WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
June 11, 2007

Upcoming Events


Pheromone Trap Counts Plant Pathology



June 28, 6:00 p.m. – Tree Fruit Grower Twilight Dinner and Meeting at Levels Fire Hall, Levels, W. Va. Following dinner, seasonal updates will be provided by WVU Extension Specialists, and a peach orchard tour which will include a deer fence and irrigation system will be provided by hosts Garry and Kane Shanholtz. For more information contact the Hampshire County Extension Office at 304-822-5013.


Codling moth first generation egg hatch is estimated at 74% complete through June 10th, based on an accumulation of 603 DD since biofix on May 5th at the WVU KTFREC. Refer to the May 14th issue of this newsletter for control recommendations. 

Tufted apple bud moth first generation egg hatch is estimated at 35% complete through June 10th, based on an accumulation of 668 DD since biofix on May 11th. Refer to the May 29th issue of this newsletter for control recommendations.

Oriental fruit moth injured peach shoot

Oriental fruit moth hatch of first generation eggs is complete. The second flight of moths is underway and hatch of second generation eggs is just beginning (estimated at 4% complete through June 10th, based on an accumulation of 990 DD since biofix on April 21st at the WVU KTFREC). Orchards should be inspected for shoot injury at this time in order to evaluate the effectiveness of first generation control measures. There are various options for controlling the second generation.  One strategy that could be targeted against adults is pheromone mating disruption, with various hand applied dispensers and a sprayable pheromone available.  A second strategy is to control larvae during the next few weeks with insecticides in those orchards where the pheromone trap catch exceeds 10 moths/trap/week.  In peach, recommended control options include Intrepid (12-16 oz/acre) at 1050-1100 DD after biofix (6-9% egg hatch) and again at 1350-1400 DD (45-55% egg hatch), if needed; or Imidan or Diazinon at 1150-1200 DD after biofix (15-20% egg hatch) and again at 1450-1500 DD (65-72% egg hatch) in high pressure situations.  In apple, apply Rimon at 1300-1350 DD (35-45% egg hatch); or Assail, Calypso or Intrepid at 1350-1400 DD (45-55% egg hatch); or Avaunt, Azinphos-methyl (Guthion) or Imidan at 1450-1500 DD (65-72% egg hatch).

Oriental fruit moth injured apple shoot

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 nymph and adult
Potato leafhopper injury

European red mites have increased to levels requiring treatment in some orchards already this season. In many situations, these orchards were treated with pyrethroids or Rimon late last season and/or did not receive an oil application this spring. In addition to these situations, orchards which received a late prebloom or early postbloom application of pyrethroid, or early postbloom application of carbaryl (Sevin) for thinning this spring are more likely candidates for earlier season mite problems. 

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, 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 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 based on crop load


March 19 0
March 26 2 0
April 2 121 3 0
April 9 54 28 1
April 16 23 93 0
April 23 18 640 68
April 30 22 1220 230 0 0
May 7 6 396 404 3 0 0 0
May 14 1 132 120 33 2 0 33
May 21 0 12 74 17 17 0 23
May 29 0 64 22 22 43 4 30 0
June 4 3 1280 4 17 12 3 15 1
June 11 59 1472 12 5 0 8 12 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. We recorded two (maybe three, for some of you) new infection periods since the last Orchard Monitor on May 29. The first one occurred on June 1 - 2 and was accompanied by 0.19 inches of rain. With rain beginning at around 8:00 p.m., leaves were wet for 14 hours at an average temperature of 65 F. The second infection period occurred on June 3 - 4 and was accompanied by 0.65 inches of rain. Wetting duration was 24 hours at an average temperature of 65 F. An additional short wetting period of 6 hours duration with 0.04 inches of rain occurred on June 6. Total rainfall for May was about 1.3 inches in most locations. The 65-year average for May is 3.8 inches.

Table 1. Dates and conditions for apple scab infection periods at the WVU - KTFREC, 2007.


Date 2007

Hours/ degrees F


May 10-11

14 hr/63 F


May 12-13

8 hr/60 F


May 16-17

20 hr/58 F


May 18-19

22 hr/50 F


June 1-2

14 hr/65 F


June 3-4

24 hr/65 F

Fire blight. Reducing shoot blight and reducing secondary inoculum. Here is an excerpt from Paul Steiner’s presentation at the Illinois Horticultural Society Meeting, January 2000: Reducing shoot blight: As methods for blossom blight control have improved, research on the nature and control of shoot blight has become more focused. Despite the long-held implication of sucking insects in outbreaks of shoot blight, there is little proof that such a relationship exists. Research in Pennsylvania has specifically excluded green apple aphids, while work in Virginia and Utah fairly well excludes white apple leafhoppers. In Virginia, there is some evidence that potato leafhoppers may play a role, but it is doubtful that this one species explains the worldwide incidence and continuing occurrence of shoot tip infections over several months during the season. At the same time, there is mounting evidence that gusty winds may cause small injuries to tender shoot tips through which bacteria on their surfaces may then enter and initiate infections.

From a timely control program, this presents two problems. First, streptomycin has proven to be ineffective in preventing shoot tip infections and most copper formulations have the potential for phytotoxicity. Secondly, even if a good bactericide becomes available, it hardly seems practical to try spraying whole orchards every time the wind blows with gusts more than 8 to 10 mph between petal fall and terminal bud set. The most practical approach, therefore, is still to reduce the number and distribution of secondary sources of inoculum by aggressively cutting out new infections early to reduce the supply of bacteria which colonize growing shoot tips.

One of the most promising developments for shoot blight control is a gibberellic acid synthesis inhibitor called Apogee™ (prohexadione-calcium, BASF) which appears to be on a 'fast track' for registration either this year or next. Excellent results in limiting shoot blight has been developed in Michigan (Al Jones, Michigan State Univ.) and Virginia (Keith Yoder, Virginia Tech) on the use of this material in one or two applications beginning at petal fall. There are few 'magic silver bullets' in plant disease management, however, so that even if Apogee™ does become available soon, it will still be important to continue all basic efforts to reduce the number and distribution of inoculum sources as outlined above. (Note: Apogee is available and is recommended in high risk plantings).

Reducing secondary inoculum: As fire blight epidemics get underway, the number of secondary infections increases rapidly because each infection site supplies additional inoculum for dispersal throughout orchards by wind, water and insects. Even where blossom blight does not occur or is well controlled, vegetative shoot infections can still cause much damage to the tree including a loss of total bearing surface. Cutting out or breaking off infected shoots has been tried often, but its effectiveness has always been questioned because some years it seems to work and some years it seems to fail miserably. There is also the preconceived notion that when cutting has to be done the amount of cutting required is neither practical nor economical because of the time and labor required. In truth, cutting out active infections can be extremely effective if done at the right time and in the right way.

Cutting out active infections: To be effective in slowing the current season's epidemic, cutting must begin as soon as early symptoms appear. The late Ron Covey in Washington State demonstrated that delaying the first of several cutting efforts by two weeks resulted in the removal of six times more wood than where cutting was begun immediately. 'Early', in this sense, means as soon as wilt symptoms are apparent and before significant necrosis develops. One reason for this is that even before shoot tips wilt, droplets of bacterial ooze are often present on otherwise symptomless shoots and these are sources of inoculum for further dispersal. One advantage of the Maryblyt™ program is that it has proven to be quite accurate (+ 0-2 days) in predicting the early appearance of blossom, canker, shoot and trauma blight symptoms so that orchard monitoring and cutting operations can be anticipated.

How the cuts are made is also important and has a substantial amount to do with how much carryover inoculum will be available the following year. Conventional recommendations often suggest that cuts be made 8 to 12 inches below the leading edge of symptoms and that cutting tools be surface sterilized with copper materials or alcohol between each cut. We've found the bacterial pathogen as far as 9 feet back on a branch with a single terminal shoot tip infection. This is far beyond the limit where most growers want to or is necessary to cut. In addition, because the bacteria are already internal in the infected limb, the sterilization of tools between cuts is of little practical value.

When infected shoots and branches are removed, living cells are cut and bruised, allowing their contents to be readily available for immediate colonization by the bacteria already present in xylem tissues, so that small cankers (1/4-inch or less) form around many cuts regardless of whether tools are sterilized. As this infection progresses into healthy wood where reserve carbohydrate levels exceed those of the bacterial ooze, water is denied the bacteria and canker extension stops. If cuts are made back to the next healthy branch union following conventional practice, this small canker will remain in the orchard and provide primary inoculum for next year's epidemic.

Through a process I call "ugly stub" cutting, cuts are still made 8 to 12 inches below visible symptoms, but always into 2-year or older wood (high carbohydrates) and then leaving a 4- to 5-inch naked stub above the next leaf, spur or branch. Although small cankers will still form around a significant number of these cuts, the ugly stubs can be easily recognized during the dormant pruning operation and removed at that time. A number of growers adopting this practice on a regular basis routinely spray paint the ugly stub bright orange so that they can be more easily located during the winter. This procedure is an important step in that it removes sources of inoculum in the orchard quickly which reduces the rate at which secondary infections occur, and it has longer term effects in that fewer cankers are left in the orchard to fuel next year's epidemic. It also has the very practical advantage of being much faster in that the tedious job of sterilizing tools between cuts is not necessary so long as the only consideration at the time is the removal of infected shoots. This last caution is important because such cutting forays should never be combined with routine summer pruning efforts.

The entire text of the presentation is available here: http://www.caf.wvu.edu/kearneysville/articles/FB-MANAGE00.html

Accumulated wetting hours. As of June 9, 2007, we have accumulated 101 wetting hours from a petal fall date of May 4 (last year at this time AWH = 154). 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.

Orange rust of brambles. Brambles – managing orange rust disease. Orange rust sporulation and infection is greatest during periods of cool, wet weather. There are two different periods when different types of infection occur. The first is in the spring, when the bright orange spores (called aeciospores) are produced. The spores released at this time cause localized infections on the leaves. In 21 to 40 days, another type of spore (called teliospores) form on the underside of these newly infected leaves, and produce basidiospores that actually cause the systemic infections. These systemic infections usually take place when temperatures are cool in the late summer and fall. Therefore, there are 2 periods when a fungicide should be used. The first is starting in the spring when the bright orange spores are forming (early to mid May) on a 10-14 day schedule until the infected leaves die and dry up in early summer. The second period is starting when temperatures start to decline in late summer to early fall through the first killing frost. There is a good chance of resistance development, however, so Nova used when not necessary should obviously be avoided. Also, cultural controls, such as removing wild brambles from areas near the planting, and removing any infected plants from the planting early in the season should be used to the greatest degree possible. Improving air circulation by controlling weeds and using good pruning practices will decrease the duration of leaf wetness necessary for leaf infection.

The following materials are registered for orange rust management in West Virginia: Cabrio EG at 14 oz/A. Do not use more than 2 sequential applications or more than 4 applications per year. May be used at harvest. 24-hr REI.

Pristine at 18.5 to 23 oz/A. Do not use more than 2 consecutive applications or more than 4 times/year. Can be used day of harvest. 24-hr REI.

Nova 40 W at 2.5 oz/A. Applications may be made up to the day of harvest. Do not apply more than 10 oz/A/season. 24-hr REI. Nova, or the other materials mentioned above, can be applied on a 10 to 14 day schedule until leaves on infected plants dry up and stop producing the orange spores. This is usually around mid-July.

Herbicides can be used as a spot treatment to kill infected plants.

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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