Northern Michigan FruitNet 2006
Weekly Update
NW Michigan Horticultural Research Station

Jim Nugent                 Nikki Rothwell              Bill Klein
        District Horticulturist           District Fruit IPM Agent         Farm Mgr, NWMHRS

    Duke Elsner                                                  Jim Bardenhagen
Agricultural & Regional Viticulture Agent                      Leelanau Extension Director

May 9, 2006

WEATHER

Last week was generally warm and dry. A freeze event occurred on the morning of 5/6 in NW Michigan. The May 6th inversion freeze event caused significant damage to tree fruit crops in NW Michigan. Any tree fruit crop, including apples and cherries, in an area with poorer air drainage was badly damaged. Apples were generally in pink at the time and appear to have sustained the most damage, due in part to the location of many apples relative to the sites on which cherries are planted. The freeze was severe enough that even on some high sites with good air drainage, cherries in bloom sustained some damage on the tops of limbs.

GROWTH STAGES at NWMHRS (5/8/06—1:30pm)

Apple: King bloom
Pear: Bartlett: Full bloom
Sweet Cherry: Hedelfingen, Napoleon: In the shuck; Gold: Petal Fall
Tart Cherry: Montmorency: Early petal fall; Balaton: Early petal fall
Apricot: Shuck split
Plum: NY 12: Petal fall
Grapes: Chardonnay: 1-3" shoots

PEST REPORT

Apples: A wetting event was reported for May 2^nd that resulted in a high scab infection period at the NWMHRS. Another wetting event on May 7^th was recorded at other stations in NW Michigan, but none of this moisture was enough to cause an apple scab infection. Powdery mildew is showing up in some of our apple blocks, but this disease is probably left over from last year. We caught our first Oriental fruit moth at the NWMHRS, and we had a count of 30 moths in a minimally managed block in the area. Our spotted tentiform leaf miners (STLM) counts are declining from last week. We have seen plenty of obliquebanded leaf roller (OBLR) larvae in apple blocks in the region.

Cherry: The May 2^nd wetting event resulted in a low cherry leaf spot (CLS) infection at the NWMHRS. OBLR larvae have been reported in high numbers in many sweet cherry blocks, and we have even seen a few larvae in tarts. OBLR appears to have developed OP resistance in a few sites in NW Michigan, though this observation has not yet be confirmed. American plum borers have been trapped at the NWMHRS, at an average of 7 per trap. 

Grapes: We have not seen many changes in grapes this past week. 

LOOKING AHEAD TO PETAL FALL/SHUCK SPLIT
Nikki Rothwell, District Fruit IPM Educator

Diseases

When the cherry petals begin to drop and the fruit becomes visible, the pest management season really moves into high gear. In terms of diseases, both cherry leaf spot (CLS) and brown rot have the potential to cause major problems later in the season if they take hold at this time. CLS is a pathogen that affects the foliage of the cherry trees, and this disease is especially prominent in tart cherries, although we can have CLS show up in sweets. Since we documented widespread resistance to sterol inhibitors (SI’s), growers should avoid these chemistries at this time. Bravo (chlorothalonil) is our best option through shuck split as this fungicide does not have a high potential for developing resistance. Bravo is rated ‘excellent’ against CLS, and since it is only labeled for use through shuck split (and post-harvest), this chemistry is the one to be using now. Remember that the life of our fungicides is finite, and the longer we can stretch out their use, the better we will be down the road.

Brown rot is another disease that can wreak havoc in cherry orchards, and this pathogen is particularly problematic in sweet cherry. Last year, growers in the NW Michigan area reported varying levels of brown rot control, even with our old standbys, the SI’s. The SI’s, Orbit, Elite, and Indar, are all rated excellent on brown rot blossom blight, with Indar’s formulation providing the best efficacy against this pathogen. However, with the hints and rumors of SI resistance to brown rot, growers should avoid using these chemistries at petal fall/shuck split in order to save the SI’s for harvest time when brown rot control is much more critical. As this year has started off particularly dry, brown rot may not need the ‘big guns’ so early in the season. The following chemistries are also available for this time of the year: 1) Bravo, which is only rated fair-good on brown rot, but an option for early season control, especially with dry conditions, 2) Rovral is an excellent brown rot material, but it can only be applied through petal fall, 3) tank mix of Captan and Sulfur or Captan and an strobulurin (Flint is rated good on brown rot), or 4) if pressure builds due to wet conditions, a tank mix of an SI with Captan—we should always try to tank-mix our SI’s. Recent work in apple at Cornell University suggests that SI fungicides have a lifetime of ~60 applications before resistance develops. Although this work was done on apple scab, these scary numbers are a reminder that SI resistance has and will continue to develop in orchard systems. This SI resistance issue is particularly noteworthy for sweet cherry growers who want to keep the SI’s for brown rot control as long as possible since there are no other good alternatives! To end on a positive note, brown rot susceptibility decreases after the tree is finished with bloom.

Insects

Petal fall/shuck split is also the time where growers start pulling out their insecticides. In sweet cherry, we need to be particularly diligent about keeping our eyes open for plum curculio (PC)—they love sweets and those little cherries are the first to poke their heads out this time of year. Green fruitworm (GFW) is another pest that is evident at this time. These Lepidopterans can be cyclical, with high populations one year and lower numbers in other years. We have seen GFW moths flying around for almost two months, so we expect to see hungry larvae any moment. If an orchard has both PC and GFW, one tactic has to been to apply a tank mix of a half rate of a pyrethroid and a half rate of Guthion—Guthion for PC and the pyrethroid for GFW. This tank mix is good at this time, but if continued into the season, pyrethroids will flare plant parasitic mites to beat the band.

These two insect pests in tart cherries can be handled a bit differently. A model was developed in tart cherry to determine the likelihood of a PC larva to remain in the fruit at harvest time. The premise behind this model is to delay insecticide application until the last GDD where the tree would not abort the fruit containing the PC larva; hence, the grower could save on early PC treatments because the tree would ‘remove’ its own fruit infested with PC. After a certain cut off point (375 GDD), PC that lay their eggs in the fruit have the potential to remain on the tree until that PC-filled cherry is harvested. This model can be found at www.enviroweather.msu.edu-- go to the weather station closest to you, click on Fruit, then on ‘Tart Cherry Plum Curculio’. To use this model, growers must know their biofix date for each block, and biofix for this model is the date of full bloom. From biofix, growers must either calculate the number of growing degree days, base 50F, until that block reaches 375GDD or look up the chart in Enviroweather. Growers will need to apply an insecticide for PC when they reach 375GDD because after this point, larvae have the potential to show up in fruit at harvest. This model should only be used if a grower is actively scouting for PC in tart cherry, and this model cannot be used for sweet cherry. Again, pyrethroids work well for GFW in tart cherry as well as sweet cherry. Bt and insect growth regulators also receive an excellent rating against GFW: Spintor, Intrepid, and Entrust.

A special mention about obliquebanded leaf rollers (OBLR) is necessary now. We have seen actively feeding OBLR larvae in both apples and cherries this season. As their behaviors are slightly different in both fruits, these larvae can be particularly problematic and seem to be growing more so with time. In apple, OBLR feed on the continuously growing new terminal shoots, and this type of feeding makes these insects hard to target because they are always feeding on new growth—the leaves without insecticide coverage. In cherry, OBLR are also a pain, but in a different way: OBLR feeds on leaves inside the cluster of fruits, so they are hard to reach with insecticides. This pest may lead to brown rot issues in sweet cherries close to harvest. The larvae web together the fruit clusters to feed, and this behavior creates the perfect opportunity for the brown rot pathogen (Monolinia fructicola) to invade the damaged fruit. In tart cherries, we should be scouting for OBLR because if we do not control them for this first generation, the second shows up right around harvest time. In both cherry and apple crops, OBLR numbers seem to be on the rise, and there has been documented organophosphate (OP) resistance. Growers can no longer assume they control OBLR with OP’s or pyrethroids sprays. Therefore, growers need to be monitoring for OBLR larvae and trapping for adult moths, even after insecticide applications. 

OBLR activity can be predicted using degree-day models, although the information is not as reliable as that provided by the codling moth model. Using GDD42 for OBLR, first adult emergence is at approximately 900, 1150 to 1200 for peak adult activity, and 1250 to 1350 for first egg hatch. First sustained moth capture (capture on two successive dates) in pheromone traps is used as a biofix, thus if moth flight peaks between 250 and 300 GDD after initial biofix, the heaviest egg hatch should be about 400 GDD later. If the overwintering generation was effectively controlled earlier in the spring, then scouting orchards for OBLR larvae in actively growing terminals is the best way to judge whether infestations will require further control. This investment of time could result in saving several sprays.

FIRE BLIGHT BRIEF
Nikki Rothwell, District Fruit IPM Educator

As we are entering bloom in apples, growers need to be concerned about fire blight. This disease is particularly hard to control because of a variety of reasons: 1) unlike apple scab, the fire blight bacteria are dispersed several weeks prior to 1st infection, 2) Erwinia amylovora (the FB bacterium) is a complete epiphyte, which means it grows and relies on the apple blossom for support only, 3) the doubling time of the pathogen is about 20-30 minutes when temperatures are between 65-75 F, 4) infection can occur in minutes, so almost any wetting event is a potential infection period, 5) new infections produce many new bacteria which are efficiently transmitted by insects, wind, and rain, 6) trauma events (rain, hail, or wind) put every orchard at risk, and lastly 7) overwintering cankers are often difficult to find and remove, so they are likely to be present in spring in time for warm wet weather.

With all the negatives listed above, we need to be on the look out for weather conditions that favor fire blight, especially in susceptible varieties (See list of susceptible varieties below). Bacterial populations within the flowers will build when temperatures are between 65-86 F. Infection can occur with a small amount of rain or immediately following a warm period that allows bacterial populations to reach critical levels. The Enviroweather website has a reliable chart growers can use to determine if an antibiotic spray is needed. Click on www.enviroweather.msu.edu, go to the weather station closest to you, then to Fruit, then to ‘Fire Blight of Apple Blossoms’. Locate the biofix date (the date bloom first opened OR the date a spray was applied to control fire blight) on the top row. Follow that column down to determine Epiphytic Infection Potential (EIP) for that block on each date in the left column. If this number is greater than 100, and the average temperature is greater than or equal to 60 F, this area will be shaded and rain or trauma (high winds or hail) is all that is needed for infection. 

This time of year is particularly difficult to gauge fire blight as we often have warm and rainy weather, but we don’t want to ‘waste’ an antibiotic spray if it is not truly necessary. If the fire blight model’s EIP is not at 100, but kind of close to call, there are a few rules of thumb to determine if an antibiotic application is warranted: 1) a block with a history of fire blight, 2) susceptible varieties, and/or 3) visible cankers are all pretty good reasons to go into a rainy period with a strep spray. 

The rainy weather predicted for the coming days is to be accompanied by cool temperatures. This combination of events does not favor fire blight infection, but to be sure, check the Enviroweather web site. 

Susceptible Varieties

Gala, Fugi, Jonathan, Rome, Ida Red, Ginger Gold, Mutsu (Crispin), Rhode Island Greening, Paulared

WEED STEAMER DEMONSTRATION
Nikki Rothwell, District Fruit IPM Educator

A weed steamer from Australia, The Stinger, has made its way to northern Michigan. We are currently conducting experiments for the steamer’s efficacy against weed, disease, and insect pests. We will be operating the steamer on our test plots in the vineyard at Black Star Farms on Friday, May 12^th at 11:00am. We invite all growers to come down, have a donut, and check out this new piece of machinery! 

If you decide to attend this demonstration, Black Star Farm is located just off M-22, south of Suttons Bay, on Revold Road. Please park at the upper vineyard just inside the gate of the farm. 

We will also demonstrate the steamer at the Antrim County IPM Update on June 12^th at 10:30am. We will be meeting at Jack White’s farm, located at 10877 US-31, just south of Elk Rapids.

A HANDY ENVIROWEATHER TIP
Bill Shane, District Horticulturalist and Academic Specialist 
Nikki Rothwell, District Fruit IPM Educator

The new Enviroweather web site (www.enviroweather.msu.edu) of Michigan State University is quickly becoming a favorite place to find weather-related information for fruit growers. One of the especially useful features in Enviroweather for this time of year is the Overnight Temperature Report which gives a quick look at the prospect for freeze damage based on the weather stations in a region. The report provides hourly average temperatures from 10 PM of the previous day to 7 AM of the current day.

I am providing here a quick tip for going back in time to previous time periods for this overnight temperature report. The tip requires a very slight introduction to URLs, the "Uniform Resource Locator". This is the address of a site (resource) on the Internet, such as the URL given above for the Enviroweather. The URL is usually in the format such as "http://www..." and so on. By changing the URL slightly, Enviroweather can provide reports for earlier time periods.

If you go on the Enviroweather web site and view an overnight temperature report, such as for the SW Michigan Research and Extension Center, the URL address is given, usually at the top of the screen as:

www.enviroweather.msu.edu/run.asp?stn=swm&mod=w_nt&yr=&mo=&da=

Ignore all the information in the address line except the part at the very end that says "mo=&day=". In this instance, the overnight report is given for the default time period, namely the current day and the night before. To get a report for a desired day, say April 10th, add a 4 after "mo=", and a 10 after "da=", and the new URL should read:

www.enviroweather.msu.edu/run.asp?stn=swm&mod=w_nt&yr=&mo=4&da=10

If you now push the "Enter" button on the keyboard, Enviroweather will give the overnight temperature report for the April 9 and April 10. This feature is also available for the other models on Enviroweather, even if the other models provide the last series of dates for a wetting event for cherry leaf spot (CLS). For example, if you go to the NWMHRS for CLS infection today, the chart would pull up the wetting events that may have potentially triggered an infection period for the following dates: 4/22-4/24, 4/24-4/25, and 5/2-5/3. However, you may be interested in what happened prior to those last wetting events, just simply type in the month’s number and the date you need. Piece of cake!

A more elegant method to get retrospective information will likely be added to Enviroweather at some point; however, the tip given here will be useful to many of you. 

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

Please send any comments or suggestions regarding this site to: 

Bill Klein, kleinw@msu.edu
Last Revised: 5-9-06