How to Manage Pests

UC Pest Management Guidelines

Sugarbeet

Bean Aphid

Scientific name: Aphis fabae

(Reviewed 11/05, updated 1/10)

In this Guideline:


DESCRIPTION OF THE PEST

Bean aphid is present in the Imperial Valley, but it is not a common pest of sugarbeets there.

Bean aphid is a dark olive green to black aphid. It is most easily confused with the cowpea aphid. Bean aphid has a dull, matte appearance while cowpea aphid is shiny. The cauda of the bean aphid has more hairs than that of the cowpea aphid and thus appears bushy. Except for the presence of wings, the winged form of the bean aphid is similar in appearance to the wingless one.

DAMAGE

Injury from bean aphid occurs from virus transmission and from direct feeding on sugarbeet leaves. Bean aphids transmit Beet yellows virus, Beet western yellows virus, and Beet mosaic virus. Although bean aphids do not vector viruses as efficiently as green peach aphid, generally bean aphid occurs at higher densities, which tends to negate the differences in virus transmission efficiency.

Infestations of bean aphid generally begin on young leaves in the center of the crown. As the number of individuals increases, older leaves are colonized. The aphid is found mainly on the underside of leaves and only rarely on upper surfaces. Infested leaves curl under and inward and become severely distorted. The leaf margin and eventually the entire leaf become necrotic. Heavy populations may kill foliage, even in large mature plants. Bean aphid produces large amounts of honeydew, and infested leaves are usually covered with sooty mold. If the aphids are killed, either by insecticides or natural enemies, leaves resprout from the crown and new foliage begins growing.

MANAGEMENT

The principal way of reducing virus transmission by the bean 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 bean aphid but do little in controlling the aphid itself.

Biological Control

Bean aphids are attacked by a variety of common aphid predators and parasites. Lady beetles, green lacewing larvae, and syrphid fly larvae are frequently found associated with bean aphid colonies. Note the presence of these predators and their impact on aphid populations during routine monitoring. If these predators are present and aphid numbers are declining, delay chemical intervention.

Bean aphid is attacked by a very prolific parasitic wasp, Lysiphlebus testaceipes. Parasitized aphids become bloated and their bodies turn tan in color. This parasite can control extensive populations of bean aphid in a few days, and if parasite activity is evident, chemical treatments should be delayed or canceled. Bean aphid is also attacked by a fungus disease that leaves the aphid body flattened so it appears to be glued to the leaf. Like the parasite, this fungus disease may control the aphid population within a matter of days. This disease is most prevalent in spring during rainy periods. In most cases, a combination of these biological control agents work in concert to reduce aphid numbers.

Monitoring and Treatment Decisions

Infestations of black bean aphid and infection with beet yellow virus are most damaging to the plant near the time of seedling emergence. For April to May plantings, the first 6 to 8 weeks after emergence is the most critical time to protect sugarbeet from black bean aphid and beet yellow virus. Monitor sugarbeet plants and evaluate the aphid population and the extent of direct feeding damage to plants. Determine damage levels caused by direct feeding from the following table:

Damage Level Aphid Infestations and Associated Injury
0 No visual injury; no aphids, or if aphids present, confined to isolated winged individuals.
1 No visual injury; aphids present in small colonies in center leaves of plants; up to 20% of center leaf surface covered with aphids but no plant stunting.
2 Margins of leaf curled inward toward midrib; aphids present on most leaves, covering between 20-40% of leaf surface; obvious honeydew and plant stunting.
3 Leaves severely curled but petioles upright; aphids present on all leaves, covering 40-60% of leaf surface; honeydew prevalent and plant severely stunted.
4 Leaves severely curled; aphids covering 60-80% of leaf surface.
5 Plant collapsed; aphids covering 80-100% of leaf surface.

The following treatment guidelines are provisional, but helpful in making treatment decisions. These guidelines are based on: (1) plant age (from seedling emergence) at the time of infestation; (2) severity of infestation and associated injury; and (3) the length of time the plants remain infested. Based on the above damaged levels and age of the plant, treatment guidelines are as follows:

Plant age in weeks from emergence Treat if 3-5% of plants reach damage level1
Up to 4 1
4–8 2
8–12 2
12–16 2–3
16–20 2–3
20–24 3
24 and up 3–42
1  If natural enemies are active and aphid numbers are declining, delay treatment for 3–5 days. If after this period, aphid numbers continue to decline, and the next damage level is not reached, treatment may not be necessary.
2 Plants within 2–3 weeks of harvest can tolerate up to damage level 4.

 

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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 4.9–7.5 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. METHOMYL*
  (Lannate) SP 0.25–1 lb 48 see comments
  (Lannate) LV 0.75–3 pt 48 see comments
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Preharvest interval is 21 days for roots, 30 days for tops.
 
C. 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.
 
D. CHLORPYRIFOS*
  (Lorsban Advanced) 0.75 pt 24 30–tops and roots
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Apply as a broadcast foliar spray. Do not apply more than 6 pt or make more than 3 applications/season. Avoid drift and tailwater runoff into surface waters.
 
+ 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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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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