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Arizona Veg IPM: insect losses, melon powdery mildew, nutsedge

Arizona Veg IPM: insect losses, melon powdery mildew, nutsedge

Insect loss and insecticide usage survey information helps provide ‘real world’ information on insect pest status and insecticide usage; Melon powdery mildew disease is generally favored by dry weather conditions, moderate temperatures, reduced light intensity, fertile soil, and succulent plant growth; Nutsedge is one of the most difficult weeds to control in the low desert. 

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released April 20, 2011.

Insect losses and insecticide usage in head lettuce

By John Palumbo, UA Research Scientist and Extension Specialist

Since 2004, the University of Arizona Vegetable Integrated Pest Management (IPM) Team has annually surveyed pest control advisers (PCAs) and growers to document insect pest activity and insecticide usage in head lettuce through interactive workshops. The information provided can be very useful to the lettuce industry.

First, the data can be extremely helpful in addressing state and federal regulatory issues by providing ‘real world’ information on insect pest status and insecticide usage. Secondly, from an academic perspective, the results of the surveys provide a historic record of insect occurrences which allows us to prioritize some research and extension activities.

Finally, for PCAs, it can translate their efforts into economic terms for their clientele and confirms their value to the lettuce industry by showing the importance of key insect pests and cost-effective management in desert lettuce production.

For example, results from the surveys over the past six years indicate: the costs associated with spray applications and management fees have increased steadily; western flower thrips has become an important economic pest in fall and spring lettuce; and the use of older, broadly toxic insecticides (OP/Carbamates/Endosulfan) has dropped significantly, whereas use of the newer, softer reduced-risk chemistries (e.g., Radiant, Movento) continues to increase.

These surveys document this information for those less involved with the day-to-day activities of IPM in desert lettuce.

To view a complete summary of the Lettuce Insect Losses and Insecticide Usage surveys in Arizona head lettuce from 2004-2010, go to "Assessments of Insect Losses in Lettuce.”  

Contact Palumbo: (928) 928-782-3836 or

Melon powdery mildew

Melon powdery mildew

By Mike Matheron, UA Extension Plant Pathologist

It is not too early to begin considering management options for powdery mildew on melons. The disease generally is favored by dry weather conditions, moderate temperatures, reduced light intensity, fertile soil, and succulent plant growth. The overall risk of powdery mildew increases as more of these factors become established in a melon field.

Dry weather conditions and fertile soil are givens in desert melon production fields. Spores of the powdery mildew pathogen,Podosphaera xanthii, can germinate to initiate disease at temperatures ranging from 72 degrees to 88 degrees F., and optimally at about 82 degrees. These moderate temperatures, plus reduced light intensity and succulent plant growth, all become increasingly prevalent as melon plantings grow rapidly during April and May.

Another factor to consider when determining powdery mildew risk is the inherent susceptibility of the melon cultivar grown. The cultivars known to be very susceptible to powdery mildew require implementation of a rigorous disease management program involving applications of fungicides with differing modes of action throughout the period of high disease risk.

On the other hand, melon varieties with moderate to high levels of genetic resistance to the pathogen will likely require fewer fungicide applications.

To achieve maximum levels of disease control, powdery mildew fungicide application programs must be initiated before or at the latest at the very first sign of disease in the field. These initial infection sites are often on the underside of leaves. Frequent and comprehensive examination of the melon planting is required.

For more information watch the video Effective Management of Melon Powdery Mildew in the Desert Part I and Part II.

Contact Matheron: (928) 726-6856 or



By Barry Tickes, UA Area Agriculture Agent

Nutsedge has long been one of our most difficult to control weeds. It is often misunderstood and progress in controlling it has been slow. Nutsedge is often referred to as nutgrass although it is neither a grass nor a nut and is very different from both.

Nutsedge is a monocot, like grasses, but is in the sedge or cyperaceae family. The ‘nut’ refers to the below ground tubers which are not nuts but have nutritional value and are sometimes eaten in famine stricken areas of Africa.

There are more than 5,000 separate species of sedges that exist worldwide. Some of the most widely known sedges are water chestnut and papyrus sedge which was used to make the ancient writing material.

Sedges are easily distinguished from grasses by the solid triangular flower stems. Sedges are almost all perennials while grasses, which have round stems, are most frequently annuals.

The two sedges that are a problem in the Yuma area are purple nutsedge, cyperus rotundus, and yellow nutsedge, cyperus esculentus. Purple probably accounts for 75 to 80 percent. These are not hard to identify but people sometimes have trouble distinguishing them.

Both are perennials and grow actively at the same time. Both grow from tubers and rhizomes. The seed is rarely viable and both are spread vegetatively from the tubers and rhizomes. They spread so rapidly and are so prolific that people are often surprised that less than five percent of the seed produced is viable.

The leaves do not have ligules or auricles and have a ridge along the midvein.

Yellow and purple nutsedge are similar at early growth stages but are not hard to distinguish later on. The leaves of purple are blunt and less pointed than yellow. As expected, the seed heads of purple are purple and yellow are yellow.

The tubers of purple are much larger than yellow; irregular shaped, connected by chains, bitter in taste, and have a distinctive almond odor. Yellow nutlets are small, round, not connected, and have a more sweet taste.

Nutsedge is a weed that gets worse each year because of the absence of highly effective herbicides and cultivation spreads it. Remember that the seed is not viable. The only way this weed spreads significant distances is mechanically. Soil movement should be minimized as much as possible where nutsedge is a problem.

Almost all herbicides with activity on this weed are only partially effective and require multiple applications over multiple years. It is necessary to control the below ground nutlets and rhizomes. They can persist for many years and continually put out new growth.

Nutsedge is so prolific that if a herbicide is not highly effective, the infestation is back to where you started one year later.

Several herbicides have nutsedge on the label and range in control from 20 percent to 90 percent. Twenty of these herbicides are contained in this table, "Herbicides with Activity on Nutsedge".

Question of the Week – Weed Science - What is the difference between goosefoot and lambsquarter?

A - No difference, herbicide tolerance

B - Color, appearance.

C - One is roasted and the other is baked.

D - Check Barry's answer (video).

Contact Tickes: (928) 580-9902 or

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