The Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Nov. 29, 2012.

Pest pressure on 2012 desert produce, melon crops

By John Palumbo, UA research scientist and Extension specialist

At a recent meeting, I made the statement that insect pest pressure on produce and melons crops in the Yuma area this fall was as heavy as I have seen it in many years.

This comment was largely based on my observations on and off the Yuma Agricultural Center (YAC), plus from anecdotal reports from pest control advisers and growers. This claim is further supported by a quick analysis of recent and historic data on pest abundance recorded from our research plots in the Yuma area.

Whitefly adult numbers on fall melons and produce were extremely high. My untreated melon plots at the YAC wilted and died rapidly as a direct result of heavy whitefly feeding.

Captures of whiteflies on yellow sticky traps placed near cantaloupe fields in the Wellton, Tacna, and Texas Hill areas were twice as high compared to the last five years. The incidence of cucurbit stunting disorder virus incidence in cantaloupe fields in this area was also higher in 2012.

Similarly, worm pressure - particularly the beet armyworm and cabbage looper - was higher than the last six or seven years. Populations began infesting plots in early September. Egg deposition and larval development remained steady through October.

In fact, worm numbers were three times higher this year compared to last fall.

Corn earworm was present in higher numbers than observations in past years.

Bagrada bug infestations were the highest seen at the YAC since the invasive stinkbug first showed up in Yuma in 2009. A low-to-moderate population appeared in early September, reached very high levels by mid-September, and peaked in early October.

Observed numbers were much higher than the population last season, and slightly higher than 2010.

Infestation levels in untreated broccoli plots this year were at damaging levels throughout October.

In contrast, thrips population numbers have been low, relative to normal this time of the year.

I have not picked up winged aphids or colonies on lettuce thus far.

I am unsure how this translates to potential population pressure in January and February. Growers and PCAs should anticipate an arrival as usual.

I have been asked why pest pressure was relatively heavy this year. The answer is I really don’t know. It could be the heavy monsoon moisture in July and August had an influence.

Insect abundance is dictated by many abiotic and biotic factors in the cropping system. It is nearly impossible to consider all factors necessary to draw a reliable conclusion.

Nonetheless, graphics showing these recent trends in whitefly, CYSDV, lep larvae, and Bagrada abundance can be found at Pest Abundance on Desert Produce and Melon Cops in 2012.

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“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or

Plant pathogen resistance to fungicides

By Mike Matheron, UA Extension Plant Pathologist

Plant pathogens are similar to other living organisms in a degree of genetic variability within the genes which govern physical structure and internal biochemical activities. Any selection pressure imposed on an organism population can result in visible and invisible changes within the population.

Selective breeding is a tool used to express the genetic diversity within a population of an organism, as demonstrated by the proliferation of dog breeds or varieties of agricultural crops when compared to original ancestral forms.

Other selection pressures can result in unwanted changes within a population, including the development of resistance to antibiotics to treat animal diseases and to plant health chemistries to treat plant diseases.

In the Yuma area, plant health products are used primarily against diseases caused by fungi.

Specific recommendations have been established by an organization called the Fungicide Resistance Action Committee or FRAC to manage the development of fungicide resistance within a target plant pathogen population.

These resistance management strategies include:

1 - Do not use a single mode of action in isolation. Apply the material as a mixture or in alternation with one or more fungicides with different modes of action within a treatment program.

2 - Restrict the number of applications of a particular mode-of-action within a season. Make applications only when necessary.

3 - Do not apply less than the manufacturer’s recommended dose.

4 - Target fungicide applications for disease prevention and not eradication.

5 - Use an integrated approach to disease management.

By employing these resistance management strategies and disease-resistant cultivars, biological control agents, crop rotation, and other beneficial cultural practices, the end result can be a high level of disease control, lower amounts of needed fungicides, and decreased selection of fungicide-resistant components within the pathogen population.

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Contact Matheron: (928) 726-6856 or

Weed seeds

By Barry Tickes, UA Area Agriculture Agent

A long term weed management strategy should focus on reducing the reservoir of weed seed in the soil. This can be very difficult since the characteristics of weed seed allow survival.

These strategy efforts include seed numbers, seed dormancy, longevity, the ability to disperse, and rapid establishment.

Seed numbers: A major characteristic which allows weeds to survive is sheer numbers. Most are extremely prolific. The number of seeds produced per plant and by species is extremely variable.

Examples include: canary grass - 10,000 to 30,000 seeds per plant; sowthistle – 15,000 to 20,000; purslane - 50,000 to 75,000; goosefoot - 70,000 to 100,000; and pigweed- 115,000 to 200,000.

When weeds are allowed to produce mature seeds, they are deposited back into the soil and build up year after year.

Longevity: Fall weed seeds germinated at the same time control would be much easier to control. They don’t. Some germinate today, others next week, and on and on for up to 40 years for some species. Characteristics which facilitate this include physical traits, including hard seed coating and some are biochemical.

Ability to disperse: Many weed seeds have characteristics which allow the seeds to fly, float, and attach. Sandbur, burclover, puncturevine, and others are notorious for the ability to attach to just about anything.

In fact, cocklebur was the inspiration for the development of Velcro.

Some weed seeds fly with structures which resemble parachutes (sowthistle, groundsel, and other composites), gliders (some clovers and trees including ash, maple, and box elder). Other species have structures which allow floating on water. Curley dock, for instance, has a bladder which helps it stay afloat in irrigation and drainage water.

Rapid establishment: Many weed seeds germinate rapidly before, during, or after the crop seed has germinated. Rapid establishment allows some species to be well established before the crop emerges.

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Contact Tickes: (928) 580-9902 or

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