Farm Progress

The La Niña weather prediction this winter could suggest that aphid and seed corn maggot pressure will be lighter and thrips numbers much heavier this winter and spring in desert vegetables.Plant health products are used primarily against diseases caused by fungi.Pesticide use in Arizona includes insecticides at 58 percent, herbicides 17 percent, fungicides 12 percent, and other types at 13 percent. 

December 1, 2010

4 Min Read

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona Cooperative Extension in Yuma, Ariz.

Management tips for insects in desert vegetables

By John Palumbo, UA Research Scientist and Extension Specialist

The National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center predicts a moderate to strong La Niña will be the dominant climate factor influencing weather in Arizona and California this winter. This suggests that local weather in the Yuma County area should be warmer and drier than average from December through February.

What impact will this likely have on insect pests normally found on leafy vegetables and melons this winter?  I am not real certain since predicting insect abundance is like predicting the weather.

However, like NOAA, we have collected data over the years which suggests that aphid pressure on lettuce is historically lighter during growing seasons when rainfall amounts are low (less than .25 inches). Similarly, seed corn maggot infestations are generally less severe under warm and dry growing conditions during the winter.

In contrast, western flower thrips abundance has historically been higher under warm and dry weather conditions. Last winter (January - March) we received over four inches of rain in the Yuma Valley and thrips numbers were very low in our research trials. Seed corn maggots were damaging in a number of crops last spring. 

If one chooses to rely on the La Niña predictions, one might predict that aphid and seed corn maggot pressure will be lighter, and thrips numbers much heavier this winter and spring.

Keep in mind there are a number of other abiotic and biotic factors that also influence insect abundance. Historical trends in insect abundance on desert crops and guidelines for management were presented at the 21st annual Fall Desert Crops Workshop in Imperial, Calif. last week.

A copy of that presentation can be found at this link.

Contact Palumbo: (928) 782-3836 or [email protected].

Plant pathogen resistance to fungicides

By Mike Matheron, UA Extension Plant Pathologist

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

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

In the Yuma County 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 the following points:

1 - Do not use a single mode of action in isolation. Instead, 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 and only make applications 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 utilizing as many resistance management strategies as possible plus using disease-resistant cultivars, biological control agents, crop rotation, and other beneficial cultural practices, the end result can be reduced disease incidence and the total fungicides needed, which in turn can decrease the selection of fungicide-resistant components of the pathogen population.

More information on this topic, the publication entitled "Fungicide resistance in crop pathogens: how can it be managed" is available online at

Contact Matheron: (928) 726-6856 or [email protected].

Pesticide use in Arizona, U.S. and worldwide

By Barry Tickes, UA Area Agriculture Agent

Pesticides are commonly classified as insecticides, fungicides, herbicides, and others which include rodenticides, nematicides, fumigants, and products used to control birds, fish, and other aquatic pests.

The relative amount used of each of these categories of pesticides is significantly different in Arizona compared to the rest of the U.S. and worldwide.

According to USDA statistics, on a worldwide scale, herbicides account for 36 percent of the total pesticide use while insecticides account for 25 percent, fungicides at 10 percent, and others at 29 percent.

Figures for the U.S. are similar with herbicides at 44 percent, insecticides at 10 percent, fungicides at 6 percent, and others at 40 percent.

Pesticide use in Arizona is significantly different from the U.S. worldwide. In Arizona, insecticides account for 58 percent, herbicides 17 percent, fungicides 12 percent, and others at 13 percent.

Contact Tickes: (928) 580-9902 or [email protected].

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