Washington State University Cooperative Extension

Areawide IPM Update

The Newsletter of Pheromone-based Orchard Pest Management

Vol. 2, No. 4 -- April 1, 1997

Cooperating agencies: Washington State University, Oregon State University, University of California, U.S. Department of Agriculture, and Chelan County.

Cooperative Extension programs and employment are available to all without discrimination.

Mating Disruption Use in Washington State: Grower Survey Results

In early 1997, I sent a survey to growers around Washington State asking about their experience with mating disruption (MD) for codling moth control, and for their comments and plans regarding this practice. About 130 surveys were distributed to mating disruption practitioners through agrichemical distributors or by direct mailing. My thanks to Wilbur-Ellis and Northwest Wholesale for their help. Seventy-four completed surveys were returned. To preserve anonymity, no grower identification was requested.

These 74 growers farmed a total of 25,293 acres. Yakima Valley growers (15 in number) represented 43% of the total acreage, 22% of the acreage (10 growers) was in the Columbia Basin and 35% (53 growers) was from North Central Washington (NCW). Some growers had blocks in more than one area.

Total acreage under MD in 1996 for these growers was 6,536 acres. (An estimated 22,000 acres were under MD in Washington that year, based upon information from the dispenser manufacturers). The MD acreage in the survey was in apples except for 284 acres of pears. Among the growers surveyed, MD use is more widespread in NCW. NCW growers had 36% of their acreage under MD, compared with 30% in the Basin and 14% in Yakima. The NCW growers also had more small orchards using the practice. Many different sizes of orchards were represented in the survey. The proportion of the total acreage under MD decreased as the acreage of the grower increased (see below).

Grower SizeNo. of Growers% of Orchard in MD
<20 ac1383%
21-50 ac1683%
51-100 ac1154%
101-500 ac1941%
501-1000 ac732%
>1000 ac813%

Among growers responding to the survey, acreage in MD increased 22% from 1995 to 1996. A further increase of 11% is expected within their orchards in 1997, to a total of 7,265 acres. Thirty-two percent of the growers treated all of their acreage in 1996, thus limiting the potential for increased use this season. Thirty-four percent of the growers plan to increase MD acreage in 1997, 62% will stay the same and 4% will decrease acreage. One of the 74 respondents plans to stop using MD altogether.

Pheromone dispensers: In 1996, Isomate-C+ was used by 61 growers on 79% of the treated acres. Checkmate-CM was used by 14 growers on 18% of the acres, and Disrupt-CM was used by 3 growers on 0.5% of the total MD acreage. Ten growers who used a different product in 1996 plan to use Isomate-C+ in 1997, increasing its proportion of the MD acreage represented by this survey to 97%. Five growers plan to continue Checkmate-CM use, reducing its proportion of the total MD acreage to 1%, and two growers will use Disrupt-CM again.

Dispenser rates: Isomate-C+ was used at many rates, from 200 to 400 per acre. The full rate (400 dispensers per acre) was used exclusively by 55% of the Isomate-C+ users, with the remaining 45% treating all or part of their acreage at lower rates. Lower rates were used most commonly in block interiors and after several years of full rate use. Checkmate-CM users applied dispensers twice, as indicated by the label, generally at rates of 120 to 160 per acre. Several indicated that they hung a third application in 1996. Disrupt-CM, first registered last year, was applied by the three users per label instructions (200 per acre).

Supplemental sprays: Eighty-three percent of those surveyed applied at least one spray for CM control in addition to using MD. Guthion (azinphosmethyl) was the most common material, used by 77% of all growers. The number of applications, and the amount of the orchard treated, varied greatly. Many growers indicated that the treatments depended upon CM pressure and history. Some applied from 0 to 3 covers within one orchard. Of those using Guthion, 15% spot treated or sprayed borders only, 45% applied one cover, 25% put on two covers, and 10% put on three or more.

Many other materials were used, each by less than 7% of the growers. The other materials listed for CM control included, by frequency of use: summer oil, Imidan, Confirm, Penncap-M, Lorsban, Ryania, Bt, Thiodan, Sevin and CM granulosis virus.

Comments: Most growers made comments about their MD experiences. These comments were generally positive, referring to benefits of :

Several stated that they felt MD use was important for the future of orchard pest control, in light of changing regulations and the likely loss of several insecticides.

Many concerns were also noted:

One will stop using MD, stating, "I'm still spraying for alternate pests anyway, so a couple of applications of $6/lb. Guthion would be far cheaper."

Bacillus thuringiensis (Bt) Use in Orchard Pest Management

The use of Bacillus thuringiensis (Bt) in orchard pest management programs has increased greatly over the past two decades. Worldwide, Bt has been used for 30 years on a wide array of crops. New Bt products are appearing almost annually, involving new formulations, new strains and even genetic manipulations. The genes responsible for the production of the Bt toxin have even been inserted directly into the genetic structure of a growing number of crop plants, including corn, cotton and potatoes, allowing the toxin to be expressed within the plant itself. The use of Bt products in apple and pear pest management has assumed added importance in recent years with the expanded use of pheromone-based pest management programs, and with an increase in leafroller populations in many growing regions. To get the most "bang for the buck," there are several factors particular to Bt use that must be considered. Before discussing those, let's review some basic information on Bt.

Bt is a rod-shaped, spore-forming bacterium that occurs naturally throughout the world in many different environments. It has the distinctive quality of being toxic to a limited number of insects while being completely harmless to other insects and animals, including all vertebrates. Susceptible insects, depending upon the Bt strain, include most lepidoptera larvae (including leafrollers, codling moth and cutworms), some flies (mosquitoes and black flies) and a few beetles (particularly Colorado potato beetle). Close to 20 different strains of Bt have been identified, but only a few have been developed for pest control purposes. The original strain identified was B. t. kurstaki (Btk). Btk and B. t. aizawi (Bta), are the two used in Bt formulations targeted at lepidoptera larvae, although Btk is more active against leafrollers.

Bt must be eaten to be effective, having no contact activity. The Bt organism contains a spore and a crystalline protein endotoxin. When eaten, the Bt enters the insect gut where this endotoxin is solubilized and the toxin is formed. This protein toxin then binds with specific receptors on the insect's gut wall. Feeding usually stops within minutes, and death generally follows within one to five days.

There are many different Bt formulations available. Some contain Btk only (e.g., Javelin [Sandoz/Novartis], DiPel [Abbott], and Biobit [Dupont]), others Bta only (e.g., XenTari [Abbott]) and still others contain Btk and Bta (e.g., Agree [CIBA/Novartis], Cutlass [Ecogen], and Condor [Ecogen]). Bt formulations have been developed using recombinant gene technology, including CRYMAX (Ecogen) and MVP (Mycogen). In the latter, the gene that produces the Bt crystal protein endotoxin has been inserted into another bacterium, Pseudomonas fluorescens. These bacteria are propagated, then killed, creating an encapsulated Bt toxin.

Bt use in tree fruit pest management programs has been mostly focused on the control of leafrollers, such as the pandemis (PLR) and obliquebanded (OBLR) leafrollers. Codling moth control with Bt sprays is poor, largely because the newly-hatched larvae consume only a very small portion of the fruit skin before entering the fruit, where they are no longer exposed to Bt residues. Cutworms can be controlled with Bt, provided they are actively feeding on the treated plants.

There are two key points to remember with regard to Bt products that affect success greatly:

  1. Bt sprays have a short effective residual period, generally 5 to 7 days in spring and 3 to 5 days in summer, and
  2. Larvae must eat the product in a sufficient quantity to be killed.

Therefore, for successful leafroller control, coverage of the foliage is probably the most critical factor. Applications need to be timed for the presence of actively feeding larvae. Both OBLR and PLR begin feeding by the half-inch green stage of apple bud development. Bt applications made in the period from pink until several weeks after bloom are often the most effective, as good coverage is easier to obtain then before there is extensive shoot growth. To thoroughly cover all foliage, make sure that tractor speed is low enough to allow the spray to reach throughout the tree. Dilute applications are not a requirement for good control. In fact, a concentrate application may be better IF coverage is good, because the Bt toxin concentration is higher and leafroller larval kill can be more complete.

In the spring, leafroller development is also fairly compact, allowing applications when all the population is in the susceptible stage (larvae). To apply during periods of active feeding, daytime high temperatures should be at least 65F in the day(s) following application. Good control has been obtained even if the first Bt application has been delayed until after bloom, in order to treat during a warm period. Many growers have successfully reduced a problem leafroller population in one season by use of a delayed dormant oil/Lorsban spray together with spring Bt applications, or with Bt applications alone. In each case, proper coverage and timing were critical components of their success.

Several spray adjuvants have been considered for use with Bts to increase their effectiveness. The use of wetting agents (spreaders) may improve control if their use results in more thorough coverage. Trials with organosilicone surfactants in particular have shown improved control with their use. The addition of feeding stimulants, like Coax, to Bt applications has also improved leafroller control in some field trials. In many cases, a more cost-effective improvement in control may be had by simply increasing the rate of Bt product used.

If leafroller larvae consume only a small dose of Bt they may be sickened and stop feeding for a period, but not die. These larvae later resume development, but well behind their untreated cohorts. This sublethal effect results in reduced kill and an extended period of development, complicating the timing of controls aimed at the next generation. The sublethal effect also has a bearing on the timing of repeat applications. Following a Bt application, if many of the leafroller larvae that survive do not feed for a week or more, then the next Bt spray should be delayed for over seven days in order to kill most of these survivors. The sublethal effect is minimized by attention to the same factors that provide the best control:

The Bts are an important component of pheromone-based pest management programs. Within the next two years several new materials will probably become available (the insect growth regulators Confirm and Comply, and the spinosad Success). These materials can provide good to excellent leafroller control, and in most cases fit well with pheromone-based programs, but in many instances the use of a Bt may remain the most cost-effective option. Pay attention to the factors critical to successful control with Bt, and your investment of time and money can pay off.

CAMP Site Update - April 1997

The Codling M>oth Areawide Management Program (CAMP) will be much larger this year, with total acreage increasing from 3127 acres in 1996 to close to 9800 acres in 1997. Over 260 growers will be involved this year, up from 68 last year. The five new sites added this year are receiving funding for only one year, and have no subsidy for the pheromone dispensers. This is the final year that the original five sites will receive the dispenser subsidy, but funds for monitoring and coordination will continue through 1999. The USDA-ARS at this time intends to fund at least five new areawide sites in the West each year in 1998 and 1999.

This table contains basic information about each site:

ProjectState1996Acres Add'l
in '97
Lake OsoyoosWA39329568822
Howard FlatWA1105596170157
W. Parker HeightsWA469 4697
Carpenter HillOR4001005007
Randall IslandCA760 7605
Progressive FlatWA 60325
BrewsterWA 230044
MansonWA 141071
West WapatoWA 82017
UkiahCA 5509
Total CAMP9801264

Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
e-mail: alway@coopext.cahe.wsu.edu

Partial Funding provided by: Washington State Tree Fruit Research Commission, U.S. Department of Agriculture-Agricultural Research Service.

WSU Cooperative Extension, Chelan County
400 Washington St.
Wenatchee, WA 98801

Wenatchee WA, 4 April 1997