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University of Arizona
March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Insect Management:

Whitefly Management on Spring Melons

Local whitefly populations are quietly becoming abundant on spring melons. As temperatures continue to increase on maturing crops, feeding damage from whitefly nymphs should be a primary concern on all melon types. Honeydew and sooty mold contamination on fruit of cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability. Now that whitefly adults are becoming noticeable in a number of locations, PCAs should be diligent in their monitoring and sampling. Our research has shown that to prevent melon yield and quality losses, a foliar insecticide treatment should be applied when on a threshold of 2 adult whiteflies per leaf is exceeded when averaged across an entire melon block. By timing sprays based on the adult threshold, immature populations should just be starting to colonize and applying foliar sprays at this stage in population development has been shown to significantly reduce the chance of yield / quality loss during harvest. This threshold applies for the use of recommended IGRs (Vetica, Courier, Knack, Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion) and Exirel (diamide). For more information, go to these documents on 1) IPM and Whitefly Management, 2) Whitefly Action Thresholds and 3) Whitefly Control Options. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine the products bee safety before applying any pesticide in a melon field.
Note: Cucurbit Yellow Stunting Disorder Virus (CYSDV) is not generally known to be yield limiting on spring melons. However, our local research indicates that fall melons are at greater risk of CYSDV infection when planted in areas where CYSDV symptoms were found on spring melons. Thus, keeping whitefly populations low on spring melons reduces dispersal to cotton, other alternative crops and weeds later in June and July. Ultimately, this can reduce the risks of high whitefly numbers and CYSDV on fall melons.


VIPM_Update_Vol_7_Num_8_001.jpg Name this Insect Pest. VIPM_Update_Vol_7_Num_7_004.png
First person to email John or with the answer gets a new UA Veg IPM cap!

Remember, When in Doubt . . . . . “SCOUT”

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Melon Powdery Mildew

Spring is a time of transition for agriculture in the desert southwest. Cool season crop harvest is wrapping up and spring and summer crops are being planted and grown. This is also powdery mildew season. Powdery mildew can develop on commercial crops, such as late-season lettuce, wheat or melons, as well as landscape plants. It is not too early to begin considering management options for powdery mildew on melons. Some risk factors that support development of powdery mildew on melons include a lack of rainfall, moderate temperature and relative humidity levels, dense plant canopy, fertile soil, and succulent plant growth. The overall risk of powdery mildew increases as more of these factors are present in a melon field. Lack of rainfall and fertile soil are givens in our desert melon production fields. Spores of the melon powdery mildew pathogen, Podosphaera xanthii, can germinate to initiate disease at temperatures ranging from 72 to 88°F, and optimally at about 82°F. These moderate temperatures as well as reduced light intensity within a dense leaf canopy and succulent plant growth all become increasingly prevalent as the melon plantings grow rapidly during April, May, and June. Another factor to consider when determining powdery mildew risk is the inherent susceptibility of the melon cultivar being grown. Those varieties known to be susceptible to powdery mildew will 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 that have moderate to high levels of genetic resistance to the pathogen will require less or perhaps no fungicide inputs. To achieve maximum levels of disease control, powdery mildew fungicide application programs need to be initiated before the visible detection of the fungus. Good levels of disease control can also be attained by waiting to begin fungicide applications until no later than the very first sign of disease in the field. These initial infection sites are often on the underside of leaves, so frequent and comprehensive examination of the melon planting is required.

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Weed Science:

Pigweed Identification

Pigweeds are some of the most common summer annual broadleaf weeds in the low deserts and they are also some of the most diverse. The genetic diversity of pigweed has allowed it to develop resistance to some herbicides more rapidly than most other weeds. There are 4 species of pigweed that are common here. Although they are often lumped together, there are 4 different species of pigweed that are common here and more than 10 species that occur as weeds in California and Arizona. Their growth habits and response to herbicides are similar. It is easy to identify them by physical characteristics but one species of pigweed can hybridize with another and become less distinguishable.
Palmer Amaranth: (Amaranthus palmeri) is probably the most common pigweed species found in this region. It is very aggressive and fast growing and can become 6 feet tall or higher if uncontrolled. It has one thick stem and several lateral branches. The leaves are lance shaped, hairless and have distinctive white veins on the underside. It has flowering tassels that become stiff and spiny. This species has become resistant to Glyphosate in many parts of the county.

Redroot Pigweed: (Amaranthus retroflexus) is probably the second most common pigweed species. It is shorter and the seed heads are smaller, in clusters and have stiff spine-like scales. It has leaf hairs on the margins and the veins are often reddish. The lower stems are often reddish. This species will hybridize with Palmer Amaranth and become less distinguishable.

Tumble Pigweed: (Amaranthus albus) is very different from Palmers or Redroot. It grows lower to the ground and has many branches that turn upright. The leaves are much smaller and narrower. The numerous stems are light green rather than red. The seed heads are small, spiny and at the base of the leaves rather than in long terminal spikes. When mature, the branches are sticky, stiff bristles that break off at the ground and tumble with the wind.

Prostrate Pigweed: (Amaranthus blitoides) is very similar to Tumble Pigweed but the stems are more prostrate, grow close to the ground and form mats. The stems and leaves are smaller and reddis

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Question to the IPM Team:

Spanish Needle

VIPM_Update_Vol_7_Num_9_006.jpg The Yuma IPM TEAM was asked to ID this weed. Very common in the Yuma area.
Palafoxia arida is a species of flowering plant in the aster family known by the common names desert palafox and Spanish needle.
Thanks for your questions and comments!

Wikipedia: March 20, 2013


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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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