WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
June 20, 2005

Upcoming Events


Pheromone Trap Counts Plant Pathology Horticulture



June 23, 6:00 p.m. - Twilight Fruit Growers Dinner and Meeting at Eli Cook's Farm, Slanesville, W. Va.  To reach the meeting location from Slanesville, take Route 29 south for about 4 miles, turn left on Hickory Corner Road, and travel mile to the farm on the left.  From Route 50, take Route 29 north for about 3.5 miles, turn right on Hickory Corner Road, and travel mile to the farm on the left.  Dinner will be followed by seasonal updates by the Extension Specialists from the WVU KTFREC and a tour by Eli Cook.  For more information contact the Hampshire County Extension Office at 304-822-5013.

July 13, 5:30 p.m. - Joint WV, VA and MD Twilight Fruit Growers Dinner and Meeting at the WVU Tree Fruit Research and Education Center, Kearneysville, W. Va.  The agenda will include BBQ chicken dinner, exhibits, equipment demonstrations, updates by Extension Specialists, and a tour of research plots.  To plan for dinner, reservations must be made by June 30.  For more information or to make reservations, contact the WVU KTFREC at 304-876-6353.

July 14, 12:00-7:00 p.m. - Fruit Grower Field Day at the Penn State University Fruit Research and Extension Center, Biglerville, Pa.  The agenda will include concurrent research and educational tours, and conclude with a dinner and invited speaker.  Registration of $10, which includes educational handouts, drinks, and dinner, must be postmarked by June 30 (checks payable to Penn State University).  For more information contact the PSU FREC at 717-677-6116 ext. 0.


Carpovirusine, a granulosis virus from Arvesta Corporation, was recently registered by the EPA and WV (June 9) for the control of codling moth larvae in apple and pear.  The granulosis virus particles in Carpovirusine must be ingested by larvae to provide control.  Application should be initiated at the beginning of egg hatch and repeated every 10 days throughout the egg hatch period.  The application rate is 1 pint per 100 gallons of water in a spray volume of 100-350 gallons of water per acre.  Carpovirusine has a 4 hour REI and 0 day PHI.

Tufted apple bud moth hatch of first generation egg masses is estimated at 68% complete through June 19th, based on an accumulation of 844 degree days (DD) since biofix on May 8th at the WVU KTFREC.  Refer to the June 6th issue of this newsletter for insecticide options and recommended timings to control this insect.

Redbanded leafroller moths (2nd flight) have been emerging for about 10 days.  Second generation egg masses are deposited on the upper surface of apple leaves and will hatch over the next 2-3 weeks.  Where this insect is a problem, control hatching larvae with the same materials recommended for tufted apple bud moth.

Oriental fruit moth adult emergence (2nd flight) has begun, and second generation egg hatch is estimated at 8% complete through June 19th, based on an accumulation of 1085 DD since biofix on April 11th at the WVU KTFREC.  Refer to the June 6th issue of this newsletter for insecticide options and recommended timings for control in those orchards where the pheromone trap catch exceeds 10 moths/trap/week.

Redbanded leafroller adult female and male

Spotted tentiform leafminer adults (second flight) have been emerging since the beginning of June, based on pheromone trap capture.  To determine if control of the second generation is needed, begin sampling sap-feeder mines.  Start at the orchard edge and, moving toward the center, sample every other tree until enough trees have been sampled.  Begin by selecting five mature terminal leaves from each of three trees, and count the sap-feeder mines on the underside of the leaves.  After 15 leaves have been examined, begin comparing the accumulated total number of mines found with the limits given in Table 1 for that number of leaves.  If the number of mines falls between the two values given, sample five more leaves from another tree, continuing to add the number of mines found to the running total while checking Table 1 again.  Continue sampling in this fashion until the total number of mines falls below the lower limit or above the upper limit.  If the total is less than the lower limit, sampling is stopped and no treatment is required.  If the total is greater than the upper limit, sampling is stopped and an insecticide such as Provado, Actara, Assail, Calypso, Clutch, SpinTor, Vydate, or Lannate should be applied.  If 10 trees (50 leaves) are sampled and the total number of mines is less than 98, no treatment is needed.

Spotted tentiform leafminer adult

Spotted tentiform leafminer sap-feeder mines

Table 1.  Limits to determine status of second generation spotted tentiform leafminer infestations. 

Second Generation Sap-feeder Mines

No. of Leaves Sampled Lower Limit Upper Limit
15 12 46
20 22 55
25 31 65
30 41 75
35 51 85
40 61 95
45 70 105
50 98 98
Apple maggot adult

Yellow panel trap

Apple maggot (AM) poses a threat to commercial apple orchards in West Virginia that are adjacent to abandoned orchards or wild hosts.    Fly emergence, which typically begins after mid-June, should be monitored in all commercial apple orchards that are adjacent to these sites.  Yellow pre-baited panel traps or red sphere traps should be installed on the outside row closest to the wild hosts or abandoned orchard.  Position traps about 5-6 ft above the ground so they are surrounded, but not touched or obstructed from view, by fruit and leaves.  Traps should be inspected and AM flies counted weekly. When using the yellow trap, an insecticide [azinphos-methyl (Guthion), Imidan, Diazinon, Assail, Calypso, Clutch, or Avaunt] should be applied within 7-10 days of catching a single fly.  With the red sphere trap baited with apple volatiles, apply one of these insecticides immediately if an average of 5 or more flies per trap are caught within a week.  If no apple volatiles are used with the red sphere trap, the threshold should be lowered to 1 fly per trap.  Capture of flies for 1-14 days following the insecticide application can be discounted.  Once 14 days have elapsed since the last application, retreat immediately if the threshold is reached again.

Red sphere trap
Potato leafhopper adult and nymph

Potato leafhopper can be a problem in some apple orchards, especially non-bearing blocks.  This insect overwinters in the Gulf Coast states and adults are carried to this region on wind currents, which is followed by reproduction throughout the summer.  Adults and nymphs are both yellowish-green to pale green.  This species is more active on the leaf than white apple leafhopper and nymphs will run sideways, whereas nymphs of white apple leafhopper run forward or backward.  Whereas white apple leafhoppers feed on older leaves, potato leafhoppers feed on young leaves, causing their edges to curl and their color to change to light green, then yellow, and finally to brown and necrotic ("hopper-burn").  This insect has also been shown to facilitate the transmission of fire blight.  Although no threshold is currently available, control with Provado, Actara, Assail, Calypso, Clutch, Vydate, Lannate, or Thionex is recommended if presence is detected on young trees, or where fire blight symptoms have been observed in blocks of susceptible dwarfing rootstocks.

Potato leafhopper injury


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    
May 16 5 94 163 32 76 0 18    
May 23 2 15 23 21 131 1 24    
May 31 0 0 5 4 108 2 14 0  
June 6 0 52 10 9 144 1 14 0  
June 13 34 1280 9 23 132 0 37 3  
June 20 121 704 6 7 50 17 28 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.


Infection periods.  We recorded two new infection periods since the last Orchard Monitor was published on June 6. On June 6 - 7, we experienced 12 hours of wetting at an average temperature of 64 F. Our 10th wet period occurred on June 9 - 10 with 13 hours of wetting at 70 F.

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


Date 2005

Hours/ degrees F


April 7 - 8

14 hr/58 F


April 22 - 23

33 hr/52 F


April 30 - May 1

19 hr/57 F


May 14 - 15

15 hr/64 F


May 19 - 21

18 hr/54 F


May 21 - 22

13 hr/48 F


May 23 - 25

42 hr/54 F


June 2 - 3

33 hr/60 F


June 6 - 7

12 hr/64 F


June 9 - 10

13 hr/70 F

Powdery mildew.  With the current dry weather, the disease of concern is powdery mildew. Extending intervals between fungicide applications on mildew-susceptible apple varieties will result in high levels of overwintering inoculum and reduced yield for next season. There is already too much mildew/rusty spot on susceptible peach varieties in some orchards. For apples, highly susceptible cultivars include Jonathan, Baldwin, Cortland, Ginger Gold, Idared, Rome Beauty, Stayman, 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 12 to 14 days during the postbloom period.

Accumulated wetting hours.  As of June 20, 2005, we have accumulated 125 to 171 wetting hours, for petal fall dates of May 14 and May 7, respectively. Accumulated wetting hours are useful for predicting the appearance of sooty blotch on nonsprayed fruit. Symptom development for this disease is highly dependent upon temperature and moisture conditions surrounding the fruit. The appearance of sooty blotch symptoms has been predicted with reasonable accuracy by using accumulated wetting hours (AWH). Visible signs of sooty blotch may appear following approximately 260 - 300 AWH (earlier in the season (260 AWH) if the disease was severe last year, later in the season (300 AWH) if not). The AWH threshold for making the decision to include Topsin-M in the spray program is 225 for high disease pressure and 275 for low disease pressure. Each of these threshold values presumes that 25 additional AWH will occur in the next 5 days after reaching the threshold.

See our "Current Conditions" Web page for details that are updated at least three times weekly.


Summer pruning and training.  "Pruning means removing parts of a fruit tree in order to influence its natural growth in such a way that it will bear as much fruit as possible, will produce fruit more regularly, and will produce fruit of better quality than if it were not pruned." (H. Jonkers) 

Fruit tree leaves and shoots seek sunlight and therefore vegetative growth is strongest at the top and periphery of the tree.  A principle goal of summer pruning is to prevent excessive shading of fruit in the interior of the tree.  This can be accomplished by bending branches and/or by removing upright vigorous growing shoots.

In young vigorously growing trees, summer is a good time to "shape" the tree by spreading the selected framework branches and pruning out the vigorously growing shoots in the canopy.  If, however, growth is inadequate, training may be appropriate but pruning should be approached with caution.

In bearing trees, summer pruning can be used to balance the leaf to fruit ratio.  If it happens to be an off-year, summer pruning can be used to adjust the foliage:fruit ratio and allow sunlight to reach interior fruit.  Summer pruning has also been shown to increase calcium levels in fruit thus helping to reduce bitter pit.  If apple trees have a full crop, prune them lightly in August to increase light penetration and fruit color development.  Removal of vigorous upright shoots from tree centers several weeks before harvest will increase the "red blush" on peaches. 

To avoid sunburned fruit and reduced fruit size from removal of too much foliage, a good rule of thumb is to remove no more than 15% of the tree canopy when summer pruning.


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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