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How to Manage Pests

UC Pest Management Guidelines

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Plum

Mealy Plum Aphid

Scientific name: Hyalopterus pruni

(Reviewed 5/06, updated 5/06)

In this Guideline:

Description of the pest
Damage
Management

DESCRIPTION OF THE PEST (View aphid identification photos)
Wingless mealy plum aphid adults are pale green or whitish green with three dark green longitudinal stripes on their backs. Their bodies are covered with a white mealy wax. The winged form has a dark thorax and transverse bands on the abdomen. Mealy plum aphids are often found inside the slightly curled-up plum leaves. After overwintering in the egg stage near the bases of buds, the aphids hatch during bloom and develop into wingless adults. They will have from three to thirteen generations on plums. Then winged adults appear in June and July as warm weather approaches and they migrate to reed grass or cattails. Wingless aphids that remain on vigorous growth of plum trees throughout the summer will not be capable of laying overwintering eggs in fall. Only the offspring of the winged adults that return to plum trees in fall lay the overwintering eggs.

DAMAGE

This aphid builds up in large numbers on the undersurface of leaves in spring and causes leaves to become slightly curled and stunted. High populations can devitalize the tree, retard growth, and reduce sugar content of fruit. Honeydew dropping on fruit can cause fruit cracking.

MANAGEMENT

Several natural enemies are important in the control of aphids in the orchard, but aphid populations often require treatment. The best indicator of populations is orchard history. The best time to treat is during the dormant or delayed dormant period. If aphids are a chronic problem in the orchard, apply a treatment early in dormancy; otherwise, sample during dormancy to determine the need to treat as described below. Spring treatments may also be made. After harvest, a zinc sulfate application will provide zinc to the trees as well as hasten leaf fall. Without the leaves on the tree, the aphid life cycle is disrupted. Zinc sulfate (36%) applied at 10-20 lb/acre can be applied in early to mid-October to help in this process.

Biological Control
There are many natural enemies that feed on leaf curl plum aphid; however, fruit size may still be reduced and curled leaves will not uncurl after aphids are suppressed. The recent introductions of Aphidius transcaspicus has led to substantial levels of parasitism of this aphid. Important predators include: lady beetles, green lacewings, brown lacewings, syrphid flies, and soldier beetles.

Organically Acceptable Methods
Biological control and sprays of narrow range oil or neem oil are organically acceptable methods of controlling this pest.

Monitoring and Treatment Decisions
If aphids are a chronic problem, a treatment in late fall/early dormancy (November 1) is a very effective way to manage these pests and is less likely to create water quality problems caused by pesticide runoff than treatments applied during the rainier season in January and February. If leaves are still on trees at this time, aphids and parasites can be present. Oil treatments are not recommended at this time because they are very damaging to parasite populations and not effective for aphid control.

Dormant monitoring. If the November 1 treatment is not applied, be sure to monitor during dormancy. (For more information, see DORMANT SPUR SAMPLE.) If dormant monitoring indicates treatment is necessary, two applications of oil at bloom can be used in orchards where a dormant/delayed dormant treatment is not required to manage scale problem. Parasites are not active at bloom, and they are not affected by the bloom oil sprays.

Spring monitoring. If aphids have been a problem in the past or if a dormant or delayed dormant application was not applied, monitor leaf curl plum aphid in spring along with mealy plum aphid. Follow the monitoring guidelines in SPRING/SUMMER MONITORING to determine if treatment is necessary.

Common name

Amount to Use**

P.H.I.+

(trade name)

(conc.)

(dilute)

(days)

The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, impact on natural enemies and honey bees, and impact of the timing on beneficials. When choosing a pesticide, also consider information relating to environmental impact.

DORMANT

PHOSMET

(Imidan) 70W

2.12 lb

1 lb

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

COMMENTS: Apply with a buffer to lower solution pH to 5.0. Apply as early as November 1^st even though all leaves may not be off trees. Has fewer impacts on beneficials and water quality then other materials listed. This low-label rate and early timing provide effective control and reduce the risk of runoff into waterways, mitigating concerns of surface water pollution. Early applications may not be effective for peach twig borer and are not effective for San Jose scale control.

DIAZINON* 50WP

1 lb

0.5 lb

DIAZINON* 4EC

1 pt

0.5 pt

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

COMMENTS: Apply as early as November 1st even though all leaves may not be off trees. This low-label rate and early timing provide effective control and reduce the risk of runoff into waterways, mitigating concerns of surface water pollution. Early applications may not be effective for peach twig borer and are not effective for San Jose scale control.

ESFENVALERATE*

(Asana XL)

3 oz

1.5 oz

MODE OF ACTION: A pyrethroid (Group 3)¹ insecticide.

COMMENTS: Apply as early as November 1st even though all leaves may not be off trees. This lower-than-label rate and early timing provide effective control and reduce the risk of runoff into waterways, mitigating concerns of surface water pollution. Pyrethroid residues remaining on leaves and bark will continue to affect mite predators long after application, increasing potential for spider mite infestations. Lower rates and/or early timing may not be effective for peach twig borer and are not effective for San Jose scale control.

DELAYED DORMANT

THIAMETHOXAM

(Actara)

3-4 oz

0.75-1 oz

MODE OF ACTION: A neonicotinoid (Group 4A)¹ insecticide.

COMMENTS: Direct treatment or residues on blooming crops and weeds are highly toxic to bees. Remove (mow, disc, etc.) blooming ground cover before treatment. Apply prebloom or postbloom but not from swollen bud to petal fall. Do not apply less than 2 oz or more than 5.5 oz/acre/application or exceed 8 oz/acre/season. This chemical is listed on the EPA reduced risk to the environment. Repeat applications of any neonicotinoid insecticide (imidacloprid - Provado; thiamethoxam - Actara) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance.

PHOSMET

(Imidan) 70W

2.12 lb

1 lb

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

COMMENTS: Apply with a buffer to lower solution pH to 5.0.

IMIDACLOPRID

(Provado) 1.6F

4-8 fl oz

2 fl oz

MODE OF ACTION: A neonicotinoid (Group 4A)¹ insecticide.

COMMENTS: Repeat applications of any neonicotinoid insecticide (imidacloprid- Provado; thiamethoxam - Actara) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance.

ESFENVALERATE*

(Asana XL)

3 oz

1.5 oz

MODE OF ACTION: A pyrethroid (Group 3)¹ insecticide.

COMMENTS: Pyrethroid residues remaining on leaves and bark will continue to affect mite predators long after application, increasing potential for spider mite infestations. Lower rates may not be effective for peach twig borer or San Jose scale control.

LAMBDA CYHALOTHRIN*

(Warrior)

2.56-5.12 fl oz

0.64-1.28 fl oz

MODE OF ACTION: A pyrethroid (Group 3)¹ insecticide.

COMMENTS: Residues remaining on leaves and bark may continue to affect mite predators long after application, increasing potential for spider mite infestations.

BLOOM

NARROW RANGE OIL#

4 gal

—

MODE OF ACTION: Contact including smothering and barrier effects.

COMMENTS: Apply in 100 gal water/acre. Oil must contact aphids to provide control; if aphids are sheltered in curled leaves, oil alone will not control them. Apply at green tip or popcorn to kill the hatching aphids (hatch generally occurs in early March). May be tank mixed with bloom time treatments aimed at peach twig borer and brown rot. Make a second application 10 days later. This usually coincides with full bloom in most years. Plum trees tolerate oil treatments better in spring than during full dormancy. Do not apply oil within 2 weeks of captan or within 30 days of a sulfur treatment.

ENDOSULFAN*

(Thionex) 50WP

SEE COMMENTS

MODE OF ACTION: An organochlorine (Group 2A)¹ insecticide.

COMMENTS: Label says use 1 lb/100 gallons water or 4-5 lb/acre. Cannot be applied in any situations where runoff may occur.

SPRING

DIAZINON* 50WP

1.5–3 lb

1 lb

DIAZINON* 4EC

1.5–3 pt

1 pt

MODE OF ACTION: An organophosphate (Group 1B)¹ insecticide.

COMMENTS: Avoid drift and runoff into surface waters. Where plums are grown near waterways, do not use diazinon.

NARROW RANGE OIL#

6-8 gal

—

MODE OF ACTION: Contact including smothering and barrier effects.

COMMENTS: Apply in 200 gal water/acre. Oil must contact aphids to provide control; if aphids are sheltered in curled leaves, oil alone will not control them. Harmful to parasitic wasps. Plum trees tolerate oil treatments better in spring than during full dormancy. Do not apply oil within 2 weeks of captan or within 30 days of a sulfur treatment.

NEEM OIL#

(Trilogy) 70EC

—

MODE OF ACTION: A botanical (Group 26)¹ insecticide.

COMMENTS: Repeat applications may be necessary.

THIAMETHOXAM

(Actara)

3-4 oz

0.75-1 oz

MODE OF ACTION: A neonicotinoid (Group 4A)¹ insecticide.

COMMENTS: Direct treatment or residues on blooming crops and weeds are highly toxic to bees. Remove (mow, disc, etc.) blooming ground cover before treatment. Apply prebloom or postbloom but not from swollen bud to petal fall. May cause mite outbreaks. Do not apply less than 2 oz or more than 5.5 oz/acre/application or exceed 8 oz/acre/season. Repeat applications of any neonicotinoid insecticide (imidacloprid- Provado; thiamethoxam - Actara) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance.

IMIDACLOPRID

(Provado) 1.6F

4-8 fl oz

2 fl oz

MODE OF ACTION: A neonicotinoid (Group 4A)¹ insecticide.

SUMMER

NEEM OIL#

(Trilogy) 70EC

—

MODE OF ACTION: Contact including smothering and barrier effects.

COMMENTS: Repeat applications may be necessary. Oil is harmful to parasitic wasps.

NARROW RANGE OIL#

6-8 gal

—

MODE OF ACTION: Contact including smothering and barrier effects.

COMMENTS: Apply in 200 gal water/acre. Oil must contact aphids to provide control; if aphids are sheltered in curled leaves, oil alone will not control them. Oil is harmful to parasitic wasps. Use a minimum of 6 to 8 gal of oil in 200 gal water. Good coverage (slow tractor speed) is essential for best results. Do not apply oil within 2 weeks of captan or within 30 days of a sulfur treatment or when temperatures are expected to exceed 95°F.

**	For dilute applications, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre, or lower if the label allows.
+	Preharvest interval. Do not apply within this many days of harvest.
*	Permit required from county agricultural commissioner for purchase or use.
#	Acceptable for use on organically grown produce.
—	Not recommended or not on label.
¹	Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is 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: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier

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