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

Impact of Bagrada Bug on Desert Cole Crops from 2010-2014

The bagrada bug, Bagrada hilaris, first occurred on desert cole crops at damaging levels in the fall of 2010, and has since become an established pest. In an attempt to document the severity of Bagrada bug infestations on direct-seeded and transplanted cole crops, and the intensity of chemical management, we have annually surveyed growers and PCAs from Yuma, Imperial and Maricopa counties since 2010. We recently conducted our survey in early April. Since 2010, the cole crop industry has experienced widespread bagrada bug infestations throughout the desert from September into November, although some years have been less intense than others. Last fall (2014) was one of the lighter years. Based on seasonal population abundance studies of adults infesting non-treated broccoli plants at the Yuma Ag Center (see graph below), bagrada bug infestations in the fall 2014 were much lower than we had observed the previous two seasons. However, with the warmer temperatures this winter, spring populations occurred very early and at higher numbers than in the previous 4 years. Estimates of stand losses from bagrada bug infestations at stand establishment in both direct-seeded and transplanted crops has decreased by almost 50% over the past 5 years. Lower losses in 2014 are likely due to the lower pressure experienced last season. Plant injury, defined as plants with multiple heads, forked terminals, and/or blind terminals resulting from Bagrada feeding, was also lower in 2014 compared with 2010. These data suggest that PCAs have adopted effective management programs to protect seedling crops during stand establishment. Insecticide usage to control this pest remains high, but a lower percentage of acreage was treated in 2014 than in previous years. Pyrethroids remain the primary product used for controlling bagrada bug adults either via chemigation or with foliar spray applications. Based on survey results, products that have contact activity appeared to provide the most effective control against bagrada adults on both direct-seeded and transplanted cole crops. However, more neonicotinoid products (Venom, Endigo) are beginning to be implemented into PCAs IPM programs. Overall, the results of the PCA survey are consistent with results obtained in research trials conducted at the Yuma Agricultural Center over the past four years. A summary of the 2010-2014 survey results can be found in the following report: Impact of Bagrada Bug on Fall Cole Crops, 2010-2014.


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

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Managing Powdery Mildew on Melons

What is the best way to combat powdery mildew in melon plantings? Maximum disease control requires initiation of a fungicide application program when environmental conditions favor disease development but before the first visible detection of disease. Less than optimal but good levels of disease control can also be achieved by beginning fungicide applications at the very first sign of disease in the field. Early initiation of fungicide treatment on susceptible melon varieties is essential due to the rapid development and spread of powdery mildew from the initial and usually undetected infection sites within the crop. Application of a newly registered novel active ingredient usually is effective on virtually all of the individual pathogen spores or colonies developing from spores. However, the very small number of individuals not killed or inhibited by the fungicide will become an increasingly larger proportion of the pathogen population as the use of the same active ingredient increases. This is how resistance to a particular fungicide develops within the pathogen population. The melon powdery mildew fungus Podosphaera xanthii has developed significant resistance to some fungicides in the past. An important strategy to delay development of fungicide resistance is to alternate among or mix products with different modes of action. Previous research demonstrated that fungicide application sequences containing a highly efficacious fungicide alternated with a product of lower efficacy provided a final level of disease control not significantly different to that achieved by continuous application of highly effective compounds. Data from these trials support the notion that high levels of disease control and resistance management can be realized with fungicide alternation programs containing different modes of action of only highly effective chemistries as well as application programs incorporating products with high efficacy along with those that are less effective. In the most recent (2014) fungicide evaluation trial conducted at The University of Arizona Yuma Agricultural Center, tested fungicides that reduced the leaf area covered with powdery mildew on Olympic Gold cantaloupe plants by at least 90% compared to nontreated plants included Luna Sensation (fluopyram+trifloxystrobin), Mettle (tetraconazole), Procure (triflumizole), Quintec (quinoxyfen), Rally (myclobutanil), Rhyme (flutriafol), Torino (cyflufenamid), and Vivando (metrafenone). These findings should reflect efficacy on melons other than cantaloupe as well, since powdery mildew on all melons in the desert southwest is caused by the same pathogen. Some of these tested fungicides are not currently registered for use on melons, so read labels carefully before considering their use.

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Weed Science:

Marestail, Horseweed (Conyza canadensis)

There are herbicides and herbicide tolerant crops available now that farmers couldn’t even dream about 20 years ago. Weeds are still as much of a problem as they have ever been. Many of the weed species that are widespread now are those that evade our current management practices. Marestail is one of these survivors that has become an increasing problem in recent years. It is also known as horseweed and is in the sunflower or composite family. It can grow to 10 ft. in height and doesn’t branch until it is a couple feet tall. It does branch if it is cut however. Similar to many weeds here, marestail is supposed to be a summer annual but it can be found during the winter and survive for more than one season. It can be difficult to selectively control. Many of the broad spectrum systemic herbicides do not control it. The growth regulators (2, 4-D, 2, 4-DB, dicamba, MCPA) will twist it up but often not kill it. The ALS inhibitors (Raptor, Pursuit) are weak on it and even glyphosate often will not control it. Glyphosate resistant marestail is widespread in many regions. If it is small (6” or less) it can be controlled with some of the contact herbicides such as paraquat or Buctril which are difficult to use without hurting the crop especially during the summer. Chateau is good on it as a preemergent treatment before it germinates.


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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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