The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released May 1, 2013.

Spider mites on melons

By John Palumbo, UA research scientist and Extension specialist

Over the last several weeks, I have received calls concerning spider mites on melons. Two spotted spider mites, Tetranychus spp, are widespread on melon crops throughout the southwestern U.S.

In general, outbreaks are more common on watermelons than other netted and mixed melon varieties. However, problems can certainly occur on all melon types.

Hot dry weather can be favorable for mite infestations. Mite populations can increase dramatically. For example, mites can mature from egg to adult in about 37 days when temperatures average about 60 degrees F. At an average temperature of 86 degrees F. it only requires 7-8 8 days to complete the lifecycle.

Several natural enemies - including predatory mites and thrips, minute pirate bugs, and lacewings - play an important role in regulating mite populations below economically damaging levels. Predators can keep mite populations in check by feeding slowly on developing mite populations.

When temperatures become hot and dry, mites can quickly out run the predator population due to rapid reproduction.

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Good irrigation and fertilization management increases plant tolerance to mites. Although economic thresholds have not been adequately established for spider mites in the low desert, treatment with an acaricide is recommended when significant webbing is found on leaves and predatory mites and thrips are absent.

Effective miticides for melons include Agri-Mek, Oberon, Acramite, Fujimite, Zeal, and sulfur. If leafminers are present in the field, Agri-Mek is a good option.

If whiteflies nymphs begin to build on older leaves, Oberon may be an effective option.

For more information on mites and their management please visit:Melon Insect Pest Management in Arizona.

Note: A thank you to those who completed the lettuce crop losses surveys and Bagrada surveys. The information will be very useful. If not completed yet, please return the survey as soon as possible.

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“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or

Managing powdery mildew on melons

By Mike Matheron, UA Extension Plant Pathologist

How does one successfully combat powdery mildew in melon plantings?

Maximum disease control requires the 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 initial invisible infection sites within the crop.

The application of a newly registered novel active ingredient usually is effective on most 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 becomes established.

The melon powdery mildew fungus, Podosphaera xanthii, has developed significant resistance to some fungicides in the past. An important strategy to delay 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 moderate to low 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 of moderate and low effectiveness.

Results are available from the 2012 cantaloupe powdery mildew fungicide evaluation trial conducted at the University of Arizona’s Yuma Agricultural Center. 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.

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Contact Matheron: (928) 726-6856 or

Herbicides registered for vegetable crops

By Barry Tickes, UA area agriculture agent

An Arizona vegetable acreage in 2012 chart indicates that lettuce was clearly the major vegetable crop at 65,200 acres, followed by melons - 21,700 acres, spinach – 8,000 acres, broccoli – 7,400 acres, and cauliflower – 3,600 acres.

Romaine (19,900 acres) and leaf lettuce (8,700 acres) accounted for almost half of the total lettuce acreage with head lettuce (36,600 acres) as the balance.

There are relatively few herbicides registered for vegetable crops.

There are five registered for head lettuce, seven for cole crops, and six for melons. There are four registered for romaine and leaf lettuce which is fewer than those registered for these crops over the last 45 years.

There are 25 herbicides registered for cotton, 20 for alfalfa, and 16 for wheat.

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Contact Tickes: (928) 580-9902 or

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