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Healthy Fruit 2008 Vol. 16:11

Jun 10, 2008

Current DD accumulations

  • Belchertown, UMass CSO observed (01/01/08 – 06/09/08): Base 43, 880; Base 50, 514
  • Belchertown, UMass CSO SkyBit (01/01/08 – 06/09/08): Base 43, 854; Base 50, NA

The way I see it: observations from Belchertown

Frankly, it's too hot to go out and see much -- but that should tell you something! June drop of apples has become heavy. You should definitely be seeing the result of thinning sprays applied within the last couple weeks. Hopefully you are where you want to be. Many McIntosh apples have thinned to less than one fruit per spur where thinning sprays were applied. Fruit size of king fruit are 1 inch (25 cm) and growing rapidly. It's probably good timing to apply ethephon (Ethrel) for last chance thinning where your previous thinning sprays did not work as expected, but be careful, hot weather has the trees under considerable stress. Irrigation should be running, particularly in young trees, unless you have received significant rain in the last few days.

The hot weather should ramp up insect activity too. Keep an eye out for curculio, codling moth, and potato leafhopper. Oblique-banded leafroller pheromone traps should be in the orchard so you can monitor hatch of the summer adult generation.

Peach hand thinning should be starting. Space peaches 8 to 10 inches apart, or two peaches per good 'hanger' shoot, for best size. Early thinning of peaches will give the best results.

Early cherries are starting to turn red, so now is the time to start worrying about cracking. To improve color, size, and to reduce splitting, apply 1 gallon per acre of VAPOR GARD® in adequate water for good coverage, 3-4 weeks before harvest. Flavor may be improved on some sweet cherry varieties, and anecdotal evidence suggests it may even repel birds. Do not use in spray tank combination with any pesticide. VAPOR GARD® will probably need to be applied 2 or 3 times before harvest.

J. Clements

Plum curculio model: easy button

The model for determining when the last plum curculio has become active is simple: accumulate 308 degree days (DD'as base 50) from petal fall, and then you can assume the last of curculio is out and about. Therefore, you need to maintain insecticide coverage for at least one week after this date to cover the activity of the last-emerged curculio. In Belchertown, we have reached between 268 and 296 degree days (base 50) from petal fall (May 18) through June 9 depending on how the degree days are accumulated — the model is probably based on the simple hi-lo average, so that means 296 DD's. Another day or two, and curculio are through -- at least in Belchertown and comparable orchards -- if you have applied a cover spray with an insecticide in the last few days. If your insecticide coverage is waning, your next spray (soon) should probably still include an insecticide and that will be it. J. Clements

Healthy Fruit Disease Elements: what to do, what to do about scab?

Timing is everything, particularly in managing apple diseases. By now, enough time has gone by for nearly all the primary season scab to show, but infections, if there were some, from the last primary infection period won't be visible until early next week.

There is plenty of scab visible from earlier infection periods. In fact, there is some secondary scab visible. The basic strategy in an orchard with scab from here out should be to protect fruit. That means keeping protectant fungicides on developing fruit to deal with secondary infections during rains. Of course, it's also useful to reduce the amount of active scab in an infected block, to keep the risk of fruit infections down.

Hot weather is good for scab eradication. At temperatures above 85ºF, the scab fungus is stressed, and if an appropriate fungicide is applied it will have a better chance of killing off the infection. In hot weather, captan has eradicant activity.

The strobilurine fungicides, Flint (Bayer CropScience) and Sovran (BASF), are antisporulants, meaning they reduce the ability of the scab fungus to produce conidia. Since it is the conidia that cause new infections, this is a good thing. However, the scab fungus can become resistant to the strobilurines, and using them in a post-infection application will greatly increase the chances of selecting a resistant strain of scab. In addition, note that for Flint, do not use more than 11 oz./A per season, and for Sovran no more than 25.6 oz/A per season. Do not apply more than 4 applications of a strobilurine per season, and do not apply more than two strobilurine applications in a row.

The SI fungicides, Rubigan (Gowan), Procure (Chemtura), Rally/Nova (Dow AgroSciences) and Inspire (Syngenta) can be good eradicants where resistance is not a problem. As outlined in an earlier Healthy Fruit, Inspire Super MP (Syngenta) comes as a twin pack with both the SI and Vangard, which must be tank mixed. Vangard is not a very good fruit protecting fungicide, so because protecting fruit is the primary objective, it is advised that captan or an EBDC be added to the Inspire mix. That may get expensive, and the usefulness of Vangard is marginal.

If using tree row volume with small trees, it's easy to go below an effective rate for some fungicides. To eradicate and protect fruit, don't fall below the minimum rate per acre, for SIs or strobilurines. So, for Rubigan and Procure, apply no less than 8 oz. per acre even in relatively low volumes of water, and for Rally/Nova and Inspire (that is just the Inspire, not including Vangard) no less than 4 oz. per acre. With Flint, keep rates above 2 oz. per acre, and with Sovran 3.2 oz. per acre.

All sprays that are meant to eradicate scab should be applied as dilute as possible, and coverage should be as thorough as possible. No wind, no high-speed passes, no alternate row middles.

D. Cooley

Late-season "rescue" thinning with ethephon

We all experience occasional failures during the normal apple thinning period from petal fall through the 15mm stage. Once fruit are larger than 15 mm, there are very few options for fruitlet removal. The most commonly utilized technique in New England is hand thinning. Hand thinning is usually performed in early July. Because of this timing, it has very little effect on return bloom the following year, since most flower-bud formation occurs in June. So, it may be possible to gain some fruit size with hand thinning, but if the set is heavy before hand thinning, bloom may be light the next year and trees may even become biennial.

Another thinning option is to use a late-season (early to mid June) ethephon treatment. Ethephon works by breaking down to form ethylene in the plant tissues. It can be effective as a "rescue" treatment, but we have had very little experience with ethephon thinning in New England. Below are some general guidelines based on research in Massachusetts and research and observations in the mid-Atlantic area. It is important to understand that these recommendations are very tentative and should only be used to experiment with ethephon. If conditions or concentration are wrong, then complete crop removal can occur, so be careful!

We are very close to the end of the time when ethephon will be effective. Average fruit diameter should be between 0.75 and 1 inch. When larger, they will not respond. For McIntosh, use 200-300 ppm (2/3 to 1 pt of ethephon / 100 gallons dilute). Include carbaryl at 0.5 lbs of active ingredient / 100 gallons plus a surfactant. Treat when the temperatures for the day of treatment and the next two days are in the 70's.

If all goes well, extra fruit should drop within the next 2 weeks after treatment, and final set should be optimal. Fruit size will be increased, but fruit will not be as large as situations where early thinning was optimal. Return bloom should be enhanced.

W. Autio and W. Cowgill (Rutgers)

Horticultural exercises

  • Stripping, clothes-pinning, and pinching of 1st and 2nd leaf apple trees should be done to promote central leader development, good branch angles, and proper development of fruiting 'branchlets' on vertical-axis and tall-spindle trained trees.
  • A second or third and final application of nitrogen to peaches should be made now. Calcium nitrate (CaNO3) is the preferred source of nitrogen for peaches.  Young apple trees need nitrogen too to keep them growing from now through July (More shoot growth now means more fruit in 2 years.) Calcium nitrate is also the preferred nitrogen source for 1st and 2nd leaf apple trees -- use 3 to 4 oz. CaNO3 per year of tree age in at least 2, maybe 3 applications.
  • Continue with calcium chloride, CaCl2 (or equivalent), in the tank during cover sprays. (Avoid spraying when over 85 F.) See F-119 Foliar Calcium Sprays for Apples for details and more information, but the recommended rate of calcium chloride is 2 to 2.7 lbs per 100 gallons dilute spray right now. (Add 2/3 ounces of vinegar per pound of CaCl2, do not mix with 'Solubor.')
  • It's probably about time for a second application of Apogee if you are on a growth control program with it. Dr. Duane Greene says "Currently we recommend an initial application of 3 to no more than 4 oz. per 100 gal dilute TRV dilute applied at about petal fall. This amount of Apogee should slow and stop growth nearly as effectively as higher rates. The lower rate reduces the the probability of Apogee reducing June drop and lowering the effectiveness of thinners. Because of the lower rate it must be reapplied in 2 to 3 weeks. We recommend 2 to no more than 3 oz per 100 gal. A third application will probably be necessary in July, especially if conditions are favorable for growth. All applications of Apogee should contain a surfactant and either a water conditioner or ammonium sulfate."

J. Clements