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High Density Study Group to Meet Cooperatively with New Hampshire's Dwarf Fruit Tree Growers' Study Group

Brookdale Fruit Farm
36 Broad Street (Route 130) Hollis, New Hampshire
Friday, June 15, 1:00 PM

Elwin Hardy (of Brookday Fruit Farm), Bill Lord, Wes Autio, Jon Clements, and attending growers will discuss dwarf tree management.

Brookdale Fruit Farm is located about 0.5 miles east of Hollis town center on Broad Street (Route 130). We will start at the apple packing/storage building.

Weather You like it or Not…

It's probably safe to say we've had just about every kind of weather – including drought, heat, cold, clouds, rain, and hail – that could possibly be thrown at us so early in the season. To begin, April and early May were very dry and warm. From April 15 through May 21 at the UMass HRC in Belchertown, only 0.15 inches of rain were recorded, and from May 1-4 the daytime maximum temperatures approached or exceeded 90 F. Then, on the morning of May 7, many Massachusetts orchards recorded minimum temperatures in the middle to upper twenties during full bloom (27 F at Belchertown), resulting in significant frost/freeze injury to fruit buds depending on location and elevation. Finally, it started raining on May 22, and to date, we've had just over five inches of rain at the HRC! Of course, some of this rain has come in thunderstorms with accompanying hail. Whew, it certainly has been a challenge timing thinning and disease/insect-control sprays over the past few weeks! Although it is still a little unclear as to how the potential apple crop will shape up given the frost/freeze injury and poor thinning weather, it's probably safe to say fruit set is extremely variable depending on orchard, cultivar, and weather history, and overall, yields will be down somewhat from the past two (heavy) years. It's probably also a safe bet that there is more weather coming our way – some good, and unfortunately, some not so good. So, as usual, stay tuned, and as the old saying goes, "if you don't like the weather now, wait a minute, and it will change!"

Thinning with Ethrel

As the end of the chemical thinning season ends, some may find themselves in a situation where there are far too many fruit still remaining on the tree, and time to chemically remove them is fast coming to an end. When fruit reach 20 mm or more, traditional post-bloom thinners are only marginally effective. The use of rates of NAA at high enough concentrations to remove fruit may actually reduce fruit size.

Ethrel is a last-chance thinner. It is only considered when all other options have been exhausted, generally when fruit size is 20 mm or greater. We are very reluctant to make thinning recommendations using Ethrel because of variability and a lack of a consistent response. Ethrel appears to have a very narrow range of conditions where it works optimally as a thinner. In some years, you get no thinning, in others, you get good thinning, and yet in other years, you drop the crop. When deciding whether or not to use Ethrel, one must consider not only the chance of losing a crop due to thinning but also the repercussions associated with growing a crop of very small apples with poor taste, and with little or no return bloom for a crop next year.

We do not make recommendations for thinning with Ethrel because of the uncertainties involved in getting the response that you want. However, we do provide guidelines for those who are willing to chance significant reductions in crop load with the hopes of getting good fruit size and quality at harvest and acceptable return bloom next year. We have found that the Ethrel concentration range between 200 and 300 ppm (2/3 to 1 pint per 100 gallons) has been most useful. We also suggest including 0.5 pounds actual of carbaryl WP formulation per 100 gallons. Lower rates are used if applied when more favorable weather is predicted after application, whereas higher rates are suggested when weather after application is forecast to be cool. We emphasize that these are only suggestions and that there is risk involved in using Ethrel as a thinner.

Yes, We Have Scab…

We are seeing the first scab lesions from infections that occurred at the start of the Great Rain. Most are appearing on the tops of leaves, 2 to 5 from the end of the terminal. These were leaves that were probably just emerging as the infection period started, and hence they were not sufficiently protected when they were bombarded by ascospores.

What if you have scab? Well, the only relatively new option for fungicides is one of the strobilurines, Sovran or Flint. The good news is that these fungicides hit scab hard, and provide excellent sporulation suppression. That means that the new scab spots will not be pumping out thousands of new spores, causing more scab spots, that pump out thousands …. well, you get the picture. These two fungicides would be particularly well used right now, because they not only give excellent scab suppression and protection, but do a great job on flyspeck. The down side is that these fungicides are relatively expensive. However, unlike the SI fungicides, they don't have to be tank mixed with a protectant fungicide to deal with fruit scab issues at this time. This reduces costs a bit. For suppressive activity, full rates are important, so use Sovran at 1.6 oz/100 gallons (dilute) rather than the 1.0 oz/100 gal rate. It isn't clear whether or not a follow-up application 7-10 days later is needed. A conservative but expensive approach would be to make the application. Alternatively, Syllit (dodine) or combinations of Benlate or Topsin-M with a protectant fungicide (if resistance is not a problem in the orchard) could be used. Repeated applications of Syllit 65W at 12 oz per 100 gal (2 lb per acre) can be used to inhibit sporulation. At least follow up with a full rate of captan after 7–10 days.

For organic producers, the only real eradication option is liquid lime sulfur, applied at 1/2 gal/100 gal. This application will have to be repeated at 5- to 7-day intervals until the lesions stop producing spores. However, russet is a real problem.

Plum Curculio

Like the week before it, the weather of the past week was simply too cool to favor either much immigration by plum curculios into orchards or much egglaying. Traps designed to capture immigrating PCs at the Horticultural Research Center show the following capture pattern for the year to date:

Samples of fruit for PC egglaying scars taken in 12 commercial orchard blocks and at 5 sites of unmanaged trees show the following pattern for 2000 and 2001:

As the weather warms, we can expect one or two more flushes of PC immigration and a rise in PC injury to fruit. Another indication that we still have a ways to go before the end of the PC season is the accumulation of degree days since petal fall. The model of Harvey Reissig and Jan Nyrop in New York suggests that for effective PC control, orchards should be protected with insecticide through 340 degree days after petal fall. In Conway, we have only 114 degree days since petal fall (as of June 5).

Our recommendation is to protect perimeter rows of apple trees (the most susceptible to PC) with perimeter-row sprays that will provide effective residue for at least the next two weeks if not longer.

Leafminers

Some leafminers are in the tissue-feeding stage, with mines visible as stippled areas on the upper surface of small or mid-age friut cluster leaves. But most are still sap feeders. In general, only a few orchards (less than 10% of those sampled) are experiencing even small percentages of mined leaves thus far. The complete story of the first generation of LM is yet to unfold; however, the cool weather has held back the development and expression of miners.

Mites

The first generation of adults is now beginning to lay eggs. Overall, the weather has been very unfavorable for mite buildup and very few orchards are showing many mites at this point in time. Mites are best sampled by looking at mid-size fruit cluster leaves toward the interior of the tree. If you see some, it's best not to apply any spray at this point but wait a week or two until egglaying is complete, eggs have hatched into nymphs, and a more accurate sample of mite incidence can be taken.

Crinkled Leaves

Foliage of some cultivars (eg. Cortland) is quite susceptible to frost injury. Affected leaves may be highly crinkled, with an appearance similar to leaves infested by rosy aphid. Before deciding that you may have a sudden and massive problem with rosies, however, take a close look. Chances are you won't find any.