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Alternative Chemistries
Growers of cruciferous root crops are highly dependent on chlorpyrifos for control of cabbage maggot, as they have no tolerance for cabbage maggot; a single maggot can generate an unmarketable root. Growers currently apply chlorpyrifos prophylactically at the highest labeled rate throughout the season. Forty one percent of broccoli acreage and 31 % of cauliflower acreage is treated with chlorpyrifos (Quarles 2000). There are currently no effective chemical alternatives to Lorsban labeled for use on cruciferous crops in Oregon.

Jump to:  Trial Summaries: Radish  |  Trial Summaries: Rutabaga  |  Trial Summaries: Turnip  |  Trial Summaries: Broccoli  |  Chlorpyrifos Persistence  |  Chlorpyrifos Risks  |  Lorsban 4E effectiveness

photo of tractor applying chemicals Formulation and method of application are among factors that influence the persistence of chlorpyrifos in soil (Getzin, 1985). Getzin reported that chlorpyrifos lightly incorporated in the soil gave better cabbage maggot control than row-band surface treatments. Residual life of surface applications were extended with immediate post treatment sprinkler irrigation; however, volatilization and diluted rates can occur. However, even when Lorsban is treated 'correctly' to the soil, a proportion of the pest population can survive the treatment as shown in our data. If a chemical is not applied 'correctly', then for all intents and purposes, the crop is untreated and no conrol will take place and large numbers of flies will then be added to subsequent generations.

second photo of tractor applying chemicals Increasing overall insecticide use with increasing pressure of cabbage maggot comes the chance of producing fly strains resistant to current insecticides. It is unwise to allow cabbage maggot populations to increase in areas growing Brassicas. No insecticides in the US are labeled for used once an outbreak is underway. The current chemical control in the Pacific Northwest consists of over-the-row or in-furrow applications of Lorsban 4E (organophosphate; chlorpyrifos) for below-ground crops such as rutabagas and turnips.

third photo of tractor applying chemicals Considerable work has been carried out over the past 5 years, 2000-2005 at OSU NorthWest Research and Extension Center (NWREC) in Aurora, Oregon.

Research trials have been focusing on finding new chemical families, alternative application techniques including seed-treatments, in-furrow application, and over-the-row broadcast, and searching for ways to increase the amount of insecticide that reach the target pest and to decrease the amount of insecticide entering the environment at large.

Below are brief summaries of 19 trials testing treatments for control of the cabbage maggot in root crops (turnips, rutabaggas, radish) and broccoli.

Trial Summaries: 2000-2005
   •Radish — 3 trials
      Aug. 2, 2000
      May 14, 2002
      May 1, 2003
   •Rutabaga — 4 trials
      July 10, 2001
      May 1, 2002
      May 14, 2002
      July 9, 2002
   •Turnip — 14 trials
      Aug. 7, 2000
      July 10, 2001
      May 1, 2002
      May 14, 2002
      July 7, 2002
      July 9, 2002
      May 22, 2003
      May 29, 2003
      July 14, 2003
      Aug. 25, 2003
      May 20, 2004
      July 7, 2004
      July 29, 2004
      July 25, 2005
   •Broccoli — 1 trial
      Sept. 1, 2005

Chlorpyrifos Persistence

Chlorpyrifos Risks
Chlorpyrifos, an organophosphate, is widely used in the United States with more than 14.4 million pounds applied to cropland each year (USGS, 1997). Chlorpyrifos can enter the environment by volatilization and run-off after application. Following a rainfall event, streams near agricultural fields have been shown to receive concentrations of greater than 2.0 ppb chlorpyrifos in runoff 160 days after pesticide application (Smith et al. 1994). Due to the low solubility (1.4 mg/L) and hydrophobic nature (Log KOW 3.31-5.27), chlorpyrifos rapidly partitions from the water and adsorbs to sediment particles (Montgomery 1993). In the sediment, chlorpyrifos has a long half- life (60-100 days) making exposure to aquatic benthic organisms possible (Tomlin 1994). Chlorpyrifos exerts its toxicity by inhibiting acetylcholinesterase, an important enzyme that modulates the concentration of the neurotransmitter acetylcholine (2003 Report, #MS19B: Chemical Mixtures: Consequences of West Nile Virus Eradication on Water Quality)

1) Chlorpyrifos has low solubility (1.4 mg/L) and does not dissolve easily in water. It partitions from water and absorbs to sediment. When in sediment it has a long half-life (60-100days). When applied on foliage it has a half-life of 10 to 14 days. When the pH of water is 7.0 or higher, the persistence is less, 35-78 days.

2) This chemical is active by contact, ingestion, and vapor action.

3) When applied to moist soils, the volatility half-life of chlorpyrifos was 45 to 163 hours, with 62 to 89% of the applied chlorpyrifos remaining on the soil after 36 hours.

4) In another study, 2.6 and 9.3% of the chlorpyrifos applied to sand or silt loam soil remained after 30 days.

5) Breakdown in water: The concentration and persistence of chlorpyrifos in water will vary depending on the type of formulation. For example, a large increase in chlorpyrifos concentrations occurs when emulsifiable concentrations and wettable powders are released into water. As the pesticide adheres to sediments and suspended organic matter, concentrations rapidly decline. The increase in the concentration of insecticide is not as rapid for granules and controlled release formulations in the water, but the resulting concentration persists longer. Volatilization is probably the primary route of loss of chlorpyrifos from water. Volatility half-lives of 3.5 and 20 days have been estimated for pond water. The photolysis half-life of chlorpyrifos is 3 to 4 weeks during midsummer in the U.S. Its change into other natural forms is slow. Research suggests that this insecticide is unstable in water, and the rate at which it is hydrolyzed increases with temperature, decreasing by 2.5- to 3-fold with each 10 C drop in temperature. The rate of hydrolysis is constant in acidic to neutral waters, but increases in alkaline waters. In water at pH 7.0 and 25 C, it had a half-life of 35 to 78 days.

6) Residues remain on plant surfaces for approximately 10 to 14 days. Data indicate that this insecticide and its soil metabolites can accumulate in certain crops.

7) US Geological Survey Circular 1161, Water Quality in the Willamette Basin, reported 50 pesticides, and 10 of those pesticides (e.g. chlorpyrifos) exceeded criteria established by the USEPA for the protection of freshwater aquatic life from chronic toxicity, including chlorpyrifos (Wentz et.al. 1998)

8) Phosphates dissolve less readily. Eroded soil can transport considerable amounts of attached phosphates to streams, rivers and lakes. Chlorpyrifos was the third most frequently detected insecticide in streams draining from agricultural lands.

9) USGS & USEPA are now working together to target this pesticide for occurrence in monitoring and guidance, including health advisories, as required by safe drinking water act.

10) Data has shown risks of neurotoxic effects from exposure and inhalation, and acute and reproductive risks to many non target terrestrial and aquatic organisms neurotoxicity to young animals. This prompted EPA to invoke the 10-fold safety factor for chlorpyrifos, which has led to elimination of some uses.

11) Growing public concern of food safety, with increases in federal regulations, to monitor for allowable residues on certain crops

12) Organophosphates can be acutely toxic to those growers that apply it. Chronic toxicity can be a problem where there are many sources of exposure to the same pesticide. After a pesticide is applied, there is a 3-day and 21-day wait for harvesting.

13) Top priority to reduce the risks of using this pesticide regularly including resistance, worker protection, aquatic organism destruction. (http://www.epa.gov/espp/wtc/maps.htm)

14) A citizen suit was filed under the Endangered Species Act against EPA by a group of environmental organizations (Washington Toxics Coalition, et al. v. EPA). In response, the United States District Court for the Western District of Washington issued on January 22, 2004, an order that establishes pesticide buffer zones. Buffer zones are areas adjacent to certain streams, rivers, lakes estuaries and other water bodies, in which the court is ordering certain pesticides not be used. Generally, the buffers established by the Court are 20 yards for ground application and 100 yards for aerial application, adjacent to certain "salmon-supporting waters" in Washington, Oregon and California. The order applies to pesticide use in these three states, for any product containing one or more of the pesticides subject to the court order.

15) The Court Order which became effective on February 5, 2004, defines salmon-supporting waters as certain water bodies below the "normal high water mark" and thus, any buffer should be measured from that normal high water mark.

16) Do not use within 20 yards of salmon-supporting waters for ground applications or for any applications of a granular formulation. Salmon-supporting waters include all relevant estuaries in addition to many streams and rivers.

Lorsban 4E effectiveness (untreated vs treated beds)
We studied the effectiveness of Lorsban 4E by comparing damage in unreated Brassica bedsfor control of cabbage maggots in 2002–2005. There was no significant differences in root damage caused by cabbage maggots in the chemically-treated crop (standard Lorsban 4E treatment) and the untreated crop (n=25 fields) of Brassica plants. The percent root damage in the Lorsban-treated plots averaged 23.1% loss and the untreated plots had an average of 24.7% root damage loss.

Table 1. The percent root damage loss by cabbage maggots in treated and untreated root crops.