|
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
|
 |
|
|
My second problem with how the NMFS research has been viewed is that no one has noted that the average responses of fish at the 10 ppb dose were actually lower than at the 1 ppb dose. Unless some unexpected mechanism of toxic effect is operational, or alternatively, the maximum effect on behavior is reached at 1 ppb diazinon, the results do not show an unequivocal dose-response relationship.
While the relationship between diazinon dose and magnitude of predator avoidance behavior may be somewhat hazy, diazinon's effect on salmon smell is given plausibility by U.K. research on the Atlantic salmon (10). Slicing open the male salmon's nasal cavity to expose receptor-rich nasal tissue (called olfactory rosettes), the U.K. team recorded the electrical potential (called an electro-olfactogram, EOG) when the tissue was exposed to female reproductive priming pheromone and then to a series of increasing doses of diazinon. Electrical signals increased in the presence of the female pheromone, but progressively higher doses of diazinon seemed to inhibit the response (Figure 2).
|
|
|
|
 |
|
|
While I agree with the U.K. researchers that diazinon did impair
olfactory responses to the priming pheromone, I disagree that
levels of 1 ppb were sufficient to definitively cause the effect.
Perhaps when salmon survival is at stake the argument over whether
1, 2, or 5 ppb diazinon causes an effect is trite, but remember
we're trying to decide whether diazinon at levels known to occur
in the environment has adversely impacted their populations.
As the saying goes, the devil is in the details, and in this case understanding just what doses cause stuffy salmon noses requires a short statistical detour. Researchers measure behaviors (and other sublethal effects) on individual fish, and individuals react a little differently from one another even in the presence of a toxicant. Determining whether responses are actually changing parallel to dose (as opposed to being random events) is complicated by the fact that a researcher measures a distribution of possible effects at each level of exposure. Thus, researchers use statistical techniques to determine how much overlap occurs between the distributions of behavioral measurements recorded at two or more doses. The gold standard for deciding whether two or more distributions of responses are sufficiently different because of dose or just due to chance alone is to determine if the overlap is 5% or less. When distributions overlap by no more than 5%, the researcher declares the responses at each dose significantly different from one another at the 95% level of confidence.
When researchers publish their data, they show the average responses and only indicate the distribution of all responses with an estimate called the variance, which can be expressed in several forms. Numerous statistical techniques are available to determine whether the variance associated with the average responses for various doses are significantly different. However, different techniques of analyzing data can lead to different conclusions about whether two distributions of measurements meet the 5% criteria and are therefore a dose-related effect.
Researchers often don't show their raw data when they publish, but you can figure out what is significant by examining the variance terms. In doing so, I graphed and conducted a statistical analysis of EOG data reported by the U.K. researchers (Figure 2). Contrary to their conclusion that 1 ppb inhibited olfactory response, I cannot conclude any significant effect occurred until doses higher than 5 ppb were introduced to the fish nasal tissue.
Nevertheless, doses of diazinon between 5 and 20 ppb inhibit electrophysiological measurements of olfaction. The next question is what biological relevance would such inhibition have? When salmon are primed by the female reproductive pheromone, which is released in the urine of ovulating females, circulating blood levels of male steroid hormones like testosterone are increased, consequently stimulating increased production of milt. Milt is the sperm-containing fluid that salmon secrete to fertilize eggs. Researchers can forcefully express the milt from the male and measure its weight.
The U.K. researchers noted that males exposed to diazinon for five days followed by a three-hour exposure to female urine had lower levels of reproductive hormones than unexposed males. They hypothesized that milt production would also be affected. Upon "milking" the diazinon-exposed fish, the researchers concluded that "there was no significant difference in the level of expressible milt when compared to fish not exposed to female urine" (10).
The researchers' conclusion was based on comparing milt levels in fish exposed to diazinon and fish not exposed to diazinon with milt levels in fish prior to exposure to urine. While their conclusion is unarguable, the graphical presentation of the data begged the question of whether the milt production in primed diazinon-exposed fish was really different than the production in primed unexposed fish. I re-analyzed the data to calculate the variance, and then I examined the overlap of the distributions of milt weights to determine whether there was any overlap among unexposed and exposed fish. Using the 95% confidence interval, I noted that the overlap in distributions of milt weights from every diazinon exposure level except one were too great to affirmatively conclude that unexposed and exposed fish produced different amounts of milt (Figure 3). Thus, the U.K. research in my opinion cannot be used to conclude that reproductive potential of Atlantic salmon has been affected as a consequence of olfactory inhibition by increasing doses of diazinon.
|
|
|
|
 |
|
|
My analysis aside, let's take the NMFS and U.K. research reports at face value and assume that fish may be impaired by diazinon at doses of 1 ppb but not at 0.1 ppb. Step three in risk analysis is determining the range of exposures in the environment. Two sources of data are available for this exercise--real measurements and computer-simulated data.
When assessing ecological effects during the pesticide registration process, EPA uses computer models that simulate how much pesticide may run off and drift into a pond. The resulting residues, called estimated (or expected) environmental concentrations (EECs), vary somewhat among different pesticide use patterns. For example, EPA simulated diazinon residues in a six-foot deep, one-acre pond following three applications to a fruit orchard and to a lawn (6). The peak or initial residues in the hypothetical pond affected by the lawn treatment were over five times greater than the residues from the fruit orchard (Figure 4). Even at 60 days after application, diazinon residues were estimated to be 160 ppb in the pond following the lawn application.
|
|
|
|
|
|
 |
|
While EPA takes a very conservative approach to estimating environmental residues, real monitoring data are collected by the U.S. Geological Survey in its National Water Quality Assessment Program program (NAWQA) (8). These residue measurements form a database that encompasses over 1000 separate monitoring sites. The highest diazinon concentration reported in the database was 3.8 ppb. Pertinently, there were large differences between urban and agricultural stream sites (6, 8). Diazinon was found in only 24% of agricultural sites with a 95th percentile concentration of 0.042 ppb (Figure 4). In other words, 95% of all diazinon detections were 0.042 ppb or less. In stark contrast, diazinon was detected in 50% of urban stream sites with a 95th percentile concentration of 0.24 ppb (Figure 4). For both agricultural and urban stream sites, half of the samples contained diazinon at or below its detection limit (0.002 ppb).
Although EPA's modeled EECs for diazinon seem in the right direction (i.e., applications to lawns result in significantly greater residues than applications to fruit orchards), the numbers do not characterize stream reality. Using such numbers makes for an extremely conservative risk characterization.
EPA presumes four categories of risk that cover acute and chronic toxicity, endangered and non-endangered species (Table 1). Risk is characterized by calculating a risk quotient (RQ), which is essentially the ratio of the EEC to some toxicological endpoint for the most sensitive species tested. Exposures are considered acceptable (i.e., below EPA's levels of concern, LOC) if the RQ is below a predefined value that has a safety factor incorporated into it (Table 1).
|
|
|||
|
|
|||
| Presumed Risk Category |
|
|
|
| Acute High Risk |
|
|
|
| Acute Restricted Use |
|
|
|
| Acute Endangered Species |
|
|
|
| Chronic Risk |
|
|
|
| *EEC=estimated environmental concentration; LC50=concentration of pesticide lethal to 50% of test subjects in 96 hours; NOEC=no observable adverse effect concentration | |||
For example, to characterize diazinon, EPA divided the EECs in pond water for orchard and lawn uses by the LC50 for rainbow trout (90 ppb) and an aquatic crustacean known as a scud (0.2 ppb). Thus, any diazinon concentration protective of scuds should also be protective of Chinook and Atlantic salmon, which were reportedly affected by 1 ppb but not 0.1 ppb diazinon. The resulting RQs for the acute high risk category, which is presumed protective for non-listed species, skyrocketed above EPA's LOCs for both fish and invertebrates (Figure 4). Application scenarios for lawns were worse than for apples and pears. Because the acute high risk presumption was exceeded, the characterization for endangered species didn't stand a chance of being concluded "safe" (Table 2).
|
|
|||
|
|
|||
| Exposure Scenario |
|
|
|
| Apple/Pear |
|
|
|
| Apple/Pear |
|
|
|
| Lawns |
|
|
|
| Lawns |
|
|
|
| USGS 95th percentile | |||
| Urban Sites |
|
|
|
| Urban Sites |
|
|
|
| Ag Sites |
|
|
|
| Ag Sites |
|
|
|
| Apple/pear and lawn exposure scenarios from reference 6; RQs for USGS 95th percentile calculated for this essay. | |||
When the USGS data are used to calculate the RQs, the risk to fish does not exceed EPA's levels of concern. However, if the more sensitive invertebrates are considered, levels of concern are exceeded for the risk presumption categories of acute restricted use, acute endangered use, and chronic risk. RQs were over five times higher for urban uses of diazinon than for agricultural uses.
The bottom line is that the research on diazinon's impact on salmon olfaction does not change the characterization of its ecological risk. With or without the research, diazinon was in big trouble.
In response to its own risk assessment, EPA did not sit on its hands. A little jawboning with diazinon's manufacturers led to voluntary removal of all urban indoor and outdoor uses of diazinon by 2003. Furthermore, some agricultural uses were also voluntarily dropped. Ironically, diazinon dietary exposures were safely below EPA's LOCs. Thus, diazinon seems to be the first OP yanked from a major use market largely owing to concerns of excessive ecological risk.
While diazinon smells stinky when ground through EPA's risk assessment mill, its hypothesized effect on salmon populations is dubious. Diazinon has been in use for nearly forty years. We now know that low levels of pesticides have been running off into streams since the beginning of their use. Therefore, a hypothesis of diazinon or any other pesticide affecting salmon populations would have to account for the much larger returns during the 1970s and 1980s than during the 1990s (3, 4). The hazards of diazinon over the years have not changed, but our detection capability and monitoring intensity have.
EPA is being sued because a coalition of groups have seized upon the hypothesis that low levels of diazinon affect salmon's sense of smell. They argue that EPA has not consulted with NMFS over these sublethal effects. I hate to come to EPA's defense, but the lawsuit seems much ado over a problem that has already been solved. Diazinon is gone from the market that generated the most exposures. EPA's overly conservative risk characterization methodology provides plenty of protection for salmon. Why waste money on lawyers when it could be used to fund further research that tests the interesting hypotheses about the remarkable olfactory capabilities of salmon?
Dr. Allan S. Felsot is an Environmental Toxicologist with the Food and Environmental Quality Laboratory on Washington State University's Tri-Cities campus. He can be reached at afelsot@tricity.wsu.edu or (509) 372-7365.
For the past two years the Pesticide Information Center (PIC) has taken a monetary look at Section 18 exemptions in Washington State. "Section 18s" are short-term pesticide registrations that allow a pesticide to be used in the case of an emergency condition. Section 18s provide for pesticide use outside the full-blown registration process provided for in Section 3 of the Federal Insecticide Fungicide and Rodenticide Act. For each Section 18 that is granted in Washington (27 in 2000), someone must gather data and prepare the initial request. The request is reviewed by the Washington State Department of Agriculture (WSDA) and is then passed along to the Environmental Protection Agency (EPA) where it must be reviewed again. With any luck, EPA grants the request and a Section 18 exemption is issued. All of this takes a bunch of time. Time on the part of the original requestor, WSDA, and EPA. The old catch phrase "time is money" begs the question, "Is it worth it?" We think so.
Economic data is included with every Section 18 request that is submitted to EPA. In this annual look back, we use this data to figure the value of Section 18s to Washington agriculture. Typically the economic estimates are given as net-per-acre returns but they may often include more than one set of numbers. For example, a Section 18 for pesticide use on strawberries may include one set of numbers assuming that the strawberry field has a three-year life span while another set assumes a four-year life. Other Section 18s will provide two sets of numbers assuming different percentage losses (examples include blueberry, sugarbeet, Christmas tree, and cranberry Section 18 requests made in 2000). All this just serves to underscore that these estimates are just that: estimates.
The total estimated worth of the year 2000 Section 18 exemptions to Washington agriculture is (drum roll, please):$466 million.
This is up from over $447 million in 1999 and $443 million in 1998. While $466 million sounds like a significant savings, and it is, even this estimate is likely to be low for the following reasons:
So a big thanks is due to all the preparers and reviewers of Section 18 packages, both inside and outside WSDA and EPA. $466 million--it's worth thanking about.
Jane M. Thomas is the Pesticide Notification Network Coordinator and is also known as Her Royal Highness the Queen Bee of Labels. She reigns from the Tri-Cities campus of WSU and can be reached at jmthomas@tricity.wsu.edu or (509) 372-7493.
Any actions that delay or block the intended use of a Section 18 pesticide could prove economically devastating to Washington agriculture. The Washington State Department of Agriculture (WSDA) believes Section 18 pesticides are at great risk to third party lawsuits under the Endangered Species Act. While WSDA does not suspect Section 18 pesticides are affecting threatened and endangered fish species, it is imperative that WSDA verifies this with a solid review process and valid compliance data to forestall additional federally mandated protections.
In March 2000, WSDA implemented the Section 18 Pesticide Use Compliance Project to prove that the existing WSDA Section 18 pesticide registration and compliance activities are adequately protective of threatened and endangered fish species. (See related article, "Defending Section 18s" in AENews No. 169, May 2000.)
During the first phase of the project, WSDA focused on collecting evidence that the Section 18 granting document, pesticide label, and applicable state laws and rules are being followed in critical fish habitat areas. WSDA conducted fifty-eight systematic Section 18 pesticide use compliance inspections. The inspections covered ten Section 18 pesticides affecting eight crops.
WSDA found through these fifty-eight inspections that the pesticides were being mixed, loaded, and applied according to granting document and label requirements, but that Worker Protection Standards (WPS) requirements were not routinely followed. The most common violations were failure to adhere to Restricted-Entry Interval (REI) requirements for short-term activities, not wearing all of the required protective clothing, and a cavalier approach to managing the posting of treated fields.
Of the fifty-eight applications inspected, fifty-six (ninety-six percent) were in compliance with label requirements and applicable laws and rules. WSDA issued Notices of Correction to the two growers cited for non-compliance and required that both growers initiate appropriate corrective action.
|
|
||||
|
|
||||
|
|
|
|
|
|
| Pre-Notification Calls |
|
|
|
|
| Inspections Completed* |
|
|
|
|
| Number in Compliance** |
|
|
|
|
|
|
||||
| *Expressed as a percentage of pre-notification calls. | ||||
| **Expressed as a percentage of completed inspections. | ||||
The second phase of the project began on November 13, 2000, when WSDA formally requested pesticide application and distribution records from individuals and dealers. WSDA is spot checking these documents to determine if records are being kept correctly and to further assure that the pesticides were used properly. The results of this review will augment the data gathered in the Phase One compliance inspections.
Unlike the site visits in Phase One, preliminary results from Phase Two record reviews indicate significant areas of concern. Numerous pesticide application records failed to supply the information required by the Washington Pesticide Application Act. Some indicated failure to apply Section 18 pesticides properly. WSDA has no evidence to suggest that any of these violations resulted in Section 18 products entering critical fish habitat, but proper use of Section 18 pesticides in all respects is critical for maintaining the availability of Section 18 pesticides to Washington growers. Phase Two is targeted for completion by the end of March, 2001.
In Spring 2001, the third phase of the project, WSDA will continue to conduct use compliance inspections and records review on Section 18 pesticides, adding the Entiat and Wenatchee River watersheds for a more complete picture of Section 18 pesticide use compliance. WSDA expects to enhance the information gathered in the 2001 Section 18 pesticide use compliance inspections with an affiliated water-sampling program. WSDA is currently exploring the possibility of coordinating water sampling and analysis with several on-going water quality assessment programs.
WSDA encourages review of Section 18 granting documents and labels to assure that these pesticides are used in accordance with requirements. It is crucial for Washington agriculture to have an expeditious Section 18 pesticide registration program to manage emerging pest or disease problems or mitigate the loss of previously available pest control tools.
Deborah Bahs is the Section 18 Use Compliance Project lead for WSDA. She can be reached at (360) 902-2037 or dbahs@agr.wa.gov. Additional information about the project is also available on the WSDA website at http://www.wa.gov/agr/pmd/pesticides/compliance.htm#sect18comp.
|
Improved public communications about forest vegetation management programs is needed to increase support for these important efforts. A key to improving communication strategies and methods of public involvement is a better understanding about how the public perceives the risk and acceptability of vegetation management technologies. Understanding how public perceptions differ from those of forest managers also can be valuable when developing communication strategies. Recent research from Canada provides some insight into these issues.
Public perceptions of risk and acceptability for nine alternatives to controlling forest vegetation were evaluated in a survey of 1,500 people in Ontario (1). The proportion of respondents indicating whether an alternative was difficult to control, potentially catastrophic, a problem for future generations, and a personal worry determined perceptions of risk for each vegetation management alternative. Ranking of alternatives from highest to lowest perceived risk was: aerially-applied herbicides, biological control, ground-applied herbicides, mulches, prescribed fire, heavy equipment, cover cropping, manual cutting, grazing animals (3).
Public acceptance was lowest for aerially-applied herbicides (18%) followed by ground-applied herbicides (37%), biological control (57%), prescribed fire (57%), mulches (65%), heavy equipment (72%), cover cropping (80%), grazing animals (82%), and manual cutting (89%). Public acceptability of various agents for biological control differed depending on the proposed agent. Natural plant toxins were viewed as most acceptable (73%) followed by microorganisms (42%), genetically-engineered organisms (39%), and viruses (21%).
There was a strong correlation between risk perception and acceptability of the alternatives for the general public and those in timber-dependent communities. These results suggest that stronger public support can probably be achieved for forest vegetation management programs that include non-herbicide alternatives.
Differences between the Ontario public and three groups of forestry professionals (government biologists, government foresters, and industry foresters) also were examined (4). Forestry professionals tended to be less supportive of some environmental values and forest management goals, to perceive everyday and forestry activities to be less risky, to be more trusting of science and government, and to be more accepting of forestry activities than the general public. Among the three groups of forestry professionals, industry foresters tended to be most different from the public followed by government foresters and government biologists. These differences reveal potential sources of conflict and miscommunication between the public and forest managers.
An analytical approach was used to determine which factors (perceptions of risk, environmental values, trust in forest managers, and support for forestry goals) were the best predictors of public support for herbicide use (2). Trust in those who manage decisions about the application of forest herbicides had the strongest influence on the level of support for herbicide use. Environmental values had the next strongest influence through its effect on support for timber management goals, perceptions of risk, and trust in management. This analysis suggests that current levels of trust in forest managers do not provide sufficient public support for future timber production that relies only on herbicide technology. Understanding how trust in forest managers is built and maintained appears to be vital for developing public acceptance of forest vegetation management programs.
Dr. Robert Wagner is with the Department of Forest Ecosystem Science at the University of Maine. This essay summarizes several published papers and was presented as an abstract at the 4th Pacific Northwest Integrated Vegetation Management Conference November 15, 2000. Dr. Wagner can be reached at bob_wagner@umenfa.maine.edu or (207) 581-2903.
|
|
Washington Pest Consultants Association organizes an annual series of collection dates and sites for empty pesticide containers. The table below shows April and early May dates only, a full schedule is being deveoped for dates through October; watch future editions of AENews for the rest of this schedule as it is established. Dates and locations are subject to change; it may be wise to confirm with a telephone call before participating. Contact telephone numbers for specific events are given in the table below. For general questions, or if you are interested in hosting an event at your farm, business, or in a central location in your area, contact Northwest Ag Plastics representative Clarke Brown at (509) 965-6809 or David Brown at (509) 469-2550 or dbrownwash@msn.com.
| DATE | TIME | LOCATION | SPONSOR | CONTACT | PHONE |
| 4/23 | 10a-1p | Pasco | Air Trac | Gerald Titus | 509-547-5301 |
| 4/24 | 8a-11a | Eltopia | Wilbur Ellis | Vern Records | 509-297-4291 |
| 1p-3p | Eltopia | EA WA Spray Svc | Willis Maxon | 509-297-4387 | |
| 4/25 | 8a-10a | Pasco | Pfister Crop Care | Steve Pfister | 509-297-4304 |
| 1p-3p | Connell | B&R Crop Care | Chris Eskildsen | 509-234-7791 | |
| 4/26 | 8p-10p | Othello | Conner Flying Inc. | Mark Conner | 509-488-2921 |
| 1p-3p | Royal City | Cenex | Ted Freeman | 509-346-2213 | |
| 4/27 | 8p-10p | Bruce | Simplot | Chuck Spytex | 509-488-2132 |
| 1p-3p | Othello | B&H Chemical | Larry Hawley | 509-488-6576 | |
| 5/1 | 8a-11a | Mount Vernon | Wilbur Ellis | Marty Coble | 360-466-3138 |
| 5/2 | 8a-11a | Conway | Cenex/Tronsdal Air Svc. | Will Cox | 360-445-5015 |
| Kevin Belisle | 360-661-0422 | ||||
| 12p-2p | NE Seattle | WA Tree Service | Ron Angle | 206-362-9100 | |
| 5/3 | 8a-11a | Puyallup | WSU Res Stn | Roy Jensen | 253-445-4517 |
| 8a-10a | Tacoma | Wilbur Ellis/DOT | Randy Knutsen | 253-351-6591 | |
| Dave Patterson | 253-589-7255 | ||||
| 5/4 | 8a-10a | Centralia | Lewis County Public Works | John Prigmore | 360-740-1193 |
| 8a-10a | Vancouver | WSU Res Stn | Martin Nicholson | 360-576-6030 | |
| 1p-3p | Chehalis | Farm & Forest Helo Svc | Dan Foster | 360-262-3197 | |
| 3p-4p | Morton | DOT | Craig Robbins | 360-496-5516 | |
| 5/14 | 9a-11a | George | Dependable Spray | Ceourt Rylaarsdam | 509-785-2061 |
| 1p-3p | Quincy | Cobia Spray Svc | Jim Cobia | 509-750-2888 | |
| 5/15 | 8a-10a | Quincy | Wilbur Ellis | Dale Martin | 509-787-4433 |
| 1p-3p | George | Randy Wentworth | 509-878-1565 | ||
| 5/16 | 8a-10a | Quincy | Quincy Farm Chem | Ron Turner | 509-787-3556 |
| 1p-3p | Quincy | Simplot | Butch Creameans | 509-787-1571 | |
| 5/21 | 8a-10 | Waverly | Wilbur Ellis | Monte Bareither | 509-283-2432 |
| 1p-3p | Tekoa | McGregor Co | Charles Wedin | 509-284-5391 | |
| 5/22 | 8a-10a | Oakesdale | Wilbur Ellis | Jerry Jeske | 509-285-4511 |
| 1p-3p | Garfield | Cascade Flying Svc | Doran Rogers | 509-635-1212 | |
| 5/23 | 8a-10a | Palouse | Dale's Flying Svc | Dale Schoeflin | 509-878-1531 |
| 1p-3p | Dusty | Dusty Farm Coop | Chris Crider | 509-397-3111 | |
| 5/24 | 8a-10a | Warden | Kilmer Crop Dusting | Terry Kilmer | 509-349-2491 |
| 1p-3p | Bruce | Cenex | Lori Anderson | 509-488-5261 |
Washington State University offers PRE-LICENSE courses (for those who do not have a license and need one) and RECERTIFICATION courses (for those who need to renew their current licenses). Fees are $35 per day if postmarked 14 days before the program, otherwise $50 per day. This fee DOES NOT include WSDA license test fee, which ranges from $25 to $170; for information on testing and fees, contact WSDA at (360) 902-2020 or http://www.wa.gov/agr/pmd/licensing/Licensing.htm. Recertification courses offer 6 credits per day.
Grape mealybugs, Pseudoccus maritimus (Homoptera: Pseudococcidae), are an increasing concern for Washington grape growers, primarily due to the fact that they are suspected to vector grapevine leafroll disease. We speculate that the mild winters and springs we have experienced over the past several years have contributed to the recent increase in grape mealybug infestations. Mild winters decrease overwintering mortality while mild springs likely increase the insect's developmental rate.
Grape mealybugs complete two generations per year. They overwinter as eggs or first instar crawlers in egg sacs under the rough bark on the trunk of grapevines. WSU Professor Emeritus Dr. Wyatt Cone observed that, if temperatures are mild in the fall, crawlers disperse from their egg sacs to overwinter in individual coverings or protective cases known as "hibernacula." The crawlers then migrate to and feed at the base of grape buds as the buds break dormancy in early spring. In late spring, immature mealybugs feed under the papery bark of two-year wood. Females in the first generation mature by early summer, then mate and move back to protected locations under bark and proceed to spin an ovisac and lay up to several hundred eggs. These eggs hatch in mid-summer and the resulting nymphs disperse to feed on shoots and grape clusters. These second-generation mealybugs are the ones that cause damage. By late summer, the mated second-generation adult females migrate to positions under the rough bark of vines, where they spin their ovisacs and lay their eggs, renewing the cycle.
|
|
|
|
 |
 |
Worldwide, grapevine leafroll disease is the most economically important virus disease of grapevines; it accounts for 62% of grape loss due to viruses. Several mealybug species are cited in the literature as confirmed vectors of grapevine leafroll virus. Two confirmed vector species, obscure mealybug (Pseudococcus viburni) and longtailed mealybug (Pseudococcus longispinus) are indigenous to grape-growing regions of the Western United States. Grape mealybug has not been confirmed to vector grapevine leafroll disease; however, there are no data indicating grape mealy bug cannot vector this disease. Basically, no one has ever checked. This spring, we intend to look into this possible connection.
A recent survey of grape growers throughout Washington State indicated that 7.3% percent of the vines currently in the ground are infected with an agent of grapevine leafroll disease. This disease not only reduces grape yield, but also has a negative impact on fruit quality and potentially on wine quality. Management of this disease in Washington vineyards includes both ameliorating the economic impact of the disease on vines already affected and minimizing infection of grapevines currently free of the disease.
Successful management of this disease depends upon accurate diagnosis and appropriate modification of vineyard management to reduce its spread to adjacent vines. In some vineyards, the number of vines affected with leafroll disease can be significant, and roguing infected plants may not be an economically viable option. Under such circumstances, modifying horticultural practices to diminish crop loss associated with this disease may be a more appropriate response. Such practices may include canopy management or nutritional management.
At this time, Washington State University's primary recommendation for control of grape mealybug infestations calls for a delayed dormant season (April) application of chlorpyrifos in a tank mix with petroleum spray oil. There is some concern regarding the long-term availability of chlorpyrifos due to regulatory actions that may be imposed by the Food Quality Protection Act of 1996. The Washington Association of Wine Grape Growers, Dow AgroSciences (the manufacturer of chlorpyrifos), and grape researchers have taken a proactive stance to retain the use of chlorpyrifos for suppression of grape mealybug populations. We are working with several candidate insecticides and petroleum spray oils to determine their efficacy against grape mealybug.
A comprehensive study of the impact of grape mealybug infestations on wine grapes in Washington State is currently being proposed to the Washington Wine Advisory Commission. The proposed research includes both the direct impact of grape mealybug on grape production and the ability of grape mealybug to transmit grapevine leafroll disease. If the grape mealybug is found to be a vector of grapevine leafroll disease, then the level of control must be stringent to protect disease-free vines. Control efforts, mostly in the form of insecticide applications, have increased over the past several years. Insecticide applications for mealybug control could potentially be contributing to secondary pest outbreaks. Increased knowledge of grape mealybug biology will enable more effective use of existing chemical controls and will help us understand the most effective use of biological and cultural controls as well.
Dr. Kenneth C. Eastwell is a Virologist with Washington State University; Dr. Douglas B. Walsh and Dr. David G. James are Entomologists with Washington State University. All have offices at the WSU Irrigated Agriculture Research and Extension Center (IAREC) in Prosser, and can be reached at (509) 786-2226, or keastwell@tricity.wsu.edu, dwalsh@tricity.wsu.edu, or djames@tricity.wsu.edu, respectively. Dr. Walter J. Bentley is the Area IPM Advisor at the University of California at Davis. He can be reached through the UC Davis switchboard at (530) 752-1011 or by e-mail at wjbentley@ucdavis.edu.
The Pesticide Notification Network (PNN) is operated by WSU's Pesticide Information Center for the Washington State Commission on Pesticide Registration. The system is designed to distribute pesticide registration and label change information to groups representing Washington's pesticide users. PNN notifications are now available on our web page. To review those sent out in the month two months prior to this issue's date, either access the PNN page via the Pesticide Information Center On-Line (PICOL) Main Page on URL http://picol.cahe.wsu.edu/ or directly via URL http://www.pnn.wsu.edu. We hope that this new electronic format will be useful. Please let us know what you think by submitting comments via e-mail to Jane Thomas at jmthomas@tricity.wsu.edu.
W.S.U. Pullman Home Page Comments and questions: cdaniels@tricity.wsu.edu Technical Assistance: scoates@tricity.wsu.edu Copyright © Washington State University / Disclaimer Electronic Publishing and Appropriate Use Policy University Information: 509/335-3564
