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Could farmers face a total loss of chlorpyrifos?

Crop damage to almonds from insects
<p>Almond growers rely on chlorpyrifos products to control crop damage done by insects feeding on the maturing crop. According to University of California experts, this sort of clear gumming of the nuts is indicative of feeding damage done by leaffooted bug and stink bugs.</p>
Chlorpyrifos is a restricted use pesticide in California EPA proposal could ban product use in the United States Court ruling at the center of the potential ban

The Environmental Protection Agency (EPA) continues to move forward with its plan to revoke all tolerance levels for chlorpyrifos, which will eliminate the chemical from insecticides in the United States.

Public comment on the proposed rule closed in early January.

The move comes after the 9th Circuit Court effectively ordered the EPA to revoke its use.

According to the agency, the EPA indicated its intention in June 2015 to propose revoking chlorpyrifos tolerances by April 15. This came in response to a petition by the Natural Resources Defense Council and the Pesticide Action Network North America over identified drinking water concerns.

The court ordered EPA in late 2015 to either deny the petition by the two groups, issue a proposed revocation or issue a final revocation rule. The EPA says it “is not denying the petition because at this time we are unable to make a safety finding based on science as it stands.”

Furthermore, the EPA claims it cannot issue a final rule “because we have not proposed it and have not completed our refined drinking water assessment.”

As a result, the EPA in November and December opened public comment on its proposal to revoke all tolerances for the insecticide. Meanwhile, the agency says it will update its analysis of chlorpyrifos to see if current regulations address the potential for adverse impacts on infants and children.

The latest action comes more than a year after the release of a report by the University of California Statewide Integrated Pest Management Program (UC IPM) on the importance of chlorpyrifos as an insecticide in four major California crops: alfalfa, almonds, citrus and cotton.

The California Department of Pesticide Regulations (DPR) contracted with UC IPM to determine the value chlorpyrifos has in IPM systems within the four commodities. Representatives from each of the four commodities worked with UC IPM staff to address chlorpyrifos concerns and issue recommendations to DPR.

Chlorpyrifos is an issue for those representing the four commodities because 61 percent of the total use of the insecticide in the state between 2002 and 2012 was recorded in the four crops, according to the report.

It is also an important insecticide to national corn and soybean farmers.

Restricted use

Since the report was commissioned California made chlorpyrifos a restricted use pesticide in an attempt to better control its impacts on the environment.

According to the report, chlorpyrifos is an organophosphate insecticide that has been registered and widely used for more than 40 years. In recent years, there has been public and legislative interest in addressing concerns around its use and its impacts on humans and the environment.

Lori Berger, an entomologist with the UC IPM and the project coordinator for the statewide study, said the discovery of chlorpyrifos in surface waters became an issue with regulators.

Part of what the report addresses includes alternative IPM practices to chlorpyrifos in the four crops. Questions answered in the report looked at the efficacy of other products and the effectiveness of biological control, cultural practices and best management practices to control problematic pests in the four crops.


At the time the report was written – it was submitted to DPR in late 2014 – alfalfa had the largest acreage of the four crops in California at nearly one million, though almond acreage was nearing that figure. Of the four it was the most widespread across the state as alfalfa is grown from the low desert region near the borders of Mexico and Arizona to the intermountain region of northern California.

The report breaks down the need for Chlorpyrifos into three tiers, with the first tier being the most critical to growers. In other words, its use is required to control key pests as there are few or no other IPM alternatives to address the pests.

In alfalfa, pests in the most critical tier include the alfalfa and Egyptian weevils, blue alfalfa aphid and the cowpea aphid.


Almond acreage since the report was written has climbed to over a million bearing acres, according to the latest statistics available, surpassing alfalfa in total acreage, which is forecast this year to be less than 900,000 acres.

Almond production is limited to the Sacramento and San Joaquin Valleys and is valued at about $6 billion.

Critical pests in the two valleys include the Navel orangeworm, web spinning mites, leaffooted bug, the stink bug complex, ants, the peach twig borer and oriental fruit moth. Some are more critical to control than others depending on the growing region.

The leaffooted bug and stink bug are considered Tier 1 pests, according to the report, making the need for chlorpyrifos vital to almond growers seeking to control those pests.

According to DPR statistics, the use of chlorpyrifos in almonds from 2002-2012 was relatively unchanged, in spite of a steady increase in almond acreage during the period. There was a considerable spike in its use in 2006 and 2007, but that had to do with pest issues growers dealt with during that period.


California citrus production covers more than 250,000 acres in the south half of the state. Citrus is a complex crop with regional IPM programs, according to the report. Moreover, citrus experiences the highest rate of chlorpyrifos use per application of the four crops because complete coverage of branches, trunk and dense foliage with high water volumes is needed.

Critical uses for chlorpyrifos in citrus are limited primarily to ants as there are no other alternatives to control sugar and protein-eating ants. The report goes on to say that as neonicotinoid insecticides became available, chlorpyrifos use declined.

From 2008 to 2012, chlorpyrifos use in citrus increased to control California red scale, which is not effectively controlled by neonicotinoid insecticides.

For southern California growers using biological control measures to help control the Asian citrus psyllid, control of the Argentine ant is crucial because it is highly protective of ACP nymphs and will attack the two parasitic wasps employed to help control ACP numbers.

Though there are multiple modes of action available to address the ACP, the report says chlorpyrifos “may be the best choice for regulating new invasive pests at certain times of the year,” including ACP.

This is important as the pest vectors a deadly bacterial disease in citrus called Huanglongbing, which has been found in residential neighborhoods in southern California.

Chlorpyrifos is also important for citrus growers contending with export issues. Fruit shipped to Korea is treated with chlorpyrifos to prevent egg infestations from the Fuller rose beetle, according to the report. Chlorpyrifos is the only insecticide that will kill the beetle and California red scale at the time of year applications are needed.

The report further credits the use of chlorpyrifos as a good fall-treatment choice for ACP because it has established international maximum residue limits (MRL); it acts quickly and is relatively safe on natural enemies. It is also said to be more efficacious than alternative pesticides.

The report highlights the MRL issue as particularly critical for citrus growers as a significant percentage of the California crop is exported. The report goes on to state that growers can lose export markets if products with existing MRLs are removed from labels and alternative products have not been approved by trading partners.


The two key pests cotton growers must contend with – the cotton aphid and sweet potato whitefly – have limited to no alternative control measures, according to the report.

This is crucial because both pests can cause issues in cotton resulting in ginning and milling difficulties through sticky residue left on the cotton by these pests. Sticky cotton can cause the loss of markets, which cotton executives say can be difficult to build back once the issue has been discovered in a growing region.

The report states that chlorpyrifos use in cotton is driven largely by the ineffectiveness of neonicotinoid treatments late in the season, along with the loss of older chemical compounds including organophosphates, carbamates and organochlorines.

Even in those cases where multiple modes of action are available, researchers point to the use of chlorpyrifos as an important rotational tool to avoid resistance issues. It’s also been shown to be effective on multiple pests, which experts say can reduce the overall use of pesticides.

Based on the report, chlorpyrifos plays a unique and important role in IPM for various pests. Each of the four crop teams that helped with the report emphasized the active ingredient needs to remain available to growers as an effective option to manage critical pests or when a combination of pest pressures occasionally occurs.

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