Curly Top Virus in Tomatoes 2007

Research was conducted at the Western Colorado Research Center at Orchard Mesa in 2007 to study the impact of planting date and protective row covers on beet curly top virus in tomatoes.

The demonstration plantings were non replicated. Four tomato varieties were planted on each of three dates - April 25, May 9 and May 23. All were grown under furrow irrigation.

1st Planting Date

36-40 plants of each of four varieties were planted in the field in April 25. Varieties were Shady Lady, Puebla, Mountain Spring, and La Roma. Tomatoes were furrow irrigated.
Planting Tomatoes

Floating Row Cover

Floating row covers are made of tightly woven cloth and designed to lay loosely over plants to exclude insects. We supported the row covers with metal hoops to keep them from contacting plants. In past trials, floating row covers that were moved by wind whipped plants and caused some mortality. Our row covers enhanced temperatures, and plants covered by them had better growth than those in the open.

Ten plants from of each variety were placed under floating row cover, ten plants were placed under slitted row cover, and the remaining plants were left open.

The row covers were placed out immediately after planting. The slitted covers were removed on May 18 and the floating row covers were removed on May 29.

Slitted Row Cover

Slitted row covers were clear plastic covers with slits to allow aeration. They are typically used to enhance early season heating. They were supported by metal hoops. Slitted row covers give minimal protection against frost and slits allow leafhoppers and other insects access to the plant.

Plants were evaluated six times between June 29 and August 22 for CTV symptoms. Curly top incidence was very low in all treatments. Two of 27 plants under slitted row covers were infected with curly top. No plants that were open grown or grown under floating row covers were infected.

The infection rate was too low to draw any meaningful conclusions regarding the impact of row covers on curly top infection.

2nd Planting

On May 9, forty plants of each of the four varieties were planted. Ten plants of each variety were put under floating row covers, as with the first planting date. The row covers were removed on May 29. The graph at the right show the results of the evaluations between June 9 and August 22. The floating row covers did not prevent curly top because they were removed before the leafhoppers began infecting the plants.

3rd Planting

Each of the four varieties was planted on May 23. The number of plants varied from 13 to 23, depending on availability. All plants were planted in the open, without cover of any sort. The plants were evaluated throughout the rowing season for curly top infection.

Planting Date Effect

The graph at right shows curly top infection rate plotted by planting date. The early planted tomatoes had no curly top, while May planted tomatoes had infection rates greater than 12%.

Time of Curly Top Infection

The first plants with curly top symptoms were recorded on June 9. Assuming a one week period between infection and symptoms appearing, the leafhopper must have fed no later than June 2. Very few new symptoms appeared after the Aug 2 evaluation so we can assume that leafhopper feeding after July 26 did not result in curly top infections. The blue line represents all planting dates combined, red is the first planting date, green is the second planting date and yellow the third. The data points are the total number of infected plants (not % infection).

This page was updated on April 26, 2014