May 25,1999

WEATHER:
By Jim Nugent, District Horticulturist, MSU-E

The evaporation rate this past week has been very low at only 0.36" (this is less than the daily evaporation on 5/5!), with only 2.06" during the past two weeks. This is the lowest weekly evaporation rate since April 1. Two very long, cool wetting periods have occurred during the past ten days. Rainfall at the NWMHRS has totaled 1.10" during the past week; in addition, 0.45" fell at the end of the preceding week.

DEGREE DAYS at NWMHRS: 

Base 50:320; Base 42: 643

GROWTH STAGES:

Apricot: Harcot – 20mm fruit
Plum: Stanley – 8mm
Apple: Red Delicious - 8mm
Sweet Cherry: Napoleon – 12mm
Tart Cherry: Montmorency – 11mm
Grapes: 6" shoots

COMMODITY REPORTS 

The tart cherries are setting a significantly lighter crop than in 1998. We are currently in a moderate infection period for cherry leaf spot. The current wetting period will likely extend long enough to be a heavy infection period. Growers should be sure to cover both sides for a heavy infection period. Brown rot conditions are low due to the cool temperatures. Plum curculio egg laying activity has been light so far. Insecticides can be delayed in controlling plum curculio in tarts when populations are low until 375 degree days base 50 after full bloom. We are currently 190.5 degree days base 50 after bloom at the NWMHRS. Green fruitworm are 1/2 in. long and can be found feeding on terminal leaves and fruit. 

The sweet cherry crop is looking good. Sweets should be treated with an insecticide for plum curculio at this point.

The threat of plum curculio stings in apples is low until the fruit size more. The first catch of codling moth occurred at the NWMHRS last week, although trap catches were extremely light due to the cool weather. Provado can go on for spotted tentiform leaf miner, leaf hoppers and green apple aphids. It may, however, be too late to control rosy apple aphids. The current rains, which started on Sunday morning, produced a heavy infection period for apple scab. We are approaching the end of primary scab for apples.

In apricots, plum curculio and tarnished plant bugs are a threat.

Black knot is a threat in Stanley plums with the recent 45 plus hour long wetting event. If growers weren't covered, Benlate/Captan is the best choice. Plum curculio is a threat.

Bartlett pears are at 10mm. If thinning with NAD was missed, NAA can be used at this time, but care should be taken to not over thin. Agrimek should go on the next chance that a grower has, if it has not yet been applied. Be sure one gallon of oil is used with the Agrimek. Provado and Pyramite are also labeled and should be used at the high rates. 

Grape pest pressure is extremely light.

Insect Trap Count Averages at the NWMHRS
 

Date	Codling Moth	Spotted Tentiform Leaf Miner	Lesser Peach Tree Borer	American Plum Borer	Oblique Banded Leafroller	Grape Berry Moth
5/18	0	660	8	30
5/24	1	88	1.3	14.3	0

MISCELLANEOUS:

Thinning Apples
By James E. Nugent, District Horticulturist, MSU-E

Several days of mostly cloudy weather will naturally reduce fruit set and increase the activity of thinners. In blocks where ten days ago we would have suggested thinning aggressively, rates should be reduced to a moderate thinning strategy. This weekend should provide good conditions for applying apple thinners.

Gibberellic Acid on Cherries
By Jim Nugent

The proper application timing for GA on tart cherries is typically 3 - 4 weeks after full bloom, or when trees have 5 to 7 leaves (3 to 5 leaves fully expanded) on terminal growth. Here at the NWMHRS, we are currently just entering this window. By late this week and next week the growth stage should be right for application, though orchards further north are behind.

Tips for use:

1. Apply when high temperatures are expected to be above 70 ° F for a couple, if possible. Applications made when high temps are expected to be below 60 ° F have given poor results.

2. Leaves expanding under low temperatures are less efficient at uptake than leaves growing under normal to above normal temperatures. 
 

3. For mature trees:
 

a) Use 10-20 ppm of gibberellic acid (GA). Lower rates are typically used on more vigorous orchards or where GA was used successfully last year; higher rates are used on low vigor orchards. Rates of about 15 ppm are most common.   b) Rates of Pro-Gibb 4% on mature trees are as follows:

10 ppm response = 6 fl oz/acre

15 ppm response = 9 fl oz/acre

20 ppm response = 12 fl oz/acre

c) Prefer to apply with 50-150 gal of water per acre. Lower rates of water may reduce response.   d) Research with surfactants has given results varying from no effect to over-response with phytotoxicity. (The phytotoxicity occurred with silicon based surfactants). Therefore, we suggest not using a surfactant with GA unless you have enough experience with a particular surfactant surfactant to have confidence in the response. Never use a silicon-based surfactant.   4. In non-bearing tart and sweet cherries -- used to greatly reduce flowering and fruiting to achieve faster growth and delay pollen-transmitted virus infection.
  a) Apply with a handgun either 100 ppm (40 fl. oz. Of Pro-Gibb 4% per 100 gallons of water) in a single application 3-4 weeks after full bloom (slightly later if temperatures are exceptionally cool); or   b) 50 ppm (20 fl. oz./100 gal) applied about 3 weeks after full bloom + a second application at 50 ppm 2½ - 3 weeks later. This two-application system at 50 ppm nearly always is more effective than a single application at 100 ppm.   c) Do not apply to trees the year of planting.   5. Bringing young trees into bearing following treatment with high rates during non-bearing years. It is very important to not discontinue GA as this results in oversetting of fruit and stunting of trees. In the past, we have suggested decreasing the rate to 15 ppm. This is not enough! There are probably two reasons why trees still tend to overset. First, trees that have been kept vegetative have tremendous capacity to set fruit. Second, often at this time growers are switching from handgun application to airblast and may be underestimating the amount of GA needed on these young trees. Based on recent experience (but unfortunately not on research), I suggest that approximately 30 ppm be applied if spraying dilute (18 fl oz Pro-Gibb/100 gal), or about 20-24 fl. oz./acre if applied concentrate. This rate per acre for concentrate spraying already takes into account the average tree size of this age tree; i.e., do not reduce the rate farther based on tree row volume.
  Establishing Wide Crotch Angles in Young Trees 
By Jim Nugent

Now is the time when new limbs can be readily spread to form a 90°crotch angle. With stone fruits, I suggest using spring-type clothespins. Apple limbs can be spread either with clothes- pins or toothpicks. This job needs to be done soon or the crotch angles become too set and limbs will readily break when spread.
__

Please send any comments or suggestions regarding this site to: 
Bill Klein, kleinw@pilot.msu.edu

Last Revised 5-25-99