How to Manage Pests

UC Pest Management Guidelines

Tomato

Tomato Fruitworm

Scientific name: Helicoverpa (Heliothis) zea

(Reviewed 1/08, updated 1/08)

In this Guideline:


DESCRIPTION OF THE PEST

Tomato fruitworm adults are medium-sized moths with a wingspan of about 1 to 1.3 inch (25–35 mm). They are pale tan to medium brown colored or sometimes have a slight greenish tinge. The front wings are variously marked and usually have an obscure dark spot in the center and a lighter band inside a dark band around the tip. The hind wings are drab white and have a dark gray band around their tip. A diffuse light spot is in the center of the dark band.

At hatching, tomato fruitworm larvae are creamy white caterpillars with a black head and conspicuous black tubercles and hairs. Larger larvae vary in color from yellowish green to nearly black and develop fine white lines along the body but retain the black spots at the base of bristlelike hairs. Older larvae also have patches of stubby spines on their body segments that are much shorter than the bristles and can be seen best with the use of a hand lens.

The tiny, spherical eggs are slightly flattened on top with coarse striations or ribs running from base to tip. They are easy to confuse with looper eggs, but looper eggs have finer striations. Fruitworm eggs are laid singly on both upper and lower surfaces of the leaves usually in the upper part of the plant. When first laid they are creamy white, but develop a reddish brown ring after 24 hours and darken just before larvae hatch.

DAMAGE

When there is fruit present, the tomato fruitworm will complete its larval development inside fruit. Early stage larvae enter fruit at the stem end when it is between 0.75 to 2 inches in diameter. During development, caterpillars may emerge from one fruit and enter another. Their feeding results in a messy, watery, internal cavity filled with cast skins and feces. Damaged fruit will ripen prematurely. Late in the season, small larvae will also enter ripe fruit. Small larvae are difficult to detect and, thus, may be a problem in processing tomatoes for the canner. Tomato fruitworm is less of a problem for fresh market tomatoes because damaged fruit are easily culled at harvest.

MANAGEMENT

Management of tomato fruitworm requires careful monitoring for eggs and small larvae. When control is needed, it is essential to treat before large numbers of larvae enter fruit, where they are protected from sprays. Trichogramma parasites and other natural enemies often destroy significant numbers of eggs, so it is important to check for parasites before making treatment decisions. Except in the desert valleys, early-season processing tomatoes rarely need treatment. Late-season fields may be more seriously affected.

Biological Control

Naturally occurring beneficial insects are very important in the biological control of tomato fruitworm, especially in the Delta area and the Sacramento Valley. These include Trichogramma spp. egg parasites, the larval parasite Hyposoter exiguae, and predators such as bigeyed bug and minute pirate bug. Conserve these parasites whenever possible and monitor their presence, as described in MONITORING AND TREATMENT DECISIONS.

A tomato fruitworm egg parasite, Trichogramma pretiosum, is available from many commercial insectaries. Inundative releases of 100,000 parasites/acre during the period of fruitworm oviposition and when fruit are susceptible to fruitworm feeding can reduce damage to acceptable levels. Monitor releases using the egg sampling technique to determine the success of the release (indicated by black, parasitized eggs) and use the table below to determine if pesticide treatments are needed. Be sure to monitor the releases to make certain that parasitism is occurring.

Organically Acceptable Methods

Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on organically certified produce.

Monitoring and Treatment Decisions

Damaging populations of tomato fruitworm rarely occur before August. Monitor adult activity in July using a Heliothis trap baited with a pheromone lure to determine when to sample for eggs, which are laid during the flight periods. When moths are being caught in the traps, begin sampling leaves for eggs. If eggs are detected in samples taken during July, start accumulating degree-days using a lower threshold of 55°F and an upper threshold of 92°F to predict egg laying of the generation in August that attacks the fruit. It takes an average of 968 degree-days for tomato fruitworm to complete a generation.

For fresh market tomatoes, when traps indicate flight has begun, conduct a 5-minute search of leaves for eggs. If eggs are found, a treatment may be warranted. Later in the season, sample both leaves and fruit when monitoring for caterpillars (tomato fruitworm, beet armyworm, etc.).

For processing tomatoes, starting when a significant number of green fruit are one inch in diameter, sample for eggs by picking the leaf below the highest open flower on 30 plants selected at random throughout the field. If three or more healthy, white eggs are found in the 30-leaf sample, sample 30 more leaves (stop sampling if less than 3 eggs are found). If five or more eggs are found in the second 30-leaf sample, apply a treatment to coincide with hatching. Aim insecticide treatments at newly hatched larvae. Once larvae are in fruit they have already caused damage and are difficult to kill. When sampling for fruitworm, also look for fruitworm damage. Six to eight weeks before harvest, also monitor potato aphids in your sample and record results on a monitoring form (PDF).

Assess egg parasitism for processing tomatoes in the Sacramento Valley. In the Sacramento Valley, several species of parasitic wasps (Trichogramma spp.) can be found parasitizing tomato fruitworm eggs in late August and September at sufficient densities to control the pest. Most, but not all parasitized eggs will eventually turn black. Because there is a lag period, some white eggs in field samples may actually be parasitized but not recognizable as such; consequently a threshold may falsely appear to be exceeded. The following table provides adjusted treatment thresholds, using the number of black and white eggs present in samples of 30 tomato leaves, to compensate for not being able to distinguish eggs in the early stages of parasitism.

The letter "T" indicates the ratio at which treatment is recommended. If no black eggs are recorded, collect and observe white eggs for 48 hours and subtract those that turn black due to parasitism.

Number of Black Eggs Number of White Eggs
4–8 9 10 11 12 13 14 15
0 T T T T T T T T
1   T T T T T T T
2       T T T T T
3         T T T T
4           T T T
5           T T T
6           T T T
7             T T
8             T T
9               T
10               T
Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. INDOXACARB
  (Avaunt) 3.5 oz 12 3
  MODE OF ACTION GROUP NUMBER1: 22
 
B. ESFENVALERATE*^
  (Asana XL) 0.66EC 5.8–9.6 fl oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not feed or graze livestock on treated vines. Do not exceed 0.5 lb a.i./acre/season. Note: some bleaching or spotting may occur on the foliage of young plants. This does not affect yield or fruit quality. Do not use this product if leafminers are present because it is destructive of their parasites. This material is best used late in the season or during cool months when leafminers are not present. In some areas where tomatoes are grown, resistance to this material has been observed.
 
C. FENPROPATHRIN*
  (Danitol) 2.4EC 10.66 fl oz 24 3
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not use this product if leafminers are present because it is destructive of their parasites.
 
D. METHOXYFENOZIDE
  (Intrepid) 2F 10–16 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: Low toxicity to beneficials. Time application to the beginning of egg hatch. When traps indicate moth flights have begun, sample leaves for eggs. Treat when eggs are first detected.
 
E. METHOMYL*^
  (Lannate) 90WSP 0.5–1 lb 48 1
  (Lannate LV) 1.5–3 pt 48 1
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: This material will also control armyworm and cabbage looper. Do not use if psyllids are in the field as carbamates tend to promote development of their populations; also if leafminers are present, it may cause outbreaks by destroying their natural enemies. This material is best used late in the season or during cool months when leafminers are not present. Resistance to this material is a problem in some tomato-growing areas.
 
F. SPINOSAD
  (Entrust)# 1–2 4 1
  (Success) 3–6 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
 
G. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: This material may be less effective than some broad-spectrum insecticides, but it does not destroy the natural enemies of tomato pests. Treatments applied from egg hatch up to 1st or 2nd instar larva using the egg monitoring program are generally the most effective.
 
H. METHAMIDOPHOS*^
  (Monitor) 4EC 1.5–2 pt 3 days 7
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Available under a Special Local Needs permit. See label for special re-entry and plantback restrictions. Check label and with your processor for preharvest interval. Do not use this product if leafminers are present because it is destructive of their parasites. This material is best used late in the season or cool months when leafminers are not present.
 
I. CARBARYL*^
  (Sevin) 80S 1.5–2.5 lb 12 3
  XLR Plus 1–2 qt 12 3
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Best used when larvae are present near harvest and require treatment. Do not use if psyllids are in the field as carbamates tend to promote development of their populations.
 
J. TRICHOGRAMMA PRETIOSUM# at least 100,000/acre 0 0
  COMMENTS: Make releases during the fruitworm egglaying period and when fruit are susceptible. Monitor carefully to determine if additional treatments are necessary. Released parasites are not always effective. Determine the effectiveness of parasite releases within a few days of the release by monitoring fruitworm eggs for parasitism. Host eggs can be placed in the field at the time of the release to help evaluate the effectiveness of the release. If pesticides are applied, Bacillus thuringiensis is the only recommended material that will not harm the parasite.
 
K. PYRETHRIN#
  (PyGanic) 1–4 pt 12 0
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Short residual material. Buffer to pH 5.5 or lower.
 
**  See label for dilution rates.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until harvest can take place. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest may take place.
* Permit required from county agricultural commissioner for purchase or use.
^ Do not apply when bees are present.
# Acceptable for use on organically grown produce.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470

Insects and Mites

  • F. G. Zalom, Entomology, UC Davis
  • J. T. Trumble, Entomology, UC Riverside
  • . F. Fouche, UC Cooperative Extension, San Joaquin County
  • C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the insects and mites section:
  • N. C. Toscano, Entomology, UC Riverside

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