WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
June 12, 2006

Upcoming Events


Pheromone Trap Counts Plant Pathology



June 15,  5:30 p.m. - Tree Fruit Grower Twilight Meeting at Cline's Orchard in Clearbrook, Va. To reach the orchard, take I-81 to exit 321 (Clearbrook). Turn left at the stop sign onto Hopewell Road, travel back over I-81 and look for VA Cooperative Extension signs. Please bring lawn chairs. The agenda will include a tour (5:30-6:30), catered dinner (6:30-7:15) and updates by VA Tech Extension Specialists (7:15-7:45). Please provide a head count for the caterer by contacting Josh Marvel at 540-665-5699 or at jmarvel@vt.edu by June 12

June 22, 6:00 p.m. - Tree Fruit Grower Twilight Dinner and Meeting at Shanholtz Orchards, Romney, W. Va.  Following dinner, seasonal updates will be provided by WVU Extension Specialists and an orchard tour will be conducted, which will include studies underway for weed control and pheromone mating disruption (for codling moth and Oriental fruit moth).  For more information contact the Hampshire County Extension Office at 304-822-5013. 

July 6. - 2006 Summer Tour sponsored by the Maryland State Horticultural Society and Maryland Cooperative Extension. The tour will depart from Catoctin Mountain Orchards (Thurmont, Md) and include stops at Coastal Sunbelt Produce in Savage, Md; Homestead Gardens in Davidsonville, Md; and Boyer Farms in Severn, Md. The cost of $30 per person (includes tour bus, beverages on bus and materials) must be mailed by June 30. Lunch is provided by Homestead Gardens. For more information or to request a registration form, contact Cindy Mason at 301-432-2767 x301.


Pesticide update.  On June 8, 2006, the U.S. Environmental Protection Agency (EPA) notified USApple that it planned to publish a preliminary decision on June 9, 2006 to phase out the apple use of azinphos methyl (Guthion) in 2010. Apple growers will be required to incorporate additional mitigation measures, such as increased buffers, in the years preceding the phase out. Additionally, EPA plans to increase the restricted-entry interval (REI) for phosmet (Imidan) to 7 days (REI will increase from 1 to 3 days this summer). A 60 day comment period will provide an opportunity for USApple and members of the industry to comment on the impact of EPA's preliminary decision. 

Oriental fruit moth hatch of second generation eggs has begun and is estimated at 6% complete through June 11, based on an accumulation of 1053 degree days (DD) since biofix on March 31 at the WVU KTFREC. Control of the second generation is justified where the pheromone trap capture exceeds 10 moths/trap/week in both peach and apple. In peach, Intrepid may be applied (12-16 oz/acre) at 1050-1100 DD (6-9% egg hatch, estimated on June 11-13) and again at 1350-1400 DD (45-55% egg hatch, estimated on June 22-25), if needed. If using azinphos methyl (Guthion) or Imidan, apply at 1150-1200 DD (14-20% egg hatch, estimated on June 16-18) and again at 1450-1500 DD (65-72% egg hatch, estimated on June 26-29), if needed. In apple, apply Rimon at 1300-1350 DD (35-45% egg hatch, estimated on June 21-23); or Assail, Calypso or Intrepid at 1350-1400 DD (45-55% egg hatch, estimated on June 22-25); or Avaunt, azinphos methyl (Guthion) or Imidan at 1450-1500 DD (65-72% egg hatch, estimated on June 26-29). 

Tufted apple bud moth first generation egg hatch is estimated at 37% complete through June 11, based on an accumulation of 676 DD since biofix on May 3 at the WVU KTFREC.  Refer to the May 30th issue of this newsletter for insecticide options and recommended timings to control this insect.

Codling moth first generation egg hatch is estimated at 66% complete through June 11, based on an accumulation of 560 DD since biofix on April 26.  Refer to the May 15th issue of this newsletter for control recommendations.

Potato leafhopper adults and  nymphs have been observed recently in a few orchards.  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.  On young trees or where fire blight symptoms have been observed, count nymphs and adults on 50-100 randomly selected terminal leaves on a weekly basis through July. Although there is no established economic injury level on apple, a tentative threshold of one nymph or adult per leaf is recommended in New York. Control options include Provado, Actara, Assail, Calypso, Clutch, Vydate, Lannate, or Thionex.  In a New York study with Provado, it was found that the number of applications was more important than rate. Maintaining coverage of new growth with more frequent applications of a lower rate (0.5 oz/100 gal) provided comparable control that was more economical than fewer applications of a higher rate (2 oz/100 gal).

Potato leafhopper adult and nymph
Potato leafhopper injury

European red mites have increased recently in a few apple and peach orchards to levels that require control.  Blocks most likely to experience mite problems this early are those that received applications of Rimon or pyrethroids last fall, or pyrethroids or carbaryl (Sevin) this spring. 

Monitor the mite population on 5-10 trees of the same cultivar randomly scattered throughout the block.  Collect 10 middle age leaves from each tree, count the total number of motile mites and calculate the average number of mites per leaf. Using figure 1 (for apples), estimate the projected production per acre (harvested bushels) for the affected block.  Select the threshold line on the figure for the appropriate time of the growing season.  For a given time of the growing season and a given estimated crop load, if mites per leaf exceed the threshold then some control is needed, either by predators or by application of miticides. If you are using the alternate-row-middle (ARM) system of spraying to make your miticide applications, reduce the action threshold to one-half the value in the figure since you are only spraying one-half of the tree.  If the mite population does not exceed the action threshold, it should be reassessed within 5-7 days.  If the mites per leaf exceed the action threshold, the predator population should be assessed. 

Although the black ladybird beetle, Stethorus punctum (SP), has historically been an  important predator of mites in the mid-Atlantic region, its abundance has generally been very low in recent years.  If present, determine their abundance by counting the number of adults and larvae observed during a 3 minute period, while slowly walking around the periphery of each tree sampled for mites.  Divide the 3 minute SP count by the number of motile pest mites per leaf.  For example:  25 SP adults and larvae divided by 10 motile mites per leaf equals a predator-to-mite ratio of 2.5, which is generally sufficient for biological control to occur. 

Predatory species of mites have been more abundant in recent years, and can provide significant biological control of pest mites.  The two most common predatory mites in mid-Atlantic apple orchards are Amblyseius fallacis (AF) and Zetzellia mali (ZM).  AF is similar in size to pest mites, clear to straw colored, oval to pear shaped, and moves rapidly over the leaf surface.  An AF-to-pest mite ratio of at least 1:10 has a good probability of  providing biological control.  ZM is smaller than pest mites or AF and lemon-yellow to reddish-orange.  Although there are no validated management thresholds for ZM, populations averaging 2-3 per leaf can reduce pest mite levels.  Determine the average number of predatory mites per leaf on the same leaves sampled for pest mites. 

If the action threshold has been reached and the predator-to-pest mite ratio is insufficient to provide biological control, then a miticide application is justified.  Options effective against nymphs and adults include Nexter (formerly Pyramite), Fujimite, Kanemite and Acramite.  Products having primary activity against eggs and nymphs include Zeal and Envidor.  Apollo and Savey, which act primarily as ovicides, may also be used, but should be tank-mixed with one of the other miticides if motile mite stages are especially abundant.  The orchard should be checked again in 5-7 days after application to determine if retreatment is necessary.   A different miticide should be used if retreatment is needed.  If the predator-to-pest mite ratio is only slightly too low, a half spray (ARM application) may be sufficient to  allow predators to become abundant enough  to provide biological control. 

On peach, which is only about half as sensitive to mite feeding as apple, an action threshold of 10 mites per leaf is recommended at this time of the season.  Options for control include Nexter, Envidor, Acramite, Apollo (21 day PHI) and Savey (28 day PHI).

European red mite motile stages and summer eggsStethorus punctum adult (right), larva (center) and ERM (left)Amblyseius fallacis adultZetzellia mali adult

ERM action thresholds

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 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.

Yellow panel trap
Red sphere trap

Woolly apple aphid may begin increasing this time of the season and was becoming problematic in an apple orchard inspected last week.  During the spring, nymphs that overwintered on the root system crawl up the tree to initially establish colonies on branch wounds (pruning cuts, cicada oviposition scars, cankers).  During the summer, colonies will also occur on foliar growth at leaf axils and on watersprouts.  Heavy infestations result in an accumulation of honeydew and subsequent sooty mold on fruit and leaves, and gall formation at leaf axils.  Aphids that are crushed during harvest can result in red sticky residues on fruit, and on the hands and clothing of pickers. Severe root infestations can reduce growth and production, especially of young apple trees.  Various predators and parasites, especially syrphid fly larvae and a tiny wasp, aphelinus mali, are very important in helping to keep woolly apple aphid in check in most orchards.  However, many pesticides, especially pyrethroids are highly toxic to these biological control agents which can lead to woolly apple aphid outbreaks. 

Monitor orchards for woolly apple aphid colonies by inspecting pruning cuts, cicada scars, and foliar growth (leaf axils, watersprouts).  Although no threshold is available, treatment with Diazinon, Thiodan, Provado or Actara is recommended if honeydew or sooty mold begins appearing on fruit.  Increasing the spray volume will likely improve control since colonies are difficult to penetrate because of their waxy outer covering.

Woolly apple aphid colony on pruning cut
Woolly apple aphid colony on branch


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
May 8 4 120 85 47 40 0 35
May 15 1 57 29 20 34 7 25
May 22 0 15 29 23 37 1 4
May 30 0 384 25 11 29 0 23 0
June 5 36 1300 24 28 107 4 15 0
June 12 138 1120 19 14 48 10 6 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.  With scattered showers over the past 2 weeks, some locations have picked up some much-needed rainfall, whereas other locations continue to be a bit on the dry side. At WVU-KTFREC, we recorded four wetting periods since the last newsletter on May 30th (see the list below). Our total rainfall for the month of June as of Monday morning June 12 is 1.28 inches at WVU-KTFREC, 1.70 inches at Orr's Farm Market, and 0.81 inches at Butler's Farm Market. Again, our thanks to these growers for hosting our Davis weather machines.

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


Date 2006

Hours/ degrees F


March 31 - April 1

10 hr/59 F


April 8

14 hr/49 F


April 21-23

34 hr/54 F


May 8-9

19 hr/51 F


May 11-12

25 hr/56 F


May 15

11 hr/55 F


May 31

9 hr/67 F


June 1 - 2

18 hr/69 F


June 2 - 3

14 hr/66 F


June 7 - 9

23 hr/64 F

Disease observations.  According to Dr. Keith Yoder at the Virginia Tech AREC in Winchester, we have had 28 days favorable for secondary mildew infection through June 1 (compared to 36 infection days through June 1 in '05 and 22 in '04). This was evident in many orchards this past week, with high levels of mildew visible on varieties on which mildew is not usually a problem. Under these conditions, trees should be protected until shoot growth hardens off to prevent mildew infection of buds for overwintering and a recurrent problem in 2007.

Some fire blight has been observed in blocks with overwintering infections from 2005. Some of the more established infections look like blossom blight and, based on our scouting in May, the incidence of these must have been very low. However, with some favorable weather for spread of the pathogen we are now seeing some shoot blight in areas of the tree in close proximity to the original blossom infections. In most cases the disease should be easily managed this year by removing and destroying the infected shoots.

Accumulated wetting hours.  As of June 12, 2006, we have accumulated 201 wetting hours from a petal fall date of April 27. 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.

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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PHONE:  304-876-6353
FAX:  304-876-6034
WEB:  www.caf.wvu.edu/kearneysville

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