Arkansas Fruit, Vegetable and Nut Update

Tomato Fruitworm Flights Ramping Up

by Aaron Cato - June 2, 2022

Tomato Fruitworm moths are currently laying eggs on susceptible plants across the state. Provided here are recommendations on how to easily manage them in tomato:

June is here and that means the risk of tomato fruitworm, Helicoverpa zea, begins to increase rapidly.
We generally expect an influx of moths blown in on storms each year in late May that are in search of
corn or tomatoes to lay eggs on. It looks like flights are already ramping up with over 330 tomato fruit
worm moths captured in Southern Arkansas last week at one site, and over 100 a week at many other
sites around Central Arkansas. See more information about current moth flight numbers with our
interactive map at this link www.uaex.uada.edu/hort-ipm. We held an agent training down in Bradley
county on May 25th and tomatoes there were confirmed to be well above threshold with eggs and larvae
easy to find. We are getting more reports now about high populations and even of damage behind
sprays.

Tomatoes are all over the board when it comes to maturity right now, with fully ripe Bradley county
tomatoes in the South and a lot of smaller plants as you move North. Regardless of their stage, most
people have fruit and flowers on the plants and they are prime targets for serious losses due to tomato
fruitworm feeding. See below for recommendations on scouting for this pest, effective products to rely
on for management, and some info about our latest research efforts.

Scouting for Tomato Fruitworm

As the name suggests, people usually see fruitworm once they already have some size to them and are
feeding on the fruit they hope to sell. However, the trick to managing this pest with minimal losses is to
try to target it when it is most vulnerable and before it begins feeding on fruit. As with most caterpillar
pests we deal with, this means trying to control the larvae just as they hatch.
Tomato fruitworm generally lays its eggs on the tops of leaves or other plant structures near the top of
plants. These eggs are spherical or domed in shape and are about half a millimeter in diameter and
height (Picture 1). Fruitworm eggs take about 3-4 days to hatch before 1st instar larvae will begin to feed
on small amounts of leaf material and move inward towards the center of plants. These larvae generally
feed on minimal amounts of leaf material before they molt to their 3rd instar and move to flowers and
fruit (Picture 2 and 3). Finding fruitworm eggs is relatively easy compared to looking for larvae or feeding
damage on plants. Larvae are near impossible to find after they hatch and before they start feeding on
large amounts of leaf material or reproductive parts in their 3rd instar. Begin scouting weekly for eggs
once plants begin to take off all the way through harvest. Fruit samples should also be checked for
escaped worms.

Tomato Fruitworm eggs present in large amounts on tomato leaves

Picture 1- Tomato Fruitworm eggs present in large amounts on tomato leaves.

A 3rd instar tomato fruitworm still feeding on tomato leaves and feeding damage from tomato fruitworm on unopened flowers.

Picture 2- A 3rd instar tomato fruitworm still feeding on tomato leaves and feeding damage from
tomato fruitworm on unopened flowers.

Managing Tomato Fruitworm

Insecticide applications for tomato fruitworm should not be automatic, as not all growers will see
enough pressure to warrant applications throughout the season. Thresholds for control are based on
egg counts and the number of escaped worms found in fruit or on plants (Picture 3). Initiate an
insecticide spray if you are finding 1 egg per 10 plants. I would recommend you thoroughly check 10
plants in multiple places throughout your plantings, as moths often will lay many eggs in a small area.
Continue to scout for eggs after you make an insecticide application to determine if you need additional
applications. Growers should also check fruit for escaped worms that were either initially missed during
egg scouting or were not controlled by the insecticide application. Make additional applications if 3
escaped worms are found per 100 cut fruit (Picture 3).

Escaped Tomato fruitworm larva feeding on tomato fruit.

Picture 3- Escaped worm feeding on tomato fruit.

There are many options for controlling tomato fruitworm, but only a few that work very well. Most
growers rely heavily on pyrethroids such as Warrior II or bifenthrin for suppression, but fruitworm
resistance to these products is well established and is known to lead to escaped worms. We’ve assessed
the effectiveness of pyrethroids for two years in research trials at Hope and always see inadequate
suppression, even when sprayed weekly (Figure 1). Additionally, these are broad spectrum insecticides
that can flare both mites and aphids. More selective alternatives such as the diamide products, Coragen
or Exirel, are less likely to flare secondary pests, have long residuals, and have no known resistance. We
trialed the diamides vs. pyrethroids in 2020 and 2021 and saw impressive results (Figure 1). When
targeting insecticide applications based on the egg threshold mentioned above using diamides, we saw
half as much damaged fruit compared to pyrethroids sprayed on threshold or even sprayed every week.
Other alternatives to pyrethroids include spinetoram products and some effective biologicals. Take a
look at the Southeast Vegetable Handbook for additional recommendations and efficacy data. We are trialing a number of additional products this year for this pest and the results will be posted this winter.

A graph showing the Average Damaged Fruit per 100 for each spray treatment

Figure 1 – 2021 Efficacy data for tomato fruitworm at Hope, AR. Only 1 application was made at 1x
threshold based on egglay. The red line indicates a 3% fruit damage threshold that would warrant
additional applications. Both weekly pyrethroids (6 applications) and 1 pyrethroid based on threshold failed to keep damage under this level.