The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released March 206, 2013.

Winter weather and produce pests

By John Palumbo, UA research scientist and Extension specialist

A notable Hoosier once wrote, “Don’t knock the weather. If it didn’t change once in a while, nine out of ten people couldn’t start a conversation.”

Given the recent temperatures, one might wonder if summer has arrived early this year in the Yuma, Ariz. area. The produce season is quickly winding down.

Several local growers commented lately that weather played a big role in the market volatility which the produce industry experienced this year. Looking back at the weather records for the last few months, Yuma’s winter weather was certainly unusual.

Insect pressure at the Yuma Agricultural Center (YAC) was very light this winter, lighter than the last several years.

Based on weather data collected from AZMET weather stations throughout Yuma County, average temperatures were warmer in November than the past several years, but were certainly cooler in January and February compared to last season.

This may explain why aphid and thrips populations have been lower this year compared to normal. Higher winter rainfall in some locations may have also played a role.

Not surprisingly, thrips numbers are building exponentially on late lettuce trials at YAC. This is expected given the warm-, dry-growing conditions and the migration of adults from recently disked lettuce fields.

Cabbage lopper, beet armyworm, and diamondback moth numbers are much lower this spring and are likely a reflection of the cold-nighttime temperatures in January.

Whitefly adults are showing up on early melons; more so than last year. This is a bit surprising since several freeze events occurred this winter, particularly in the south Yuma Valley and the east county.

Finally, seed corn maggots have not been a problem to date on melons or cotton. The recent warm, dry weather is not considered conducive to maggot outbreaks.

For a detailed summary of the winter weather data described above, click on this link: Winter Weather Conditions for Yuma County, 2012-2013.

Click this link to listen to John's update

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or

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Gray mold

By Mike Matheron, UA Extension Plant Pathologist

While the end of the winter lettuce production season is fast approaching, botrytis has been observed recently on romaine lettuce.

The appearance of fuzzy gray growth at the base of maturing lettuce plants is a sign that the fungus Botrytis cinerea is present.

The gray growth contains profuse amounts of spores which are dispersed in the air. When favorable temperature and humidity levels exist, spores landing on senescent or damaged lettuce tissue will germinate and then grow into healthy plant leaf and stem tissue. This can lead to plant collapse and death.

This outcome is similar to that caused by Sclerotinia minor and S. sclerotiorum, the causal agents of lettuce drop. Botrytis and Sclerotinia are related fungal pathogens. Fungicides effective against one are usually active against the other.

As with Sclerotinia, fungicide applications for Botrytis management are most beneficial when plants are young and gray mold is not yet present. The value of applications later in the crop’s life has not been determined.

Click link to listen to Mike's Update

Contact Matheron: (928) 726-6856 or

Grass control in melons

By Barry Tickes, UA area agriculture agent

The list of herbicides registered for melons is limited although most grasses can be controlled with available products on the market.

Prefar, Dacthal, and Tifluralin are registered pre-emergence but only Prefar can be applied before the crop has three leaves.

Up to nine quarts of Prefar can be applied but on pre-emergence before or after planting.

Prefar does not incorporate well with drip or furrow irrigation. It works best when incorporated with high volumes of overhead sprinkler water.

Mechanical incorporation also does not work well.

Dacthal and Trifluralin can only be used as layby treatments after melons have three-to-four leaves. These herbicides can cause unacceptable injury when applied too early.

Many grasses have emerged by this time and will not be controlled with pre-emergence herbicides. These grasses must be removed mechanically, by hand, or with a postemergence grass herbicide.

Postemergence selective grass herbicides were developed almost 30 years ago. These include fluazifop (Fusilade-1985), sethoxydim (Poast-1986, Segment, Vantage, and others), and clethodim (Select-1991, Select Max, Arrow, Envoy, Volunteer, and others).

These grass herbicides only control grasses and are registered on melons and many other broadleaf crops, plus trees and vines.

These postemergence selective grass herbicides can be slow acting, especially during the cool months, and have no soil activity. Due to the continual emergence of many grass species, it is common to make more than one application to achieve season long control.

These are all fairly broad spectrum and will control most grasses. Only clethodim will control small sprangletop and annual bluegrass. None will control sandbur.

Click link to listen to Barry's Update

Contact Tickes: (928) 580-9902 or

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