WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
June 16, 2008

Upcoming Events


Pheromone Trap Counts Plant Pathology



June 26, 6:00 p.m. – Twilight Fruit Growers Dinner and Meeting at Spring Valley Farm and Orchard, 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 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. 

July 8, 9:30 a.m. – 8:10 p.m. – 2008 Maryland Summer Tour. Tour stops will include the Virginia Farm Market, Marker Miller Orchard, Alson H. Smith, Jr. Agricultural Research and Extension Center, and the USDA Appalachian Fruit Research Station. Registration of $50 (includes bus transportation, two meals and beverages) is due by July 1. For more information contact Cindy Mason at 301-432-2767 x301.


Tufted apple bud moth first generation egg hatch continues and is estimated at 61% complete through June 15, based on an accumulation of 811 degree days (DD) since biofix on May 4 at the WVU-KTFREC. See the June 2 issue of this newsletter for information on control options and timing. 

Codling moth hatch of first generation eggs is estimated at 81% complete through June 15, based on an accumulation of 651 DD since biofix on May 2 at the WVU-KTFREC. Refer to the May 19 issue of this newsletter for control options and timing. 

Oriental fruit moth hatch of second generation eggs has begun and is estimated at 10% complete through June 15, based on an accumulation of 1119 DD since biofix on April 10 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, Assail or Intrepid could have been applied at 1050-1100 DD (5-10% egg hatch) and again at 1350-1400 DD (45-55% egg hatch, estimated on June 24-26), if needed. If using Imidan, Diazinon, Delegate or Altacor, apply at 1150-1200 DD (14-19% egg hatch, estimated on June 16-18) and again at 1450-1500 DD (64-73% egg hatch, estimated on June 28-30), if needed. In apple, apply Rimon at 1300-1350 DD (35-45% egg hatch, estimated on June 23-25); or Assail, Calypso or Intrepid at 1350-1400 DD (45-55% egg hatch, estimated on June 24-26); or Avaunt, Azinphos-methyl (Guthion), Imidan, Diazinon, Delegate or Altacor at 1450-1500 DD (64-73% egg hatch, estimated on June 28-30).

European red mites have increased to levels requiring treatment in some orchards already this season. Late season use of pyrethroids last year and/or lack of oil application this spring have been contributing factors to the early season mite problem this year. 

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 throughout the mid-Atlantic region, its abundance in recent years has generally been  low in most orchards.  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 West Virginia 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, Portal, Kanemite and Acramite.  Products having primary activity against eggs and nymphs include Zeal and Envidor.   The orchard should be checked again in 5-7 days after application to determine if retreatment is necessary.   A miticide from a different chemical class (with a different mode of action) should be used if retreatment is needed.  See Table 3 (pages 39-40) in the 2008 Spray Bulletin. 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, Onager  (28 day PHI).

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

ERM action thresholds based on crop load

Potato leafhopper adult and nymph

Potato leafhopper overwinters in the Gulf Coast states and adults are repeatedly carried to this region on wind currents, often associated with tropical storms, 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 injury


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

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 2, 2008. Our disease pressure is still considerable. On June 4 - 5, we had leaf wetting for 31 hours at 68 F with 1.47 inches of rain. On June 6 - 7, we had leaf wetting for 11 hours at 72 F with 0.08 inches of rain (this one was spotty and not everyone experienced it). On June 10 - 11, we had leaf wetting for 15 hours at 71 F with 0.42 inches of rain. Finally, on June 14 - 15, we had leaf wetting for 19 hours at 69 F. Total rainfall to date for June is 2.62 inches (normal for June is 3.4 inches). These most recent infection periods are favorable for the development of summer fruit rots on apple – especially white rot and bitter rot; as well as brown rot on stone fruits, particularly sweet cherries.

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


Date 2008

Hours/ degrees F


May 26-27

13 hr/69 F


May 31

6 hr/70 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

Accumulated wetting hours.  As of June 16, 2008, we have accumulated 189 wetting hours for a petal fall date of May 3 (last year at this time AWH = 155). 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.

Brown rot on stone fruits.  The good news on brown rot is that inoculum pressure is low in most local orchards because of good sanitation practices and low overwintering populations of the fungus. The bad news is that this disease is explosive and recent weather has been favorable. Incidence of brown rot fruit infection is proportional to temperature and wetness duration. Optimum temperature range is 72 - 77 F for infection of peach fruit and infection can occur following only 3 hours of wetting at high inoculum concentrations. Longer wet periods during infection result in shorter incubation periods. Insects (nitidulid beetles and honeybees) also can be important as vectors of the brown rot fungus during fruit ripening, carrying conidia to injury sites produced by oriental fruit moth, Japanese beetle, green June beetle, stink bugs, and other insects, or birds, that injure fruit. Wounded fruit are infected much more readily than nonwounded fruit. Hail damage near harvest can lead to a devastating brown rot problem. At harvest, apparently healthy fruit usually are contaminated with spores or latent infections that, under favorable conditions, may later produce decay during storage and marketing.

Effective control of brown rot depends on attention to orchard sanitation; proper pruning of trees to facilitate drying and penetration of spray materials; monitoring for disease every 3 to 5 days during the preharvest period, being aware of favorable weather and the potential for bird, insect and hail damage; and use of effective fungicides at 7 to 10 day intervals during the preharvest and harvest periods. See the 2008 Spray Bulletin for suggested chemicals and rates of application. The sterol-inhibiting fungicides, Orbit, Elite, and Indar, are the best fungicides for controlling the disease and show generally similar performance in preharvest assessments. Fruit treated with Indar right before harvest generally shows less rot in the postharvest environment. Recent data from studies in Virginia, New Jersey, and California show that the recently-registered reduced-risk fungicides Elevate and Pristine are good to excellent, respectively, for managing brown rot. Reduced-risk fungicides have a low impact on the environment, high specificity to target organisms, low potential for groundwater contamination, and low potential for human health risks. Pristine is registered for use on all stone fruits, whereas Elevate is limited to use on peaches, nectarines and cherries.

Alternation of the sterol-inhibiting fungicides with Pristine or Elevate may help reduce the risk of the brown rot fungus becoming resistant to the SI’s. If fruit are washed during the packing operation, the efficacy of Pristine and Elevate for preventing wound infections is likely to be reduced relative to the sterol-inhibiting fungicides. For this reason, in years when the risk of brown rot is high or if packing conditions are unsanitary, the use an SI fungicide right before harvest is recommended.

Another choice that is new for 2008 is Adament 50WG. This product is a combination of the active ingredients found in Elite and Flint/Gem (tebuconazole + trifloxystrobin). This is a package mix of a sterol inhibiting fungicide with a strobilurin fungicide, and is registered for the control of fungal diseases on cherry, peach, and nectarine at the rate of 4 to 8 ounces per acre (limit 32 ounce maximum per acre per year with a 24-hour REI and 24-hour PHI). It is rated as excellent against brown rot. Do not make more than two sequential applications of Adament before rotating to a fungicide that is not from either group. Stated more specifically, if you use Adament twice consecutively, you can not use Orbit, Elite, Indar, or Pristine (or Cabrio on cherries) for your next application. The corollary: if you use Pristine (or Cabrio on cherries), Orbit, Elite, or Indar for two consecutive applications, do not follow with Adament.

Scholar (fludioxonil), another reduced-risk material, is available for postharvest use on all pome and stone fruits (excluding cherries). Data show that infections of wounds that occur in the field at harvest are effectively stopped by post-harvest treatments with Scholar, which is typically done on the same day that fruit are harvested. Including Scholar as a postharvest treatment may be useful in years when inoculum pressure is high, conditions at harvest are favorable for brown rot infection, or packinghouse conditions are unsanitary. Scholar is stable in 100 ppm chlorine.

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

The West Virginia University Cooperative Extension Service, U.S. Department of Agriculture, West Virginia County
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