July 25, 2006

 

To:  EPA

From:  Glen Koehler, University of Maine Cooperative Extension

Re:  Proposed changes to Imidan labels for use in apple orchards

 

 

Greetings,

        As coordinator of the University of Maine Apple IPM Program, I am sending the following information and observations in hopes of providing a Maine apple perspective for EPA deliberations on the proposed Imidan label changes.  Plum curculio and apple maggot are the key pests that drive postbloom insecticide use decisions in Maine apple orchards.

 

 

Use of Imidan and Guthion alternatives for plum curculio control in New England

        In order of number of New England growers reporting use: Sevin, Asana, Avaunt, Danitol, Surround.

 

Efficacy ratings below are from the Cornell University and Penn State University (PSU) tree fruit pest management guides ( http://www.nysaes.cornell.edu/ent/treefruit/ and http://www.cas.psu.edu/docs/CASDEPT/hort/TFPG/default.htm ).  Cornell uses a three-point scale (Good, Fair, Poor).  Penn State uses a four-point scale (Excellent, Good, Fair, Poor).  The PSU Excellent and Good ratings were combined to create this list.

 

        Imidan has the highest rating given by both the Cornell and PSU guides for plum curculio control.  Alternatives to Imidan and Guthion, sorted by efficacy rating:

        Excellent or Good: Asana**, Avaunt, Calypso, Warrior**.  Actara (PSU - Good),  Sevin (PSU - Good), Danitol** (PSU - Good), Diazinon* (PSU - Good), Permethrin** (PSU - Good).

        Fair: Diazinon* (Cornell), Dimethoate*, Lannate* & **, Sevin* (Cornell), Surround, Thiodan (PSU, Cornell - not effective).

 

 

Use of Imidan and Guthion alternatives for apple maggot control in New England

        In order of number of New England growers reporting use:  Sevin, Danitol, Asana, Avaunt, Surround, SpinTor/Entrust.

 

        Imidan has the highest rating given by both the Cornell and PSU guides for apple maggot control.  Alternatives to Imidan and Guthion, sorted by efficacy rating:
        Excellent or Good: Asana**, Assail.  Calypso (PSU - Good), Danitol** (PSU - Good), Diazinon* (PSU - Good), Dimethoate*, Sevin* (PSU - Good), Warrior** (PSU - Good).

        Fair: Avaunt, Lannate* & **, Sevin* (Cornell), SpinTor/Entrust, Surround.

 

 

Notes for above listings

* = organophosphate or carbamate (Diazinon, Dimethoate, Lannate, Sevin).  A primary intent of restricting Imidan use is to reduce overall worker exposure to residues of the organophosphate/carbamate group.  Curtailed Imidan use that leads to increased use of another member of this group does not seem to support that objective.

 

** = pyrethroid or Lannate.  Use of these materials is considered disruptive to naturally occurring populations of beneficial arthropod pest predators and parasites.  Permethrin cannot be used after petal fall.   

 

Grower insecticide use reports are from the New England Apple Pest Management Survey, 2004.  http://pronewengland.org/INFO/PROInfoSurvey.htm

 

Materials are listed by brand name.  Alternate brand names with the same active ingredient as Diazinon, Dimethoate, Sevin, and Thiodan are available.

  

Actara, Assail, and Calypso are members of the same resistance class (thiacloprids).  Making more than three consecutive applications before rotation to a different insecticide resistance class is discouraged.  Neither plum curculio or apple maggot is prone to developing insecticide resistance due to large wild populations.  However, insecticide applications for these pests are also relied upon to suppress codling moth, obliquebanded leafroller, tentiform leafminers and other pests that have shown the ability to develop resistance.

 

Sevin acts as a thinner.  Repeated use for insecticidal purpose against plum curculio will not be possible in most blocks because of the risk of undesired additional thinning.  Sevin is only rated fair against European apple sawfly, a serious pest that coincides with plum curculio at petal fall.

 

Surround acts as a repellent.  It requires roughly twice as many applications as the other materials listed to provide its rated level of suppression (Fair).  Late-season use of Surround to repel apple maggot can result in undesirable visible residue at harvest.

 

 

Relative Insecticide costs

 

        Rates are based on the 2006 Pest Management Guidelines for Commercial Tree Fruit Production, Cornell University, and product labels.

 

As a two-dimensional measure, “acre” is not fully representative for a three-dimensional crop such as apple orchards, but some pesticide labels only state dosage on a per acre basis.  In those cases, the rate per acre was assumed to apply for orchards requiring 400 gallons dilute spray per acre.

 

Insecticide and miticide costs are based on Maine vendor prices as of May 2005.  Prices do not reflect volume or early purchase discounts, but they also do not include 2006 price increases.  Estimated costs per acre were rounded to nearest dollar for clarity.

 

Insecticide

Dose per 100 gallons dilute spray

Cost for 300 gallons per acre sized trees

Materials with Excellent or Good Efficacy Rating for either or both plum curculio and apple maggot

Imidan 70WP

.75 – 1 lb.

$21 - $27

 

 

 

Avaunt 30WDG

1.5 ozs.

$28

 

 

 

Actara 25WDG

1.38 ozs.

$28

Assail 70WP

0.85 oz.

$42

Calypso 4F

1 – 2 fl. ozs.

$25 - $51

 

 

 

Asana XL 0.66EC

2 – 5.8 fl. ozs.

$5 – $16

Danitol 2.4EC

2.67 fl. ozs.

$11

Permethrin 3.2EC

1 – 4 fl. ozs.

$3 - $12

Warrior 1CS

0.64 – 1.28 fl. ozs.

$5 - $10

 

 

 

Sevin XLR Plus 4EC (PSU)

1.5 – 3 quarts

$11 - $22

Diazinon 50WP

1 lb.

$23

Dimethoate 400

16 fl. ozs.

$16

 

 

 

Materials with Fair Efficacy Rating

Lannate 90WSP

4 ozs.

$19

Sevin XLR Plus 4EC (Cornell)

1.5 – 3 quarts

$11 - $22

 

 

 

SpinTor 2SC

1.25 – 2.5 fl. ozs.

$21 - $43

 

 

 

Surround

25 – 50 lbs. per acre per application

$28 - $42* - roughly twice as many applications needed as for insecticides

 

 

 

Thionex 50WP

1 lb.

$28

 

 

Key Summer Miticides

Dose per 100 gallons dilute spray

Cost for 300 gallons per acre spray

Acramite 50WS

3 – 4 ozs.

$41 - $54

Apollo 4SC

1 – 2 fl. ozs.

$38 - $76

Kanemite 15SC

7.75 ozs.

$49

Nexter 75WS

1.1 – 1.3 ozs.

$29 - $35

Savey 50DF

0.75 – 1.5 ozs.

$42 - $84

Vendex 50WP

4 – 8 oz.

$18 - $36* - may require multiple applications

Zeal  72WDG

0.5 – 0.75 oz.

$45 - $67

 

 

Observations on likely outcomes from the proposed label changes

  

Plum curculio management

 

Imidan and Guthion (azinphosmethyl) are the predominant insecticide choices for plum curculio control in New England, accounting for 73% of grower reported insecticide selections for this pest in 2004.  Plum curculio control usually requires two or three sequential applications per year.  With frequent heavy rains, four applications may be needed. 

 

With Guthion no longer available after 2010, growers relying on pick your own (PYO) sales for whom Imidan use becomes prohibited or operationally impractical (because of mixed or unknown distribution of PYO and worker-harvested trees) would likely turn to one of the pyrethroids, or select from Actara, Avaunt, or Calypso for plum curculio control. 

 

Most blocks need thinning each year.  A single application of Sevin at the insecticidal rate could serve as a combined thinner/plum curculio spray.  Sevin would provide protection against plum curculio, but for a shorter interval than an Imidan application, up to about 7 days.

 

A decision to replace Imidan for other plum curculio sprays with a pyrethroid would involve consideration of their low initial cost versus the risks caused by their harmful effects on beneficial arthropods.  Increased pyrethroid use could lead to additional summer pesticide applications for mites, leafminers, or other pests.  Miticides are generally more expensive than insecticides.

 

 

Apple maggot management

 

        Imidan and Guthion (azinphosmethyl) are the predominant insecticide choices for apple maggot control in New England, accounting for 76% of grower reported insecticide selections for this pest in 2004.  The need for apple maggot control typically generates two or three July and August insecticide applications. 

 

        Without Imidan or Guthion, there would likely be an increase in the use of pyrethroids, Assail, Calypso, and to a lesser extent SpinTor, for apple maggot control.  As with plum curculio, a decision to switch to pyrethroid products would involve consideration of their low initial cost versus potentially higher long-term costs.

 

Coincident pests

 

        In addition to its excellent efficacy rating against plum curculio and apple maggot, Imidan also provides excellent control of codling moth, lesser appleworm, green fruitworms, redbanded leafroller, and (in Maine where resistance is not documented) obliquebanded leafroller.  Some of the alternative materials listed above are less effective, or have unknown efficacy, against these other pests which require control from sprays directed at plum curculio and apple maggot.  Thus, additional applications with materials effective for those pests might be required if Imidan is not considered a viable option because of label restrictions.



Concluding comments

 

Approximately 13% of New England apples are sold as 'pick your own'.  With higher net return per bushel, pick your own sales account for an even larger portion of revenue.  For many small orchards, pick your own is an essential market.  Given potentially harmful impacts from losing Imidan as a viable option for many Maine apple growers caused by a ban on use in pick your own orchards, such action should be justified by the toxicological benefits expected.  I have not seen such justification.  I do not see how a prohibition on use in pick your own orchards would have much toxicological benefit given that pick your own customers spend so little time in orchards on an annual basis relative to commercial field workers and harvesters.  Therefore, I request that EPA reconsider the prohibition on use of Imidan in pick your own orchards.

 

As for the proposed extension of the Restricted Entry Interval to 7 days, I am not in a position to question the rationale for that change.  I do know that such a change would make Imidan a less viable option for Maine apple growers due to interference with monitoring and other orchard activity.

 

Environmentally responsible and economically viable apple orchard pest management requires regular monitoring to notice developing pest problems before serious damage occurs and while suppression can be achieved with minimum intervention.  Applying pesticide on an “as needed only” basis instead of a calendar-based approach also requires regular monitoring.  Trap-out, mating disruption, perimeter-only sprays, and other reduced-pesticide strategies require frequent monitoring.  Cultural management methods such as hand thinning, sanitation pruning to remove diseased branches, summer pruning, mowing, irrigation, crop yield assessment, and maturity testing reduce the need for pesticides and/or improve profitability.  All of these activities require worker presence in the orchard.

 

A 7-day REI would effectively prohibit such activity to a large degree.  Depending on the specific requirements, it can be uncomfortable to the point of being dangerous to wear personal protective equipment for summer work in an orchard.  In addition, complying with the reporting and communication requirements can be a considerable burden.  If a 7-day REI for Imidan is required to protect worker safety, then so be it.  But if the toxicology is ambiguous, then I request that EPA reconsider the proposed change.  A 7-day REI would greatly reduce the utility of Imidan as an insecticide option that is compatible with IPM methods to minimize pesticide reliance and expense in Maine apple orchards. 

 

 

Respectfully submitted,

Glen Koehler

 

 

Glen Koehler
University of Maine Cooperative Extension

Pest Management Office
491 College Avenue
Orono, ME  04473
Voice:  207-581-3882
Email:  gkoehler@umext.maine.edu