WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
July 18, 2005

Upcoming Events


Pheromone Trap Counts Plant Pathology Horticulture



August 2, 6:00 p.m. - Twilight Fruit Growers Dinner and Meeting at Jefferson Orchards, Kearneysville, W. Va.  The orchard is located on State Route 9, 1.5 miles east of Kearneysville.  Following dinner, seasonal updates will be provided by WVU Extension Specialists and a tour will be conducted by host Ron Slonaker.  For more information contact the WVU KTFREC at 304-876-6353.


Envidor 2SC Miticide from Bayer CropScience was recently registered by the EPA and WV (July 7) for use on all pome and stone fruits and grapes for the control of European red mite, twospotted spider mite, apple and pear rust mites, and peach silver mite.  The active ingredient, spirodiclofen, acts as a lipid biosynthesis inhibitor, with contact activity against mite eggs, immature stages and adult females; adult males are not affected.  Due to its insect growth regulator properties, Envidor should be applied on a preventive basis or at a low mite threshold, with performance evaluation conducted 4-10 days following application.  Application rate is 16-18 oz per acre, with a maximum of one application per season.  Minimum application volume (ground application only) is 50 gal/acre on stone fruits, and 100 gal/acre on pome fruits and grapes.  The pre-harvest interval (PHI) is 7 days on pome and stone fruits, and 14 days on grapes.  The restricted-entry interval (REI) is 12 hours, with a 6 day REI for certain post-application activities in grapes.

During a study conducted over the past three weeks at the WVU KTFREC, Envidor applied at 18 oz/acre on apple reduced a European red mite population from 12.5/leaf to 3.0 and 2.8/leaf at 7 and 13 days after application, respectively.

Codling moth hatch of second generation eggs is estimated at 16% complete through July 17, based on an accumulation of 1365 degree days (DD) since biofix on May 6 at the WVU KTFREC.  An application of Azinphos-methyl (Guthion), Imidan or Avaunt should have been completed the latter part of last week in those orchards where the pheromone trap capture has exceeded 5 moths/trap/week.  A second complete application  in 10-14 days, or three additional alternate-row-middle applications 5-7 days apart should be made of these materials, or Assail, Calypso, Clutch, Rimon or granulosis virus (Cyd-X, Carpovirusine) where needed.

Oriental fruit moth hatch of second generation eggs should be about completed, with third generation egg hatch just beginning (estimated at 3% through July 17), based on degree day accumulations (1928 DD).  In reality, it is likely that there is currently overlap in egg hatch between the second and third generations.  The third generation poses a threat to peach fruits near or during harvest.  Larvae can enter anywhere on the fruit, resulting in the exudation of gum and frass (excrement) from the wound area.  As the gum ages, a sooty mold may form on it, turning the entire wound area black.  Larvae can also enter the fruit through the inside of the stem, and therefore leave no evidence of entry except for a small mark at the stem end of the picked fruit.

Control of the third generation is justified where the pheromone trap capture exceeds 10 moths/trap/week.  On peach, an insecticide application is recommended at 2100-2200 DD after biofix (10-20% egg hatch).  A second application at 2450-2500 DD after biofix (50-56% egg hatch) may be needed, depending upon pest density and proximity to harvest.  Control options [days to harvest] include Azinphos-methyl (Guthion) [21], Imidan [14], Intrepid [7], Lannate [4 on peach, 1 on nectarine], and carbaryl (Sevin) [3].

As a general guideline on apple, apply Intrepid, Assail, Calypso, Clutch, or Rimon at 2350-2400 DD after biofix (35-42% egg hatch), then at 2800-2900 DD after biofix (88-93% egg hatch), if needed.  If using Avaunt, Azinphos-methyl (Guthion) or Imidan apply at 2450-2500 DD after biofix (49-55% egg hatch), then at 2900-3000 DD after biofix (93-96% egg hatch), if needed.  Since actual egg hatch often falls behind DD based predictions on apple, it is best to treat within 7-10 days of exceeding the above trap threshold and to maintain spray intervals on a 2 week (complete) or 5-7 day (alternate-row-middle) schedule for as long as this condition continues.

Oriental fruit moth fruit injury

Western flower thrips (WFT) is a potential threat to peach and nectarine fruits near harvest, especially if weather conditions become dry.  WFT adults are slender, about 1/16 inch long, yellowish, and hold their wings over their backs.  Larvae are smaller and wingless, but otherwise resemble adults.  Several generations occur per year as populations buildup in white clover and other weeds in and around orchards, as well as in field crops such as alfalfa.  Flight activity of WFT peaks in July through September in stone fruit orchards.  If conditions are dry near harvest, ground cover hosts will become less attractive and make it more likely that thrips will move to stone fruit trees.

Feeding on fruit near harvest results in silvering injury, a benign surface blemish that can be quite extensive if thrips populations are unchecked.  Injury usually occurs in protected sites, such as in the stem end, the suture, under leaves and branches that contact the fruit, and between fruit.  Inspect the earliest maturing varieties during final swell for silvering injury.  Monitor thrips by counting adults on 10 fruit at 5 locations in the orchard.  Sample fruit from the ends of branches in the lower third of the tree canopy.  Five adult thrips per 50 fruits and the presence of silvering injury may justify control, depending upon the potential market, because extensive silvering can result in downgrading of the fruit.  Control options [preharvest interval] include SpinTor [14 days on peach, 1 day on nectarine (Section 24C label in Virginia and West Virginia)] and Lannate [4 days on peach, 1 day on nectarine (Section 24C label in Virginia and West Virginia)].

Western flower thrips larva on nectarine

Western flower thrips silvering 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  
June 27 135 1728 14 1 9 13 13 3 0
July 5 122 1312 30 8 1 15 11 2 0
July 11 34 640 7 13 2 14 4 0 1
July 18 17 1280 9 17 1 8 2 0 4

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 six new infection periods since the last Orchard Monitor was published on July 5th. The 11th infection period of the season occurred July 5 - 6 with 0.31 inches of rain and 18 hours of leaf wetness at 68 F. The 12th infection period resulted from the movement of Hurricane Cindy through the area on July 8th, bringing much needed rain (1.8 inches here). That storm provided another 18 hours of wetting at an average temperature of 66 F. Afternoon thunderstorms and night-time wetting events have increased with the recent bout of hazy, hot and humid weather. These conditions are ideal for summer diseases of apples, particularly bitter rot and white rot (also called "bot" rot), as well as brown rot of peaches and nectarines. Use higher fungicide rates, better spray materials and shorter spray intervals when disease conditions are favorable on an almost-daily basis.

Table 1. Dates and conditions for summer infection periods at the WVU - KTFREC, 2005.

No. Date 2005 Hours/ degrees F
8. June 2 - 3 33 hr/60 F
9. June 6 - 7 12 hr/64 F
10. June 9 - 10 13 hr/70 F
11. July 5 - 6 18 hr/68 F
12. July 8 18 hr/66 F
13. July 13 - 14 15 hr/71 F
14. July 15 7 hr/72 F
15. July 16 10 hr/74 F
16. July 16 - 17 14 hr/74 F

Accumulated wetting hours: Threshold warning.  As of July 18, 2005, we have accumulated 239 to 285 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 these diseases 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, Sovran or Flint 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.

Control failures with sooty blotch and flyspeck occur either because of poor spray coverage during the latter part of the growing season or because trees were left unprotected through more than 270 hr of accumulated wetting during the preharvest interval. Because fungicide protection on fruit is exhausted after 2 inches of rain, fungicide sprays may be needed in late August and September if heavy rains occur with more than 25 days remaining before fruit will be harvested. Twenty-five days is a "worst-case" scenario, based on experience, for accumulating 270 wetting hours.

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


Tissue Analysis - A valuable tool.  Managing the nutritional needs of your orchard has become a critical component of overall management decisions.  Combined with soil test, tissue analysis can provide valuable insight into what's happening, nutritionally in your trees. 

Between mid-July and mid-August is the optimal time in the mid-Atlantic region for tissue analysis.

Leaf analysis kits are available from the WVU KTFREC.  The cost for complete nutritional analysis is $24 per sample.

Here are ten easy steps to successful leaf analysis:

1.   Trees to be sampled should be uniform and representative of the condition in question (i.e. similar vigor, same variety).
2.   Sample healthy leaves, free of insect, disease or mechanical damage.
3.   Collect leaves from all quarters of the tree at about shoulder height.
4.   Select the correct plant part -- leaves with petiole attached, from the mid-region of current season's terminal shoots.
      Spur leaves should not be selected.
5.   Fifty to 100 leaves are needed per sample.  Randomly collect these from 5-10 trees.
6.   Sample leaves at the stage of tree development when nutrient levels are most stable (mid-July to mid-August in West
      Virginia).  Take samples annually and on approximately the same date to improve the value of leaf analysis results.
7.   If the leaves are covered with dust or spray residue, gently wash them in distilled or soft water.  Do not allow the leaves
      to stand in water for more than one minute.  Dry the leaves at room temperature until they become crisp.
8.   Mail each sample in a paper bag or other container provided in kit.  Properly identify all samples and complete orchard
      information sheet.
9.   Keep yearly records of leaf analysis results and recommendations.  Fertilizer rates should be adjusted for cultural
      practices that influence tree nutrition (i.e. pruning, orchard floor management).
10. Ideally, you should sample leaves from every orchard block every year.  In large orchard operations, this may not be
     feasible, so divide the orchard into thirds for sampling purposes and make an effort to sample each block at least every
     three years.


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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