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Healthy Fruit 2010 Vol. 18:6

May 11, 2010

Current (through May 10) degree day (DD) Accumulations

Location: UMass Cold Spring Orchard (CSO), Belchertown, MA

  • Base 43: 535
  • Base 50: 290

Significant upcoming orchard events based on degree days (Base 43):

  • Spotted tentiform leafminer sap-feeders present: 343-601
  • Lesser appleworm 1st flight peak: 355-773
  • Codling moth 1st catch: 399-579
  • Oriental fruit moth 1st flight peak: 348-542
  • European red mite 1st summer eggs present: 447-555
  • Plum curculio oviposition scars present: 485-589
  • Redbanded leafroller 1st flight subsides: 574-882
  • McIntosh at petal fall: 447-523

Orchard Radar insect synopsis (for Belchertown)

  • Codling moth development as of May 11: 1st generation adult emergence at 7% and 1st generation egg hatch at 0%
  • 1st generation Oriental Fruit Moth (OFM) flight starts: April 15, Thursday. 1st generation - 55% egg hatch and first treatment date, if needed: May 21, Friday
  • Increased risk of Plum Curculio (PC) damage as McIntosh and similar cultivars increase fruit size:
    May 5, Wednesday. Earliest safe date for last PC insecticide spray: May 26, Wednesday
  • Spotted Tentiform Leafminer (STLM): 1st generation sapfeeding mines start showing: May 7, Friday. Optimum sample date is around Saturday, May 8, when a larger portion of the mines are visible.
  • 1st generation White Apple Leafhopper (WAL) found on apple foliage: May 1, Saturday
  • Sunday, May 2 McIntosh 95% petal fall; Wednesday, May 6 fruit set

The way I see it

Well, here we are and in fact the timing of fruit growth right now -- thanks to much cooler weather -- is just a bit ahead of average. And of course a touch of frost and/or freezing temperatures last night is typical for the 2nd week of May. Hopefully, there is not much freeze damage, although temperatures did get down into the upper 20's. Be sure to check some fruitlets for frost/freeze injury if you are wondering. Make sure you read the observations by Duane Greene about thinning below.

Otherwise, hope you put the Tree Fruit Twilight Meetings next week on your calendar. JC

Massachusetts airports on NEWA

Through a cooperative effort with the New York State IPM Program, and the Northeast Regional Climate Center, Massachusetts airport locations have been added to the NEWA (Network for Environmental and Weather Applications) website (http://newa.cornell.edu/). (Note that the map is draggable to the left wherein the Massachusetts airport locations are revealed on the map. You can also choose a location from the drop-down list.) Pests forecasts, typically based on temperature, precipitation, and relative humidity are available for various crops (fruit and vegetable). For apples, available forecasts include: codling moth, Oriental fruit moth, obliquebanded leafroller, plum curculio, spotted tentiform leafminer, apple maggot, apple scab, and fire blight.

For more information on how to use NEWA, see 'Pest Forecasts in Real Time -- NEWA' in the April 19, 2010 issue of Scaffolds. I urge you to look at the NEWA website and give us your feedback. This is the future of IPM information delivery! JC

Duane Greene thinning thoughts

Weather for the next 3 to 4 days is forecast to be very unfavorable for thinning. Even though fruit have grown into the size range where we normally consider applying thinning chemicals this is not the time to thin. Since developing fruit have not been stressed, the thinning window of opportunity has widened. At this point in time the weather starting this weekend and extending into next week looks favorable for thinners activity. While it is not necessary to have temperatures in the upper 60s and 70s to apply thinners, it is important that they be in place when the warm weather arrives. As it appears now our suggestions is to apply thinners later this week as long as wind and rain are not factors that will influence proper application and coverage.

All thinning chemicals are effective during the 8 to 14 mm stage of fruit development. Carbaryl is a relatively mild thinner. BA (MaxCe and other fomulations) is a mild thinner when used by itself, however, when combined with carbaryl it is or can be a strong thinner. NAA used at low rates is not a strong thinner. Higher rates of NAA can cause strong thinning activity especially if temperatures in reach into the upper 70s after application.

The weather this spring, especially over the past 10 days, presents us with a thinning dilemma since damage may have occurred that is not apparent. There was a general and wide-spread frost last night. The good news is, if any, that you will have 2 to 3 days to assess any potential damage to fruit or foliage well in advance of potential thinner application later in the week. If severely damaged, the center of developing fruit will be back. Look for darkened areas in a fruit that may signal damage but not death of a fruit . These fruit are vulnerable even to mild thinners so judgment must be exercised in what to do here. Foliage damage or foliage crinkling may seriously affect fruit set. If spur leaves are damaged, it is possible that fruit set will be reduced naturally and application of thinner or leaf-damaged trees may result in very heavy and inappropriate thinning.

If conditions change during the next 2 to 3 days that substantially change the suggestions that we are providing here, will will alert you. DG

Editor's note: on Orchard Radar - Belchertown, MA, there is a very useful 'Thinning weather synopsis chart' that gives " Thinning weather estimates that are based on the influence of night time temperatures and daytime cloud cover on sensitivity of young apples to postbloom thinning agents." It is updated daily. Below is a sample output for Tuesday, May 11, but you should check out the full page on Orchard Radar. JC

thin chart

Pest watch

  • although primary apple scab season is largely over based on the ascospore maturity model, you should continue fungicide coverage until you are sure you have no developing scab on foliage from previous infection periods; other apple diseases are ongoing too, such as powdery mildew, rust diseases, and black rot. See the Guest Article 'Apple Diseases Targeted by Early Cover Sprays.'
  • expect plum curculio to become very active during the next period of warmer, more humid and wet weather (early next week?) so be prepared with an insecticide spray
  • otherwise the cool weather is keeping insect activity at a bay; be prepared for an upsurgence with the return of warm weather though

Guest article

APPLE DISEASES TARGETED BY EARLY COVER SPRAYS
(Dave Rosenberger, Plant Pathology, Highland. Reprinted from Scaffold Fruit Journal, Vol. 19, No. 8, May 10, 2010,

Apple growers often breathe a collective sigh of relief each year when they reach the end of the discharge period for apple scab ascospores. Traditionally, that has meant that the greatest disease threat to the crop has passed, fungicide programs can be relaxed a bit, and the focus for timing pesticide applications can be shifted from disease control to insect control.

As of May 10, the NEWA models for apple scab ascospore discharge showed that most areas in New York State have already reached the end of the scab ascospore discharge period or will do so later this week. However, even though the supply of scab ascospores may be depleted, maintaining fungicide coverage is still important because scab and other diseases remain as threats for several weeks after scab ascospores are depleted.

Apple scab
Although the supply of ascospores in overwintering leaves may be depleted (or, depending on location, will soon be depleted), apple scab remains a threat for at least three weeks after petal fall. The ascospores may be gone, but no one can be certain that early season sprays provided 100 % control of primary scab. If just a few ascospores managed to find and infect unprotected leaves, then conidia from those primary infections can still cause a lot of damage. The risk of secondary infections is especially high during the first few weeks after petal fall because terminal shoots are growing rapidly and new leaves are being unfolded every day. If these new leaves are not protected with regular fungicide sprays, then conidia dispersed during rains will find receptive host tissue and scab may become so prevalent that the orchard will require high rates of fungicide throughout the remainder of the growing season.

That is what happened in many orchards in 2009. Orchards that are carefully scouted and still appear to be scab-free three weeks after petal fall are unlikely to develop severe scab problems later in the season. However, scab risk never totally disappears until we get some hot weather. Production and viability of scab conidia both drop off rapidly following several days with high temperatures in the mid-80s, and repeated exposure to high temperatures almost guarantees that scab will remain inactive through summer. In years like 2009 when the summer remains cool, scab can continue to pose a threat through June and July. Nevertheless, the risk of secondary scab infection is always greatest right after petal fall when it is difficult to maintain fungicide coverage on new terminal leaves.

Powdery mildew
The period right after petal fall is also the period of peak risk for powdery mildew. Just as with apple scab, only young unfolding leaves are susceptible to infection by the powdery mildew pathogen. The period after petal fall provides a rapid succession of unfolding leaves. If mildew is not controlled during the several weeks after petal fall, then it often becomes sufficiently established to ensure that there will be abundant inoculum for the following year. Young trees that are still filling their spaces may need mildew protection all the way through August because they will remain susceptible to mildew until most terminal growth has stopped. And don't forget about newly planted trees because mildew can severely compromise first year tree growth if new trees are exposed to high levels of inoculum from adjacent older orchards where mildew is poorly controlled.

Cedar rust diseases
Fruit infections from cedar apple rust and quince rust occur mostly between tight cluster and first cover, so the period when fruit are at risk from rust diseases is nearly past. The DMI fungicides provide excellent post-infection activity against rust on both leaves and fruit. Including a DMI in petal fall and first cover sprays usually guarantees that rust will not be a problem on fruit.

However, the cedar galls that release cedar apple rust basidiospores remain active for three to four weeks beyond petal fall. Spore releases up to three weeks after petal fall can cause severe infections on newly developing terminal leaves on susceptible cultivars. Where susceptible apple cultivars are grown in the vicinity of cedar trees, trees should be protected from rust for at least three weeks after petal fall, and in high-risk areas, four or five weeks of protection may be required. Captan and Topsin M will NOT provide adequate protection against rust diseases. The QoI or stroby fungicides (e.g., Flint, Sovran, Cabrio), the mancozeb fungicides, Polyram, and Ziram are all effective for protecting leaves, but none of them will provide post-infection activity for suppressing rust on new leaves that become infected between sprays. The DMI fungicides remain the best option for controlling rust diseases from petal fall through early June.

Black rot
Fruit decays caused by Botryosphaeria obtusa, the black rot fungus, rarely become noticeable until late summer. However, infections can occur after petal fall, remain quiescent through summer, and then appear in late summer, so sprays applied after petal fall can have a large impact on the amount of black rot that appears prior to harvest.

Equally as important is the fact that fruitlets that are killed by thinning sprays often become infected by the black rot fungus if the fruitlets fail to drop from the tree. These fruitlets then become mummies (Fig. 1) that supply inoculum for infections later in the summer or during the following year. Captan, Topsin M, and the QoI fungicides (Flint, Sovran, Cabrio) are the most effective for protecting fruit, whereas the DMI fungicides and the mancozeb fungicides have been considered less effective.

Recently, Kerik Cox and collaborators compiled results from a study where they collected mummified fruitlets in late fall from Cortland trees in fungicide test plots that received various fungicides. They then attempted to isolate B. obtusa from large numbers of mummies from each plot to determine how sprays applied after petal fall might influence the number of dying fruitlets that become infected. Their results showed that 70–75% of mummies collected from unsprayed trees at the Hudson Valley Lab were infected with B. obtusa, whereas only 40–45% of fruitlets from unsprayed trees at Geneva were infected. Differences between locations may have been caused by differences in the strains of Cortland at the two sites, differences in chemical thinners and the times they were applied, differences in weather during the thinning period, etc. None of the fungicide treatments eliminated B. obtusa infection of mummies. In the Hudson Valley, fungicides provided only about 10–50% reduction in B. obtusa, but at Geneva, the best fungicide treatments reduced infection in mummies by about 80%. Surprisingly, at both locations, mancozeb applied alone was as effective or more effective than Flint applied alone. (Captan was not included in these trials.) Thus, while Flint may be more effective than mancozeb for protecting living fruit, protectant fungicides like mancozeb and captan may be more effective for keeping B. obtusa out of dying fruitlets that eventually become mummies and supply inoculum for later infections. Thus, including a contact fungicide such as mancozeb or captan with DMI or QoI fungicides applied after petal fall may help to suppress the amount of black rot inoculum that develops in mummified fruitlets.

Sooty blotch and flyspeck (SBFS)
Fungicides applied in July and August are usually considered the most important sprays for controlling SBFS. However, sprays applied between petal fall and 3rd cover can also influence the amount of disease that appears at harvest because flyspeck ascospores begin blowing into orchards from wild hosts in the orchard perimeter soon after petal fall. Mancozeb, Topsin M, the QoI or stroby fungicides, and Inspire Super are all very effective for controlling SBFS during the period after petal fall. Captan applied at high rates (e.g., 4 to 5 lb/A of Captan 80W) can provide fairly good control, but Captan-80 at 2 lb/A is relatively ineffective. The first generation DMI fungicides (Rally, Procure, and Vintage/Rubigan) are also ineffective. Thus, combinations such as Rally plus Captan, while good for controlling powdery mildew, black rot, and scab during the period after petal fall, may allow early establishment of SBFS if spray intervals are longer than about 7 days.

In summary, the period after petal fall is still a critical period for controlling apple diseases. Careful selection and timing of fungicides during the three to four weeks after petal fall can minimize the risks of having disease problems on fruit at harvest.

Useful links

UMass Extension Fruit Program

UMass Cold Spring Orchard

Scaffolds Fruit Journal

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