see a couple of instances of pythium root rot, which may have been exacerbated by overwatering during this cloudy period. Keep an eye to the forecast and if another stretch of cool, cloudy, weather is predicted, do your best to increase air circulation in the greenhouse and reduce watering accordingly. Damp weather may also lead to an increase of populations of slugs and snails. The Horticulture Program is interested in reports of unusual snails and slugs, especially any potential Arion slugs (large, 3 to 5 inch long slugs that are brown, red or black). Email pictures of any unusual slugs to the Horticulture Program.
Browntail Moth – Damp weather isn’t all bad news. Wet spring weather could lead to an increase in the fungal and viral pathogens that help keep browntail moth populations in check. So far this spring, the Maine Forest Service has not observed these pathogens in their monitoring sites, but it is still early! Browntail moth caterpillars are out and actively feeding, if you live or work in an area where there are significant populations be sure to take the necessary precautions to help reduce your exposure to the caterpillar’s itchy hairs. If you are considering using pesticides to control BTM now is the time. Applications aimed at reducing the amount of BTM hairs in the environment should be applied before late May. Applications on plants for sale should be continued as long as caterpillars are present on plants.
 Life stages of the browntail moth
Viruses – Leaf mottling and other unusual markings in leaves and flowers have been observed on petunias this spring. While the symptoms look like what you’d expect to see with a viral infection, due to the small number of plants affected growers have chosen to discard plants rather than go through the process of having the plants tested. We are currently in the process of following up on a report of roses being sold at box stores that may be infected with rose mosaic virus and another of hostas potentially infected with hosta virus x. In addition, other states have reported finding chili pepper mild mottle virus on calibrachoa in greenhouses again this spring. Watch for viral symptoms in your plants (mottling, mosaic, ringspots on leaves, flower breaking or other unexpected flower coloration, and stunted, twisted or strange growth of plants). Contact the Horticulture Program is you have any concerns about viral diseases.
Spotted Lanternfly – Growers should continue to inspect incoming plants and any hard goods for spotted lanternfly egg masses, especially on goods arriving from the mid-Atlantic region. Eggs are starting to hatch in states to our south; start looking for early instar nymphs on both newly arriving plant material and plants that were received earlier this year. This pest is not known to be established in Maine. Report any suspicious insects by sending a picture to the Horticulture Program, if possible collect a sample in a sealed container.
 Lifes stages of the spotted lanternfly
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