How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Proba bug is a native insect that occurs on coyote brush, Baccharis pilularis, a common shrub on coastal mountain range hillsides from Oregon to Los Angeles. In the central coast, coyote brush commonly grows along highways next to the artichoke fields. Proba bug can be a major pest of artichokes that are grown both as perennial and annual crops.

Adults are about 0.2 inch (0.5 cm), uniformly light brown, and lack any obvious marks on their body, unlike lygus bugs, which have a prominent yellow, triangular-shaped marking at the base of the forewings. The newly hatched nymphs are pale greenish yellow, somewhat similar to small aphids with the exception that the proba nymphs move faster with their overly long legs. The second- and third-instar nymphs are reddish brown and the fourth- and fifth-instar nymphs exhibit light and dark alternate bands on the abdominal segments.

Proba bug is active throughout the year in the central coast growing districts; however, because of low temperatures during winter, the insect develops very slowly and causes minimal damage at this time. As air temperature begins to rise in March, the bug becomes more active. Proba bug nymphs quickly molt into adults and egg laying occurs following mating. A large number of eggs are laid in the artichoke leaf petioles and hatch in 20-30 days. Soon after hatching the nymphs start feeding on young leaves.

DAMAGE

Proba bug nymphs and adults feed mainly on the very young leaves that are in the frond stage. As they feed with their piercing-sucking mouthparts, they inject a toxin into the plant that results in the death of the leaf tissues around feeding wound. As the developing leaves expand, the feeding punctures turn into brown necrotic spots that fall off, leaving the leaf with a shot-hole appearance. In a severely infested artichoke field, affected leaves are abnormally small and light yellow; as the leaves age they turn brown. The damage to the artichokes by the proba bug is very similar to that caused by lygus except that proba bug is more aggressive in its feeding habit.

Proba bug also feeds at the base of the young artichoke bud, causing it to turn partially or completely black and rendering it unmarketable.

MANAGEMENT

In the past, the use of organophosphate and chlorinated hydrocarbon insecticides kept this insect out of artichoke fields. Cancellation of most of these insecticides has resulted in the resurgence of proba bug as a pest of artichoke in recent years. The destruction of any nearby coyote brush shrubs and stalk removal following harvest helps to manage this pest. Artichoke fields where methidathion (Supracide) is used in spring in the early, nonproduction phase of the crop are least affected by this pest.

Biological Control
Naturally occurring predators that feed on the nymphal stages of proba bug include bigeyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), minute pirate bugs (Orius tristicolor), and several species of spiders.

Cultural Control
Cut bare stalks at the base and remove them from the field or disc them under at harvest. This practice, called stumping, will kill the immature stages (eggs and nymphs) that would otherwise reinfest plants. Remove any coyote brush in the immediate vicinity of the field as it may harbor large number of proba bugs.

Organically Acceptable Methods
Biological and cultural controls are acceptable for use on organically certified crops.

Monitoring and Management Decisions
Monitor the crop for the physical symptoms of damage in March. When the damage is evident, determine the proba bug population level by sampling the shoots during the vegetative phase and the fruiting terminals during the production phase of the crop at weekly intervals. To sample the vegetative shoots, cut one off at ground level and shake it vigorously in a 5-gallon white bucket. Count all the dislodged proba bugs. To sample the semi-exposed terminal fruiting bud, cut the productive shoot off just below the lower secondary bud and vigorously shake it in the bucket. Sample a total of 10 to 15 shoots. A population level of three nymphs per shoot is considered the treatment threshold. If not treated, the crop can suffer 20-30% loss of yield due to leaf damage and more if fruiting shoots are attacked.

Common name		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees and to the environment. Not all registered pesticides are listed. Always read label of product being used.
CROP'S VEGETATIVE STAGE
A.	METHIDATHION*
	(Supracide) 25WP	4 lb	3 days	see comments
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: Application allowed during the nonproductive phase of the crop only; do not apply after buds begin to form.
REPRODUCTIVE STAGE
A.	THIAMETHOXAM
	(Actara) 15WDG	3 oz	12	4
	MODE OF ACTION GROUP NUMBER1: 4A
	COMMENTS: Do not use on plants in vegetative stage. Highly toxic to bees. Use limited to two applications a year. Also controls lygus bug and silverleaf whitefly.
B.	BIFENTHRIN*
	(Brigade) WSB	16 oz	12	5
	(Brigade) 2 EC	6.4 fl oz	12	5
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Do not exceed 0.5 lb a.i./acre/season.
C.	PERMETHRIN*
	(Pounce) 25WP	6.4–19.2 oz	12	0
	(Pounce) 3.2 EC	4–12 oz	12	0
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Mixing bifenthrin and permethrin at their half rate gives acceptable control at low cost. When pesticides are used in tank mixes, observe all directions for use on crops, rates, dilution ratios, precautions, and limitations that appear on the labels of all products used in the mixture.
+	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 to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
*	Permit required from county agricultural commissioner for purchase or use.
#	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/.

PUBLICATION

UC IPM Pest Management Guidelines: Artichoke
UC ANR Publication 3434
Arthropods
M. A. Bari, Artichoke Research Foundation, Salinas
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Arthropods:
W. E. Chaney, UC Cooperative Extension, Monterey County
W. L. Schrader, UC Cooperative Extension, San Diego County
L. Handel and T. K. Shannon, Kleen Globe, Inc., Castroville, CA

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