May 2018
Homeplace & Community

Are Your Vegetable Crops Protected from Aphids?

A multifaceted management approach is recommended to provide maximum protection from harmful infestations.

 

Aphids are small insects easily identified by their cornicles, two tail-pipes, at the end of their abdomen. There are many species of aphids in the Southeast that commonly infest vegetable crops in summers and warm winters; for example, the green peach aphid (Myzus persicae), potato aphid (Macrosiphum euphorbiae), melon aphid (Aphis gossypii), cowpea aphid (Aphis craccivora), and cabbage aphid (Brevicoryne brassicae).

Here are some interesting facts about aphids:

  • Not all aphids are small and dull-looking; certain species can be brightly colored and large. For example, cowpea aphids are 2.5 mm [0.1 inch] long and shiny black, making them easily visible. All aphids form large colonies and suck plant sap, making their host very weak.

  • Same species of aphids can occur in different forms (winged and wingless) or colors (potato aphids can be green or pink). There are some other key anatomical details helping to identify aphid species, but a good hand lens or a microscope is a must to see small details. Many universities have insect diagnostic facilities – make sure to collect samples and have aphids identified correctly.

  • Aphids are excellent vectors of many plant viruses and there is no antiviral solution for plants. Control is key to the reduction of infection.

  • Some aphids can have a waxy coating on their body; it can be difficult to manage aphids with pesticides in such situations.

  • Many species of aphids have a broad host range (for example, green peach aphid) while some others are restricted to a narrow host range (for example, cabbage aphid on brassica crops).

  • Aphids can have many generations in a year, depending on weather conditions and food availability. Aphids overwinter in the egg stage while the adult aphids reproduce without mating in warm weather on appropriate host plants. This is called parthenogenesis and basically resembles cloning (mothers giving rise to mothers). Too much heat or cold weather slows aphid activity.

  • The sugary excreta produced by aphids is called honeydew. This carbohydrate-rich substance attracts ants, often the first indicators of an aphid invasion. Thereafter, many predatory insects may move in and start feeding on the rapidly growing population of aphids. Destruction of natural enemies such as lady beetles, lacewings and others is often the primary reason for aphid outbreaks in commercial farms.

 

Aphid Management

Aphid control doesn’t always include conventional or organic insecticides. There are some alternative approaches.

Cultural practices (Level 1 IPM Tactic): Trap cropping is a good tactic for distracting aphids away from a main crop, but success is dependent on careful planning. Trap crops such as early planted okra and certain brassica crops have been beneficial in some tests in Alabama; however, those trap crops can be management-intensive and ineffective in some years.

Exclusion systems (Level 2 IPM Tactic): Research in Alabama and many other states shows the benefit of insect fabric and row covers for deflecting the early establishment of aphids. Research in Alabama using a light, insect-barrier fabric such as Super Light Insect Barrier (Gardens Alive, Lawrenceburg, Indiana) or AgroFabric Pro (Seven Spings Farm, Check, Virginia) is great for deterring aphids, flea beetles and grasshoppers in the early season.

Remember to put the fabric on immediately after transplanting crops and seal carefully. Producers can use fixed metal or plastic frames over the small plants. Remove the fabric when the pest risk is over or when the plants are too big. Insect barrier fabric early in the spring can also trap extra heat that may promote plant growth.

Organic insecticides (Level 3 IPM Tactic): Any insecticidal approach should be the last option for producers. Aphid management with organic insecticide is a very common question asked at grower conferences, and it is difficult to answer.

Two years of organic products screenings have indicated that it is possible to slow down aphids in open field conditions with early insecticide applications, but constant rainfall in some years can be disruptive to persistence of those products that could result in control failure. Overall, it appears that Beauveria bassiana-based products (Mycotrol, Botanigard Maxx), oil blends (Pyola), insectidal soap, Chromobacterium (Grandevo) and pyrethrin (Pyganic) are some of the better materials for use in an early invasion.

Protection of natural enemies is more important for aphid control and insecticide use should be justified. Always rotate insecticides to discourage insecticide resistance.

 

Home and Urban Garden IPM Toolkit is Now Available!

A brand new Urban Farm IPM Toolkit is now available for urban farmers and community gardeners. This wheel slide chart has both conventional and organic insecticide listings for nearly 20 different crops. This publication also has listing of common insect pests with images that may help when scouting garden vegetables. Email This email address is being protected from spambots. You need JavaScript enabled to view it. or check with your local Quality Co-op to get your own copy.

 

Ayanava Majumdar is an Alabama Cooperative Extension System entomologist and state SARE Program coordinator for Auburn University.