The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released June 26, 2013.

Whitefly management on fall produce, melons

By John Palumbo, UA research scientist and Extension specialist

As the spring melon harvest winds down, it is important to think about whitefly management in fall produce and melons crops.

The first line of defense to avoid whitefly issues in fall vegetable plantings is for pest control advisers and growers to be vigilant in whitefly management program on cotton. In the Yuma, Ariz. area, cotton is the primary host crop for whiteflies during the summer. Alfalfa and sudangrass may serve as alternate hosts in some areas.

Before whitefly management begins in cotton, whitefly populations should be prevented from building up in large numbers in spring melons in recently harvested fields, or field to be harvested in the next week or so.

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In surveying melon crops for cucurbit yellow stunting disorder virus (CYSDV) this spring, it was readily apparent that a large proportion of the spring melon acreage throughout the area was grown near cotton.

In fact, UA surveys suggest that on an area-wide basis almost 75 percent of the melon acreage this spring were grown adjacent to or within one-half mile of cotton.

Although whitefly numbers have been relatively light thus far, increased whitefly numbers have been observed over the last week in cotton, coinciding with higher temperatures and area-wide melon harvests.

Proper sanitation in spring melons is critical for preventing unnecessary whitefly buildups in cotton. It is highly recommended that melon growers quickly destroy plant residue as soon as possible following harvest.

A delay in disking under melon fields following harvest can provide a large source of adult whiteflies which can readily disperse into cotton, especially when the insects do not need to fly very far. These whiteflies may also move into nearby weeds many of which (e.g., common mallow and silverleaf nightshade) are hosts for CYSDV.

Another source of whiteflies and CYSDV during July and August can be volunteer melons in fields where spring melons were previously grown. These plants also potentially extend the host acquisition transmission period for CYSDV. This may be important since CYSDV incidence in spring melons, albeit at non-economic levels, was quite evident this year.

Our experience to date suggests that the incidence of CYSDV in fall melons is generally much higher in fall plantings growing in proximity to where melons were produced the previous spring.

For more information on sanitation practices see Whitefly Management on Desert Vegetable and Melons.

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Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.