Lettuce XXVII-1

Aphids

Whitney S. Cranshaw

Green Peach Aphid

Identification (and life cycle/seasonal history)

Adult aphids, or plant lice as they are sometimes called, are usually green, but can be brown, yellow, pink, or black, depending upon the species. They tend not to get any larger than 1/16 to 1/8 of an inch in total body length. In general, a female (males are often unknown or absent in several species) gives birth to another female. This is called parthenogenesis. Ovoviviparous is the term used when the egg stage is kept within the female and the young insects emerge alive. Internally, each immature aphid is already reproducing another female inside her, so when you kill one aphid, you could be killing three or four generations at once! Within one to two weeks, a single aphid may produce 50 to 100 offspring. All of these aphids are wingless, even when they finally reach maturity. Winged aphids, or alates, begin to appear in the population when overcrowded conditions occur. These alates can fly to other plants and are called the spring migrants.

Towards the end of the growing season, the aphids use the light and temperature changes as a cue to produce an all winged generation that contains both males and females known as the fall migrants. The females of this generation then give birth to a new batch of females that are wingless and they must mate with the winged males from the generation before them. These are true females, and after mating they usually lay one to four eggs in a sheltered place on or near the plant. These eggs over winter and become the first generation of females, known as stem mothers, next season. This cycle is highly standardized and should not be assumed for
every aphid encountered.

Plant Response and Damage

On lettuce, root aphids may be present, but are unlikely to slow growth. Aphids on leaves may cause curling or stunting, but in general aphids are a problem because of contamination of marketed heads. Aphids tend to be more numerous in late-summer.

Management Approaches

Biological Control

There are many beneficial predators and parasitiods that can help manage aphid populations. While the lady bird beetle is one of the most commonly used predators, it is generalistic and opportunistic. This means that it will eat any small, soft bodied insect that it encounters and so it does not specialize in feeding only upon aphids. Predators that do specialize are generally more efficient at hunting and feeding upon the specified prey. Also, the immature lady bird beetles consume more aphids than an adult beetle will, but when ordering the beetle as a control agent, adults are usually the only option. Green lacewing (larvae are known as "aphid lions") and certain syrphid fly larvae are much better predators than the lady bird beetle is.  There are specific wasps that parasitize aphids.  To parasitize an animal, the wasp injects a single egg into the host, in this case the aphid. The aphid dies while the young wasp matures inside it, feeding upon the aphid's organs. When the wasp is ready to emerge as an adult, it chews or cuts a circular hole out the back of the aphids bloated and browned body.

Chemical control

Control should occur one week before harvest when used to avoid contaminated heads.

 

Product List for Aphids:

Insecticide

Product per Acre

Preharvest Interval, remarks

Cygon 400, Dimethoate 400

Dimethoate 267

0.5 pt

0.75 pt

(7 days). Four day reentry interval. Systemic insecticide. Organophosphate insecticide (dimethoate). Do not store below 45 degrees.

Thiodan 50W

Thiodan 3E, Endocide 3E

1.5-2 lb

0.7-1.3 qt

(14 days) 48 hour reentry interval proposed. Some rotational restrictions with root crops. Chlorinated hydrocarbon insecticide (endosulfan).

Orthene 75S

0.7-1.3 lb

(21 days) Organophosphate insecticide (acephate). Has systemic activity. Do not feed trimmings to livestock,

Metasystox-RR1

1.5-2 pt

(14 to 28 days, depending on number of applications) Proposed 72 hour reentry interval requirement. Organophosphate insecticide (oxydemetonmethyl).

Admire 2F

 

 

 

 

 

Provado 1.6F

10-24 fl oz

 

 

 

 

 

3.75 fl oz

21 days.  Chloronicotinyl insecticide.  Soil treatment with systemic activity.  Can be used pre-planting, at-planting, or post-emergence.  Registered for both head and leaf lettuce.

7 days.  Chloronicotinyl insecticide.  Maximum 18.75 fl oz, at minimum 5 day interval, may be applied per crop.  Registered for head and leaf lettuce.

Assail 70WP

0.035 – 0.054 lbs a.i. (0.8 – 1.2 ounces)/A in 5 gal/A by air or 20 gal/A by ground

Begin applications when treatment thresholds have been reached.

RRestricted Use Product. 1Labeled for chemigation
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies.  State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

 

Categories: Lettuce, Insects, Aphids

Date: 05/03/02