How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

The potato aphid has both a pink and a green color biotype. This aphid is much bigger than the green peach aphid with a more elongate body shape and is generally found on the terminals of tomato plants later in the season than green peach aphids. It is also considered to be more damaging.

DAMAGE

High potato aphid populations can distort leaves and stems, stunt plants, and cause necrotic spots on leaves. These aphids also secrete a large amount of honeydew that promotes development of sooty mold on foliage and fruit. Plants are particularly susceptible to yield losses from high infestations during the period from 6 to 8 weeks before harvest. Yield losses from equally high aphid populations decline substantially as harvest approaches, unless aphid densities are reducing leaf area enough to permit sunburn.

MANAGEMENT

Monitor potato aphids from 6 to 8 weeks before harvest as well as the level of parasitism and the activity level of predators. Treatments may be necessary if natural enemy activity is low and populations are increasing.

Biological Control
Naturally occurring parasites and predators of the potato aphid are common and can provide control. Monitor the proportion of aphid mummies relative to unparasitized aphids and the numbers of predators such as lady beetles, lacewing larvae, and syrphid larvae. If the proportion of mummies is increasing or predators appear to be gaining control and aphid populations are not yet damaging, avoid sprays that will disrupt these natural enemies.

Tolerant Varieties
There is considerable difference in tomato variety susceptibility to potato aphid feeding. Varieties containing the Mi gene, which confers resistance to nematodes, have been reported to be more tolerant of potato aphid infestations. However, this resistance no longer appears to be as effective as it once was, particularly against the pink form of the potato aphid.

Organically Acceptable Methods
The use of tolerant varieties, biological control, and sprays of herbal oils, pyrethrin, or insecticidal soap are acceptable for use on an organically certified crop. Repeated applications may be necessary for control.

Monitoring and Treatment Decisions
Monitor potato aphids from bloom to early fruit set by picking the highest open flower on 30 plants selected at random throughout the field. Record on a monitoring form (95 KB, PDF) the presence or absence of potato aphids on each leaf, while noting natural enemies. Treatment is warranted if 50 to 60% or more of the leaves are infested. During late fruit set, combine monitoring for potato aphid with monitoring for tomato fruitworm : pick the leaf below the highest open flower on 30 randomly selected plants from throughout the field. Record observations on a monitoring form (122 KB, PDF). If 50% of these leaves are infested during the period 6 to 8 weeks before harvest, the resulting loss is about 1 ton per acre. Good spray coverage is important in controlling high populations. Ground sprays using hollow-cone nozzles or air-assist sprayers will provide the best canopy penetration. Higher spray volumes are also helpful.

• Summary of Important Links

Common name		Amount/Acre**	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
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.	ACETAMIPRID
	(Assail) 70WP	1.2 oz	12	7
	MODE OF ACTION GROUP NUMBER1: 4A
	COMMENTS: Allow 7 days between applications with a maximum of 4 applications/season.
B.	METHAMIDOPHOS*^
	(Monitor) 4EC	1.5–2 pt	3 days	7
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: Available for use under a Special Local Needs permit. Ground application recommended. 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.
C.	LAMBDA-CYHALOTHRIN*
	(Warrior with Zeon)	3.84 fl oz	24	5
	MODE OF ACTION GROUP NUMBER1: 3
	...PLUS...
	ACETAMIPRID
	(Assail) 70WP	1.2 fl oz	12	7
	MODE OF ACTION GROUP NUMBER1: 4A
	COMMENTS: For high populations. Allow 7 days between applications with a maximum of 4 applications/season. Do not use this product if leafminers are present because it is destructive of their parasites.
D.	LAMBDA-CYHALOTHRIN*
	(Warrior with Zeon)	2.56–3.84 fl oz	24	5
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Do not use on cherry tomatoes or other varieties where mature fruit size is less than 1 inch in diameter. Do not use this product if leafminers are present because it is destructive of their parasites. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i.
E.	METHOMYL*^
	(Lannate) 90SP	0.5 lb	48	1
	MODE OF ACTION GROUP NUMBER1: 1A
	...PLUS...
	FENPROPATHRIN*
	(Danitol) 2.4 EC	10.66 fl oz	24	3
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Do not use Group number 1A insecticides if psyllids are in the field as carbamates tend to promote development of their populations. Do not use either product if leafminers are present because it is destructive of their parasites. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i.
F.	DIMETHOATE
	(Dimethoate) E267	1.5 pt	48	7
	(Dimethoate 400)	1 pt	48	7
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: Do not use this product if leafminers are present because it is destructive of their parasites.
G.	THYME OIL#
	(Proud)	0.5–1% solution	0	0
	MODE OF ACTION: Contact including smothering and barrier effects.
	COMMENTS: Short residual material.
H.	PYRETHRIN#
	(PyGanic) 1.4EC	Label rates	12	0
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Short residual material that provides moderate control with repeated applications. Always buffer to pH 5.5 or lower.
I.	ROSEMARY OIL/PEPPERMINT OIL#
	(Ecotrol)	1–1.5 pt	0	0
	MODE OF ACTION: Contact including smothering and barrier effects.
	COMMENTS: Short residual material. Apply with organic spreader/sticker.
J.	INSECTICIDAL SOAP#
	(M-Pede)	2.5 oz/gal water	12	0
	MODE OF ACTION: A contact insecticide with smothering and barrier effects.
	COMMENTS: Soaps provide less than 50% control of potato aphid, but can be used to reduce populations, particularly when parasite activity is noted.
	**  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

• Photos of natural enemies of aphids
• Potato aphid monitoring form (95KB, PDF)
• Potato aphid and fruitworm monitoring form (122KB, PDF)

Back to management

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 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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