New thrips flight prediction tool now available

Tobacco plant with systemic TSWV infection in a research plot; Craven County, NC, 2008. Photo: HJB

For the past 2 years, a group of NCSU entomologists and climate scientists have been developing a website designed to predict tobacco thrips (Frankliniella fusca) flights and make management recommendations to suppress tomato spotted wilt virus (TSWV) in tobacco.  We are proud to roll out this tool for tobacco grower, cooperative extension agent, and crop consultant use today! The TSWV and Thrips Exposure Tool for Tobacco uses temperature and precipitation data to predict tobacco thrips flight timing.  We then provide management recommendations based on grower provided transplant dates. 

Why do we need a tool to predict thrips flights?
Losses in tobacco to tomato spotted wilt virus (TSWV), which is vectored by thrips, vary greatly depending on year and location, with losses since 2000 in NC alone ranging from several million to over 45 million dollars per year.  In addition to killing young plants, TSWV reduces the uniformity, yield, and leaf quality of infected plants that are not killed. Tools for managing TSWV in tobacco are limited and must be applied before TSWV spreads into the crop. Imidacloprid (Admire Pro®) and Actigard® applied to transplants in the float house are the most commonly used TSWV management measures. However, the level of TSWV control provided by these materials has been inconsistent. 

Field studies at multiple sites in NC and GA have confirmed the value of using both Admire Pro® and Actigard® in reducing losses to TSWV. Results demonstrated that condition of the plants when float bed applications of either product were made influenced the degree of phytotoxicity, with the highest and most persistent levels of phytotoxicity always associated with the weakest transplants. Phytotoxic effects of pre-transplant applications of Admire Pro® and Actigard® can be minimized by applying them separately at least 1 day apart.  These studies confirmed that the greatest reduction in TSWV can be obtained when Admire Pro® (applied as a float tray treatment) and Actigard® are used, and demonstrated that the most effective application timing of Actigard® varies with year and location depending on when the spring flight of tobacco thrips and spread of TSWV occur. Tobacco thrips are the most important species for TSWV transmission in North Carolina and much of the southeast.

How do we know that treatments timed to predicted thrips flights are effective?
Field trials conducted by NCSU entomologists for the last 3 years and Clemson entomologists for the last 2 years have demonstrated that Actigard® treatments timed to thrips flights lower TSWV incidence.

Who should use this tool?

The TSWV and Thrips Exposure Tool for Tobacco should be used by tobacco growers in high risk TSWV areas in North Carolina. An area is considered high risk if it has a historical average TSWV incidence over 10%.

Distribution of tomato spotted wilt virus in North Carolina (based on county reports 1993-2008). The darker colors represent counties where TSWV incidence may be high (10 – 15%) in several fields every year.  Figure from Mina Mila, 2011. Flue Cured Tobacco Information, Chapter 8. Managing Diseases.

How do growers/agents/consultants use this tool?
For example, growers in high TSWV risk areas enter their location, tobacco type grown, anticipated transplant date, and any known or planned greenhouse treatments.  The models then predict, based on grower location, if tobacco thrips are expected to fly within the next 2 weeks.  If thrips flights are predicted, then the website suggests possible management options.  For example, if the predicted flight is within 2 weeks of transplant, a greenhouse treatment of Actigard® will likely result in the greatest TSWV suppression. On the other hand, if the thrips flight is predicted 3 to 4 weeks after transplant, a field treatment of Actigard® may be most effective.  Finally, if thrips are not expected until 8 weeks after transplant, treatment is likely not needed.  Of course, whenever using pesticides, always read and follow the label.  The label is the law! 

Thrips flight predictions are only available 2 weeks out at this time due to forecast data available.  As weather forecasting tools improve, so will the prediction length.

What if I am not in North Carolina?

We have tested the website in South Carolina, and predictions are reasonably close to those for North Carolina.  However, we have not tested the website in another southeastern states, so for the time being, we are recommending it only for use by North Carolina tobacco growers.


What if I grow other crops affected by TSWV?
Tobacco thrips may not be the most important vector in other crops affected by TSWV, such as peppers and tomatoes, so our models are intended only for use by tobacco growers.  We plan to expand these models for other crops in the future.

More information
TSWV and Thrips Exposure Tool for Tobacco
North Carolina State Climate Office
Tomato Spotted Wilt Virus - University of Georgia
Admire Pro - Product Label
Actigard - Product Label


We gratefully acknowledge the support of the Tobacco Research and Education Council, Inc., Altria, Phillip Morris International, and the R.J. Reynolds Fund for Excellence in developing and delivering the TSWV and Thrips Exposure Tool for Tobacco.

What to watch for in 2010: Thrips

Over the next few weeks (0r until the field season gets busy), I will be posting pest watches for 2010. These are designed to provide updates on pests that may be problematic or for which management strategies may differ in 2010.

First up is a group that has become near and dear to me in the last 2 years: Thrips!

Western flower thrips (Frankliniella occidentalis), www.bugwood.org. Photo: J.T. Reed

Thrips as pests

Thrips are of concern to southeastern growers for 2 reasons: 1. They vector potentially devastating plant viruses, and 2. Thrips can directly damage crops in their own right. In the cropping systems I work in thrips are both virus vectors (tobacco and caneberries) and cause direct fruit or plant injury (strawberries, blueberries, and grapes).

In tobacco, thrips vector Tomato Spotted Wilt Virus (TSWV) which can result in significant losses. Colleagues in the NC State Entomology Department developed a degree day model which predicts tobacco thrips (Frankliniella fusca, the most important TSWV vector in the southeast) flights. We have adapted these models for a website that will be launched for use by county agents and select growers this Thursday, April 1st.

Flue cured tobacco plant infected with TSWV. Photo: www.bugwood.org.

Thrips also vector Impatiens Necrotic Spot Virus (INSV), which infects many plants, including caneberries. Caneberry viruses are the topic of a multi state USDA Specialty Crops Research Initiative (SCRI) project with which I am involved. Lead by the University of Arkansas, this project is designed to identify and development management strategies for virus complexes in caneberries. Unlike many other plant-virus pathosystems, caneberries are often infected with 2 to 3 virus before they show symptoms. The virus complex appears to vary regionally, as do the likely vectors.

Blueberry fruit damage caused by thrips oviposition (egg laying) and feeding. Photo: Insect Management in Blueberries in the Eastern United States, Tuner & Liburd.

In strawberries, grapes, and blueberries, fruit injury by thrips is of greatest concern. Thrips feeding on blueberry can also damage blooms. Blueberry injury by thrips is weather and variety dependant in NC. Late blooming varieties (rabbiteye and northern highbush) are more prone to damage, but growers generally do not need to treat these varieties every year. Thrips injury to strawberries is rare in NC, and other injury is often misdiagnosed as thrips-caused.

Thrips can cause bronzing near the calyx in strawberries. Photo: Jack Kelly Clark, UC IPM Program.

Thrips do not cause malformed fruit. The damage in this image is due to lygus bug injury, but malformed fruit can also be caused be poor pollination or dried calyx disorder. Lygus bug injury is also rare in NC and has only been observed on late season or day neutral strawberries. Photo: UC IPM Program.

Thrips injury to grapes is more common in NC than injury to blueberries and strawberries. Grapes bloom and develop later in the spring, when thrips populations have built to higher numbers and are less susceptible to spring weather conditions.

What to watch in 2010

Thrips management in 2010 will be different than in a typically year, because we will likely have fewer thrips than normal and they may move into crops later. If this holds true, we may have fewer problems with thrips in tobacco and small fruits in 2010 than in a typical year.

Tobacco thrips models currently indicate that this spring will have low numbers of thrips. This is not surprising because cool, wet weather negatively impacts thrips during March and early April. This spring, much like last year, has been both cool and wet, until recently. It is possible that weather patterns could become more favorable for thrips, but unless the weather changes dramatically (rapidly warming and drying), I suspect that thrips movements will occur later this year and that populations will be lower than normal.

What does this mean practically? I anticipate that thrips treatments in blueberries may not be needed, and that strawberry injury may also be rare. As always, SCOUT and SAMPLE before making any treatment decision!

We continue to track and model tobacco thrips populations, and we will not have concrete predictions until the end of April, but I will continue to update as this picture becomes clearer.

Tobacco meetings in full swing

With 5 tobacco meetings this week, the winter extension season in full swing! Duplin, Wayne, Johnston, Pitt, Nash, and Beaufort Counties all have meetings this week (see meeting list for dates and locations). Next week (1/19 through 1/21) is the Tobacco Workers Conference in Lexington, KY. At this meeting, we will be rolling out a new TSWV (tomato spotted wilt virus) online decision making tool, a project we have worked very hard on in the last year with support from Altria, PMI, and recently, the Tobacco Education and Research Council (TERC). This tool was developed with the expertise of the NC State Climate Office.

Also at the Tobacco Workers Conference, Monique Rivera, MS student, will be presenting her 2009 findings on tobacco splitworm biology, a very rewarding project, and Richard Reeves, PhD student, will share plans for his upcoming research on tobacco insect threshold revisions.