WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
June 30, 2008

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Pheromone Trap Counts Plant Pathology



July 4. – West Virginia University Holiday. The WVU-KTFREC will be closed in observance of Independence Day. 

July 8, 4:00 p.m. – Joint MD, VA, WV Twilight Fruit Growers Dinner and Meeting at the USDA Appalachian Fruit Research Station, Kearneysville, W. Va. The facility is located at 2217 Wiltshire Road (1 mile from State Route 9 at Bardane). The agenda will include a tour and presentations by USDA scientists, catered dinner, and seasonal updates by Extension Specialists from MD, VA, and WV. For more information contact the WVU-KTFREC at 304-876-6353.


Oriental fruit moth second generation egg hatch continues and is estimated at 68% complete through June 29, based on an accumulation of 1471 degree days (DD) since biofix on April 10 at the WVU-KTFREC. For control options, refer to the June 16th issue of this newsletter.

Codling moth first generation egg hatch is virtually complete (estimated at 99%) based on an accumulation of 933 DD since biofix (May 2) through June 29 at the WVU-KTFREC.  First generation fruit injury (both side and calyx entries) can be found, and apple orchards should be inspected at this time for fruit injury in order to evaluate the effectiveness of management programs.  Fruit injury is more likely to occur in the upper parts of apple trees since more moth mating and egg-laying occurs in this area, and spray coverage is likely to be weakest in this portion of the tree.  Larvae may enter fruit from either the side or calyx end, resulting in the presence of frass (excrement, see photo) on the surface where tunneling has been successful.  First generation larvae usually have greater success entering the calyx end because the side of the apple is harder early in the season.  Injury also may be expressed as “stings”, which consist of small shallow holes resulting from the death of young larvae that have been poisoned after puncturing the apple skin.  The absence or size of larvae (1/2-5/8 inch long when mature in 3-4 weeks) found in injured fruit can indicate when the control failure occurred during the egg hatching period.  The absence of a larva and the presence of an exit hole in apples with frass indicates that the larva has already matured and left the apple, having entered the apple in the beginning of the egg-hatching period (latter part of May).  The presence of larger larvae in fruit indicates a control weakness during the early part of the egg-hatching period (early June), whereas smaller larvae indicate inadequate control during the latter part of the egg-hatching period (mid to late June).  Small larvae found in fruit at this time could also be the second generation of oriental fruit moth, so it is important to have larvae identified to know which species is responsible for the injury. Knowledge of larval size and species in injured fruit, when coupled with pesticide record information can increase understanding of management failures and lead to improved control against future generations. 

The second moth flight is expected to begin within a week.  In order to prevent fruit injury, control of the second generation should be implemented in those orchards where the pheromone trap capture exceeds 5 moths per trap per week.  In order to delay the development of resistance, materials selected for control of the second generation should be from a different chemical class (different mode of action) than was used against the first generation (see pages 39-40 of the 2008 Spray Bulletin for a listing of chemicals by class).  Recommended options include Rimon at 1050-1150 DD (0-2% egg hatch, estimated on July 5-9); Intrepid, Esteem, Assail, Calypso, or CM granulosis virus (Cyd-X, Carpovirusine) at 1150 DD (2% egg hatch); or Altacor, Avaunt, Azinphos-methyl (Guthion), Delegate or Imidan at 1250 DD after biofix (6% egg hatch, estimated on July 13).  An initial spray should be followed by a second complete application in about 10-14 days (300 DD), or three additional alternate-row-middle applications 5-7 days apart.  Complete sprays of Cyd-X or Carpovirusine should be repeated every 7-10 days for a total of 3-4 applications.

Codling moth external fruit injury
Codling moth larva & internal fruit injury
Japanese beetles & leaf injury

Japanese beetle adults have just begun to emerge.  The most important threat from this insect is to dwarf and non-bearing apple trees and to stone fruits near and during harvest.  Feeding injury on apple leaves results in a “lace-like” appearance as beetles consume the leaf tissue between the veins.  Honeycrisp is a highly susceptible cultivar to foliage injury and should be monitored closely. Injury to most apple fruits is not common and usually only occurs on mature fruits that have already been damaged by some other factor. However, in 2007 there were reported cases of direct fruit feeding on Ginger Gold, Honeycrisp, and Fuji.

All stone fruits are highly susceptible to attack as they reach maturity.  Beetles are often found in clusters on fruit that is within two weeks of harvest, and may be accompanied by Green June beetles.  Although, like Japanese beetles, Green June beetles prefer ripe fruit, they also may cause injury on green fruit.   Since feeding may be “clumped” or unevenly distributed, care should be taken in looking at a representative sample before making a spray decision.  Control is recommended if fruit feeding injury exceeds one percent. 

 Sevin is considered the most effective control option, with the XLR Plus formulation considered to be less disruptive to mite predators than other formulations.  Other options include Lannate, Assail and Surround.  Surround is most effective if application begins before beetles begin feeding on trees. Since beetles will continue to move into trees throughout the month of July, multiple applications may be needed in higher pressure situations.

Japanese beetles on peach
Green June beetle on peach
Apple maggot adult

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 in late June, should be monitored in all commercial apple orchards that are adjacent to these sites, especially if fruit injury has occurred in the past.  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, 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.

Yellow panel trap
Red sphere trap


March 17 0
March 24 6 0
March 31 31 17
April 7 98 376 2
April 14 74 2688 84
April 21 109 1152 376 0
April 28 33 392 329 3 0 0
May 5 12 114 210 19 3 0 1
May 12 1 114 138 14 16 0 12
May 19 1 37 51 30 31 1 38
May 27 0 17 78 31 36 7 36
June 2 0 448 20 24 46 4 16 0
June 9 46 1504 13 19 42 27 27 0
June 16 127 1520 13 15 2 17 24 1
June 23 88 1792 45 9 8 6 12 2
June 30 43 1344 65 6 1 12 9 2 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 and general disease update.  We’ve recorded four additional infection periods since the last Orchard Monitor on June 16, 2008. Our disease pressure is moderate to high, with some locations actually needing some moisture, and other locations suffering from hail damage. On June 16, we had leaf wetting for 6 hours at 67 F with 0.26 inches of rain. On June 16 - 17, we had leaf wetting for 10 hours at 59 F with 0.35 inches of rain. On June 28 - 29, we had leaf wetting for 14 hours at 68 F with 0.25 inches of rain. Finally, on June 29 - 30, we had leaf wetting for 8 hours at 67 F with 0.43 inches of rain. Total rainfall to date for June is 4.18 inches (normal for June is 3.4 inches). These most recent infection periods are favorable for the development of apple summer diseases.

Table 1. Dates and conditions for infection periods at the WVU - KTFREC, 2008.


Date 2008

Hours/ degrees F


June 4-5

31 hr/68 F


June 6-7

11 hr/72 F


June 10-11

15 hr/71 F


June 14-15

19 hr/69 F


June 16

6 hr/67 F


June 16-17

10 hr/59 F


June 28-29

14 hr/68 F


June 29-30

8 hr/67 F

Accumulated wetting hours – threshold reached.  As of June 30, 2008, we have accumulated 249 wetting hours for a petal fall date of May 3 (last year at this time AWH = 210). 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 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.

Fungicide considerations for hail-damaged orchards.  (courtesy of Dr. Dave Rosenberger, Plant Pathology, Hudson Valley Lab). Over the past few weeks, hail has damaged the fruit crop in scattered areas throughout New York State.  After a hailstorm, growers are faced with many difficult decisions.  If the crop is a total loss, then the objective will usually be to minimize inputs throughout the remainder of the season without endangering tree viability and/or potential for good return bloom next year.  If part of the crop is still salvageable, then continued fungicide coverage may be needed, but fungicide selection and timing may need to be adjusted to reduce costs even if that adjustment increases risks that some diseases will not be completely controlled.

This article summarizes my perspectives on disease control for orchards damaged by June hailstorms.  The suggestions that follow are based on "best guesses" rather than on scientific research because there is little published data on how to deal with hail damage.  In cases where I suggest that there is no biological reason to apply more fungicides, that advice may need to be modified if insurance coverage will be diminished in cases where hail-damaged fruit become infected with fruit rots and summer diseases.  Other adjustments may be needed on a block-by-block basis depending on cultivar susceptibility to diseases, marketing strategies, and options for diverting the crop to juice, processing, or some other alternative market.

APPLES: Fire blight.  Where blight was present in orchards or in adjacent upwind blocks, growers should have applied streptomycin ASAP after the hailstorm but within 24 hr if at all possible.  Applications up to 48 hr after hail events may still provide some benefits, but effectiveness will be greatly diminished after 24 hr.  To maximize effectiveness, I would use streptomycin at 2 lb/A along with Regulaid or another good spreader.  (This rate is higher than the standard rate recommended during bloom, but trees have much more foliage to cover at this time of year than they do at bloom, and getting the streptomycin to penetrate injured leaves and fruit is essential for maximum effectiveness.)  Where no streptomycin was applied within 48 hr, the window for strep applications has closed and streptomycin should NOT be applied if hail-induced trauma blight shows up next week.

Remember that the preharvest interval for streptomycin on apples is 50 days, so cultivars harvested in early August might not be harvestable if sprayed with strep in mid-June.  The risk of hail-induced trauma blight is relatively low if apple shoots are not actively growing, so mature orchards with a full crop should not need a strep spray if hail occurs after terminal buds are set.

Apple scab.  No additional fungicide sprays should be needed this year in orchards where primary scab was completely controlled and the crop will not be harvestable.  Also, I would probably stop spraying non-harvestable orchards that had "a little scab" even if that will cause scab to build up during summer.  This advice is based on the assumption that it will be cheaper to attack over-wintering scab with a ground spray of urea next spring rather than paying for captan sprays through the rest of the summer.

Summer fruit rots.  The fungi that cause black rot, white rot, and bitter rot might infect fresh cuts in fruit caused by hail, but green fruit are relatively resistant to infection and cuts will heal and become resistant to infection fairly quickly (perhaps within 24 hr?). If no fungicide was applied immediately after the hail storm, one application of Topsin-M, Sovran, or Flint might still serve to arrest decay organisms established in fruit cuts because all three of those fungicides will be absorbed into sprayed fruit surfaces where they may provide some post-infection activity. Where black rot or white rot spores are deposited in fresh cuts and no fungicides are applied for the rest of the season, I suspect that some fruit will develop decay as fruit begin to ripen because the natural inhibitors present in green fruit disappear as fruit ripen, thereby allowing quiescent infections to become active. If the crop has no value, having decayed fruit present in the fall will not be an issue although some of these fruit may mummify and will then need to be knocked out of trees during winter pruning.

PEARS.  Where the crop is lost, no fungicide sprays should be needed for the rest of this year UNLESS the blocks have a history of Fabraea leaf spot.  Where Fabraea is a threat, growers should maintain fungicide coverage because Fabraea can cause early defoliation that will result in complete loss of return bloom next spring.  Mancozeb fungicides are the most effective, BUT they can be used during summer ONLY where no fruit will be harvested and in blocks that have not yet received the annual label limitation of 21 lb/A/yr.  Orchards sprayed with mancozeb should be resprayed every 30 days or after 2.5 inches of accumulated rainfall if that occurs in less than 30 days.  Adding one percent spray oil to mancozeb or to any other fungicide registered on pears will increase fungicide efficacy against Fabraea leaf spot.

PEACHES.  Even where the crop is a total loss, one or two sulfur sprays may be needed as fruit ripen so as to suppress brown rot fruit decay.  Sulfur is presumably the cheapest way to slow the spread of brown rot.  It is not effective enough to recommend in an orchard with marketable fruit, but it might suffice if the objective is to suppress brown rot at minimal cost.  If no fungicides are applied and weather during fruit ripening favors brown rot, then brown rot might become so severe that it will invade and kill shoots.  Shoots infected with brown rot this summer can provide inoculum for next year's crop, thereby complicating brown rot control for the next season.

If summer fungicides for brown rot control are reduced or eliminated, then special care may be required to manage peach leaf curl this fall and/or next spring.  Fungicides used for brown rot suppress peach leaf curl, so leaf curl is often worse in the year following a complete crop loss, especially if the intervening winter is rather mild.  Leaf curl can be easily managed with copper sprays or other leaf curl fungicides applied at leaf drop in late fall and/or at bud swell in spring.

PLUMS.  Comments about brown rot in peaches apply to plums as well.  Otherwise, no fungicides should be needed.  Black knot spreads earlier in spring and should not be an issue at this time.

CHERRIES.  On sweet cherries, one or two additional sprays may be required to control brown rot, and sulfur may not be adequate.  If brown rot is not controlled, an immense amount of inoculum can be carried through winter and brown rot control in 2009 might be difficult if weather conditions favor brown rot next year.  With peaches and plums, it is feasible to knock brown rot mummies out of the trees during winter pruning, so I am less concerned about having brown rot mummies in those trees at the end of the season. With cherries, removing brown rot mummies can be nearly impossible, so more attention should be given to keeping hail-damage fruit from mummifying on the tree.

On tart cherries, several additional sprays may be needed to keep cherry leaf spot under control through late summer.  Trees receiving no additional fungicides may defoliate early, leaving them susceptible to winter damage.

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


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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FAX:  304-876-6034
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