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University of Arizona
March 2nd 2014 Vegetable IPM Updates
 
 
 
Insect Management
Diseases
Weed Science
Pheromone/Sticky Trap Monitoring Network
 
Insect Management:


Corn Earworm in Spring Head lettuce

As the produce season begins to wind down, it would be wise to keep a look out for corn earworm (CEW); they are historically active on spring head lettuce. In the last few years, unusually high CEW abundance has been reported by PCAs on late head lettuce, particularly in the Dome/Wellton areas. Given the CEW trap catches this fall and winter, one might expect to see more CEW than normal, but then again it is impossible to predict. Nonetheless, CEW can be very damaging in spring crops where once head formation begins larvae will usually bore into the head 1-2 days upon hatching. Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera
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larvae, rendering the heads unmarketable. Larvae may enter the head from any point on the plants, but can often be found burrowing in from the top half of the head. If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is almost impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head, it would be a good idea to treat. The UA nominal threshold for CEW in head lettuce from early heading to harvest is 1-2 larvae / 100 plants. Repeated insecticide treatments may be required to maintain low population levels near harvest. Most contact insecticides recommended for Lep larvae are active against CEW. Furthermore, the addition of a pyrethroid with thrips, aphid and/or fungicide sprays may be cheap insurance against larvae infesting heads as you approach harvest. For more information on CEW management and control recommendations see Insect Management on Desert Produce: Corn earworm / Tobacco budworm and the 2015 Lep Control Chart.


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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:


Differences Between Downy and Powdery Mildew on Lettuce

This is the time during the lettuce production cycle in Yuma County that downy and powdery mildew can both be present in the field. There are some straightforward clues that will help identify which mildew disease is present. Symptoms. Spots or lesions caused by downy mildew can first appear as one or more yellowish areas on the upper leaf surface usually bordered by leaf veins, giving the affected portions of the leaf a somewhat angular appearance. In time, these lesions will increase in number and older ones will turn brown and necrotic. On the other hand, first evidence of powdery mildew is the appearance of very small circular colonies of the pathogen growing on the upper or lower lettuce leaf surfaces. Over time, these colonies enlarge, produce spores that start new colonies, and eventually the entire leaf surface can become covered with the powdery mildew pathogen. Spores. Spores of the downy mildew pathogen (Bremia lactucae) usually arise from the underside of leaves, are ovoid in shape, and are produced singly on the ends of branching mycelium, much like fruit are borne on many types of fruit trees. Large numbers of these spore-bearing
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mycelium and attached spores produce a downy white growth that we see, again usually on the bottom surface of leaves. Keep in mind that on head lettuce, the bottom of the leaf can appear to be the upper surface due to the curving of leaves to form the lettuce head. However, for the powdery mildew pathogen (Golovinomyces cichoracearum), spores are produced in chains on pathogen mycelium growing on either side of lettuce leaves, giving the appearance of powder on the leaf. Required environment. Development of downy mildew requires free moisture on leaves, which can be supplied by rainfall, dew, or sprinkler irrigation. In contrast, powdery mildew development requires moderate to high relative humidity, but not free moisture. In fact, free water will actually kill spores of the powdery mildew pathogen. Due to changing environmental conditions during the development of a lettuce crop, it is possible to have symptoms of both mildew diseases on lettuce at the same time.
Click picture to listen to Mike's update video link
To contact Mike Matheron go to: matheron@ag.arizona.edu.

 

Weed Science:


Weeds in Seed Crops

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Crops that are grown for seed often can be a problem when double cropped with something else. Small grains, cotton and seed crops commonly need to be controlled in the following crop. Fresh market vegetables are not left to produce seed and are rarely a problem. Vegetable seed crop seeds that are left in the field can, however, be difficult and costly to remove. This is a cost that is often not considered when the costs of production are calculated. It can cost $200 to $300 an acre or more to remove broccoli, cauliflower, onion, herb or other volunteer seed crops that come up after harvest. The Yuma area has some of the best custom harvest operators in the world for vegetables but is impossible to capture every seed and it doesn’t take many to cause a problem. Many seed crops are planted in September when summer annuals and perennial weeds are a problem, grown through the winter when winter annuals are a problem and are not harvested until may or June when summer and perennials weeds have again emerged .Weeds that emerge in the spring are difficult to control in seed crops because it is often too late to cultivate or spray. Unlike many common weed seeds, crop seed is selected to all emerge at the same time. Some, however, can continue to be an annual problem for years to come.
Click picture to listen to Barry video link
To contact Barry Tickes go to: btickes@ag.arizona.edu.


Upcoming Events:
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Link to 2015 International Spinach Conference

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Link to Lettuce Day site

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Southwest Ag Summit February 25-26, 2015.
http://www.swagsummit.com/



Real IPM
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Send your questions to:
CALS-Yuma-AZVegIPM@email.arizona.edu

 

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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