May 11,1999

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

Rain this past week helped to lay the dust, but conditions remain quite dry in most areas. Evaporation rates have slowed in recent days. Evaporation in the past 7 days (5/5 - 5/11) amounted to 1.20", and the prior week (4/28 - 5/4) was 1.94". Since April 1, evaporation has totaled 6.30". Rainfall this past week at the NWMHRS totaled 0.57". This was the first precipitation since snow fell on 4/12. For irrigation scheduling purposes in tree fruit, research suggests that rainfall and irrigation should replace about 75% of evaporation to match moisture losses due to a combination of transpiration and soil moisture evaporation. This suggests that during the past two weeks tree moisture needs have been 2.35" (75% of 3.14" of evaporation), while rainfall has replaced only 0.57" of this demand. I should note that this 75% estimate may overstate water needs in early season due to low leaf surface area for transpiration.

DEGREE DAYS at NWMHRS: Base 50: 200; Base 42: 428

GROWTH STAGES:

Apricot: Harcot – shuck split
Plum: Stanley – late petal fall
Apple: Red Delicious - full bloom
Sweet Cherry: Napoleon – late petal fall
Tart Cherry: Montmorency – petal fall
Grapes: Bud break to 1/2" shoot

DISEASES:

A light cherry leaf spot infection period occurred last Thursday at the NWMHRS. Saturday's rain did not result in an infection period.

Fire blight pressure in apples was high during rains last week, if bloom was open long enough. Most pears were open for enough time and required streptomycin sprays. Weekend rains came when temperatures were too low for fire blight infection.

An apple scab infection period occurred last Thursday at the NWMHRS. No infection took place on Saturday.

Powdery mildew - Initial infections require rain for germination and development. Growers should be cautious with this disease this year, as inoculum levels should be high due to the mild winter.

INSECTS:

Black cherry aphids can be found in sweet cherries. Control is rarely needed in NW Michigan.

Rosy apple aphids can be found on suckers in the interior of Ida Reds. Provado at petal fall is the next control option.

Plum curculio adults are active in trees now. Any stone fruit coming out of the shuck are at risk to injury.

Adult American plum borers have begun flight.

European red mite nymphs hatched out last week. Overwintering mites are generally low this year due to great predator populations last year. 

Tarnished plant bugs are active. Strawberry growers are at risk from the nymphs feeding during bloom.

Strawberry clippers have been reported in strawberries. Damage from this pest is usually very light in NW Michigan.

MISCELLANEOUS:

Apple Thinning
By Jim Nugent, District Horticulturist, MSU-E

Following are some factors to consider as you assess apple thinning strategies:

1. Last season's early harvest and mild fall allowed for an unusually long period post harvest for trees to build overwintering reserves. This should result in larger reserves in the trees, making thinning more difficult.

2. Bloom looks strong in most blocks, which generally results in heavy fruit set.

3. Some blocks have frost damage in low areas that might result in adjusting rates down in those areas or even avoiding thinners altogether in these areas.

4. Weather has generally been quite nice so far this spring for fruit set; ie., generally warm and sunny. The more sunny weather that occurs the next 3 weeks, the heavier will be natural fruit set, resulting in the need for more aggressive thinning.

5. I do not expect dry conditions to decrease fruit set.

6. With apple markets getting more competitive, there is no money to be made growing small fruit. Therefore, I think that based on observations to date that thinning needs to be fairly aggressive, with the exception of frost damaged and low areas and trees with very little return bloom.

Finally, I've become progressively more convinced that warm temperatures following thinning are very critical for success. Phil Schwallier reported earlier this month at a grower meeting here at the Station that several researchers are now finding that temperature at the time of application is not so important. What is more important is temperatures during the first 2-3 days following application. In other words, apply when a warm spell is predicted.

While the ideal time for thinning is 8-12 mm king fruit size, this window is too narrow to expect in NW Michigan to have the warm conditions necessary for good thinning year in and year out. Therefore, both Phil Schwallier and I now suggest beginning to look for the right conditions at petal fall or shortly there after. When they arrive, apply thinners at the same rate as you would apply if using at 8-12 mm. Remember, apples are actually more difficult to thin both before and after the 8-12 mm size. They do not thin easier prior to 8 mm. Phil has written an excellent thinning guide, which suggests using lower rates when thinning early, but he has since changed his opinion and now agrees that early thinning requires the same rates as 8-12 mm thinning.

Thinning early also gives a better opportunity to reapply if thinning is inadequate while fruit is still small enough for applying thinners. 

Phil's thinning guide is titled, "Apple Thinning Guide" and is available for $13.00 (includes shipping and handling) from Great Lakes Publishing, 343 S. Union St., Sparta, MI 49345, 616/887-9008.
 




The Small Hive Beetle
By Greg Hunt, Bee Specialist
"Facts for Fancy Fruit", May 5, 1999 Issue
Purdue University

A new pest of the honey bee called the small hive beetle, Aethina tumida, was found in Florida last year and caused extensive damage to bee hives. Thousands of hives were destroyed. This pest has also been found in Georgia, South Carolina and North Carolina. Recently, the beetle also showed up in some packages of bees that were shipped to Ohio. There is a good chance that some of these beetles could be introduced to Indiana this year. We don’t know how these beetles will survive in Indiana. They are used to warm weather because they come from South Africa. It seems they were present in South Carolina for two years before they were found in Florida without causing any serious problems. The adult beetle is small - about half a centimeter long. The adults and larvae eat bee brood and honey. They spoil the honey for the bees and they can quickly ruin the hive for the bees, at least in Florida. 

Beekeepers receiving packages of bees this spring should be on the lookout for beetles in their hives. But be aware that many non-harmful beetles are often present in hives. Indiana has just received permission under EPA section 18 to use Coumaphos to control this beetle and also varroa mites. The Coumaphos can be bought from Mann Lake company in the form of Checkmite Strips. They look like the Apistan strips that are used for controlling varroa mites, but contain a different pesticide. But at this point, we cannot recommend that beekeepers buy these strips unless they have a problem with small hive beetles or varroa mites that are resistant to the compound in Apistan strips. Neither small hive beetles or Apistan-resistant varroa have been found in Indiana. Beekeepers should use special care when handling and using the Checkmite strips because they contain an organophosphate pesticide which is a nerve toxin. The EPA says they will have a zero tolerance for Coumphos in honey. Never leave honey supers on hives when using either Checkmite or Apistan strips. 

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

Last Revised:5-12-99