ISSUE 1 May 13, 2010
WHEAT CURL MITES FOUND IN VOLUNTEER WHEAT SAMPLES FROM NC REGION OF ND
Wheat curl mites were found in volunteer spring wheat and winter wheat samples collected last week near Berthold, ND in Ward County. Wheat curl mites vector wheat streak mosaic virus (WSMV) and High Plains Virus (HPV). The ND Plant Diagnostic Laboratory confirmed the presence of WSMV)in these samples, and some samples also tested positive for HPV. Additionally, a Hessian fly ‘flaxseed’ pupa was collected from one of the samples. Fields with moderate to high WSMV symptoms (Fig. 1) have been reported in Renville, McHenry, McLean, and Bottineau Counties (D. Waldstein, NCREC, Minot).
Figure 1. Wheat streak mosaic symptoms
(D. Waldstein, NCREC, Minot).
Wheat curl mites are white and carrot-shaped, but are microscopic (1/100th of inch) and not visible to the naked eye (Fig. 2). These mites overwinter in all life stages, and have a short life cycle of only 8-10 days at 77 F. Hosts include wheat, corn, foxtail, millet and grassy weeds. Wheat curl mites feed deep in the curled leaves or whorls and are protected from pesticides. Injury from leaf feeding is minimal and secondary to the deadly vectored viruses. During heading, mites move up to the heads and can affect yields by 10% under very high mite populations. Winds readily disperse mites from an infested field to neighboring fields.
Figure 2. Wheat curl mite (F. Peairs, CSU, bugwood.org)
I’ve received many questions about how to control wheat curl mites with insecticides or acaricides in wheat. Unfortunately, we have NO insecticides or acaricides registered in wheat that will kill wheat curl mite. In the past, growers have applied Furadan (carbofuran) at winter wheat planting to control fall mite infestations and reduce the incidence of WSMV the following spring. The use of carbofuran on wheat was voluntarily cancelled by the registrant. Additionally, all tolerances for residues of carbofuran on food crops were revoked by the EPA, effective December 31, 2009. Carbofuran CAN NOT be used on wheat. Neonicotinoid insecticides such as imidacloprid (Gaucho) and thiamethoxam (Cruiser) are systemic seed treatments commonly used for control of soil insects (like wireworms), but are NOT effective against wheat curl mites. In fact, field studies have shown that imadacloprid can increase wheat curl mite populations.
The bottom line is that there are no currently labeled insecticides or acaricides with proven efficacy against wheat curl mite. Please avoid ineffective and costly pesticide applications for wheat curl mite.
The best control strategy is breaking the ‘green bridge’ by destroying living plant host material with herbicides or tillage for at least a two week period prior to planting winter wheat. Mites must have GREEN living host plant material to survive, and can only live for 48 hours off of a host. Herbicides that kill the mite’s hosts quickly will lower the chances of mite survival. Herbicides are typically more effective in moist conditions, whereas tillage will be faster than herbicides in dry conditions. Cool temperatures (40-50 F) will slow down mite reproduction whereas warmer temperatures (70-80 F) will speed up mite reproduction and increase the likelihood of dispersion to other fields.
Our observations have led us to believe that winter wheat planted prior to Sept 25, 2009 is at the highest risk for infection (D. Waldstein, NCREC, Minot). Early planting in fall does not break the ‘green bridge’ and allows for a longer period for mites to develop and transmit viruses. It is best to avoid early planting of winter wheat in the fall. The warm September in 2009 and insulating snow cover this winter provided two additional factors that favored mite development and virus transmission.
FLEA BEETLES OBSERVED FEEDING ON VOLUNTEER CANOLA
Flea beetles have been observed feeding on volunteer canola in the Fargo and Devils Lake areas in spite of the cool spring weather. Only 4% of spring canola has emerged, and 75% still needs to be planted (USDA NASS, North Dakota Field Office, released May 10, 2010). It’s too early to start scouting; however, as soon as more canola is planted and temperatures start to warm to 60-70 F, scouting will be in full swing on emerging canola!
VOLUNTARY CANCELLATION OF ALL METHYL PARATHION REGISTRATIONS
EPA has received requests from the registrants to voluntarily cancel all product registrations containing methyl parathion, a restricted use organophosphate insecticide and acaricide used primarily on cotton, corn, and rice, as well as on other agricultural crops. These requests would terminate the last methyl parathion products registered for use in the U.S., effective December 31, 2012. End-use products will not be sold after August 31, 2013, and end-use products cannot legally be used after December 31, 2013. All end use product labels will be amended to reflect the last legal use date.
The Registration Review docket for methyl parathion opened in June 2009 and a Final Work Plan was signed in October 2009. EPA's registration review decision will be based on the cancellation of all registered products. Any party wishing to pick up the registrations will be responsible for submitting all required data. Methyl parathion is named in the Washington Toxics Coalition v. EPA Endangered Species Act lawsuit, and the National Marine Fisheries Service is scheduled to issue a Biological Opinion on methyl parathion and other pesticides later this year. Methyl parathion is also included in the group of 58 pesticide active ingredients on the initial list to be screened under the Endocrine Disruptor Screening Program.
In addition to cotton, corn (field, pop, and sweet), and rice, methyl parathion is currently registered for use on the following crops grown in North Dakota: alfalfa, barley, canola/rapeseed, grass (forage), oats, onions, potatoes (sweet and white), rye, soybeans, sunflowers, and wheat. The three registrants are: Cheminova A/S, Cheminova, Inc, and United Phosphorus, Inc.
In an April 28, 2010 Federal Register notice, EPA is inviting comment on the voluntary cancellation requests until May 28, 2010. Additional information on methyl parathion and the voluntary cancellation requests is available in registration review docket EPA-HQ-OPP-2009-0332 at:
Janet J. Knodel