The 1998-1999 Apple Pest Management Guide -- Further Delayed

We have just received word from Glen Koehler of UMaine Coop.Ext, the editor of this year's Guide, that we should not expect to receive the publication before May 15th. Apparently, there were many unplanned delays and basically the system broke down for getting it out in a timely fashion.

Fortunately, the 1996-1997 edition needed few factual changes. However, many of the "time sensitive" changes that are in the new edition of the Guide are presented below. If you do not have a 1996-1997 Guide to use until the new edition is mailed out, the 1996-1997 edition is available on the Internet and can be accessed through the AIM site:

If you do not have access to the Internet and have questions, please contact us.

Needless to say, changes will be made in how the Guide is published to prevent this from happening again.

In This Issue....
   Horticulture Notes

    Workshop
    Critical Temperatures
    Apple Thinning
         Factors influencing chemical thinning
        Thinning Windows
        Materials
        Recommendations
        Determining the size of the fruitlets
        Summ. & Comments from Dr. Ed Stover
        Sugg. Beginners Chem Thinning Program From Win Cowgill
        Estimating Fruit Set
How is Your Weed Control?

IPM News
Disease Management
Apple Scab
Powdery Mildew
Fire Blight (FB)
Arthropod Management
European Red Mites (ERM)
Leafminers (LM)
Monitoring Reminder
Getting the Most Pollination for Your Dollar
Contact Information

  Horticulture Notes
           M. Elena Garcia

Workshop

There will be an orchard tour at 3 locations. This will be an orchard update on horticulture and IPM issues. The topics covered will depend on the stage of development the trees are in at the time of the tours.
 
 

Orchard	Location	Date	Time
Belmont Orchard (Geoffrey Demong)	Shoreham	Tue, May 12	3:30 p.m.
Green Mt. Orchard (Evan and Matt Darrow)	Putney	Wed, May 13	3:00 p.m.
Allenholm Farm (Ray Allen)	South Hero	Tue, May 19	3:30 p.m.

Directions to the orchards:

Belmont Orchard: Shoreham. In Shoreham village (22A), turn right on Route 74 West. Just past 2 cemeteries, go straight on Witherell Road. Turn left into Belmont Orchard at the first house on the left.

Green Mountain Orchard: Putney. From Hwy 5, turn right if you are going south or left if you are going north at Putney General Store. Go north for ~1 1/2 miles. Past the Putney Central School, turn left at West Hill Rd. Go ~ 1/2 mile. The orchard will be on the right.

To Allenholm Farm: South Hero. From Hwy 2, turn left on South St. You will pass the school. The packing house will be on the right just past Hackett Orchard

 Critical Temperatures

Apples are beginning to bloom at the HRC (Horticulture Research Center) in Burlington. According to Dr. B. Boyce, the average full bloom date at the HRC for the past 20 years is May 20^th, with the earliest bloom date recorded on May 6 ^th and the latest on June 6 ^th. This year may be a be the earliest full bloom date in the past 20 years which means the trees are very vulnerable to freeze damage. Temperatures below 32⁰F just before the flower opens can injure the ovules and prevent fruit set. Pollen grains will generally not germinate at temperatures below 41⁰F, and if temperatures fall below 51⁰F, the pollen tube may not grow, and fertilization may not occur even if pollination occurred.

The easiest way to assess any freeze injury is to collect fruitlets, in a random manner, throughout the trees and the block. Cut the fruitlets lengthwise and check to see if there is any browning of the tissue. It is easier to determine damage to the female part (ovary and pistil) of the plant than the male parts (stamen). Knowing the amount of injury is very important in determining the amount of thinning you will have to do. Table 1 (from WSU) will give you an idea of the amount of damage you should expect for most cultivars at critical temperatures and developmental stages

                Table 1. Critical Temperatures (F) for Tree Fruit Bud Stages* (WSU)

Apple Thinning

It has been estimated that 90% of apple growers in the United States use some form of chemical thinning to improve fruit size and to promote annual cropping. However, no single thinning program applies to all cultivars. Each cultivar requires a slightly different thinning program, and the thinning response varies depending on climate and cultural conditions. The past history of the orchard, the grower's experiences with particular blocks, the cultivar, and the weather conditions should be used to determine the best time of application and the rates of the individual or combinations of thinners.

Factors influencing chemical thinning

Temperature

Temperatures during a thinner application and temperatures after the application are critical to successful thinning. All thinners have a greater response as the application temperatures increase because in order for thinners to work, they have to be absorbed, and absorption increases as the temperatures increase. Also, high temperatures increase the waxy cuticle of the foliage, thus decreasing the absorption of the thinner. Data from Michigan indicate that high temperatures improve NAA uptake.

Light

Factors that decrease photosynthesis such as cloud cover or within tree shade increase the effectiveness of thinners. Conversely, sunny weather, which increases photosynthesis, decreases the sensitivity of the fruitlets to the thinners.

Fruit size

Fruit size is very important in determining the efficacy of thinners. Most chemical thinners are most effective at fruit diameter's of 4 to 14 mm. At about 50 days after bloom, fruits begin to accumulate starch, and for approximately 6 weeks,   the fruit can not be induced to drop by the use of chemical thinners.

In spur Delicious, fruit diameter and temperature interact to determine the efficacy of the thinner. For example, when the fruit was less than 8mm in diameter, thinning results with carbaryl were similar regardless of the temperature. However, for larger fruit thinning (14 to 16 mm) was better when the temperature was at 70 or 80 than at 50 to 60.

Drying conditions

Poor drying conditions such as high humidity increase the amount of time the thinning chemical stays on the leaf surface, thus increasing the amount of chemical that is absorbed.

 Cultivar

Cultivars vary in their thinning response. Table 2 includes common cultivars and their thinning response.

Thinning Windows

The following information has been adapted from the Apple Thinning Guide by P. G. Schwallier, which is an excellent thinning guide, and it is available from:

The Great Lakes Publishing Company.

343 South Union St.

Sparta, MI 49345

Phone: 616/887-9008

Fax: 616/887-2666

E-mail: mac82nd@aol.com

P. G. Schwallier divides the period in which the fruitlets are receptive to thinning into 5 subwindows opening at bloom and closing at about 30 days DAFB (days after petal fall), and include Bloom, Petal Fall, Early Fruit Set, Late Fruit Set, and Closing. Each subwindow is approximately 5 days wide depending on weather conditions.

The best general chemical thinning generally occurs at petal fall; however, if the weather is not favorable for thinning during that window, spays should be applied as soon as possible. If you need to thin aggressively, then early applications at good rates should be used. Moderately and mild thinning occur at later dates using lower rates of the thinning materials.

Materials

Bloom Thinners

Wilthin® is a urea sulfuric acid complex, which is not yet registered in Vermont. We will be doing some testing on this compound to determine its use in the state.

Petal Fall (up to 8mm)

Thinning at this time will result in greater fruit size, but it usually must be followed by a later thinner application to decrease the fruit number. Labeled thinning materials include NAA, NAD, and Sevin. ACCEL (6-BA and GA₄₊₇) is a mild thinner. It has a wide thinning window, from bloom to 30 DAFB). It is not compatible with NAA or NAD on the same tree within the same year. ACCEL may reduce fruit size at higher rates. For more information on specific materials, refer to your New England Apple Management Guide and the LABEL.

 
Early Fruit Set (8mm to 12mm)

Same materials recommended for during petal fall. However, usually higher rates on some materials are recommended, and combination of materials are generally more effective than single materials.

Late Fruit Set (15mm to 20mm)

Use same materials as in PF, but higher rates must be used at this time.

Recommendations

Table 5 was developed by Duane W. Greene and Wesley R. Autio of Umass. There are differences in the recommendations of this table and what is in the Guide. The materials that are recommended in this table are more up to date to what is now available for you to use.

Determining the size of the fruitlets

A general estimate of fruitlet size can be obtained by measuring the diameter of the king blossoms. Measure as many as possible to get an average of the Fruitlet diameter. If frost damage has occurred and some of the king blossoms are damaged, then your measurements should consist of half king and the other half side blossoms. As the number of king blossoms decreases, so will the average diameter of the fuitlet decrease. You will have to use a smaller diameter size to start your thinning (i.e., instead of thinning at 8mm king blooms, thin at 6mm).

Summaries and Comments from Dr. Ed Stover of the Cornell Univ. Hudson Valley Lab
    Time of Thinning

• In general, earlier thinning will give larger fruit size at a comparable cropload.
• Use of multiple thinning treatments may give better control of cropping in difficult to thin blocks, with higher profitability and probably better return bloom.

From Win Cowgill, Rutgers University

• at petal fall of your latest blooming variety, apply 3-5 ppm NAA
• on all apples (whether you think they need thinning or not).
• Do not use this method on varieties ripening earlier than Paula Red.
• Wait 5-7 days. Evaluate thinning results.

                    Spray #2-

• Apply 7-15 ppm of NAA on those varieties that still need thinning.

• Wait 5-7 days and evaluate thinning.

• Apply 10-20 ppm of NAA on varieties that still need additional thinning.

 

Early fruit set is the window the first chance to evaluate fruit set. Characteristics of fruitlets that are setting include:

1. Fruitlet stems that curve upwards towards the sun
2. Fruitlets that are steadily increasing in diameter
3. Fruitlets and stems that retain a green color
4. The sepals fold in and close over the calyx end

1. Fruitlets stems that remain straight
2. Fruitlets that stop growing
3. Fruitlets and stems that have yellow or red color
4. The sepals remain folded open

J. Clements

Weed control -- like every other pest management decision -- ought to be thought of in the context of the overall orchard management picture. A new Cornell Cooperative Extension Bulletin, titled Integrated Weed and Soil Management in Fruit Plantings, does just that, discussing not only chemical control options of problem weeds, but also interactions of weeds, soils, crop, water; IPM systems for weed control; and ground cover management systems.

The Bulletin is a result of research in the weed control/ground cover management fields by Drs. Ian Merwin and Warren Stiles of the Department of Fruit and Vegetable Sciences at Cornell University. Public and governmental concern over ground water contamination and general pesticide use has predictably guided their recent research on orchard ground cover management systems. This has resulted in a publication that‹although short on specific weed control recommendations‹discusses several orchard ground cover management and weed control options, as well as their potential impact on the orchard environment and profitability.

For example, consider the following research results highlighted in the Bulletin:

• where no weed control was practiced in a six foot wide row strip, total shoot growth of apple trees in the first year of planting was reduced by 38% compared to a 100% weed free area
• for maximizing trunk growth, the months of May, June, and July were most important for maintaining weed free strips during the first year after planting
• the ratio of crop value to weed control costs in the first three years of planting was highest when a two meter square weed free area per tree was maintained (vs. four and six meter square, and no weed control)
• estimated costs to maintain a weed free row strip ranged from $15 to 55 per acre per year for herbicide strip; $300 to 550 for hay-straw mulch; and from $185 to $10,000 for various plastic/synthetic mulch/row covers and weed collars. It's also interesting to note that mowed sod grass cost $70-100 per acre per year to maintain

He also notes that glyphosate is more effective when lower volumes of water -- such as 20 gallons or less per sprayed acre -- are used during application. Also, as noted in the Bulletin, low rates of glyphosate (about 10% of standard recommended rates) have showed promise as chemical mowers for middles and tree rows. Such low rates appear to suppress grass and weed growth sufficiently to reduce competition for water and nutrients and the frequency of mowing in orchard middles and rows. Keep in mind when using glyphosate that green bark and foliage needs to be shielded from the herbicide spray.

Integrated Weed and Soil Management in Fruit Plantings is a good primer for introducing and discussing options for sustainable, commercial orchard ground cover management practices in the Northeast. It is brief, yet comprehensive in that it succinctly discusses weed and soil management in the context of the overall orchard production environment. Plus, it draws on the latest wisdom of two prominent researchers in the orchard weed control and ground cover management fields. For more specific herbicide usage recommendations and options, however, you need to consult the New England Pest Management Guide; read the LABEL; or contact your Extension fruit person.

To order Integrated Weed and Soil Management in Fruit Plantings (Information Bulletin 242, $7.00 postpaid), contact:

Cornell University

Media Resources Center

7 Cornell Business and Technology Park

Ithaca, NY 14850

Tel: 607-255-2080

Fax: 607-255-9946

E-mail: <Dist_Center@cce.cornell.edu

Web: http://www.cce.cornell.edu/publications/catalog.html

Contact Information

 
A Commitment to Excellence and Service:

We a committed to excellence and service to you. If you have any questions, problems or want to arrange for an orchard visit regarding your concerns, please call or write.

  For horticulture questions contact:

M. Elena Garcia

Tree Fruit Specialist

Plant and Soil Science Dept.

206 Hills Bldg.

University of Vermont

Burlington VT 05405-0082

Phone: 802/656-2824

Fax: 802/656-4656

E-mail: elena.garcia@uvm.edu

For IPM questions contact:

Lorraine P. Berkett

Plant Pathologist and IPM Specialist

Chair, Dept. of Plant & Soil Science

University of Vermont

Burlington, VT 05405

Phone: 802/656-0972

Fax: 802/656-4656

E-mail: lorraine.berkett@uvm.edu