IN THIS ISSUE
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Onion Field Day Scheduled
Onion producers, seedsman and other interested parties are invited to an onion field day scheduled for Tuesday April 14 at 10:00 a.m. on Griffin & Brand's Fronton Farm south of Roma in Starr County, Texas (see map below).
The field day includes a variety trial with 27 different varieties including yellow, red and white onion types and several advanced breeding lines from the Texas A&M onion breeding program. Dr. Leonard Pike will be on hand to discuss new developments in the onion breeding program.
For more information contact Starr County Agricultural Extension Agent, Enrique Perez at (956) 487-2306.
Impact of FQPA on Vegetables by Rodney Holloway
The food Quality Protection Act (FQPA) of 1996 became official on August 3, 1996. The change to the Federal Food Drug and Cosmetic Act (FFDCA) and the Federal Insecticide and Rodenticide Act (FIFRA), significantly changed the way pesticides are registered in the United States. Problems with previous pesticide laws were corrected, particularly where conflicts occurred. The law established a new uniform standard for setting pesticide tolerances in foods and specifically pesticide risk to infants and children.
Under the FQPA all pesticide tolerances must be reviewed within 10 years. The United States Environmental Agency has established a time-limited tolerance process for FIFRA Section 18 registrations and began implementing other FQPA mandates. One of these is a prioritization of chemicals to be re-registered. The first compounds to be reviewed are the organophosphate and carbamate insecticides plus those on EPA's carcinogen list.
Organophosphate and carbamate products represent 30 of the 59 insecticide active ingredients used in the United States. Fifty two percent of the materials recommended in the TAEX Vegetable Insect Guide are impacted by FQPA. Pesticide use estimates for Texas vegetable crops indicate that possibly more than 50% of the insecticides currently used in horticultural crops are targets of this recent legislation.
Materials used for disease control in vegetables in Texas will also be impacted by FQPA because of EPA's B-2 carcinogen interpretation. There are 18 vegetables or vegetable groups with commonly occurring disease pests. The diseases and the resulting symptoms are managed by numerous chemical materials. Noting the number of diseases for each crop and the respective control materials for each, one can determine those controlled by B-2 chemicals. The crops with a relatively large number of B-2 materials include spinach (43%), corn (40%), cucurbits (32%). Use estimates for pesticides find 70% of cabbage, 39% of carrot, and 56% of onion acreage treated with chlorothalonil (Bravo) a B-2 material. Onion acreage treated with a B-2 material includes iprodione (Rovral) (57%), mancozeb (46%), and maneb (33%).
Summing up FQPA we need to remember the following points:
Silverleaf Whitefly on Melons by Alton Sparks
Based on reports from USDA-APHIS personnel that are following SLWF populations on vegetables and weed hosts, SLWF populations are high for this time of year. Combine this with the generally warm, dry weather we have had thus far (which favors SLWF increases), and SLWF could become a problem on spring vegetables.
The current section 18 registration for use of Admire and/or Capture on melons for control of SLWF expired on March 1. I have heard and seen the expiration date of March 31, but that date was for expiration of the time-limited tolerance, not the section 18. Because the law does require that the applicator has the section 18 registration in their possession at the time of application (and I'm sure it is reviewed carefully), I am sure that this confusion did not result in any questionable applications. For those that did not treat at planting and plan on alternate in-season applications of Admire or Capture, TDA has submitted a request for a section 18 for these uses. In addition, TDA has granted a section 18 crisis exemption (on 3/26) to allow use of Admire only while EPA reviews the specific request.
Resistance Management with the Use of Quadris by Tom Isakeit
Quadris (azoxystrobin) is a fungicide in the strobularin group. Fungicides in this group (and Quadris is the only one on the market at this time) have a mode of action that is different from other fungicides currently on the market. Quadris interferes with energy production by the fungus. It binds to a specific part of the mitochondria, the cytochrome bc1 complex, and blocks the chemical reaction which generates energy. This prevents spore germination and growth.
However, the single-site mode of action of Quadris has the same problem of other fungicides with single-site mode of actions, such as benomyl (Benlate) and mefenoxam (Ridomil Gold), in that there is a greater chance for development of resistance than with fungicides that have multi-site mode of actions, such as chlorothalonil (Bravo) and mancozeb (Dithane). A mutation in the mitochondrion of a fungal cell could prevent binding of Quadris, resulting in resistance. Since there are many mitochondria within a cell, most of them would still be sensitive to Quadris. The result of this is that while the fungus would survive the effects of Quadris, it would have reduced fitness. That is, it would not be as pathogenic or survive in the environment as well as the original, Quadris-sensitive strains. This initial resistance "penalty" could be overcome with additional mutations. Additionally, in the presence of a low dose of Quadris, the chances of survival of these mutants would be increased. Thus, the development of pathogen resistance to Quadris would be incremental.
The above scenario is theoretical, since resistance to Quadris has not been seen in any plant pathogens. Because resistance development would have to proceed in small steps, there is the possibility of managing it to prolong the useful life of Quadris. The risk of resistance is lowered by applying the optimal dose in conjunction with alternating to a fungicide with a different mode of action. Applying the optimal dose means applying the Quadris at the manufacturer's suggested rate. Going below this rate could allow the survival of mitochondria that would otherwise be sensitive to Quadris.
The amount of Quadris applied to the crop should not exceed 30-50% of the total fungicides applied per season. The crop should not receive more than three sprays of Quadris. If there have been two consecutive sprays of Quadris, the following spray should be a different, non-strobularin fungicide. Zeneca, the manufacturer of Quadris, is not recommending tank mixing of Quadris with a different fungicide as a means of resistance management. They feel that the absence of Quadris from the crop for a period of time through the use of a different fungicide will allow the least opportunity for resistance development, rather than having the continuous presence of Quadris in a crop, even when it is applied with a different fungicide.
Another key in resistance management is applying Quadris on a preventative basis. Quadris will prevent new infections and it will stop the progress of infections that are not yet visible to the eye. It will not work very well when disease symptoms are visible and applying it under these conditions represent the greatest risk for development of resistance.
Other companies, such as DuPont, BASF, and Novartis have developed different chemicals that are also strobularins and thus share the same mode of action. In the next few years, as these other chemicals become available, pathogens resistant to Quadris will likely be resistant to these chemicals. This is known as cross-resistance. For example, fungi resistant to benomyl, which is in the benzimidazole group, are usually resistant to other members of that group such as thiophanate methyl (Topsin M) and thiabendazole (Mertect). Cross-resistance is a real possibility with strobularin fungicides, and so, none of the fungicides in this group should be used in alternation with Quadris.
Lynn Brandenberger/Editor
The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.