Farm Progress

Whitefly adults are now easier to find on spring melons - damage from feeding is a concern;Effectively managing powdery mildew with fungicides is best achieved by an initial application ideally before but not later than the first visible disease detection;Dodder is a difficult weed to control – 15 species are found in Arizona.

May 4, 2011

5 Min Read

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released May 3, 2011.

Whitefly management on spring melons

By John Palumbo, UA Research Scientist and Extension Specialist

Within the last week whitefly adults have become easier to find on spring melons. As temperatures continue to increase, damage to spring melons from whitefly feeding should be a concern.

Sooty mold contamination on cantaloupes, mixed melons, and watermelons can significantly reduce fruit quality and marketability. Although whitefly numbers have been low up to now, pest control advisers should monitor and sample. With the warmer weather, numbers are likely to increase rapidly in the next few weeks.

Our research has shown that to prevent melon yield and quality losses a foliar insecticide treatment should be applied when a threshold of two adult whiteflies per leaf is exceeded. This threshold applies for the insect growth regulators, neonicotinoids, and synergized pyrethroids.

Click on these URLs for more information on  whitefly management, thresholds, and insecticide efficacy).

Note: Cucurbit yellow stunting disorder virus (CYSDV) symptoms have been observed on a few cantaloupe plants in a Yuma Valley field. Lab results are not back yet. If you spot suspicious CYSDV symptoms on melon leaves this spring, please let us know.

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

Managing powdery mildew on melons

Managing powdery mildew on melons

By Mike Matheron, UA Extension Plant Pathologist

Effectively managing powdery mildew with fungicides is best achieved by an initial application ideally before but no later than the first visible detection of the disease. Subsequent applications of fungicides are usually necessary throughout the life of the crop.

Several products are highly effective in controlling powdery mildew as demonstrated in yearly fungicide trials conducted at the University of Arizona’s Yuma Agricultural Center. One trial, completed in 2009, illustrates the comparative efficacy of several tested fungicides.

Podosphaera xanthii, the fungus responsible for powdery mildew on melons, has developed resistance to some fungicides in the past so maintaining long-term effectiveness of those materials currently available requires the use of resistance management strategies.

One effective approach is to alternate among products with different modes of action.

Two recent field trials evaluating treatment programs containing different fungicides and application sequences yielded very similar results. In most recent of the trials completed in 2009, fungicide application sequences containing a highly efficacious fungicide alternated with a product of moderate to low efficacy provided a final level of disease control equivalent to that achieved by continuous application of the highly effective material.

This data suggests that high levels of disease control and resistance management can be realized with fungicide alternation programs not only employing highly effective chemistries with differing modes of action, but also incorporating products with high efficacy along with those of moderate and low effectiveness.

To review the reports, click on Efficacy of Fungicides and Fungicide Application Programs.

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



By Barry Tickes, UA Area Agriculture Agent

Dodder has been a difficult to control weed in the Yuma County area for a long time but it seems worse in recent years. It is listed as one of the 10 most problematic weeds in the U.S. by the Department of Agriculture.

There are more than 150 species of dodder. Fifteen of these are found in Arizona, three are common, and one field dodder, Cuscuta campestris, is a problem in the lower Colorado River region. It can be a problem on many crops grown during the summer months including melons, safflower, asparagus, sugar beets, beans, alfalfa, and others.

Dodder is an unusual weed. It is a parasitic annual with no leaves or roots after it is attached to a host. It obtains all of its energy from the attached plants. Dodder germinates near the soil surface and lives off food reserves in the seed. It must attach to a host within five to 10 days or it will die.

After it has found a suitable host, it produces adventitious roots called haustoria that grow into the vascular system of the host plant. After it is attached, the lower portion of the dodder seedling dies and all contact with the soil ends.

Dodder seed is small - about 1/16 inch in diameter - and germinates in the spring or summer once the soil temperature reaches about 60 degrees. Each plant can produce several thousand seeds.

The seed is hard and less than one-third can germinate the following season. The remainder can remain dormant but viable for 20 years or more. The seed is small and light enough to float in water and blow in the wind.

Most of the movement is probably from contaminated crops, seed, and equipment. Controlling this weed starts by reducing seed movement into an area. Most states and countries have laws that prohibit the import of dodder seed.

Only certified seed should be planted. A major cause for dodder spread in Arizona is non- certified alfalfa seed. Once dodder is in a field, annual crops that are poor hosts can reduce the spread of this weed. Poor host crops include grasses, grains, and other monocots. Other weeds can serve as hosts and should be eliminated.

Pre-emergent herbicides can be effective in keeping this weed from becoming established. Post-emergence herbicides should at least temporarily destroy the host.

Perennial crops including alfalfa can be temporarily burned to the ground with contact herbicides including Gramoxone, Chateau, or Scythe plus an adjuvant. Dodder can be selectively killed with glyphosate in Roundup Ready Alfalfa.

The most effective control is with pre-emergent herbicides. These include trifluralin, pendimethalin, benefin, Dacthal, and others.

When the herbicide levels have dropped to sub-lethal amounts, dodder seed will germinate and survive. Repeated applications are normally required.

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

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