May 14, 2007

ENTOMOLOGY

Codling moth adult emergence began on May 3, with biofix set on May 5, which is 9 days later than last year based on pheromone trap capture at the WVU KTFREC.  Using a base temperature of 50�F and upper temperature of 88�F, degree days (DD) should be accumulated from biofix in order to properly time spray applications. Control is justified to prevent fruit injury  in those orchard blocks where the pheromone trap catch has exceeded 5 moths/trap/week.  The best timing for spray applications, based on degree day (DD) accumulations after biofix, depends on the insecticide used. Some materials (Rimon, Intrepid, Assail, Calypso) perform best when applications are initiated before the beginning of egg hatch. The ideal timing to initiate applications is 50-150 DD for Rimon and 150 DD for Intrepid, Assail and Calypso. Applications of Avaunt, Azinphosmethyl (Guthion), Imidan, Diazinon, Carbaryl (Sevin) or CM granulosis virus (Cyd-X, Carpovirusine) should be initiated at 250 DD (3% egg hatch). An initial spray should be followed by a second complete application in about 14 days (7-10 days for CM granulosis virus), or three additional alternate-row-middle applications 5-7 days apart (3-5 days apart for CM granulosis virus). Through May 13, 107 DD have accumulated since biofix at the WVU-KTFREC.

White apple leafhopper nymphs are appearing on the undersides of apple leaves.  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 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, Clutch, Lannate and Provado.  Materials rated as good include Agri-Mek, Sevin, Surround, Thionex, and Vydate.

European red mites which hatched from overwintering eggs have reached the adult stage, and females are beginning to deposit eggs on the leaves.  Populations have been high enough to require treatment already this season in some apple orchards. The use of pyrethroids late last season and/or lack of oil application this spring have been responsible for the mite increase in some situations. If this has been the case in your orchard, it is recommended that you determine the abundance of mites at this time in order to implement early season management strategies where warranted. 

Determine mite abundance from a sample of 5-10 leaves (collected from the middle of a fruit spur) from 5-10 trees per block of the same cultivar.  If oil or another acaricide has already been applied, examine each leaf and determine the average number of mites/leaf for the total leaf sample.  If no oil or other acaricide has been applied, examine each leaf for the presence or absence of one or more motile mites, and calculate the average percentage of mite-infested leaves for the total leaf sample.  Refer to Table 1 below and determine the expected number of mites/leaf for a given percentage of mite-infested leaves.

^aLeaves with at least one motile stage.

A preventative acaricide should be considered if mite density averages three or more per leaf, or in orchards where mites are an annual problem.  The most effective treatments recommended at this time include Agri-Mek, or the ovicides Apollo or Savey.  To minimize the development of resistance, do not use Agri-Mek or either one of the ovicides in two successive years.  Agri-Mek, which will also control spotted tentiform leafminer and white apple leafhopper, should be applied within 7-10 days of petal fall and combined with 1 gal/acre of oil.  Other preventative strategies, although usually less effective, include the early postbloom application of Vydate (can be substituted for Sevin as a thinner), or the use of Damoil or Ultra-fine oil at 2 gal/acre at petal fall, first and second cover.

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, Nufos) has been 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 timing of chlorpyrifos for control, including high efficacy in petal fall applications. Chlorpyrifos application 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.

PHEROMONE TRAP COUNTS
WEST VIRGINIA UNIVERSITY KTFREC

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.

PLANT PATHOLOGY

Apple scab. We recorded two new infection periods since the last Orchard Monitor on April 30. The first one occurred on May 10-11 and was accompanied by 0.24 inches of rain. With rain beginning at around 9:00 p.m., leaves were wet for 14 hours at an average temperature of 63� F. The second infection period occurred on May 12-13 and was accompanied by 0.13 inches of rain. Wetting duration was 8 hours at an average temperature of 60� F. In clean apple orchards with no visible lesions, these infection periods are unlikely to result in significant scab infection. Our temperature data put into the Cornell ascospore maturity model suggests that our cumulative ascospore maturity might be just about 100%. However, our extended dry period during the latter half of April and early May is likely to result in an extended period of apple scab ascospore availability. The potential for primary apple scab infection will remain high under these conditions and will likely remain high until we get the wetting events needed to discharge the ascospores. I think we need at least two more good rains to be certain that we are past the period of primary scab.

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

Fire blight. Warm temperatures during the period April 22 – 25 resulted in rapid progression of plant development into the bloom stage and high fire blight infection risk with the first open blossoms. We did not record any wetting during this period and, therefore, no fire blight infection was recorded. However, fire blight infection did occur during this time, with blossom blight symptoms observed in one commercial orchard on May 8th. Upon examining the weather data from this location, it is likely that the infection was related to the high wind speeds recorded on April 23rd. The potential for fire blight blossom infection also occurred on May 1st. First symptoms from this infection are predicted for May 14th. Later blooming apple cultivars experienced the potential for blossom infection daily during the period of May 9-12. Risk of blossom infection on late-blooming varieties remains high on Tuesday and Wednesday, May 15 and 16. See our "Current Conditions" Web page for details that are updated at least three times weekly during the bloom period.

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. Our "Fire Blight Conditions" webpage has some recent photographs of these early symptoms.

Cedar-apple rust and quince rust. The wetting periods recorded on April 26 – 27 and May 10 – 11 were favorable for cedar-apple rust and quince rust infection. The lesion on the upper leaf surface contains 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 2009. 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.

Rust "quick pix": (click to view) Cedar-apple rust gall on cedar; cedar-apple rust lesions on leaf, leaf petiole, and fruit. These symptoms on apple could be showing up within the next week or so.

READ THE LABEL CAREFULLY AND USE THE CHEMICALS IN ACCORDANCE WITH LABEL CAUTIONS, WARNING AND DIRECTIONS. REQUEST A MATERIAL SAFETY DATA SHEET (MSDS) FROM THE MANUFACTURER FOR EACH PRODUCT YOU USE.

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