FruitNet Weekly Report

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Nikki Rothwell
District Horticulturist

Erin Lizotte
District Fruit IPM Agent

Bill Klein
Farm Mgr, NWMHRS

Duke Elsner
Agricultural & Regional Viticulture Agent

Rob Sirrine
Leelanau Extension Director

May 6, 2008

GROWING DEGREE DAY ACCUMULATIONS AS OF MAY 5th AT THE NWMHRS

Year	2008	2007	2006	2005	2004	2003	18yr. Avg.
GDD42	272	309	390	292	222	239	261.3
GDD50	125	127	179	123	83	97	112.8

Growth Stages at NWMHRS (5/5/08—9:00am)

Apple: Tight Cluster
Pear: Bartlett: Green Cluster
Sweet Cherry: Hedelfingen: 80% bloom
Napoleon: Full bloom
Gold: 1^st bloom
Tart Cherry: Early white bud
Apricot: Full bloom
Plum: Early white bud
Grapes: Early bud burst

Weather Report

Although the weather has seemed chilly, our growing degree day (GDD) accumulations are similar to last year’s GDD: 125 base 50 this year compared to 127 base 50 in 2007. The numbers are likely due to the extremely warm temperatures in the third week of April. However, temperatures have dropped since then, and the last week of April and first of May have remained cool; average temperatures have been in the mid to upper 40’s. On 28, 29, and 30 of April, cold overnight temperatures were recorded—mid 20’s to low 30’s.

Crop Report

The cold overnight temperatures varied in the northwest regions last week, but overall we believed there was minimal damage to cherry or apple buds. However, as we have been cutting buds and hearing grower reports, we may have sustained more damage than our original assessments indicated. In some tart cherry blocks, we recorded ~50% damage while adjacent blocks sustained no damage. King bloom in some apple blocks was impacted by the cold temperatures, and sweet cherry damage appears to be minimal in many tested blocks. With time, we will have a better assessment of overall damage.

Pest Report

Things are starting to move along in the region despite the consistently low temperatures of the past week. Plum curculio has begun emerging in Northport orchards late last week. Here at the NW station, Oriental fruit moths have been captured in pheromone traps and oblique banded leafroller larvae have been detected in apple. European red mite eggs are at low to moderate levels in the region, and the first two spotted spider mites have been found on the underside of apple leaves and are laying eggs despite the temperatures. Aphids have also been observed in apple blocks. Over the weekend, a moderate apple scab infection was forecasted for most of the northwest region, and as sweets leaf out, the cherry leaf spot infection levels are now a concern.

CONTROL OPTIONS FOR MITES IN FRUIT CROPS

Table prepared by Drs. John Wise, Rufus Isaacs, and Larry Gut, Dept of Entomology, MSU and can be found at http://www.maes.msu.edu/nwmihort/mitecontroltable.pdf

COVER SPRAY OPTIONS FOR CHERRY LEAF SPOT CONTROL
George W. Sundin, Plant Pathology
Erin Lizotte and Nikki Rothwell, NWMHRS

Cherry leaf spot is the most important fungal disease of tart cherry in Michigan. The leaf spot fungus Blumeriella jaapii infects leaves with symptoms first appearing on upper leaf surfaces as small purple spots. As spots accumulate on leaves, the leaves turn yellow and fall. The amount of lesions required to cause leaf yellowing and drop is variable. Sweet cherries can tolerate quite a few lesions before leaf drop occurs, but Montmorency tart cherries will drop with only a few lesions, signifying the importance of proper leaf spot management. Balaton trees can tolerate more lesions that Montmorency, but they too drop their leaves more readily than sweet cherries.

The optimum conditions for lesion development are temperatures of 60-68 F with rainfall or fog. After lesions appear on upper leaf surfaces, examination of the underside of leaves reveals a large number of white spore masses. These spores are dispersed by rain and wind; such secondary cycles can continue repeatedly under favorable conditions through autumn.

Preharvest defoliation can result in a crop that does not mature adequately and causes serious tree damage. Even late summer (August, early September) defoliation reduces the ability of trees to store photosynthate in roots leading to an overall loss of vigor and leaving trees more susceptible to killing by winter injury. Early-defoliated trees typically exhibit reduced flower bud formation and often set less fruit the following season.

Ascospores (primary inoculum) of the leaf spot fungus are released from leaves on the orchard floor by rainfall from early bloom to about six weeks after petal fall. Infection takes place through natural openings (stomata) located on leaf undersides. Once leaves are unfolded, they are susceptible to the CLS pathogen and remain so throughout the season.

Management of cherry leaf spot should be initiated around petal fall or sooner if susceptible leaf tissue is present. The use of chlorothalonil (Bravo) is not allowed after shuck split (except post-harvest). As this product is less likely to develop resistance, Bravo should be used pre-shuck split, as both a protectant and a resistance management tool.

There are six major classes of fungicides registered for leaf spot control that could be used as cover sprays (Table 1). Each of these classes of fungicide, except copper compounds and Captan, has resistance concerns as resistance in leaf spot or other fungal pathogens has been demonstrated. Therefore, growers must be aware of fungicide resistance potential and be thinking about maintaining fungicide chemistries now and in the future. Resistance to SI fungicides is widespread in the leaf spot pathogen in Michigan.

Growers should also consider the timing of compounds to control the other important tart cherry fungal diseases. For example, the first cover spray timing after shuck split is a good timing for Pristine or a strobilurin, because these fungicides are also effective in powdery mildew control. Currently, the SI's remain an important tool for brown rot control, particularly if we experience warm and humid or wet weather 3-4 weeks before harvest. Any use of SI's in Michigan should be in a tank mix with 3-4 lbs. of Captan per acre.

The strobulirin/boscalid (Pristine) and strobilurin (Flint or Gem) fungicides are our best tools for multiple disease control. However, both are single-site fungicides with the potential for resistance development. Do not apply these fungicides more than twice consecutively or more than four times per season. Our recommendation is that these fungicides not be used more than twice per season. The risk of resistance is high with these fungicides and loss of a class of fungicide means fewer tools for future disease control.

We envision that copper compounds will become more and more important for leaf spot control as other fungicides are lost due to resistance. Copper is highly effective in leaf spot control with the only downside being the potential for phytotoxicity. We are currently recommending a rate of 1.2 lbs per acre of metallic copper with hydrated lime added at 6-9 lbs per acre to reduce phytotoxicity. Do not apply copper compounds prior to periods of warm, dry conditions (temps at or above 80 F). Scout orchards for phytotoxicity symptoms on leaves (bronzing on leaf undersides, conspicuous large yellow blotches on a few leaves, and/or blackening of leaf veins) prior to the next copper application. Do not apply a second copper application if trees are exhibiting phytotoxicity symptoms.

Cherry leaf spot can be successfully managed using currently available fungicides. However, it is uncertain if companies are developing additional classes of fungicides that would ultimately be registered for leaf spot control. It is incumbent upon everyone to maximize the lifespan of these current fungicides through effective resistance management.

Table 1. Class of chemistry and fungicides registered for cherry leaf spot control.

Boscalid	Pristine^a
Strobilurin	Flint
Metal ion	Copper compounds
Sterol-inhibitors	Elite, Indar, Nova, Orbit, Rubigan
Guanidine	Syllit (dodine)
Heterocyclic	Captan^b

^a Pristine is a mixture of a strobilurin and boscalid, another fungicide (separate chemistry).

^bCaptan should only be used in combination with another compound because the rate (4 lbs/a) allowed on cherries is too low for effective disease control. Tank mixing Captan with other classes of fungicides will help delay resistance and will help control isolates of the fungus that may be developing resistance.

SIGN UP TODAY FOR THE CONSERVATION SECURITY PROGRAM (CSP)

CSP is a voluntary conservation program and has a unique role among USDA programs. It identifies and rewards those farmers and ranchers who meet the highest standards of conservation and environmental management on their operations. It creates powerful incentives for other producers to meet those same standards of conservation performance on their operations, and provides public benefits for generations to come.

Only landowners and producers in designated watersheds are eligible to sign-up for CSP. In Michigan, six watersheds have been designated since 2004 and 574 Michigan producers were accepted into the program. As funding becomes available, NRCS announces the addition of new watersheds into the program.

The Boardman River/Charlevoix River Watershed has been selected to participate in the 2008 CSP sign-up. More information about the sign-up can be found on the Boardman Charlevoix River Watershed Web page http://www.mi.nrcs.usda.gov/programs/csp.html.

Many agricultural producers in Leelanau, Grand Traverse, Antrim and Charlevoix Counties are eligible to sign up for this rewarding Farm Bill program. The CSP sign up period is April 18 – May 16, only 11 days left! Agricultural producers that have signed up to date are receiving anywhere from $60 - $80 per acre on lands enrolled into the program!

Call your local NRCS office for more details and to set up a pre-interview appointment:
-Traverse City USDA-NRCS Service Center 941-0951 ext. 103
-Bellaire USDA-NRCS Service Center at 533-8709 ext. 101

Information on cherries is available at the new cherry website: http://www.cherries.msu.edu/

Insect and disease predictive information is available at:
http://www.enviroweather.msu.edu/home.asp

This issue and past issues of the weekly FruitNet report are posted on our website at: http://www.maes.msu.edu/nwmihort/faxnet.htm

ACTUAL AND PREDICTED DEGREE-DAY
ACCUMULATIONS SINCE MARCH 1, 2008

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

Last Revised: 5-6-08