It's Time to Scout for Tomato Fruitworm
by Aaron Cato - June 2, 2023
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.
We’ve seen some high numbers already in 2023 with over 600 tomato fruit worm moths
captured in Southern Arkansas on May 17th in Lafayette County, another 300+ in Lafayette County on May 24th , and multiple traps over 100 moths a week at many sites around Warren, Arkansas the
week of the 24th (Picture 1) . Moth trap numbers have lessened in some locations heading into the last week of
May, but don’t expect that to continue for too long as more storms can move through
and successive generations already in Arkansas become adults. See more information
about current moth flight numbers with our interactive map at this link www.uaex.uada.edu/hort-ipm . We are continuing to scout tomatoes in our trials and on grower operations for tomato
fruitworm activity and will post updates on Facebook and the pest page linked above.
Picture 1- Tomato Fruitworm Moth Trap in Lafayette County. Picture of 300+ moths caught from
May 17-24. Picture by Jerri Dew, County Extension Agent and Staff Chair, Lafayette
County.
Tomatoes are all over the board when it comes to maturity right now, with large green
tomatoes in Bradley County almost pushing maturity 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.
What we do know is that the moths we captured in mid-May have already yielded fruitworm
larvae feeding on commercially grown tomatoes (Picture 2 – May 30th). Field scouting in South Arkansas this week revealed a number of one-week old larvae
on fruit, which lines up exactly with what we would expect to see based on those 100+
moths found in many traps. This is a good sign for many growers to get out and scout
ASAP so control can be achieved prior to those larvae moving on to their 2nd , 3rd , or even 4th fruit to munch on! See below for recommendations on scouting for this pest, effective
products to rely on for management, and some info about our latest research efforts.
Picture 2 – Tomato damaged by tomato fruit worm. Frass can be seen by a feeding hole in the
fruit. Picture taken 5/30/2023 in Hermitage, AR by John Gavin – Bradley County UAEX
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 tomato plants. These eggs are spherical or domed in shape and are
about half a millimeter in diameter and height (Picture 3) . 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 4) . 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. They become much easier to find when they burrow into fruit, but that is
after large economic losses are already incurring. 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 after applications, but also in initial scouting to ensure
you aren’t missing worms.
Picture 3 – Tomato fruitworm eggs present in large amounts on tomato leaves.
Picture 4 – A 3rd instar tomato fruitworm still feeding on tomato leaves (left) and feeding damage
from tomato fruitworm on unopened flowers (right).
Tomato Fruitworm Threshold Insecticide applications for tomato fruitworm should not be automatic (Figure 1) , 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 (Pictures 2, 3, and 5) . 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 (Pictures 2 and 5) .
Picture 5 – Escaped worm feeding on tomato fruit.
Insecticide Options for Tomato Fruitworm 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 three years in research trials at Hope and always see inadequate suppression,
sometimes even when sprayed weekly (Figure 1) . Additionally, these are broad spectrum insecticides that can flare both mites and
aphids. We think the uptick in mite issues across southern Arkansas are directly correlated
with reliance on these broad-spectrum insecticides. More selective alternatives such
as the diamide products, Coragen, Shenzi, Harvanta, or Exirel, are less likely to
flare secondary pests, have long residuals, and have no known resistance.
We have trialed the diamides vs. pyrethroids for 3 years now and have observed 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 in 2021. In 2022 pressure was higher and we
still did not see a significant difference in our weekly sprays vs. 2 shots of Coragen.
One thing to consider when using diamide products like Coragen or Shenzi is the residual
activity you can expect. We think you should expect 21 days of activity when using
a mid-high rate of those products.
Other alternatives to pyrethroids include proclaim, spinetoram products and some effective
biologicals. Take a look at the Southeast Vegetable Handbook for additional recommendations and efficacy data. One product that likely isn’t in
the handbook yet is Shenzi . This is a new generic version of Vantacor (row-crop version of Chlorantraniliprole,
previously known as Prevathon) but also has many specialty crops on the label. Shenzi
is likely to be much more easily available in Arkansas since it has the row crop label,
and also should be at a row crop price. Be sure to check rates before mixing up, Shenzi,
Coragen, and Vantacor all contain different amounts of chlorantraniliprole and have
different use rates.
As always, give me a call at 479-249-7352 if you have any questions at all. We are
trialing a number of additional products this year for this pest and the results will
be posted this winter.
Aaron Cato
Figure 1 – 2021 and 2022 insecticide threshold data for tomato fruitworm at Hope, AR. Weekly
pyrethroid plots were sprayed each week during fruiting (5-6 apps) while only 1 and
2 applications were made in 2021 and 2022 respectively for scouting based sprays.
Scouting-based sprays were made at a threshold of 1 egg per 10 plants. The red line
indicates a 3% fruit damage threshold that would warrant additional applications and
is a good metric for economic losses. Based on these data, applying weekly pesticide
applications for tomato fruitworm is not necessary and not sustainable. 1 to 2 well
timed applications of a diamide (Coragen) performed as good or better than weekly
pyrethroid sprays. Pyrethroid resistance is present in Arkansas but may vary in impact
from year-to-year. Pyrethroid-based thresholds are not likely to be effective and
weekly sprays are likely to still yield unacceptable levels of escaped worms and fruit
damage, while flaring other pests.
