April 7, 2008

ENTOMOLOGY

Rosy apple aphids that hatched from overwintering eggs are all wingless females called stem mothers that become adults by the pink stage of apple bud development.  Whereas the newly hatched nymphs have a dark green color, adults are purplish or dusty gray.  A single stem mother is capable of curling a leaf, and it is from within this protected shelter that numerous live young are produced.  Rosy apple aphid must be controlled before petal fall in order to prevent fruit injury.  To monitor aphid abundance, make a 3-minute examination of 5-10 trees per block at the prepink stage and count the number of fruit spurs showing curled leaves with live aphids.  An insecticide application is recommended before petal fall if an average of one or more infested fruit clusters per tree are found.  The neonicotinoid materials (Actara, Assail, Calypso) and Beleaf are considered the most effective options.  Actara should not be applied later than early pink, or within 5 days of placing beehives in the orchard, since it is toxic to bees exposed to direct treatment or residues on blooming plants. Beleaf is relatively non-toxic to bees, whereas Assail and Calypso are toxic through direct contact and may be applied from pink through bloom if sprays are allowed to dry before bees begin foraging in the orchard.

Tarnished plant bug adults overwinter under bark and leaves in woodlots, fence rows and rock breaks, and around alfalfa, other legumes or weeds that are seeded late in the summer or early fall.  They become active and fly to apple trees near the tight cluster stage.  Feeding on apple buds before bloom usually results in early bud abscission and is rarely a problem, whereas feeding from bloom to shortly after fruit set results in a deeply sunken dimple in the side or calyx end of the fruit.  A white visual, non-UV reflecting sticky trap has been useful for monitoring tarnished plant bug populations and for making decisions regarding management in apple orchards.  Where these traps are installed at green tip, prebloom control is recommended if the cumulative capture averages 2.4 per trap by tight cluster or 4.1 per trap through late pink.  Control options include pyrethroids (Ambush, Asana, Battalion, Baythroid, Danitol, Decis, Lambda-Cy, Mustang Max, Perm-UP, Proaxis, Tombstone, Warrior), Actara, Beleaf, Calypso, Thionex, or Carzol.

Green peach aphid typically overwinters in this area as wingless females in protected places on the tree and in ground debris.  Aphid feeding on flower parts or on the underside of leaves is usually first observed during the late bloom to petal fall stage of peach and nectarine.  Infestations are often first detected on leaf clusters attached to the trunk or scaffold limbs in the lower part of the tree.  Feeding on leaves causes them to curl, become yellow, and drop prematurely from the tree.  Feeding on fruit may result in distortion, cracking and drop, especially on nectarine.  Provado, Actara, Assail, and Beleaf are the most effective treatments and are recommended for control if more than an average of one colony per tree is found.

Pheromone traps should be installed for the monitoring of codling moth and tufted apple bud moth at the beginning and near the end of apple bloom, respectively.

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.

HORTICULTURE

Peach bloom thinning.  Peach trees are now entering the bloom period. As we know, blossom thinning in peaches is extremely important because of the high cost of hand thinning and lack of any postbloom chemical thinner. The mode of action of peach blossom thinners is that they are caustic and reduce fruit set by damaging different flower parts, including anthers, stigma, style, and pollen tubes, and thus prevent fertilization. The fertilized flowers will not be affected by blossom thinners and continue to grow, while unfertilized flowers will drop. The advantages of peach bloom thinning are that: a) flower thinning can increase fruit size; and b) flower thinning can increase flower bud formation compared to hand thinning 35 to 50 days after full bloom. However, there is a disadvantage for peach bloom thinning: the risk of spring frost which may cause damage to fruit and affect yield.  You can use either mechanical methods, such as brushes, rope drags and water, or chemical thinners to do bloom thinning. There are two chemical thinners for peaches:

 1). WILTHIN: It is labeled for blossom thinning of peaches and nectarines to reduce fruit set. WILTHIN should be applied as a dilute spray to achieve adequate wetting of flowers at 3 to 6 quarts in 100 to 250 gallons of water per acre. Regulaid at 1pt/100 gal should be added to the solution. Application should be made when about 70-80% of the flowers have opened, with 20-30% of the buds in the pink stage of development. Minor leaf burn may occur on expanded leaves after spraying. It has been reported that leaf injury at this stage will not affect yield and fruit quality. Growers are encouraged to apply this material to only a few trees to gain experience before wide scale use.

2). Ammonium thiosulfate (ATS): ATS is a fertilizer. The use of ATS fertilizer for flower thinning has been commercially practiced in peach orchards. Rate of formulated product is 3 to 4 gal in 100 gallons of water per acre. ATS is most effective when about 70 to 90 percent of flowers have opened. ATS will also cause some injury to leaves, but the leaf injury at this stage will not affect yield and fruit quality.

Do not apply WILTHIN and ATS too early or too late. You will not have enough fruit on trees if you apply too early. On the other hand, you will not get good thinning effects if you apply too late. (Modified from article prepared by Dr. Rongcai Yuan, Virginia Tech Horticulturist).

PLANT PATHOLOGY

Apple scab.  We’ve recorded two infection periods on varieties showing green tip on March 31, including Red Delicious, some Gala’s, Empire, Ida Red, etc. On March 31 – April 1 we had 17 hours of wetting at 54� F with 0.01 inches of rain. Other locations may have had no rain or rain up to 0.04 inches. Apple scab ascospores were caught in traps during this infection period at the Winchester Fruit Station. Because of our low overwintering scab populations, I consider this wetting period to be insignificant in terms of scab infection. The second infection period on April 3-4 was more convincing in terms of rainfall amount (0.56 inches) and wetting duration (31 hours in a split infection period, at an average temperature of 46� F). The rain event on April 6 did not meet the criteria for an infection period. The wetting period of March 31 – April 1 will be recorded as our first apple scab infection period for the 2008 growing season.

Why do we always make such a big fuss about early scab control? It is important to avoid early infections on sepals, as these are difficult to detect and can provide conidial inoculum throughout the early part of the growing season. Copper sprays, even at the low label rate, will provide scab protection similar to that provided by a mancozeb fungicide applied at 3 lb/acre. However, Cu does not provide back action against scab. The relatively new AP-type fungicides, Vangard 75WG and Scala 5SC will provide about 48 hours of back action. These products should be used in a tank mix with a protectant material, preferably one of the EBDC’s or captan (3 ounces of Vangard or 5 fluid ounces of Scala, combined with the 3-lb. rate of mancozeb 75DF or Polyram 80DF).

Apple scab ascospore maturity degree-day tracker.  With a green tip estimate for March 31, 2008, estimated ascospore maturity is approximately 3% (90% confidence interval 0 to 14%) as of Monday, April 7, 2008.

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

Powdery mildew spores are showing now on overwintering shoots that have started to emerge. There is a lot of overwintering inoculum out there, so it looks like 2008 could be another heavy mildew year. For best mildew control, fungicide applications should begin at tight cluster and continue until terminal growth stops in midsummer. The spray interval is generally 10 days from tight cluster through petal fall, when leaf tissue is developing rapidly, and is lengthened to 14 days after petal fall. Excellent powdery mildew control can be expected when SI-class fungicides are used on a 7 to 10-day interval for scab control. The strobilurin fungicides, Sovran and Flint, also provide good control of powdery mildew. (Deciding how to configure sprays of SI's and strobilurins should depend upon other disease concerns, particularly the rust diseases, where SI’s are better, and whether or not your orchard contains scab that is resistant to the SI’s). Severity of powdery mildew is directly related to the amount of overwintering inoculum in shoot and blossom buds and the length of the spray interval. Check blocks of highly susceptible cultivars (Jonathan, Ginger Gold, Rome Beauty, Stayman Winesap, Idared, Paulared, Granny Smith) to determine the amount of overwintering inoculum. Where mildew is a problem, maintaining shorter spray intervals (not over 7 days) more effectively reduces mildew infection than increasing fungicide rates. On highly susceptible cultivars, special mildew sprays applied between the regular sprays from pink through the cover sprays is the most economical way to effectively manage the disease and prevent a repeated buildup of mildew for the following year. These extra spray applications will easily pay for themselves with increases in yield and quality. When the protectant fungicides mancozeb, Polyram, captan, and Ziram, are being used for scab control, the addition of sulfur will usually provide good control of mildew.

New Fungicide Labels for tree fruits include PropiMax from Dow Agrosciences and Inspire Super from Syngenta. PropiMax is an EC formulation of propiconazole (the same active ingredient in Orbit 3.6EC). It has a Section 3 label for disease control in all stone fruits, and is active at 4 fl. oz./acre against brown rot, cherry leaf spot, and rusty spot. Think of it as a generic Orbit. Inspire Super is in a multi-pack with difenoconazole (an SI fungicide) and Vangard. It is labeled for disease control on all pome fruits at a rate of 4 oz. of Inspire Super plus 4 oz. of Vangard. It shows good activity against scab, mildew, and rust, and sooty blotch and fly speck, but has a 72-day preharvest interval. It may have a good fit in the early part of the disease management program.

Current Conditions.  Fruit producers with access to the World Wide Web can access a web page called "Current Conditions" that will provide daily (or "as-needed") updates on current disease and insect development issues.  The page should help to bridge the information gap between issues of The Orchard Monitor and provide the grower with the timely information that is needed for making good pest control decisions.

To view the "Current Conditions" page, click here, or go to the WVU - KTFREC Home Page at: http://www.caf.wvu.edu/kearneysville/wvufarm1.html and select "Current Conditions" from the menu.

New Weather Data from Kearneysville Davis Vantage Pro 2 includes an electronic leaf wetness sensor and a soil temperature probe. The information is viewed on an hourly basis on the link labeled "hourly weather data for the previous 8-day period." We will try to update the Vantage Pro machines to Vantage Pro 2’s as time and resources permit.

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
Boards of Education and County Commissions Cooperating.  Equal Opportunity / Affirmative Action Institution