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Agriculture >> Resources >> Plant and Disease Identification

Agriculture

Plant and Disease Identification

Aphids

Description
Aphids or plant lice are small, soft-bodied slow moving insects which feed by sucking juice from plants. They can usually be recognized by the pear-shaped body and fairly long antennae. Aphids vary in color - white, gray, green, brown, red, yellow or black. They are usually found in large numbers (colonies) on the underside of leaves or on stems. There are both winged and wingless aphids in most species. As the aphids feed, they secrete honeydew - a sweet sticky shiny substance seen on leaves. Honeydew consists mainly of excess sap ingested by the insect and passed through the body.

Injury
Aphids may damage many plants including fruits, vegetables and ornamental trees and shrubs. The major damage is caused by the aphids sucking the juices from the stems and leaves causing a reduction in vigor, curling and distortion, and reduction in yield. Some species inject saliva into the plant tissue as they feed and may transmit virus diseases from one plant to another.

In addition to the direct damage caused to the plant by the aphids feeding a black fungus, known as sooty mold, grows on the honeydew secreted by the aphids. Sooty mold is unsightly and in association with honeydew it is objectionable to the buyer of affected plant material, fruits or vegetables.

Life History
Most species of aphids overwinter in the egg stage. The eggs hatch in the spring to produce a generation of females. These female aphids give birth to living young. Generally the first young aphids are wingless, however, when a colony becomes too crowded, winged forms may be produced. The winged forms migrate to new host plants and begin new colonies. Enormous populations are built up from these overlapping generations all summer long.

Late in the season the aphids migrate back to the original host plant, and a generation consisting of both males and females is produced. These individuals mate and the females lay eggs which will overwinter.

Monitoring
Carefully inspect plants for the beginning of an aphid population buildup. Check for natural enemies such as mummies (gray-brown bloated parasitized aphids indicating wasp parasites at work), and the alligator-like larvae of lady beetles and lacewings.

Yellow sticky boards are also used as a monitoring tool for aphid populations. Aphids are attracted to the yellow color and often are visible on the cards before they are detected on the plant.

Management
If there are high numbers of mummies, or large populations of ladybird beetles, or lacewings along with the aphids, additional treatments may not be necessary. Ladybird beetles and lacewings are beneficial because both the adults and larvae actively feed on aphids.In general, controlling populations early in the season often eliminates the need for later spraying. In a few cases, however, treatment may need to be carried out all season long. Wash off aphids with water occasionally as needed early in the day. A hard stream of water directed at aphids will remove many from plants.

Insecticides suggested for controlling aphids on the following vegetable plants:

• Beans: use insecticidal soap, oil (horticultural), pyrethrins, malathion.
  
• Cabbage, cauliflower, broccoli, Brussels sprouts, and other cole crops: insecticidal soap, oil (horticultural), pyrethrins, malathion; spray when infestations are excessive and weekly as needed. If using malathion, wait seven days before harvest.
  
• Cucumber, pumpkin: insecticidal soap, oil (horticultural), or malathion; spray as needed when vines are dry. When using malathion wait one day before harvesting.
  
• Eggplant: insecticidal soap or malathion as needed.
  
• Pea: insecticidal soap, malathion; spray one to three treatments at weekly intervals as needed. With malathion wait three days before harvesting.
  
• Pepper: insecticidal soap, oil (horticultural), malathion; spray as needed. Wait three days before harvesting if using malathion, one day if using insecticidal soap.
  
• Potato: malathion; spray weekly as needed.
  
• Tomato: insecticidal soap, oil (horticultural), or malathion; spray as needed. Wait one day before harvesting.

Before using any pesticide, check the label. Both the crops you wish to treat and the pest you are treating for must be listed on the label. If not, do use the pesticide. Also make sure to read the label to determine how long you need to wait before harvest. Harvesting treated vegetables too soon after a pesticide application may result in excessive residue being present when consumed.

For information on controlling aphids on ornamental trees and shrubs, annual and perennial flowers, houseplants, fruit crops, etc. refer to a current copy of Part I Guide to Pest Management Around the Home, Cultural Methods and Part II -- Pest Management Around the Home, Pesticide Guidelines, which are mentioned below.

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9/95 Prepared by: Carolyn Klass, Senior Extension Associate, Cornell University Cornell University

Pesticide and management recommendations obtained from: Part I Guide to Pest Management Around the Home, Cultural Methods and Part II -- Pest Management Around the Home, 2003-2004 Pesticide Guidelines, Miscellaneous Bulletins 139S74-I and 139S74II, Cornell Cooperative Extension Publications. Contact our office for information on ordering copies.

The Pesticide Management Education Program (PMEP), in cooperation with the New York State Department of Environmental Conservation (NYSDEC), maintains a web site with a searchable database for pesticide products currently registered in New York State. Homeowners who have Internet access can locate currently registered products at http://pmep.cce.cornell.edu/pims/current. Several different queries are available that will produce a summary for the product(s) that the system locates. If the system fails to locate the product in question, then that product is not currently registered in New York State. The database also provides a summary of important information related to every product currently registered. Two data fields "Status" and "Expiration Date" are provided in each summary. Products with a status of "Registered - Discontinued" are currently registered but will probably be discontinued for use, sale, and distribution in New York State after the date noted in the "Expiration Date" field.

This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available, and some uses may no longer be legal. All pesticides distributed, sold or applied in New York State must be registered with the New York State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension Specialist or your regional DEC office. Read The Label Before Applying Any Pesticide.

Source: Horticulture Leaflets Online, Suffolk County, 10/03