Arizona Crop Information Site logo
University of Arizona
March 2nd 2014 Vegetable IPM Updates
 
 
 
Insect Management
Diseases
Weed Science
 
Insect Management:


Aphid Movement in Leafy Vegetables

Now that the weather has finally broken a bit and the wind is actively blowing out of the north and west, you should begin to see an increase in winged (alate) aphids showing up on desert produce crops. This is an annual occurrence as our key aphid pests on produce do not over-summer here, but rather migrate into our cropping system from mountainous regions of southern California via wind currents during the late fall. Once the aphids reach our desert valleys, they typically move from crop to
VIPM_Update_Vol_5_Num_23_Snip_001.PNG
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., pea 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. Don’t be surprised if you start 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 weird weather this year may be more conducive to their development than normal. So, 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.
VIPM_Update_Vol_5_Num_23_001.jpg
Remember, When in Doubt . . . . . “SCOUT”

Click picture to listen to John’s update video link

To contact John Palumbo go to: jpalumbo@ag.arizona.edu

 

Diseases:


Impact of the Environment on Plant Disease Development

Three factors are required for development of plant diseases: a susceptible plant, a pathogen capable of infecting that plant, and a favorable environment. Temperature and moisture are aspects of the environment that critically affect 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 temperature and/or moisture levels prohibit the pathogen from interacting with the host plant to cause disease. This explains why some diseases only appear during a particular time period during the growing season of a particular crop. For example, Fusarium wilt on lettuce in the desert is found primarily during the fall, but not during the winter months.
VIPM_Update_Vol_5_Num_23_Snip_001.PNG
Why? Because soil temperatures in the fall, but not the winter months, favor the growth of the pathogen and disease development. Also, downy mildew on winter vegetables such as 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 can’t control the weather; however, they do have control over 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. Also, during periods of rainfall and high humidity, sprinkler irrigation can extend the duration of high foliar moisture and thus increase the severity of downy mildew.

VIPM_Update_Vol_5_Num_22_002.jpg
Click picture to listen to Mike's update video link
To contact Mike Matheron go to: matheron@ag.arizona.edu.

 

Weed Science:


Weeds in Leaf Lettuce

There are more than 50 broadleaf and grass weeds in this area that are common and have been here for a long time. We would like to have a herbicide that will control them all, not hurt the crop and be gone the day after harvest. We are a long way from achieving this. What we have done instead is to select for the weeds that escape
VIPM_Update_Vol_5_Num_23_Snip_001.PNG
our weed control practices. Anything that shifts the advantage to the crop instead of the weeds will help. This includes herbicides, mechanical techniques and hand hoeing. Good weed control can be achieved using all three but may not be economical. Weed selection due to herbicide availability can currently be seen in leaf lettuce. Kerb, Prefar and Balan were the standard herbicides used in lettuce for the last 50 years. The postemergence grass herbicides were registered about 20 years ago but for broadleaf weeds there has been nothing new in half a century. To the contrary, with the loss of Kerb on leaf lettuce 5 years ago, there is less available on that crop than ever before. Prefar will control grass consistently, purslane and pigweed most of the time, lambsquarters and goosefoot some of the time and all of the other weeds never. Balan will control grass consistently and many of the small seeded broadleaves some of the time. Kerb will control the grasses and most of the broadleaves consistently including many that are not controlled by the other two such as shepardspurse, London rocket and wild mustard. The longer that Kerb is unavailable the more prevalent it will become.
Click picture to listen to Barry video link
To contact Barry Tickes go to: btickes@ag.arizona.edu.


The Annoying Aphid
VIPM_Update_Vol_5_Num_23_003.jpg
Area wide Insect Trapping Network

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.


 
USDA_WIPMC_Logo
Homeotton.html"> Cotton tml"> Veggies | Forages | Grains | Citrus | Crop x Crop
Insects | Diseases| Weeds | Pesticides | News | Weather | Research | Photos | Contacts | General Info.





document located at: http://cals.arizona.edu/crops/vegatables/advisories/archive.html
Copyright © 2001 University of Arizona,
College of Agriculture and Life Sciences
Webmaster: Al Fournier (acis@ag.arizona.edu)