How to Manage Pests

UC Pest Management Guidelines

Sugarbeet

Green Peach Aphid

Scientific name: Myzus persicae

(Reviewed 11/05, updated 1/10)

In this Guideline:

DESCRIPTION OF THE PEST

Green peach aphid is among the most common aphid species found on sugarbeet. The aphid may be present at any time throughout the year but is most common in the Imperial Valley from December through April. Generally its color is pale green, although at times individuals may be present that are pinkish. During cool weather, individuals are usually more deeply pigmented and may be confused with the potato aphid (see section on Other Aphids), but the two can be distinguished on close examination. The frontal tubercles at the base of the antennae in the green peach aphid are very prominent and convergent. The potato aphid is much larger than the green peach aphid with longer legs, antennae, and cornicles. While they do have prominent frontal tubercles, they are divergent, not convergent as in the green peach aphid. Winged forms of the green peach aphid have a distinct dark patch on the top of the abdomen; wingless forms lack this dark patch.

DAMAGE

Injury caused by the green peach aphid is mainly through its ability to transmit a number of destructive beet viruses. It is the principal vector of Beet yellows virus, Beet western yellows virus, and Beet mosaic virus. It does not transmit Curly top virus, Lettuce chlorosis virus, or Rhizomania (Beet necrotic yellow vein virus).

Green peach aphid can also damage the plant by sucking plant sap. When damaging levels occur, large numbers of aphids can be found on the underside of leaves. Extensive feeding causes plants to turn yellow and the leaves to curl downward and inward from the edges. Aphid damage is most prominent on newer, younger leaves in the center of the plant.

MANAGEMENT

The principal way of reducing virus transmission by the green peach aphid is adherence to the beet-free restrictions and planting dates established by grower and processor agreement. These planting date restrictions are established to avoid planting during major aphid flights and to prevent the virus source (i.e., infected sugarbeet plants), from bridging the time between old and new plantings. Planting date restrictions and beet-free periods vary considerably from location to location; contact your farm advisor, processor, or the California Beet Growers Association for the latest restrictions in your area. Strict adherence to these restrictions is absolutely necessary in order to reduce the amount of virus.

A second, and equally important factor in reducing virus spread, is good field sanitation. Infected keeper beets that produce new vegetative growth after harvest act as sources of virus inoculum for new plantings. Following harvest, thoroughly disc fields and chop remaining beets into small pieces. Watch fields closely and redisc if new growth appears. Take special care where keeper beets resprout in other crops, such as cereals or alfalfa. In such cases, herbicides may be required to control the new growth in order to reduce virus inoculum. These measures help control the incidence and spread of viruses transmitted by green peach aphid but do little in controlling the aphid itself.

Biological Control

Green peach aphid is attacked by a number of common predators and parasites and is susceptible to the fungus disease that commonly attacks aphids. Aphid sampling should always include an evaluation of the presence and activity of natural enemies.

Monitoring and Treatment Decisions

Treatment of aphids to prevent or reduce the incidence of beet viruses is of little value and is not recommended. Treatment thresholds for green peach aphid, as a pest in its own right, are not well established. Heavy populations can do extensive damage, particularly on seedlings or young plants. Consider treating plants less than 12 weeks of age if aphids are present in numbers sufficient to cause stunting. Older plants can tolerate considerably more aphids and if heavy infestation occurs 3 to 4 weeks before harvest, harvest the field instead of spraying.

Common name		Amount/Acre	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
NOTE: The green peach aphid has developed high levels of resistance to many of the insecticides used for its control. These insecticides may provide only partial control.
The following materials are listed in the order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees as well as the environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
A.	PHORATE*
	(Thimet) 20G	4.5 oz/1000 row ft	72	30–at planting
		or 4.9–7.4 lb		30–postemergence
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: Do not place phorate granules in direct contact with seed. Do not feed tops or silage to dairy cattle. Place granules to the side of seed or in a band over the row. Do not apply by air or make more than one applications /season.
B.	OXYDEMETON-METHYL*
	(MSR Spray Concentrate)	1.5–3 pt	72	30–tops and roots
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: No more than 2 applications/year.
+	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.
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 more information, see www.irac-online.org.
*	Permit required from county agricultural commissioner for purchase or use.

PUBLICATION

UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469

Insects and Mites

E.T. Natwick, UC Cooperative Extension Imperial County
Acknowledgement for contributions to Insects and Mites:
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
D. R. Haviland, UC IPM Program, Kern County
L. D. Godfrey, Entomology, UC Davis

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