WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
May 9, 2005

Upcoming Events


Pheromone Trap Counts Plant Pathology Horticulture



May 17, 7:00 p.m. - Spring In-depth Fruit Meeting at the Alson Smith Research and Extension Center, Winchester, Va.  Dr. Chris Bergh, VA Tech entomologist, will discuss "Internal Worm Issues: Pesticide Trials, Resistance Monitoring, and Management Options". For more information contact Cyndi Marston at 540-665-5699 or at cmarston@vt.edu.

May 26, 6:00 p.m. - Tree Fruit Grower Twilight Dinner and Meeting at Gourmet Central (in Hampshire Industrial Park), Romney, W. Va.  Following dinner, seasonal updates will be provided by Extension Specialists from the WVU Kearneysville Tree Fruit Research and Education Center.  For more information contact the Hampshire County Extension Office at 304-822-5013.


European red mites are likely to be more abundant and require control earlier this year in those blocks where pyrethroids were used last year for the control of periodical cicada. Mites that hatched from overwintering eggs become adults around the petal fall stage of apple, which is when females begin depositing eggs on the leaves.

To determine mite abundance, sample 5-10 leaves (collected from the middle of a fruit spur) from 5-10 trees per block of the same cultivar.  If oil or another acaricide has already been applied, examine each leaf and determine the average number of mites/leaf for the total leaf sample.  If no oil or other acaricide has been applied, examine each leaf for the presence or absence of one or more motile mites, and calculate the average percentage of mite-infested leaves for the total leaf sample.  Refer to Table 1 below and determine the expected number of mites/leaf for a given percentage of mite-infested leaves.

Table 1.  European red mite densities predicted
from the percentage of mite-infested leaves.

Percentage of
infested leavesa
Expected density
in mites/leaf
40 0.7
45 0.9
50 1.1
55 1.3
60 1.6
65 2.0
70 2.6
75 3.4
80 4.7
85 6.8
90 11.4
95 26.4

aLeaves with at least one motile stage.

A preventative acaricide should be considered if mite density averages two or more per leaf.  The most effective treatments include Agri-Mek, or the ovicides Apollo or Savey.  To minimize the development of resistance, do not use Agri-Mek or either one of the ovicides in two successive years.  Agri-Mek, which will also control spotted tentiform leafminer and white apple leafhopper, should be applied within 7-10 days of petal fall and combined with 1 gal/acre of oil.  Other preventative strategies, although usually less effective, include the early postbloom application of Vydate (can be substituted for Sevin as a thinner), or the use of Damoil or Ultra-fine oil at 2 gal/acre at petal fall, first and second cover.

White apple leafhopper nymphs are beginning to appear on the undersides of apple leaves.  White to yellow in color, first generation nymphs are more abundant on spur leaves, with the second generation more abundant on shoot leaves.  Feeding injury ranges from light stippling to complete chlorosis that is visible on the upper surface of leaves.  High populations can result in sufficient honeydew deposits to cause black speckling on the surface of fruit.  To monitor leafhopper populations, determine the average number of nymphs per leaf by examining the undersides of 10 leaves on 5-10 trees per block.  The action threshold for control is an average of 3 nymphs per leaf.  Materials rated excellent include Actara, Assail, Calypso, Carzol (cannot be applied after petal fall), Lannate and Provado.  Materials rated as good include Agri-Mek, Avaunt, Dimethoate, Sevin, Surround, Thionex, and Vydate.

White apple leafhopper nymphs

White apple leafhopper injured leaves (right)

Catfacing insects refers to a complex of pests that cause various types of injuries on peach and nectarine fruits.  Feeding on young fruits up until pit hardening results in fuzzless, corky, depressed areas and fruit deformity called "catfacing" injury.  Feeding on slightly larger fruits results in scarring injury, which is similar to catfacing injury but without deformity.  The primary insects responsible for this early season injury in West Virginia are tarnished plant bug, and brown and dusky stink bugs.

This pest complex is difficult to manage because they are not full time residents on fruit trees, but move frequently between broadleaf weed hosts and fruit trees to cause injury.  Maintaining thorough and frequent spray coverage with pyrethroids, azinphosmethyl (Guthion), Imidan or Actara from shuck split until a few weeks after shuck fall is critical to minimizing fruit injury.  Pyrethroid use should be limited to reduce the likelihood of mite outbreaks.  Practicing good broadleaf weed control will also reduce the injury from this pest complex. 

Catfacing injury

Scarring injury

Codling moth adult emergence began the end of last week, based on pheromone trap capture at the WVU KTFREC.      Biofix was set for May 6, which is six days later than last year.  Using a base temperature of 50ºF and upper temperature of 88ºF, degree days (DD) should be accumulated from biofix in order to properly time spray applications (more in next newsletter) in those orchards where the pheromone trap capture exceeds 5 moths/trap/week.

Codling moth adult

Dogwood borer adults normally begin to emerge around mid-May, so pheromone traps should be installed now for monitoring of this insect.  Larvae are  commonly found infesting burr knots that are prevalent on rootstock shanks of most dwarf and some semi-dwarf rootstocks.  In addition, some cultivars such as Gala often produce burr knots on the scion (upper trunk, scaffold limbs) which are likely to be infested.  Larval feeding may extend beyond the burr knot into healthy tissue and result in a decline in vigor and yield.  Chronic infestations can result in girdling and death of trees, especially in younger orchards. 

Lorsban has been the most effective treatment, primarily because of its ability to penetrate wood and kill borers within burr knots.  Research in New York has demonstrated much flexibility in timing of Lorsban for control, including high efficacy in petal fall applications. Lorsban contact with foliage and fruit is prohibited in the postbloom period.  When used at petal fall or later, application is restricted to the lower 4 ft of the trunk (no foliage or fruit contact) from a distance of no more than 4 ft using low volume handgun or shielded spray equipment.

Various cultural practices can reduce the severity of dogwood borer injury.  Infestations are more extensive where plastic spiral tree guards are used.  These type guards also prevent spray contact with the lower trunk and therefore should be replaced with more porous types.  Practice good weed control around the trunk because shade and increased humidity promote the development of burr knots.  Mound soil around the burr knots on the exposed rootstock up to the graft union, but do not cover the graft union in order to prevent scion rooting.

dogwood borer larva in burr knot

Mounded soil around burr knots


March 21 0            
March 28 3 0            
April 4 17 9 0            
April 11 73 720 3            
April 18 51 896 42            
April 25 34 1372 186            
May 2 7 256 89 0 0 0 0    
May 9 8 140 53 15 7 0 0    

RBLR = Redbanded leafroller; STLM = Spotted tentiform leafminer; OFM = Oriental fruit moth; CM = Codling moth; TABM = Tufted apple bud moth; DWB = Dogwood borer; LPTB = Lesser peach tree borer; PTB = Peach tree borer; AM = Apple maggot.


Apple scab. We recorded our third apple scab infection period of the season last week on April 30 - May 1 for 19 hours of intermittent wetting at 57° F. Conditions may have been favorable for rust infection, also. Additional wetting due to scattered storms may have occurred at some locations on Saturday evening, May 7. Six to eight hours of wetting would have been required for infection following that brief rain event.

Table 2. Dates and conditions for apple scab infection periods at the WVU - KTFREC, 2005.

No. Date 2005 Hours/ degrees F
1. April 7 - 8 14 hr/58 F
2. April 22 - 23 33 hr/52 F
3. April 30 - May 1 19 hr/57 F

Fire blight. Conditions favorable for fire blight infection occurred on April 20th, if wetting occurred on the 19th or 20th. Symptoms from that infection may be visible on or around May 13. Now is the beginning of our first extended period of high risk for fire blight, due to warmer temperatures that will dominate our region for the next several days. Blossom infection could occur following any event that supplies the moisture needed to move the bacteria into the blossom nectary. In addition to rain, wetting events that trigger infection may include heavy dew, episodes of fog, or periods of high relative humidity. High wind gusts on May 8 did not constitute a fire blight threat because of low epiphytic infection potential. See our "Current Conditions" Web page for details that are updated at least three times weekly.

Streptomycin reminders: For best blossom blight control, apply Streptomycin just before an anticipated infection, then re-apply it in 4 days if high risk conditions persist. High risk occurs with any combination of three out of the following four criteria: 1) blossoms open, 2) bacteria present on blossom surface, 3) average temperature for the day of 60 F, and 4) sufficient moisture in the form of rain or dew. Note that infection of susceptible cultivars is very likely to occur if all four of these criteria are satisfied. Streptomycin applied after infection can provide acceptable control, however the level of control that is achieved declines with time and declines more rapidly as temperature increases.

Avoid alternate-row-middle programs for fire blight control. If this method is used and if infection conditions occur after the first half spray, follow immediately with the second half spray of streptomycin. Do not exceed 3 - 4 antibiotic sprays per year in order to minimize the chance that the fire blight bacterium will develop resistance to streptomycin. Make blossom treatments strictly on whether an infection is expected or has occurred, not on how severe that event might be.


Update on Sinbar® label. The Sinbar® (terbacil) label has been changed to include application on newly planted and young non-bearing apple, pear, peach, plum, apricot and cherry trees. Application at rates of 0.5 to 1.0 lb/A may be made once the soil around newly planted trees has been settled by significant rainfall or an irrigation. Up to 2 applications can be made per year, but do not exceed 1.0 lb/A per year. Do NOT use on soils that have less than 2% organic matter. Do NOT use on soils coarser than a sandy loam.

Several new brands of plant growth regulators. Fine Americas Inc. of Walnut Creek, California has entered the plant growth regulator market for fruit. They are a subsidiary of Fine Holdings Ltd. of Worcester, UK. They are marketing a cytokinen, 6-benzyladenine for thinning (exilis Plus®); a GA3 formulation for cherries called falgro®; a GA4A7 mixture for reduced russetting in apples called novagib®; and a GA4A7 plus 6-benzyladenine mixture for improving typiness of apples called perlan®. Valent BioSciences Corporation has also released a new formulation of Provide (gibberellinsA4A7) in the form of water dispersable granules. Provide® 10 SG has a 10% active ingredient and can be used in a similar fashion as the liquid formulation for reduction in russetting and cracking of Stayman apples.

We do not have first hand knowledge on how these materials perform in Pennsylvania since they have not been in any university trials. We wanted you to be aware of the products.

Source: Rob Crassweller, PSU, Dept. of Horticulture (Fruit Times, Vol 24. No. 4).

Some notes on thinning. After assessing the fruit set in your trees, you will very likely need to apply chemical thinners.  Some experts state that the apple market today has caused chemical thinning to become the most important cultural practice many growers undertake.

As you know, fruit thinning is done to increase fruit size and enhance return bloom.  In general, reducing the number of fruit to 4 to 6 per cm of limb diameter is required for good sizing.  Another rule of thumb is one fruit each 6 to 8 inches on the branch.   Ideally, apples can be thinned any time from bloom to 3 to 4 weeks after fruit set.  The reasoning is that once the apple blossom has been pollinated, the fruit begins to form seeds.  The endosperm within the developing seed begins producing gibberellic acid (a growth regulator) which promotes the enlargement of fruit.  Gibberellic acid, however also inhibits the development of next year's flower buds.   So, the more seed produced, the more gibberellic acid present and the fewer flowers and potential fruit next year.  This chemical activity contributes to the biennial bearing habits of many varieties.

Through appropriate dormant pruning and thinning practices, alternate-year fruiting can be avoided by elimination of "extra" fruit and its seeds which produce the gibberellic acid.

      .    Only 7-8 percent of a tree's flowers are needed to set a full crop of fruit.
.    Trees that carried a light crop last year will very likely require extensive thinning this year.
.    Weather conditions 24 hours before and 72 hours after the application of thinners may be more important than fruit size 
      at the time of application.

.    Along with weather, certain thinning materials are more effective on different fruit sizes.
.    Cuticle wax on leaves, flowers and young fruit becomes thicker during sunny dry weather and thinner on cooler cloudy
      days.  This obviously affects the absorption rate of thinning chemicals.
.    Cool, cloudy weather conditions generally extend the effective thinning period.
.    Young trees thin very easily and reduced rates of chemical thinners should be used.
.    Winter injured, frost damaged, vole damaged and low vigor trees are generally easily thinned.
.    Chemical thinning is challenging and perhaps more art than science.
.     Inadequate thinning usually results in the loss of more crop value than all the other problems growers face.


Trade and brand names are used only for the purpose of information, and the West Virginia University Extension Service does not guarantee nor warrant the standard of the product, nor does it imply approval of the product to the exclusion of others which may also be suitable. The West Virginia University Extension service assumes no responsibility in the use of hazardous chemicals.

Individuals requesting an accommodation at a meeting because of a disability should contact one of the Extension Specialists at the WVU Kearneysville Tree Fruit Research and Education Center at 304-876-6353 at least five days prior to the event.

Helping you put knowledge to work

P. O. BOX 609
PHONE:  304-876-6353
FAX:  304-876-6034
WEB:  www.caf.wvu.edu/kearneysville

The West Virginia University Cooperative Extension Service, U.S. Department of Agriculture, West Virginia County
Boards of Education and County Commissions Cooperating.  Equal Opportunity / Affirmative Action Institution

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