The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Nov. 14, 2012.

Aphid management on lettuce with imidacloprid and foliar insecticides

By John Palumbo, UA research scientist and Extension specialist

In a recent update, we anticipated that pest control advisers would soon find aphids infesting local lettuce and cole crop fields. Thus far, we have not found any colonizing aphids and have spotted only an occasional alate (winged adult).

The timing of aphid colonization in leafy vegetables varies by species, and depends largely on temperature, rainfall, and planting dates.

My experience over the years, plus observations from numerous field trials, suggests that aphid species which infest leafy vegetables are historically the most severe on crops planted from mid-November through December.

There are exceptions to the rule and aphids can occur when least expected. Consequently, you should begin planning now for spring aphid management.

Growers and pest control advisers have effective options for aphid management on spring leafy vegetable crops.

First, there is the responsive approach that relies on foliar insecticide sprays to reduce aphid numbers when found on crops. A number of insecticides have cost-effective activity against aphids when applied as foliar sprays targeted at aphid populations as the pests begin colonizing plants.

There is also the preventative approach where growers can apply neonicotinoid insecticides at-planting - 1.5 to 2 inches below the seed line. The insecticide is taken up by the plant roots, systemically translocated throughout young plants for several weeks following emergence, and ultimately prevents aphid colonization early in plant development.

Both approaches can be very effective and can be used on the same field.

Among the neonicotinoids, imidacloprid has been the standard soil insecticide applied on spring lettuce for aphid control for 20 years and provides long-residual control when used properly.

More recently, Movento, with its excellent systemic activity against aphids via foliar application, has been incorporated into lettuce IPM programs along with other novel insecticides with aphid activity.

The question has recently been posed - which approach to aphid management is better?

Our research suggests a combination of both - imidacloprid applied at planting followed by a foliar insecticide(s) if needed under heavy late season pressure.

For more information, review this research report - Aphid Management on Head Lettuce Using Imidacloprid and Foliar insecticides.

Click this link to listento John.

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Environmental influence on disease development

By Mike Matheron, UA Extension Plant Pathologist

Three factors are required for the development of plant diseases: a susceptible host, a pathogen capable of infecting the host, and a favorable environment.

Temperature and moisture are aspects of the environment which critically impact the development and severity of diseases caused by bacterial and fungal pathogens. A plant disease caused by these types of pathogens will not occur if the temperature and/or moisture levels prohibit the pathogen from interacting with the host to cause disease.

This explains why some diseases only appear during a particular time period during the growing season for a particular crop.

For example, Fusarium wilt on lettuce in the desert is found primarily during the fall, but not during the winter months, as soil temperatures in the fall favor the growth of pathogen and disease development.

Also, downy mildew on winter vegetables - including lettuce, cruciferous crops, onions, and spinach - is usually a concern in the winter and early spring, but only when periods of leaf wetness caused by rainfall and dew are present.

Periods of high humidity and leaf wetness are essential for the downy mildew pathogens to grow, proliferate, and cause disease.

The generally dry conditions prevalent in the desert benefit growers by restricting foliar diseases caused by bacteria and many fungi. These organisms can flourish in regions receiving abundant rainfall.

Growers cannot control the weather. However, they can control irrigation practices which in some cases can influence the severity of vegetable crop diseases.

For instance, the severity of Sclerotinia drop on lettuce can be increased by over irrigation, especially if this results in prolonged wetting of the bed top.

During periods of rainfall and high humidity, sprinkler irrigation can extend the duration of high foliar moisture and increase the severity of downy mildew.

Click this link to listen to Mike's Update.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Re-registration update on pronamide (Kerb) for leaf lettuce

By Barry Tickes, UA Area Agriculture Agent

Pronamide (Kerb) is the most broad spectrum and widely used herbicide on leaf lettuce. It was first registered in 1969 by Rohm and Haas. It was acquired by Dow AgroSciences in 2001.

Until 2009 Kerb was registered on all types of lettuce, endive, escarole, and radicchio.

The registration for leaf lettuce was removed in August 2009. Prior to this, the registration did not differentiate between the types of lettuce. Most of the work done by Rohm and Haas to register this compound was done on head lettuce.

The Environmental Protection Agency (EPA) now considers head and leaf lettuce to be in different crop groups requiring separate studies.

The cancellation was the result of regulatory action by EPA and not because of any known problem with food safety or environmental contamination.

Kerb is still used on other leafy vegetables, including head lettuce, and was used safely for 40 years on leaf lettuce. The percentage of leaf lettuce acreage has increased significant. In 2009, about half of the lettuce grown in the greater Yuma area was leaf lettuce.

This is the fourth season that Kerb will not be registered for leaf lettuce. Dow AgroSciences is committed to regaining this registration and has made a significant investment to develop the data needed by the EPA.

There are two parts to re-gaining the leaf lettuce label:

1 – A cancer reclassification of pronamide, the active ingredient in Kerb, and its metabolites is needed to make additional room in the risk cup. This makes it possible to register leaf lettuce.

2 - The EPA must establish a tolerance for leaf lettuce.

Both of these are expected to be completed in mid to late 2014.

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Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

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