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

Proposed EPA Labels Changes Could Impact Desert Crops

The U.S. Environmental Protection Agency (EPA) recently proposed additional mandatory pesticide label restrictions that would prohibit the application of acutely toxic pesticides during the time crops are in bloom and commercial bees have been placed in or near fields for pollination services. If these proposed label changes are implemented they could have important implications for managing key pests on desert crops which require the use of contracted bees for pollination. Specifically, the proposed labelling reads as follows: “Foliar application of this product is prohibited from onset of flowering until flowering is complete when bees are on-site under contract”. This label would apply to pesticides that have an acute contact toxicity value less than 11 micrograms per bee (LD50<11 μg/bee). Unfortunately for desert producers, the list of acutely toxic insecticides includes all of the pyrethroid, organophosphate, carbamate and neonicotinoid insecticide active ingredients currently used for control of major pests. Also included in this list are Exirel, Radiant, Success, Sequoia, Abamectin, Proclaim, Avaunt and Torac. Even insecticides approved for organic production are not exempt, as azadirachtin (e.g., Aza-Direct), pyethrins (e.g., Pyganic), spinosad (Entrust) and rotenone are also on the restricted list. The full description of the proposed label changes, including the list of acutely toxic pesticides (Appendix A) affected and proposed label language (Appendix B), can be found here: EPA’s Proposal to Mitigate Exposure to Bees from Acutely Toxic Pesticide Products. In my view, fall melons would be most directly affected by this proposed label change. Economic production of fall melons requires pollination services, but of course also requires adult whitefly control during the bloom/pollination period to suppress the spread of virus (CYSDV). Based on EPAs proposed label restrictions, application of industry standards like Assail, bifenthrin, fenpropathrin, and Exirel would not be allowed anytime, day or night, on fall melons as long as commercial bee hives are present. This could make whitefly/CYSDV control during bloom very difficult. UA research has clearly shown that the remaining alternatives labeled for whitefly control not on EPAs proposed list (i.e., Knack, Vetica, Oberon, Coragen, Fulfill, Beleaf) have little effect on preventing virus infection. Under this scenario, spread of CYSDV in some fields could essentially go unchecked for several weeks. If you are interested in voicing your opinion on this new proposal, EPA is currently accepting public comments until July 29, 2015. For more information on how to submit comments go to: and!docketDetail;D=EPA-HQ-OPP-2014-0818.


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

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Sudden Wilt and Death of Melon Plants

Temperatures are rising, melon plantings are maturing, and sudden wilt and death of melon plants is occurring. What causes this sudden collapse of plants? In the desert melon production areas of Arizona and California, symptoms of melon plant wilting and collapse usually can be attributed to one of four diseases; Charcoal rot, Fusarium wilt, Monosporascus root rot, or Pythium sudden wilt. Each of these diseases is caused by a different soil-borne plant pathogen, so knowing what management options might be available first requires accurate identification of the responsible pathogen. Charcoal rot and Fusarium wilt, caused respectively by the fungal pathogens Macrophomina phaseolina and Fusarium oxysporum, are not effectively controlled by fungicides. Preventative actions that may lessen the severity of these diseases include planting resistant melon varieties when available (for Fusarium wilt) and minimizing plant stress. Plant stress due to over- or under-irrigation can be managed; however, other crop stress factors such as fruit load and hot temperatures are obviously beyond your control. Monosporascus vine decline, caused by Monosporascus cannonballus, can be suppressed by application of the fungicide Cannonball at seeding or transplanting followed by additional applications as specified on the product label. The other disease mentioned was Pythium sudden wilt. Pythium, the pathogen that causes this disease, is a fungus-like soil-borne organism that can be managed by fungicides, such as mefenoxam. However, the difficulty in preventing extensive Pythium sudden wilt is that once this disease is initially identified in a field, rapid deployment of an effective fungicide treatment will protect noninfected plants but may not save plants already infected but not yet displaying sudden wilt symptoms. Knowing the disease history in a particular field for melons can help in preparing for possible recurrence of that disease in a future planting.

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Weed Science:

New Weeds!!!

The weeds here are constantly changing due mostly to changing production and management practices. These changes are normally slow although once a species becomes widespread, it may seem like it has come out of nowhere. Some have come out of nowhere when they are introduced with seed or equipment from another area but most are not new. Three weed species that have been brought to us in recent years that we have never seen here before are Seaside Petunia, Hairy fleabane and Southern brass buttons.

Seaside Petunia (Calibrachoa parviflora)
This was found in melons in the Yuma area this season. It is in the nightshade family and is native to the southwestern U.S. It has small petunia-like purple flowers and fleshy, sticky leaves. The stems are thin, creep along the ground and root at the nodes. It can form dense mats. The flowers resemble a miniature version of cultivated petunias.
Images provided by Mr. Bill Fox

Hairy Fleabane (Conyza bonariensis)
This was found in onions in the Parker Valley this year. It is widespread in California but not in S.W. Arizona. It resembles and is in the same family as horseweed or marstail. Marstail has become more widespread in recent years. Marstail is Conyza canadensis and Hairy fleabane is Conyza bonarinsis. Glyphosate- resistant biotypes have been confirmed in California. It is classified as a summer annual but can be found here year round. When fleabane is small it looks very similar to marstail. It is prolific and produces large quantities of seed that are distributed by wind. Unlike many weeds, fleabane seed does not have a long longevity. It is viable for only 3 or 4 years.
VIPM_Update_Vol_6_Num_13_003.png Image provided by Mike Chumley

Southern Brass Buttons (Cotula cornopifolia)
Found in the Parker are 4 or 5 years ago, Brass buttons is often confused with swinecress. The leaves and flowerhead look very similar to swinecress. It is salt tolerant and often found in saline areas. It gets its name from its flowers which are bright yellow, round and thick. It is a perennial in the composite family that was introduced from Europe and Africa. It is relatively short, branches and can root at the nodes.
VIPM_Update_Vol_6_Num_13_004.png Image source: Grower Weeds ID Handbook University of California

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The Vegetable IPM Updates Archive page provides links to updates from previous weeks.

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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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