WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
May 1, 2006

Upcoming Events


Pheromone Trap Counts Plant Pathology



May 4, 7:00 p.m. - Spring In-depth Fruit Meeting at Virginia Tech's Alson Smith Agricultural Research and Extension Center, Winchester, Va.  The agenda will include seasonal updates by VA Tech Extension Specialists and a presentation on apple thinning.  For more information contact the Frederick County Extension Office at 540-665-5699. 

May 9 - West Virginia University Holiday.  The WVU-KTFREC will be closed for the Primary Election. 

May 18, 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.


Lorsban 75WG (chlorpyrifos) from Gowan Company was recently issued a supplemental label by the EPA for foliar application through the petal fall stage and for postbloom trunk application for borer control on apple.  The postbloom foliar application of other chlorpyrifos formulations and use of the 75WG formulation after petal fall is prohibited.  Use of Lorsban 75WG is limited to a maximum of two applications per season, whether as a foliage or trunk spray.  Our recommended application rate for foliar application is 10 oz per 100 gal dilute and 2 lb per acre concentrate, with a maximum permitted by label of 2.67 lb per acre in a minimum spray volume of 100 gal per acre.  A petal fall application would have activity against plum curculio, redbanded leafroller, Oriental fruit moth and rosy apple aphid.  For trunk borer control, Lorsban 75WG application is restricted to the lower 4 ft of the tree trunk (foliage and fruit contact prohibited) and should be applied as a dilute spray at the rate of 2 lb per 100 gal of water.  The restricted-entry interval (REI) is 4 days and the preharvest interval (PHI) for the trunk application is 28 days. 

Proclaim 5SG (emamectin benzoate) from Syngenta has received registration for insect control on pome fruit (apple and pear).  In our area, Proclaim would have excellent activity against spotted tentiform leafminer and various leafroller species, but only provides suppression of codling moth, Oriental fruit moth and pear psylla.  It acts by interfering with the neurotransmitters in insects, which results in a loss of cell function and disruption of nerve impulses.  Primary activity is through ingestion, with limited contact activity for a short period after application.  Application rate is 0.8-1.2 oz per 100 gal dilute and 3.2-4.8 oz per acre concentrate.  Applications should be initiated at the beginning of egg hatch of the target insect to control small larvae.  Proclaim should be applied in a minimum of 40 gal of water per acre in combination with a horticultural spray oil or a nonionic surfactant (do not use a sticker/binder type adjuvant).  Restrictions include a season maximum of 14.4 oz per acre, an REI of 48 hours and a PHI of 14 days.

Codling moth
adult emergence began on April 21, based on pheromone trap capture at the WVU KTFREC.  However, due to no or little capture for a few days after, biofix was not set until April 26, which is 10 days earlier than last year.  Using a base temperature of 50F and upper temperature of 88F, 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.

European red mites
which hatched from overwintering eggs become adults around the petal fall stage of apple, which is when females begin depositing eggs on the leaves.  This is an excellent time to access mite abundance in order to implement early season management strategies where warranted. 

Determine mite abundance from a sample of 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 at right and determine the expected number of mites/leaf for a given percentage of mite-infested leaves.

A preventative acaricide should be considered if mite density averages two or more per leaf, or in orchards where mites are an annual problem.  The most effective treatments recommended at this time 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.

Codling moth adult

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



aLeaves with at least one motile stage.

White apple leafhopper nymphs

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, Sevin, Surround, Thionex, and Vydate. White apple leafhopper injured leaves (right)

Dogwood borer adults normally begin to emerge in early to 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 application for apple trunk borer control 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 20 0
March 27 29 0 0
April 3 155 920 38
April 10 105 1600 39
April 17 90 2820 224 0
April 24 20 1064 239 2 0 0
May 1 14 293 224 7 5 0 2

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 one wetting period since the last newsletter on April 17th. Infection period #3 occurred on April 21 - 23 and was initiated by about 1.25 inches of rain and lasted for 34 hours at 54 F. Additional wet periods have been recorded but have not officially qualified as infection periods. On April 25, we recorded 0.11 inches of rain with a wet period lasting for 7 hours at 55 F.

Table 1. Dates and conditions for apple scab infection periods at the WVU - KTFREC, 2006.

No. Date 2006 Hours/ degrees F
1. March 31 - April 1 10 hr/59 F
2. April 8 14 hr/49 F
3. April 21 - 23 34 hr/54 F

The peak period of ascospore release usually occurs during the pink through petal fall stages of bud development, so now is the time to be using the most effective materials. Growers who suspect decreased effectiveness of the sterol-inhibiting fungicides (Nova, Rubigan, Procure) may want to consider using the strobilurin class of materials (Flint, Sovran, Pristine) for two applications at this time.

Cedar-apple rust and quince rust.  Weather conditions on April 21 - 23 were favorable for the rust diseases. Apple leaves that were 4 to 8-days old at the time of infection are most susceptible to the cedar-apple rust fungus. Lesions take about 1 to 2 weeks to develop and will appear as orange to brown pycnia on the upper surfaces of leaves. Quince rust causes dark green lesions and puckering at the calyx end of infected fruits.

Powdery mildew.  Secondary powdery mildew lesions are visible now. Conditions have been favorable so far this year for this "dry weather" disease. In locations where mildew is a problem, susceptible varieties should be protected until shoot growth hardens off and terminal buds are set. Excellent mildew control can be achieved with the sterol-inhibiting fungicides (Nova, Rubigan, and Procure) and the strobilurin fungicides (Flint and Sovran).

Powdery mildew occurs wherever apples are grown. In some areas of the country it is a major foliar disease. In other areas, it is only a minor problem. Economic loss from mildew varies with climatic conditions, cultivar susceptibility, and orchard or nursery management practices. Apple leaves, blossoms, and fruit can be infected. Infections on leaves first appear as whitish, felt-like patches of fungal mycelium and spores, most commonly on the lower surface. These lesions may appear as yellowish spots on the upper surface or may spread to the upper surface and cover the entire leaf with a white, powdery mass of spores and mycelium. Infections along the leaf margin often result in leaf curling or crinkling. Severely infected terminals are stunted, have shortened internodes, and are covered with a silver-gray mat of mycelium that may persist through the dormant season.

Fruit infections are common on severely infected trees. Apple blossoms emerging from infected buds may give rise to small, russetted fruit. When apples are infected during bloom, their growth is stunted, and a fine network of russetted cells that may merge into a solid patch covers their surface, and is visible at harvest.

The powdery mildew fungus overwinters on apple as mycelium in dormant buds infected during the previous growing season. Conidia produced on overwintering mycelium initiate the primary infections in the disease cycle. Conidia infect young leaves, blossoms and fruit, which in turn provide inoculum for secondary cycles as new leaves, shoots and fruit develop. Leaves are susceptible for only a few days after they emerge. Conidia germinate readily over the range of 50 to 78 F (optimum 68 to 72 F) at relative humidity as low as 70%. Germination is slower at temperatures below 50 F, and no germination takes place in free water or at high temperatures (above 86 F). Conidia from overwintering mycelium can be found as early as the tight cluster stage and are released during early bloom. Infection that causes fruit russet occurs from about 3 weeks before to about 3 weeks after bloom. Infection of lateral and fruit buds occurs within a month after they are formed, apparently before the protective bud scales suberize. After bud infection, the mycelium is quiescent until budbreak the following spring. The percentage of terminal buds infected can be especially high when growth resumes in late summer following terminal bud set.

Management of powdery mildew depends upon cultivar susceptibility, the desired market quality of the fruit, and the importance of other diseases to be controlled. The main strategy is the timely application of effective fungicides. Excellent powdery mildew control can be expected when Nova, Rubigan, or Procure are used on a 7 to 10 day interval for scab control. Highly susceptible cultivars include Jonathan, Baldwin, Cortland, Ginger Gold, Idared, Rome Beauty, Stayman Winesap, and Granny Smith. Less susceptible cultivars include Delicious, Golden Delicious, Winesap, York Imperial, and Nittany. The practice of interplanting cultivars of different susceptibilities in an orchard often results in applications based on the need of the most susceptible cultivar, or more commonly, poor mildew control on the susceptible cultivar. Supplementary sprays may be required on highly susceptible cultivars to reduce inoculum for infection of less susceptible cultivars and other hosts (rusty spot on peach). Fungicide applications to control mildew should be made from the tight cluster stage until terminal growth ceases in midsummer. The interval between sprays is generally 7 days during the stages of rapid leaf development before petal fall, and 12 to 14 days during the postbloom period.

Fire blightConditions favorable for fire blight occurred on April 14, 21, and 23. On April 14, we recorded 0.03 inches of rain and 2 hours of wetting at 60 F. We did not record any wetting on April 15, but wetting did occur in some locations. On April 16, we recorded 0.02 inches of rain; however temperatures were a few degrees below those that favor infection. Infection may have occurred in locations with warmer temperatures. Symptoms from the April 14 infection should be visible later this week. There may be an increased risk of infection later this week (May 4) if temperatures are slightly warmer than those forecasted and if wetting occurs. Always be aware that fire blight risk can increase rapidly with warm temperatures and wetting. See our "Current Conditions" Web page for details that are updated at least three times weekly during the bloom period.


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.

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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
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