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University of Arizona
March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Insect Management:

Aphids in Desert Vegetables

With the changing weather patterns (wind actively blowing out of the north and west), PCAs can anticipate an increase in winged (alate) aphids showing up on desert produce crops. Based on my observations over the past two decades, this is an annual occurrence with our key aphid pests on produce. Aphids that typically infest leafy vegetables do not over-summer in the desert. Rather, winged adults migrate into our cropping system from mountainous regions of California via wind currents during November/December. Once the aphids reach our desert valleys, they typically move from crop to crop until they find a suitable host to feed and colonize on. But don’t panic just because you suddenly find a few winged aphids on the plant. It is not uncommon to find winged aphids on lettuce or broccoli that do not colonize on the crop. An example of these would be cabbage aphid which will colonize and infest cole crops but not lettuce, spinach or celery. Other examples would include aphids that colonize small grains (i.e., corn leaf aphid) or alfalfa (i.e., blue alfalfa aphid). Because these aphid species will not colonize produce crops, it is important to be able to distinguish them from the aphids that do colonize and require management to prevent problems at harvest (i.e., green peach aphid, foxglove aphid, lettuce aphid, cabbage aphid). Proper aphid ID can also influence your choice of insecticide, but more on that in a later update. As mentioned in the last update, PCAs have been finding small colonies of cowpea aphids showing up on frame leaves in lettuce. That is a common occurrence every fall. Not to worry, experience has shown us that although small cowpea aphid colonies may be found on lettuce, the populations generally stay low on the plant on the frame leaves and rarely increase to levels causing contamination issues. But you never know. So keep an eye for these guys, as our El Nino weather this year may be more conducive to their development than normal. Local research has shown that aphids tend to be more abundant at harvest in lettuce in years with higher winter rainfall than average (see Impact of Lettuce Planting Date on Aphid Contamination). Also, don’t forget that proper aphid identification is important; it can save a PCA time and money, and prevent unnecessary insecticide applications. If you find an unusual aphid in your produce, don’t hesitate to drop it by the Ag Center and we’ll get it identified for you. But if you want to be fast and accurate you might use the attached publication Aphid Identification in Desert Produce Crops that may assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole crops.


Remember, When in Doubt . . . . . “SCOUT”

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Lettuce Downy Mildew

We are approaching that time in the desert lettuce production season when downy mildew can become a concern. Development of downy mildew on lettuce is strongly regulated by the presence and duration of free moisture on plant leaves. This moisture can be supplied by rainfall, dew, and sprinkler irrigation. Optimal management of downy mildew is achieved by having a fungicide in place before disease symptoms become apparent. Less than optimal control of downy mildew will result when fungicide applications are not started until downy mildew symptoms are seen on plants. This is due to the fact that there is a lag time between infection by the pathogen (Bremia lactucae) and appearance of visible symptoms. This incubation period can range from 10 or more days, depending on temperature, relative humidity, and lettuce variety susceptibility to the pathogen. By the time lettuce downy mildew lesions are observed, many more are likely present but have not yet matured to a sufficient extent to be visible. Fungicide evaluation trials conducted at the Yuma Agricultural Center in Arizona as well as in other states have demonstrated statistically significant reduction in disease by application of fungicides such as Actigard, Aliette, Cabrio, Curzate, Dithane, Forum, Orondis (registration pending), Presidio, Manzate, Previcur Flex, Prophyt, Ranman, Reason, Revus, and Tanos. Several different modes of action are represented by these compounds, thus facilitating alternation among different chemistries for effective disease management as well as pathogen resistance management. A new publication entitled “Biology and Management of Downy Mildew of Lettuce” provides additional information on the biology and management of this disease and is available.

Lettuce Downy Mildew
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Weed Science:

Postemergence Weed Control in Lettuce

Once broadleaf weeds become established in lettuce, there are no herbicides that can be used to selectively control them. Kerb( Pronamide) will control some emerged weeds when they are very small but if they get more than about 0.25“ in diameter they will recover. Grasses can be controlled selectively postemergence with Poast( Sethoydim) or Select Max(Clethodim) although only Clethodim worls on annual bluegrass and sprangletop and neither works on sandbur. Several herbicides have been tested to control emerged broadleaf weeds in lettuce but nothing has been both safe to the crop and effective on the weeds. Some work was done in recent years with low rates of Pursuit( Imazethypyr) on lettuce. It looked like it might be ok on head lettuce only but has a long soil residual and would likely cause problems with subsequent crops planted in the same field. Cultivation and hand weeding are the only options for established broadleaf weeds in lettuce..

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Area wide Insect Trapping Network:

November 11, 2015

Our area-wide trapping network is up and running. The project is designed to measure the activity and movement of adult populations of a number of key pests. The project is being funded by the Arizona Iceberg Lettuce Research Council, and will hopefully provide an indication of when pest activity (e.g., corn earworm moth flights) is increasing based on pheromone/sticky trap captures. The data is not intended to indicate field infestations, as trap data is largely a reflection of adult movement. If nothing else, the data may make PCAs aware of increased pest activity in some areas and encourage intensified scouting in susceptible produce fields. The pests being monitored include: corn earworm, tobacco budworm, beet armyworm, cabbage looper using pheromone traps; aphids, thrips and whiteflies using yellow sticky traps. A total of 15 trapping locations have been established. Traps will be checked weekly and data will be made available in the bi-weekly Vegetable IPM updates. If a PCA or grower is interested in weekly counts, those can be made available by contacting us.
Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: Corn earworm moth activity has deceased across all trapping locations over the past two weeks, and particularly last week with the cooler temperatures. Activity is significantly lower than this time last season.

Beet armyworm: BAW activity decreased slightly in most areas, but moth captures remained fairly steady in the easy county growing regions. Activity is significantly lower than this time last season.

Cabbage looper: Cabbage looper moth activity remains light compared to last year, and remains unusually low for this time of the year.

Whitefly: Adult movement continues to decrease with the completion of melon harvests.

Thrips: Thrips movement is on the decline in most areas, with the exception of slightly higher activity in traps near Ave 39E.

Leafminers: Adult activity is low area wide.

Aphids: Aphids are consistently showing up in many locations moderate numbers and on the rise in the Yuma Valley. Anticipate higher numbers showing up in fields with cool and windy weather.

To contact John Palumbo go to:


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The Vegetable IPM Updates Archive page provides links to updates from previous weeks.

The Vegetable IPM Video Archive page contains a collection of educational videos from current research work in vegetable crops by University of Arizona Researchers.


For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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