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Healthy Fruit 2008 Vol. 16:16

Jul 29, 2008

Observations from Belchertown

Peach harvest has started, with PF-1 and Earlystar already being picked and gone-by. I really like Earlystar, it has much better color than PF-1, good flavor, and fewer split pits. Next up are Risingstar, PF-7, Sentry, and Garnet Beauty. Which will bring us close to Redhaven the 2nd week in August.

We recorded over seven inches of rain last week, so the summer diseases of apples and stone fruit -- sooty blotch and flyspeck, and brown rot respectively -- are on our minds, With this amount of rain, weekly fungicide sprays (or sooner) are necessary. Apple summer disease articles have previously appeared in Healthy Fruit. But please read the peach and nectarine brown rot control article from Rutgers in this issue. Fruit rots are also likely to be an issue if the wet weather persists. Rotating fungicides is important!

I had to treat sweet cherries for Japanese beetles this week, 3 pints/acre of Sevin XLR PLUS seems to have vanished them (for now). Interestingly, they do not seem to be bothering apples too much this year, but I expect them to still. Keep an eye out, especially on Honeycrisp, which they seem to favor.

Don't forget to collect apple leaves for leaf analysis if warranted. Peaches and cherries can be analyzed too.

J. Clements

Peach and nectarine disease management: pre-harvest period

Reprinted from Rutgers Plant & Pest Advisory, Fruit Edition, July 15, 2008

Norman Lalancette, Ph.D., Specialist in Plant Pathoiogy

On stone fruit crops, the "preharvest period" refers to that period during which the fruit matures and begins to ripen. This is also a period of considerable fruit enlargement. Adequate rainfall and/or irrigation is critical at this time so that fruit cells can increase in size. As the fruit ripens, the background color changes from green to yellow and the fruit begins to soften.

Preharvest diseases. During the preharvest period, anthracnose and Rhizopus fruit rots occasionally occur in New Jersey peach and nectarine orchards. However, brown rot, caused by the plant pathogenic fungus Monilinia fructicola, is by far the most important disease. Indeed, brown rot is generally considered the most important disease of stone fruit worldwide.

Temperatures during the ripening period are almost always adequate for brown rot development. Thus, free moisture, typically in the form of rainfall, is the most important environmental factor contributing to epidemics. If frequent rains occur during the preharvest period and disease control measures are inadequate, then 100% crop loss can occur. Fruit infections are visible as firm, brown lesions that rapidly spread throughout the fruit causing complete decay in a few days. Spores produced on these fruit can then disperse and infect additional healthy fruit.

Fungicide timing. Fruit become susceptible to brown rot as they begin to ripen. Of course, not all fruit on a particular tree ripen at the same time. Ideally, the first preharvest fungicide application (PH3) should be applied when 1-5% of fruit are starting to ripen (background color changing to yellow). Typically, this timing occurs sometime between 21- and 14-days preharvest.

In our own research studies at Rutgers, we generally apply the first application at 18-days preharvest (PH3). Subsequent fungicide applications are then scheduled at 9-days (PH2) and 1-day preharvest (Ph2). The final spray, which provides protection during picking and transport process, can also be applied between the first and second pickings. Such timing may be particularly important if rainfall interrupts the harvest period. Many fungicides have a PHI of 0-1 day and an REI of 12-24 hours, making this timing possible. This final spray may also be very important for farm

Seasonal disease progression. We tend to think of each cultivar block as a separate entity. This view makes sense since preharvest fungicide timings and harvest dates are a function of that cultivar's fruit maturation and ripening. However, in New Jersey M. fructicola cause brown rot during the entire harvest period from mid-July through early September. Rotted fruit from earlier maturing cultivars provides inoculum for subsequent cultivars. Adjacent blocks of different cultivars or cultivars planted together in the same block help facilitate this movement of inoculum.

Given the above process, inoculum tends to "build up" as the season progresses. Thus, in general, the risk of brown rot fruit infection increases as the harvest season progresses. Two factors determine the severity of this risk: (1) the level of control exerted by the fungicides throughout the harvest period and (2) the favorableness of the environment for infection, namely frequency of rainfall. Most orchards have some initial inoculum (blossom blight cankers, infected green fruit) to begin the epidemic, although good sanitation (e.g., removal of fruit mummies during the winter) and earlier [bloom] sprays can help reduce these sources. Preventing insect injury is also critical, as open fruit wounds are an invitation for rot.

Fungicide choice. Selection of preharvest fungicides for the PH3, PH2, and Ph2 application timings is one of the most important disease management decisions. The types of materials chosen are dependent on the fungicides' efficacy, the fungicides' chemistry (for resistance management), and the current fruit infection risk. Recommended fungicides providing excellent control are (1) the sterol inhibitors Elite, Indar, and Orbit (Propi-Max, Bumper); (2) Pristine, a strobilurin + carboximide; (3) Adament, a strobilurin + sterol inhibitor; and (4) Gem, a strobilurin. Recommended fungicides providing good control are (1) Abound, a strobilurin; (2) Captan, a phthalimide; and (3) Topsin M + Captan, a benzimidazole + phthalimide. Peach and nectarine fungicides and their chemistries are listed on page 92 of the 2008 NJ Commercial Tree Fruit Production Guide.

The sterol inhibitors (also called DMI's), strobilurins, and benzimidazoles are all prone to development of resistance by the brown rot pathogen M. fructicola. Thus, none of these fungicide chemistries should be used alone for all three preharvest sprays. For example, a preharvest program of PropiMax/Indar/Elite should be avoided since all three materials are the same DMI chemistry. Indeed, if this program was utilized the entire season at 10 different harvest periods, then a total of 30 applications of DMI's would have been applied! So, ideally, as many different fungicide chemistries should be employed in the preharvest programs, preferably in an alternating pattern. During early to mid-season, when disease pressure is generally lower, a fungicide providing good control is adequate for the first PH3 application. The subsequent PH2 and Ph2 sprays should be from the excellent control category. Examples of such programs are Captan/Pristine/Indar, Topsin-M + Captan/Gem/Elite, and Abound/Indar/Pristine. This type of program can continue as long as disease pressure remains low, as during a dry growing season. During late season, if the infection risk becomes high, then all three fungicides should be from the excellent control category. Examples of such programs are Elite/Pristine/Indar and Adament/Pristine/Elite. Note that Pristine plays an important resistance management role since it currently is the only "excellent-rated" peach fungicide having carboximide chemistry.

Jmcextman blog posts

TUESDAY, JULY 29, 2008 What's with these apple prices?

Very, very early apple harvest update

Apples are sizing up nice, what with all the rain we have had. Before we know it, the first summer apples will be picked. Can September be far behind? I used weather data from Belchertown and the model for forecasting harvest windows from 'Predicting Harvest Date Windows for Apples,' and using the Central New York formula came up with a date of September 23 as the last day for McIntosh apples to be harvested for CA storage. Given an app. three week harvest window, that means Labor Day we'll be underway. (What else is new?) I am leading somewhere, however, and that is ReTain application. The latest research suggests ReTain is best applied 2 to 3 weeks before the start of 'normal' harvest, which I would like to peg as the first two full weeks in September (Sept. 7-20). Backing off 2-3 weeks puts the ReTain application window at about August 20 to 25. Now, hot weather in August may push this back (August 16, 17?) a little bit, but for now most growers will be applying ReTain the middle of that 3rd full week in August. We will be publishing the next 'Healthy Fruit' right about then, and we will includes some application details, but for now make sure you have ReTain (and organo-silicone surfactant) on hand if you plan to apply.