How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Both snails and slugs are similar in structure and biology, except slugs lack the snail's external spiral shell. Snails and slugs move by gliding along on a muscular "foot." This muscle constantly secretes mucus, which later dries to form the silvery slime trail that signals the presence of these pests. They are most active during the night and early morning when it is damp. In southern California, particularly along the coast, young snails and slugs are active throughout the year.

Adult brown garden snails lay about 80 spherical, pearly white eggs a month in shallow depressions in the topsoil. They may lay eggs up to six times a year.

DAMAGE

Slugs and snails are of major concern on perennial artichokes especially in winter. The juveniles and adults feed on all parts of the plant. In heavily infested fields, slug feeding on foliage causes shot holes on the leaf lamina. Slugs are particularly injurious to the buds when they scrape off soft tissues from the artichoke bracts. This injury later turns black and the quality and marketability of the affected produce is greatly reduced. Mollusks do not pose any threat to annual artichokes throughout California.

MANAGEMENT

Controlling weeds and applying bait are important practices in keeping snail and slug populations under control.

Cultural Control
Cutting-back artichokes annually helps reduce the slug population. Regions where the artichokes are cut shallower or not cut at all usually sustain higher infestations of both slugs and snails. Keeping weeds under control reduces the plant cover under which the slugs and snail take refuge during the day. Similarly, artichokes planted in heavier soils are more prone to slug and snail damage than in lighter soils. Frequent cultivation and tillage generally keep the infestation under control by killing the slugs and exposing their eggs to natural predators like ground beetles and birds. However, slugs staying very close to the base of the plants or under the crown remain unaffected by this operation and in due course their populations rebound.

Management Decisions
In fields that have yearly problems with these pests,start baiting immediately after the annual cutback of the perennial artichokes in May and June by broadcasting the bait on the ground around the base of the plant. Avoid applying the bait directly to plant foliage or as a heap on the ground near the base of the plant. Continue baiting at 2-3 week intervals through November preferably after irrigating the field. In the past, control with baits has been only marginal in part because slug and snails have always been dealt with on a crisis basis. Research indicates that peak egg-laying in slugs occurs from late September through early November. Most eggs deposited before late October hatch during fall; those deposited in November hatch from late February through spring. Therefore, slugs are best controlled during October when they are more mobile on the ground surface in search of food and mate.

Several new formulations of metaldehyde bait have been introduced in recent years. Granular baits and micro-pellets have given better control, as the individual particles remain intact in the rain and irrigation water. Also, when the sand-based granular formulations are used during the production phase of artichokes, individual granules can get lodged in the flower buds and become a health hazard to the consumers. Slug control with metaldehyde is dependent on many factors, including weather. Metaldehyde rapidly breaks down in irrigation and rainwater. Adverse weather conditions such as the rain and wind keep the slugs, especially the juveniles, inactive and either they do not consume enough bait or they are able to recover from the poisoning.

Common name		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relative to environmental impact.
A.	METALDEHYDE
	(Deadline) 4% bait	10–20 lb	12	0
	(Durham) 7.5% G	8 – 15 lb	12	0
	(Metarex) 4% bait	5.5 -15 lb	12	0
	(Orcal) 3.25% bait	15 – 20 lb	12	0
	COMMENTS: Use higher rate for heavy infestation. This bait has minimal impact on other organisms in the field. Avoid contamination of buds by spreading the bait on the ground; tolerance has not yet been established.
B.	IRON PHOSPHATE
	(Sluggo) G	24–44 lb	0	0
	COMMENTS: Can be applied to a field approaching bud harvest without concern of contamination because this product is exempt from tolerance. Apply using standard fertilizer granular spreader. If ground is dry, wet it before applying bait. Reapply as bait is consumed or at least every 2 weeks. Check with your organic certifier to determine if this product is acceptable for use on organically certified produce.
	+  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 R.E.I. exceeds the P.H.I. The longer of these 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.

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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