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

Bagrada Bug Management on Desert Cole Crops

With fall produce now underway bagrada bugs have begun to show up on direct seeded and transplanted cole crops. Reports of bagrada in local cole crops are beginning to trickle in from PCAs and so far, the pressure does not appear to be as heavy as we’ve seen in the past few years. Populations of bagrada bugs at the Yuma Ag Center however, are as heavy as ever and are quickly causing damage to untreated broccoli plots. Based on research conducted over the past four growing seasons, peak abundance of bagrada bug has occurred from late September to early October. So, what should a PCA expect for this season? Can’t say for sure, but don’t be complacent just because you’re not finding a lot of bagrada adults on your first few fields. It would be wise to assume they will eventually show up in some intensity in some of your acreage, and you should prepare for them accordingly. Monitoring for bagrada at stand establishment should focus on fresh feeding signs on new plant tissue, and adults later in the day when they are most active. Research and anecdotal observations in fields conducted over the past 2 years suggests that direct-seeded and transplanted crops are susceptible to bagrada bug infestations during stand establishment and up to the 6 leaf stage. Furthermore, results suggests that it doesn’t take a large number of bagrada adults to cause significant stand losses or crop injury. In untreated plots, we have consistently observed significant damage (15-20% blind plants) to direct seeded plants during the first 7 days after emergence (cotyledon to 1-leaf Stage) with only finding an average of 1 bagrada adult / 6 row ft. If you readily find fresh feeding signs and/or adults during stand establishment, control should be initiated immediately. This can include chemigation or aerial applications with pyrethroids. Contact insecticides (such as pyrethroids, Lannate, and Lorsban) should be used once stands are lined out and pipe is pulled. After stands are established and plant size increases up to the 2 leaf stage, or on tagged transplants, consider alternating to dinotefuron (Venom/Scorpion) to protect plants from bagrada feeding. This neonicotinoid will also provide knockdown of adult whiteflies and nymphs. More information on bagrada bug management on fall cole crops can be found in these Veg Update briefs: Bagrada Bug Management Tips for the Low Desert and Knockdown and Residual Control of Bagrada Bug With Foliar Insecticides in Broccoli: 2013 Efficacy Report.

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

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Lettuce Pathogens in Soil

Since another lettuce growing season has begun in Arizona, it is an appropriate time to think about lettuce diseases that can occur at this time. The diseases of most concern during the early autumn are caused by soil-borne fungal pathogens and would include Fusarium wilt, Sclerotinia drop, and bottom rot. Symptoms of Fusarium wilt, caused by Fusarium oxysporum f. sp. lactucae, can appear on lettuce any time after thinning. Effective fungicides generally are not available to manage Fusarium wilt, although fumigation with Vapam has suppressed disease severity in some field trials. This disease can be effectively dealt with by not planting susceptible types of lettuce (virtually all head lettuce varieties, for example) in ground known to contain the pathogen, especially during September or October. Soil temperatures during these months favor the growth of Fusarium oxysporum and the resulting development of the wilt disease. Romaine lettuce cultivars generally are more tolerant to the Fusarium wilt pathogen and can be planted in fields harboring the pathogen in cooler months when the pathogen is less active. Sclerotinia drop and bottom rot usually do not become apparent in fields until plants are at or past the rosette stage of development. Successful management of Sclerotinia drop, caused almost exclusively by Sclerotinia minor on lettuce that will be harvested in November and December, as well as bottom rot caused by Rhizoctonia solani, require application of effective fungicides well before the appearance of disease symptoms. Sclerotinia minor and Rhizoctonia solani exist in soil as small resistant structures called sclerotia. Successful management of the diseases caused by these pathogens is closely tied to preventing the germination of these sclerotia; therefore, applications of fungicides are made to the soil, where the sclerotia exist. Early application of fungicides, when plants are very small, facilitates thorough coverage of the bed surface. As plants grow and cover more of the bed surface, fungicide coverage of soil and disease control decline.
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Weed Science:

Rainfastness of Herbicides

When rain is a possibility, people begin to ask how much time they need before or after foliar applied herbicides are applied. In this area, herbicides are more likely to be washed off with irrigation water then they are by rain but the same principles apply. As always, there is no universal answer and it will depend upon many factors. Almost all are rainfast in from 1 to 4 hours. Only15 minutes is needed for some and others require eight hours. 2 to 4 hours is a good rule of thumb. Some of the most important factors affecting how fast the herbicide gets into the foliage are mode of action, leaf surface characteristics, surfactant use, environmental conditions and age of the plant. Plants that are small and actively growing absorb herbicides faster than those that are larger and more mature. Contact herbicides do not have to be translocated through the plant, work quicker and are not as sensitive to growing conditions. Water-based formulations are more easily washed off than are oil-based products. Herbicides need more time to get into plants that have a thick waxy cuticle or leave hairs. The addition of a surfactant that helps the herbicide spread and stick to the leaves reduces the time needed before rain or irrigation. All of these factors interact with each other and can affect how much time is needed.

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Question to the IPM Team:

Can You ID This Worm?

It was reported to the IPM TEAM in Yuma AZ by some adventurous hikers and PCAs that the caterpillar shown in the picture was found in the Telegraph Pass at the Yuma foothills. The request to identify the larvae was because they were so abundant that it was hard not to step on them while walking up the mountain. The insect was identified as the White-lined Sphinx Moth caterpillar. (Hyles lineata). We decided to take the hike on August 17th and witnessed thousands of larvae crawling and feeding on the vegetation. Quite a beautiful display for insect admirers. A picture of the adult is included in this update for complete identification.

Check Out These Videos!

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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