How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Several kinds of stink bugs feed on tomatoes, but all are similar in life history and damage. The most common species statewide is the consperse stink bug, which tends to be the most important species in the Sacramento and northern San Joaquin valleys. The redshouldered stink bug is considered the most prevalent species in the southern San Joaquin Valley. Chlorochroa sayi and C. uhleri are most prevalent on the west side of the San Joaquin Valley. The southern green stink bug, Nezara viridula, occurs in parts of the Sacramento and northern San Joaquin valleys, but is kept at relatively low levels by an imported parasite.

Adult stink bugs are distinctly shield shaped and either brown or green. Some species have red, pink, or yellow markings. Adults overwinter on the ground under leaves, in orchards, legume crops, blackberries, or on certain weeds such as Russian thistle, mustards, and little mallow (cheeseweed). They become active in March and April and begin laying eggs at this time. Eggs are drum shaped with circular lids and are laid in clusters on foliage. Immatures resemble adults but do not have developed wings.

DAMAGE

On green fruit, damage appears as dark pinpricks, surrounded by a light discolored area that turns yellow or remains light green on ripe fruit. Fissures below the surface turn corky. Stink bugs may also carry yeast and other pathogens that may cause decay when introduced into fruit on the bugs' mouthparts. A few fields have been significantly damaged by yeast introduced by stink bugs; this damage is scored as "mold" by state graders.

MANAGEMENT

Monitoring stink bug populations and their levels of parasitism are important for making treatment decisions. Treatment thresholds vary according to the market for which the crop is grown.

Biological Control
Both predators and parasites attack stink bug egg masses. One parasitic wasp, Trissolcus basalis, has been introduced into California for control of the southern green stink bug. Examine stink bug eggs to determine levels of parasitization. Parasitized eggs are dark; if parasites have emerged, the emergence holes will be irregular as opposed to round holes caused by stink bugs pushing off the top cap of the eggs to emerge. Trissolcus basalis does not appear to parasitize the other stink bug species in the field. However, a large complex of native parasites do parasitize these native stink bug species; these parasites occur in most growing areas and can result in parasitism in excess of 80% late in the season. Although these parasites are not commercially available, monitoring for stink bug egg masses to detect black eggs (those that are parasitized) is a useful practice. If parasitized egg masses are found, treatment for newly hatched nymphs might not be necessary. If damaging levels of nymphs and adults are present, treatment will still be needed. Parasitism can be enhanced for short distances from plantings of nectar plants such as alyssum when the flowering of these plants begins in May and June.

Cultural Control
Destroy weeds (legumes, blackberries, Russian thistle, mustards, and little mallow) that are good overwintering hosts for adult stink bugs around fields that are to be planted to tomatoes in spring.

Organically Acceptable Methods
Preserving naturally occurring biological control agents, good weed management around the field, and kaolin clay and insecticidal soap sprays are acceptable for use on organically certified produce.

Monitoring and Treatment Decisions
Stink bugs often are not observed until damage has begun. When the bugs are common, they may be found by beating or by shaking the vines. After shaking, look for stink bugs on the ground and between clods of soil. Or place a 16-inch cafeteria-style tray on the ground and shake the plant onto that. The presence of stink bugs can also be detected by the brown liquid frass that they produce, which leaves dried spots (0.06-0.12 inch) on leaves and fruit where they are active. Treatment is more likely to be necessary in fresh market plantings and in processing fields committed to solid-pack or dice canning. Treatment is generally not recommended in processing tomatoes intended for paste or juice unless conditions, such as wet, dense canopies, are favorable for the development of yeast or fungal pathogens introduced by the bugs.

To monitor consperse stink bug activity and distribution in a field, place clean, double-cone traps baited with an aggregation pheromone in fields at flowering. (Pheromones are not commercially available for the other species.) In areas of the field where stink bugs are consistently found in traps, take samples beginning when fruit reach one inch in diameter. Sample with a beating sheet or tray, and also examine the soil under the beating.

A phenology model has been developed for consperse stink bug that can help predict nymphal emergence, which is the stage most susceptible to control by any available pesticide. To use the phenology model, begin calculating degree-days from the date adult stink bugs are first captured in pheromone traps. The lower developmental threshold is 53.6°F (12°C); no upper developmental threshold has been established, although it is believed to be near 98.6°F (37°C). Most nymphs will be present at about 558 DD (°F) or 310 DD (°C), and shake sampling as described previously to determine the need for treatment should be made at this time.

Treatment thresholds vary according to the use of the tomatoes, but a good rule is that one-third to one-half of a stink bug per tray shake on average will result in about 5% damaged fruit. Distribution of samples within the field depend on whether an area of the field can be treated separately from the whole field. If an infested portion of the field cannot be spot treated, average tray shake samples from the entire field to make a treatment decision.

Because a significant portion of a stink bug population is located on the ground at any given time of day, good canopy penetration of any control material applied is essential. Ground applications provide much better coverage than do aerial sprays and are recommended when treatment is necessary. Using hollow-cone nozzles or air-assist sprayers improves canopy penetration. Consider reducing tractor speed and increasing application volume to improve coverage. If water volume is increased, use the highest label rate of pesticide.

• Summary of Important Links

IMPORTANT LINKS

• Degree-day calculator
• Degree-day table

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PUBLICATION

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
C. F. Fouche, UC Cooperative Extension, San Joaquin Co.
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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