May 18, 1999








WEATHER:

By Jim Nugent, District Horticulturist, MSU-E

We received some much-needed rain in NW Michigan, but amounts were variable. At the NWMHRS rainfall on 5/16-17 totaled 0.45". Rainfall for the past 5 weeks has totaled only 1.02". Evaporation during the past week has totaled 1.40". Evaporation since April 1 totals 7.70". Soil moisture conditions are very dry in most areas under heavy vegetation.

DEGREE DAYS at NWMHRS: 

Base 50:272; Base 42: 543

GROWTH STAGES:

Apricot: Harcot – 15mm fruit
Plum: Stanley – early shuck split
Apple: Red Delicious - petal fall
Sweet Cherry: Napoleon – 9-10mm
Tart Cherry: Montmorency – shuck split
Grapes: 3" shoots

DISEASES:

-Cherry leaf spot. The rains of the last few days have produced a moderate and a currently ongoing heavy infection period. Growers should take these very seriously and have a full cover of protection on tart cherries in particular.

-Apple scab. Monday we had a moderate infection period, and today we have a moderate ongoing apple scab infection period.

-Fireblight. The recent rains have produced an infection period for fireblight. Growers needed to have a strep spray on prior to the rain or within 24 hours after the beginning of the rain. 

-Brown rot. Sweet cherries, once out of the shuck, enter into their most resistant stage of growth. Growers should still keep some level of protection on sweet cherries. Elite, Indar, Ziram and Ferbam are all options. Keep in mind that Ziram and Ferbam are weaker on leafspot and brown rot in high-pressure situations. Orbit can be used again in the preharvest period.

INSECTS:

-Codling moth. The first catch of adults was reported last week in the warmer regions of NW Michigan. 

-Plum curculio. Sweet cherries, peaches, apricots and plums are all susceptible to injury at this stage.

-Green fruitworm are approximately 1/2 " long and can be found feeding in terminals.

-Pear psylla nymphs are feeding on the underside of leaves. Agrimek should go on 10 days after petal fall and no later than 14 days. Don't forget the oil with the Agrimek.

-White apple leafhopper nymphs have been found in apples.

-Rosy apple aphid colonies are building and curling up in the leaves.

-Green apple aphid colonies are developing.

-American plum borer trap catches are up, at 25-30 per trap. Trunk sprays targeting American plum borer should start to be applied on May 23^rd in the warmer parts of the district.

-Lesser peach tree borer. First trap catches occurred this past week. Trunk sprays targeting this pest should begin on May 27^th.

-Spotted tentiform leafminer. Provado should be used at petal fall to control the sap feeding stage.

NW Michigan Horticultural Research Station
Insect Trap Count Averages - 1999 
 

DATE	Codling Moth	Spotted Tentiform Leaf Miner	Lesser Peach Tree Borer	American Plum Borer
5/18	0	660	8	30


 

MISCELLANEOUS:

Deer are becoming active in young orchards. Growers need to check for damage and put on appropriate repellants.

Apple Set 
By Jim Nugent, District Horticultural Agent

As thinning time rapidly approaches, one important factor to consider is that trees naturally thin fruit more readily if conditions are particularly cloudy during the period from pink to about 12mm fruit size. The amount of cloudiness is probably most critical between bloom and 10mm. So this current period of cloudy weather is coming at a critical time, but if it lasts for only three days or so, I don't think it would be advisable to count on it for very much reduction in fruit set. If, however, the weather were to remain mostly cloudy for the coming week, one would want to be significantly less aggressive with thinning. Cloudy weather will also result in a thinner leaf cuticle, a phenomenon which enhances the uptake of chemical thinners. The cuticle will re-thicken with a few sunny days prior to application, so the effect on increasing uptake will be minimized.

Armillaria Site Needed!
By Jim Nugent

Amy Iezzoni and I are looking for a cherry site with armillaria, where we could plant a few trees to test for armillaria resistance. The species of cherry being evaluated is black cherry (the forest species of cherry native to northern Michigan) to see if it has the genetic potential for resistance. The trees will only need to be grown for 5-6 years, so we would like to find a block of cherries with armillaria that is at least 5-6 years from removal. If we can find natural resistance, Amy can then use the genetics in her rootstock breeding. 
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Please send any comments or suggestions regarding this site to: 
Bill Klein, kleinw@pilot.msu.edu

Last Revised:5-18-99