WEATHER

Cool temperatures and some much needed rainfall occurred this past week. Unfortunately, rains on Friday evening, May 12, also brought some heavy and widespread hail to NW Michigan. Evaporation for the past week slowed dramatically from 1.85" for the week ending 5/9 to 0.86" for the week ending 5/16. Rainfall for the week at the NWMHRS totalled 1.04". Freezing temperatures occurred in many areas on the morning of 5/15.

GROWING DEGREE DAY ACCUMULATIONS as of May 15^th at the NWMHRS

Year       2000      1999      1998      1997
GDD42    508        501        566        223
GDD50    239        239        285          77

GROWTH STAGES:
Apricot: Harcot -- 16mm
Plum: Stanley -- shuck split
Pear: Bartlet -- petal fall
Apple: Red Delicious -- petal fall
Sweet Cherry: Napoleon -- shuck split
Tart Cherry: Montmorency -- petal fall
Grapes: Chardonnay -- 1" - 3" shoots

COMMODITY REPORTS

Sweets: As the sweet crop comes out of the shuck, it is becoming increasingly apparent that many varieties and/or locations have a light crop. Freezing temperatures on 5/15 caused some additional damage, mainly in low areas. Some of this damage will show up as frost marks on the upper side of exposed fruit.

INSECT & DISEASE REPORTS

Last week's rain resulted in heavy infection periods for apple scab, cherry leaf spot and brown rot. Apple and cherry are susceptible to powdery mildew infections when it rains. Fireblight pressure has been low due to the cool temperatures.

Plum cucurlio egg laying has begun in stone fruits that are out of the shuck. Lesser peach tree borer adult first catch occurred yesterday at the NWMHRS. American plum borer trap catch averaged 7 per trap at the NWMHRS. Trunk sprays can go on if you are timing for American plum borer. Egg hatch of lesser peach tree borer won't happen for approximately 10 days; trunk sprays timed for them should go on between now and then, depending on the acreage that needs to be covered. Green fruitworm are 1/2" long and most reports indicate that populations are low this year. 

Codling moth first trap catch occurred Monday in Benzie and Leelanau Counties. Spotted tentiform leafminer trap catches declined this week to 169 per trap at the NWMHRS. Rosy apple aphid are curling up in the leaves, so if you are going to use Provado, it should go on as soon as possible. European red mites are mostly hatched out now.

A few pear psylla have hatched out and are in the first instar. Grape berry moth trap catches averaged 2 per trap at the NWMHRS. Grapes are not susceptible to powdery mildew yet. Early powdery mildew infections may occur with rain events, however the critical time is at bloom.

APPLE THINNING
By James E. Nugent
District Horticulturist, MSUE

Thinning apples properly is never easy, and 2000 appears to be no exception. The problem is always difficult to access because so many factors influence natural fruit set and the effect of thinners on that process. Some factors to be considered for 2000:

1. Cold injury to leaves makes thinning easier.

2. Most orchards carried a large crop last year, so trees are apt to have lower than normal stored reserves going into this year, a factor that should make thinning easier.

3. Heavy fruit set (hard to thin) is favored by warm, sunny conditions from pink to petal fall. This was the case for the early part of this period, but now we have cool, cloudy conditions, which favor easy thinning.

4. Thinning compounds are influenced by temperature. It appears more all the time that the critical time is not so much just the temperature at the time of application, but the temperature for the first 48-72 hours after application. Therefore, try to apply thinners when daytime highs are predicted to be relatively warm (preferably 70's) for 2-3 days. Or stated another way, it's better to apply thinning compounds at the beginning or during the warm period rather than at the end of a warm period.

5. Blocks where apples were left unharvested last year would be expected to be particularly low on reserves and easy to thin.

6. Even in blocks where bloom was light may require light thinning to help break up clusters.

7. In blocks where the fruit appear to be mainly in the tops of the trees, be sure to get the thinner mainly into the tops.

8. Much of the above implies that light to moderate thinning strategy may be adequate. However, keep in mind that a smaller crop of large fruit is worth more in today's market than a large crop of small fruit. We still need to be more aggressive at thinning than we were a decade ago to get the large fruit size demanded by today's market.

9. Nearly all thinners are most effective when applied at 10-12 mm king fruit size. However, because temperature is so important at and following application of thinners and because our temps are often cool at this time of year, I suggest looking for a window of good weather beginning as early as petal fall or shortly thereafter to apply thinners. In blocks where fruit set is expected to be light, maybe this is a year to delay until the traditional 8-12 mm window to better assess what is happening in the block. If thinner is applied earlier than the 8-12 mm stage, I suggest using the same rate that would normally be applied as fruit is not easier to thin early -- actually it's a little more difficult.
 

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

Last Revised:5-16-00