WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
May 5, 2008

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Pheromone Trap Counts Plant Pathology



May 13. – West Virginia University Holiday. The WVU Kearneysville Tree Fruit Research and Education Center will be closed for the Primary Election. 

May 22, 6:00 p.m. – Tree Fruit Grower Twilight Dinner and Meeting at Gourmet Central (in Hampshire Industrial Park), Romney, W. Va.  Following dinner, WVU Extension Specialists will provide an update on orchard conditions and discuss pest management strategies. For more information contact the Hampshire County Extension Office at 304-822-5013.


Most area apple orchards will reach the petal fall stage this week. This is an especially important stage for insect management since there are numerous pests that pose a potential threat at this time. The success or failure in managing pests at this stage can have a significant impact on fruit quality, and difficulties encountered for the remainder of the season.

Plum curculio adult

Plum curculio is an important direct pest of both apple and peach, causing injury to developing fruit in the early postbloom period.  Adult beetles, which overwinter in hedgerows, trashy fields and woods, usually begin moving into orchards during the bloom stage.  Maximum activity occurs when temperatures reach 70F and above.  The primary injury results from egg-laying, consisting of a crescent-shaped scar on the fruit surface.  In apples that remain on the tree,   most   larvae   do   not  complete development as they are crushed by the expanding fruit.  Larvae successfully complete development in peaches and fallen apples.  Typically, most of the injury from this insect has occurred in apple blocks of mixed cultivars with a wide range in bloom periods.  Injury usually occurs on the earlier blooming varieties while waiting for the later blooming varieties to reach petal fall.  Recommended control options in peach include Imidan, Diazinon, Actara, Assail, Avaunt, pyrethroids (Ambush, Asana, Baythroid, Lambda-Cy, Mustang Max, Perm-UP, Pounce, Proaxis, Tombstone, Warrior), and Surround. In apple,  recommended options include azinphosmethyl (Guthion), Imidan, Diazinon, Avaunt, Assail, Calypso, Actara, and Surround.

Plum curculio fresh egg-laying injury

Rosy apple aphid control should have been implemented in the prebloom period. In those orchards where prebloom control was not effective, this insect can cause significant indirect injury to apple fruit in the early postbloom period.  As aphids feed within curled leaf clusters, their saliva is translocated to nearby fruits which causes them to remain small and become deformed and unmarketable.   Conduct a thorough inspection of apple orchards for this insect prior to the petal fall spray application.  Make a 3-minute examination of 5-10 trees per block and count the number of fruit clusters showing curled leaves with live aphids.  Pay particular attention to the center region of trees.  Also, inspect root suckers around the trunk for colonies which could disperse later into the tree canopy.  Apply Provado, Actara, Assail, Calypso, Clutch, or Beleaf at petal fall if an average of one or more infested fruit clusters per tree are found.

Rosy apple aphid fruit injury
Dogwood borer adult

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. 

Chlorpyrifos (Lorsban, Yuma) continues to be 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 control timing, with especially high efficacy in a petal fall application. Application of chlorpyrifos 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

White apple leafhopper nymphs

White apple leafhopper nymphs will begin to appear on the undersides of apple leaves over the next couple of weeks.  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 spur 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), Clutch, Lannate and Provado.  Materials rated as good include abamectin (Agri-Mek, Abacus, Abba, Temprano, Zoro), Sevin, Surround, Thionex, and Vydate.

White apple leafhopper injured leaves (right)

Codling moth adults were first detected in a single pheromone trap on April 25-26 at the WVU KTFREC.  However, sufficient capture didn’t occur to set biofix until May 2, which is 3 days earlier than last year.  The very beginning of moth flight is the optimum time to install pheromone mating disruption dispensers (Isomate CM/OFM TT, Isomate C+, Isomate CTT, Disrupt CM-Xtra, or CheckMate CM-OFM Duel) for the control of this pest. Isomate CM/OFM TT and CheckMate CM-OFM Duel will also provide mating disruption of Oriental fruit moth. The use of pheromone mating disruption dispensers should especially be considered as a  supplement to traditional chemical application in those problem orchards where pesticides alone have failed to provide adequate control.

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.

Codling moth adult


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

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 cedar-apple rust and quince rust infection periods.  We’ve recorded three or four additional infection periods since the last Orchard Monitor on April 21, 2008. On April 25 – 26, we had 16 hours of wetting at 62 F with 0.07 inches of rain. This infection period also was favorable for the rust diseases (cedar-apple rust and quince rust). The second infection period, on April 26 – 27, gave us leaf wetting for 15 hours at an average temperature of 56 F with 1.16 inches of rain. This infection period also was favorable for the rust diseases. At KTFREC on April 28, we were wet for 16 hours at an average temperature of 52 F, for an apple scab infection period with 0.81 inches of rain. This is just one hour short of being an infection period when dark hours are subtracted (wet 11 hours at an average temperature of 52 F). Finally, on May 4 we had a nighttime wetting with 0.02 inches of rain; duration 10 hours at 55 F. This is an apple scab infection period if you have visible scab lesions in the orchard. Total rainfall for the month of April at KTFREC was 8.61 inches (5.31 inches more than a "normal" April).

Apple scab ascospore maturity degree-day tracker. With a green tip estimate for March 31, 2008, estimated ascospore maturity is approximately 97% (90% confidence interval 86 to 100%) as of Sunday, May 4, 2008.

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


Date 2008

Hours/ degrees F


March 31-April 1

17 hr/54 F


April 3-4

31 hr/46 F


April 11-12

16 hr/62 F


April 20-21

48 hr/58 F


April 25-26

16 hr/62 F


April 26-27

15 hr/56 F


April 28

16 hr/52 F


May 4

10 hr/55 F

Fire blight.  We’ve had three fire blight infection periods during the apple bloom period this year. According to the Maryblyt model, fire blight blossom infections occurred on April 19 - 20, April 25 - 26, and May 4. Early symptoms from the first infection may be visible by mid-week (May 7) and, for the second infection period, at the beginning of next week. Recognizing early fire blight symptoms is important for good disease management. Catching fire blight early allows you to focus your efforts on quick removal of a limited number of infections before the disease gets well established and more difficult to remove. Look for darkened blossom centers, dark green and water-soaked fruit pedicels, and bacterial ooze droplets on fruit pedicels. See our "Current Conditions" Web page for details that are updated at least three times weekly during the bloom period.

Cedar-apple rust and quince rustThe wetting periods recorded on April 11 – 12, April 20 - 21, April 25 – 26, and April 26 – 27 were favorable for cedar-apple rust and quince rust infection. Symptoms of cedar-apple rust on leaves are visible at some locations, most likely from the first infection period. The yellowish lesions on the upper leaf surface contain the pycniospore stage of the rust fungus. The pycniospores function as spermatia and when mated with a compatible mating type will lead to the formation of the aeciospore stage on the underside of the leaf later this summer. The aeciospores will infect eastern red cedar when weather conditions are favorable, and then about 18 months later, galls on cedar will provide the inoculum in spring 2010. Quince rust causes dark green lesions and puckering at the calyx end of infected fruits. Aeciospores of the quince rust fungus are produced on fruit and often are visible by mid-June.

Peach leaf curl is showing up in some orchards, most likely from infections that occurred on March 31 – April 1. Usually this disease should be controlled in the spring with a fungicide application before the buds swell, or with leaf curl application in the fall. If leaf curl is severe in your peach and nectarine blocks in 2008, you may need both a fall (2008) and a spring (2009) fungicide application to control the disease for 2009. This disease does not spread or worsen after the initial symptoms have developed. If infection is severe on young trees, defoliation may be severe. Remove fruit from severely infected young trees and make sure the tree has the nutrients it will need to refoliate.


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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