Current DD Accumulations

Nitrogen by the Numbers

Now is a good time to address the nitrogen fertilizer needs of young and bearing fruit trees. Keep in mind the best way to get a handle on tree nitrogen status is with a leaf analysis. Lacking that, shoot growth is a reasonable indicator—it should average 15 to 18 inches over the course of the growing season in apples. Shorter indicates a nitrogen deficiency, or vice-versa, longer spells too much nitrogen. The exception is young trees, where maximum shoot growth is desirable during first through third or fourth leaf. As a rule of thumb, mature apple trees require from 0.1 to 0.5 pounds actual nitrogen per tree per year. (Based primarily on tree size, taking into account age and rootstock/vigor. This equates to 50–60 pounds actual nitrogen per acre.) Care should be taken to not over-fertilize soft-flesh varieties such as McIntosh. Young apple trees should be fertilized with 0.05–0.1 pounds actual nitrogen per tree in the first leaf, and then increased to 0.1–0.15 pounds per tree in the second and third leaf. Common sources of nitrogen include granular urea (46% N), ammonium nitrate (34% N), and calcium nitrate (15.5% N). Care should be taken when fertilizing young trees to distribute the fertilizer evenly around the rooting zone. In fact, calcium nitrate is recommended in the first leaf (0.5 pound per tree total, usually a split-application), followed by ammonium nitrate in the second and third leaf at 0.5 pounds per tree over two applications. Peaches need more nitrogen than apples. For mature, bearing peaches plan on applying 80 pounds actual nitrogen per acre per year. Young peach trees require 0.1 (first leaf), to 0.3 (third-fourth leaf) actual nitrogen per tree in a split-application.

Growth Control Short Course: Part I

As you know, Apogee has been added to the growth control toolbox in 2001. Growers should remember, however, that several cultural and one other chemical method of growth control are available. Over the next several Healthy Fruit issues, these will be discussed in some detail, starting with scoring. But first, keep in mind the major reasons for the controlling growth: trees planted too tight resulting in crowding and significant crop loss resulting in season-long, vigorous shoot growth. Scoring is a moderate attempt to control growth. Simply, it is the process of making a single cut with a knife (a linoleum knife works very well) completely around the trunk of the tree somewhere between the soil and the lowest scaffold branches. This process is done when new growth is approximately 4" to 6" in length, usually about ten days after petal fall. Caution is advised when selecting trees to score. Weak or moderately vigorous trees may be overly devigorated by the scoring treatment, and this effect may last for several years. On the other hand, overly vigorous trees may need to be scored in successive years to achieve the desired degree of growth control. Scoring breaks the flow of nutrients, photosynthates, and growth regulators between the tree canopy and its roots. The score will heal, but prior to healing it will reduce both the length and diameter of the new growth. Additionally, it is likely to enhance fruit set and increase flower bud formation for the next season. Next week: a more serious approach, trunk ringing.

Abuzz About Bees

It's hard to believe just a few short weeks ago there was snow on the ground. Now, with the recent and forecasted warm weather, we are clearly headed for an ‘on-time' bloom. Hopefully, by now, you have made arrangements to get bees in the orchard as soon as king bloom opens. Good fruit set and size cannot be achieved without good pollination! Having healthy, active hives in the orchard at king bloom is essential! For more pollination information, visit The Pollination Home Page. Be sure to check out the ‘Crop by Crop' link for some excellent articles on tree fruit pollination.

Bud Development

As of April 30, flower bud development ranged from early pink in southern orchards to tight cluster in central orchards to late half-inch green in some parts of the western hills. Amazingly, this is pretty close to where we stood last year on this date. With predicted warm weather for most of this week, some orchards could be in bloom by late in the week or early next week. Growers concerned about pollination may want to consider mowing later this week to knock down dandelions that can compete with apple blossoms for pollinators. This can be especially important if the weather turns windy during bloom.

Tarnished Plant Bugs

For the great majority of orchards where TPB traps have been placed, captures remain well below threshold levels. Captures have neared or exceeded thresholds in only one monitored orchard. TPB adults respond pretty good to well-placed traps through tight cluster but less well from pink onward. As orchards come into pink, we can expect to see trap captures dropping even though some TPB adults might be observed puncturing developing buds. In years of heavier TPB activity, damage can accumulate through the blossom period, resulting in fruit with deep dimples or rough, tan scabby patches similar to curculio scars.

TPB can be controlled to some extent (perhaps 50%) by a pink application of Guthion or Imidan. As indicated in the March Message, Danitol is the best newly labeled material capable of providing better TPB control than an organophosphate. Danitol is a synthetic pyrethroid (in the same chemical class as Ambush and Pounce). Unlike Ambush or Pounce, it may provide temporary suppression of pest mites (for a couple of years or so). But experience suggests that as pest mites become resistant to Danitol, they are apt to flare because of the negative effect of Danitol on mite predation. So, growers interested in promoting biocontrol of mites should carefully weigh potential short-term benefits against potential long-term costs of using Danitol against TPB and other pests.

Leafminers

Except for one monitored orchard where captures of LM adults on red trunk traps have reached about 50 per trap, LM captures are pretty low across the state. LM overwinter as pupae in leaves on the orchard floor. Like the state of maturity of apple scab spores, LM pupae may be comparatively slow in developing this year relative to tree bud development. This is not surprising given the lateness of snow cover that kept the ground cool through early ~ mid-April. Trunk trap captures of LM predict the size of the emerging population of adults, especially well when LM adults emerge early relative to tree bud development and the LM are predominantly apple blotch LM. Given that LM emergence might be on the late side and that most Massachusetts orchards are now dominated by spotted tentiform LM, this may be a year when we can not rely too strongly on trunk trap captures as indicators of adult population size.

A pre-bloom spray of Ambush, Pounce, Danitol or Vyoate can control LM adults and eggs well. But each has a potential downside. An approach to LM control more consistent with IPM philosophy would be to wait until petal fall and treat with Provado, Spintor or Agri-Mek.

Mites

Even though a couple of mite nymphs have been seen on blossom cluster leaves (indicating a bit of egg batch), tight cluster through pink is still a favorable period for oil application. Oil has its greatest effect against eggs just about to hatch (the majority usually do so at early to mid-pink), but oil can still kill a meaningful proportion of newly hatched nymphs. Two pre-bloom oil applications provide much better mite suppression than one application. So even though many (even a majority) of mite eggs may have hatched by mid-pink, a late pink application of oil can still do some good provided it does not affect blossom quality. To be on the safe side, don't apply oil at a rate greater than 1 gallon/100 after tight cluster.

Pear Thrips

In some years, pear thrips can have a major impact on blossom quality, especially in orchards in the western hills where maple trees are close to orchard borders. Thrips overwinter as pupae in soil beneath maple trees (a favored host). Emerging adults can move into orchards in great numbers anywhere from half-inch green through pink. Adults are about 1/25 inch long, slender and brown with fringed wings. Injured bud tissue at pink is brownish and shriveled. Bees are reluctant to visit and pollinate thrips-injured blossoms.

So far this year, rather few thrips have been seen even in traditionally vulnerable orchards. But we could still be on the early side of thrips emergence. This week will determine if control will be needed. A tentative threshold is 4-6 thrips per blossom. Even a quarter rate of Guthion or Imidan can provide effective control.

Apple Scab Update

(Dave Rosenberger, Plant Pathology, Highland)

Apple scab ascospore counts as determined from squash mounts:

Leaves collected by Kevin Iungerman on April 25 show that the Saratoga/Champlain Valley areas are still lagging other areas in the state vis-a-vis scab ascospore maturity. The Saratoga/Champlain Valley samples show that scab in those areas is now approaching or has just passed our action threshold of 15% mature spores. However, the low counts in the shooting tower suggest that it will take a few more days of warm weather or perhaps some rain to get leaves wet enough to allow maturation to proceed before any major discharges will occur. The slower maturation of ascospores in the Saratoga/Champlain region compared with the Hudson Valley/Western N.Y. regions has been quite striking this year. The last several weeks of dry weather apparently arrested spore development in northeastern N.Y. before spores were at threshold levels, whereas the southeastern and western parts of the state had already passed threshold levels before the dry weather began.