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University of Arizona
March 2nd 2014 Vegetable IPM Updates
 
 
 
Insect Management
Diseases
Weed Science
Some Videos to Check Out
 
Insect Management:


IRM Guidelines for Beet Armyworm in Lettuce

The beet armyworm (BAW) is the most common lepidopterous pest infesting lettuce throughout the desert southwest where larvae are most prevalent from August through November. Historically, PCAs have been able to effectively control this pest using available insecticides. Because many of the products have different modes of action (MOA) that can be alternated throughout the growing season, the rapid development of resistance by BAW to any of these insecticide compounds should not readily occur. In fact, resistance by BAW to insecticides has not been recorded in nearly 20 years in the desert as a result of the judicious usage of these insecticide chemistries. However, if an insecticide compound, or products with the same MOA, are used repeatedly for worm control in the same field, the risk of resistance increases significantly. This is particularly important with the Diamide group of insecticides (IRAC group 28) which can be applied as both foliar sprays and soil injections. With the recent registration of cyantraniliprole (Exirel and Verimark), PCAs now have eight different diamides insecticide products within the diamide chemistry (IRAC group 28) to choose from for worm control. Foliar uses include Coragen, Voliam Xpress, Voliam Flexi, Exirel, Belt and Vetica; Soil uses include Coragen, Durivo and Verimark. Applying these Diamide products to the soil at planting, and then following with foliar sprays of Dimades in the same field, can expose multiple generations of Lep larvae to the same MOA. This places increased selection pressure on populations. That’s not a good way to use these products if you want them to remain effective for more than a couple of years. Since the Diamides, as well as the other products currently available (Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of worms in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds. The most effective way to delay the onset of resistance by BAW in leafy vegetables is to consider the recommendations provided in the guidelines recently prepared entitled Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce.
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BAW Egg Mass and Neonates
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Remember, When in Doubt . . . . . “Call Barry Tickes”

Click picture to listen to John’s update video link

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

 

Diseases:


Plant Pathogen Survival in the Desert

As the seemingly unending days of summer heat in the desert persist, we can seek refuge in air-conditioned vehicles or buildings and can obtain food from any number of sources at any time. Not so for plant pathogens, which must survive high temperatures and lack of food by employing other tactics. A few plant pathogens can thrive at temperatures common in the desert during the summer and cause disease on plants growing at that time; however, most others cannot function at temperatures much above 90°F. To survive inhospitable temperatures or lack of a host on which to feed, fungal pathogens often produce thick-walled durable spores or other structures that will allow the organisms to survive hostile environments in a dormant state. The visible dark-colored sclerotia produced by the lettuce Sclerotinia pathogens are such structures. Much smaller sclerotia and thick-walled spores facilitate long-term survival of the soil-borne pathogens Rhizoctonia and Fusarium, respectively. On the other hand, bacterial plant pathogens do not have recognized survival structures, but can subsist for some time in a reduced metabolic state on, in or near living or dead plant tissue. Virus pathogens also cannot make resistant structures, so survival usually occurs in vectors or living plants. These plants can include weeds or cultivated crops that do not express disease symptoms, but serve as sources of virus to visiting insect vectors. Finally, nematode survival stages can include eggs and certain larval forms. Many of the cultural disease management methods that we employ are effective because they disrupt the normal survival capacity of these plant pathogens.
Click picture to listen to Mike's update video link
To contact Mike Matheron go to: matheron@ag.arizona.edu.

 

Weed Science:


Purslane

Common Purslane (Portulaca oleracea) is at the same time one of the most troublesome weeds in vegetable crops and one of the most nutritious leafy vegetables. It is very widespread in the desert southwest but is also on the list of Arizona Prohibited Noxious Weeds which means that it is prohibited from entry into the state. Common Purslane is eaten in Mexico (Verdolaga), Europe and Asia and contains more omega 3 fatty acids than any other leafy vegetable. It also contains vitamins A, B and C and dietary minerals.

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Common Purslane is often lumped together with Horse Purslane although the two are in different families. Common Purslane is in the Portulaca family while Horse Purslane is in the Trianthema or Carpetweed family.

In lettuce, Purslane is often controlled during ground preparation where it is geminated and killed with chemicals or tillage. Timing is important with both of these techniques. Purslane grows rapidly and one plant can produce thousands of seeds. These seeds can germinate in 12 hours after receiving moisture in August and September. They can also germinate in January and February but will take 3-7 days to germinate at that time. The stems are very succulent and unless they are completely killed and desiccated they can reroot at the nodes. Tillage that does not completely desiccate the plants can spread rather than eliminate this weed.

Herbicides used to kill this weed during ground preparation include both contact (Gramoxone, Aim and ET) and systemic (glyphosate) herbicides. Results can range from 0 to 100% depending upon weed size, rate and adjuvant used at the time of application. The contact herbicides can produce almost 100% control when the Purslane is less than 2 inches in diameter and less than 50% control when larger than this. This is especially the case with Aim where control can drop from excellent to poor in 3 - 5 days.

Purslane has a thick waxy cuticle and an adjuvant is needed with all of these herbicides to help penetrate into the leaves and stems. A non-ionic surfactant will help the herbicide spread and stick while crop oil concentrates help break up this waxy layer. Time of day when applied can also be important. During the morning hours leaf pores are open, new growth is occurring and the plant is more sensitive to herbicides than during the middle of the day when the plant is conserving water and energy. There is a wide range of rates used with Aim, Gramoxone and glyphosate to control Purslane during ground preparation. Normal rates vary from 0.5 to 2.0 oz. with Aim, 1.5 to 4.0 pt. with Gramoxone and 1.0 pt. to 2.0 qts. with glyphosate when used alone or in combination. All of these herbicides only work on emerged weeds and people often wait until they are sure most of the weeds have emerged to avoid making multiple applications. As a result, there can be a wide range of weed sizes at the time of application. Rates should target the largest weeds. It is less costly to choose a higher initial rate than to have to make additional applications.

Click picture to listen to Barry video link
To contact Barry Tickes go to: btickes@ag.arizona.edu.

Real IPM
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To contact Barry Tickes go to: btickes@ag.arizona.edu.
 

Check Out These Videos!
Links:

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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