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A rapid onset of bloom and then right into petal fall is upon us. Some things to think about when considering that first thinning spray:
Bloom has generally been heavy and pollination conditions have been good. With the exception of the potential impact of a heavy crop last year, there is every reason to believe a good fruit set will occur.
The extended (7-10 day) weather forecast does not call for any prolonged periods of cool, cloudy weather. Therefore, trees will want to ‘hang on’ to developing fruitlets, particularly if we have sunny, warm weather.
As mentioned in last week’s Healthy Fruit, a petal fall thinning spray is a good place to start. Even if set is lighter than expected, a petal fall thinning spray should not result in over-thinning. The recommendation is to apply one quart of Sevin XLR per 100 gallons dilute. NAA can be added at app. 4-6 ppm if extra thinning is desired.
You will have the opportunity to evaluate the results of this petal fall thinning spray in a week and follow-up with an additional thinning spray if necessary.
We appear to have the potential for a nice crop of peaches in 2000. Peaches love fertility -- mature peach trees require 0.025-0.05 pounds of actual nitrogen per year of tree age. Ideally, you should make a split application of nitrogen, with the first application pre-bloom and a second application at shuck split. If you missed the first application, go ahead and apply half the recommended amount now, and follow-up in two to three weeks with the remainder. For example, seven year-old peaches on lighter soil would need 0.35 pounds of actual nitrogen (7 X 0.05) during the growing season. A split application of ammonium nitrate (34% nitrogen) at 0.5 pounds per tree each application (1.0 pound total ammonium nitrate = 0.34 pounds actual nitrogen) would do the job. Non-bearing trees (1-2 years old) require 0.1-0.2 pounds actual nitrogen per year of tree age. Of course you should also do soil and leaf analyses on a regular basis to fine tune and justify your fertilizer program.
(Fertilization recommendations derived from an article by W. Cowgill and M. Peters, Rutgers Cooperative Extension. If you'd like a copy, please let me know. J. Clements)
With the record-setting heat of early May, plum curculio emergence and invasion has started like gangbusters—suggesting that our prediction of a light PC season (due to overwintering mortality) may be off base. There are, however, two pieces of good news associated with the dense early-season PC immigration. First, a stretch of hot, humid weather at or near bloom is conducive to concentrated emergence and immigration of PC adults—meaning that a petal fall spray is certainly in order and should yield excellent control of the bulk of the PC population.
The second piece of good news stems from an early-season research project aimed at developing an effective monitoring trap for immigrating PCs. In all, 112 traps are placed in Belchertown and Conway, set against the edge of the woods to intercept PC invading the apple trees from overwintering sites. To date, we have captured nearly 300 PC adults—importantly, a few synthetic fruit volatiles (used in conjunction with these traps) seem to be drawing PC to these interception traps. For the first time, we have been able to chart the level of PC immigration from overwintering sites into blocks of apple trees; the first captures occurred on 5/2, and there has been a major influx every day since. Refined odor-baited traps may allow growers to track the progress of PC immigration into commercial orchards—reductions in trap captures may signal the end of invasion and subsequently indicate the end of need for chemical applications.
As mentioned earlier, trap-capture patterns indicate that a petal fall treatment is well justified in most orchards. There are two basic approaches to the first application targeting PC: border-row spraying (treating the first two perimeter rows) and whole-orchard treatment. In most years, a border-row spray is effective against early-season immigrating PC because of their slow, methodical approach through the orchard perimeter toward the interior. Research in New York and Quebec suggests that a season-long border-row spray program is successful, but not quite as effective as a whole-orchard spray program. Growers are again left to weigh the risk of possible increases in PC damage with the obvious benefits of a border-row treatment routine.
When deciding what strategy to employ for the first PC application, growers should also consider the benefit of second-hand control of European apple sawfly offered by whole-orchard sprays of Guthion or Imidan (border-row treatments are not particularly effective against highly mobile EAS).
That said, captures of EAS thus far have remained light, so a dire need for EAS control may not enter into the petal-fall tactical decisions. Most growers will likely consider whole-orchard sprays against PC which, coupled with fairly consistent petal fall across cultivars, should yield effective control of EAS.
All assembled data indicate that no available chemicals can approach the efficacy of Guthion or Imidan for PC control. However, there are a handful of new materials on the horizon that will be labeled for use against PC, notably Actara (Novartis) and Avaunt (DuPont)—neither of which will be available for the 2000 season.
Another alternative is Surround—the only newly labeled material that provides reasonable PC control (though not as good as Guthion or Imidan). Along with a number of other pests, Surround (kaolin clay, 95% WP) is labeled as moderately to very effective against PC, codling moth, leafrollers, apple maggot, leafhopper, leafminer, sawfly, and thrips—if applied every 10 days or so during the time of activity of the target pests. Maximum benefit requires thorough and uniform application to dry foliage before pest damage occurs. Importantly, Surround is not recommended as a border-row treatment as it does not kill the target pests—the clay particles form a white film on treated surfaces and disrupt activities of target insects through particle attachment to feet and body parts (adapted from the 2000-2001 New England Apple Pest Management Guide).
When used against PC at a 10-day interval (3 treatments), the data suggest that Surround offer control 80-90% as effective as 2 applications of Guthion or Imidan. This material is available for purchase from Crop Production Services in South Deerfield and United Agricultural Products in Sterling. The cost is roughly $1/lb., and the label recommends treatment with 50-75 lbs. per acre, depending on tree size.
Trap captures of adult leafminers have leveled off statewide. Although captures were substantial in many orchards (averaging 100 or more LM per trap), the overall population is much lower than last year’s record LM crop. Surveys of egg densities on leaf clusters have shown moderate to low egglaying to date; growers are again faced with the decision of whether to treat against the first-generation mines (based on trap captures and egg counts) or the second-generation mines (based on first- and second-generation mine densities). Data of the past several years suggest that treatment targeting the first-generation mines is most effective, though delaying application of a petal-fall material about 2 weeks (until first-generation mines appear) somewhat diminishes the effectiveness. Tests in other states in 1999 suggest that Provado, Agri-Mek, and SpinTor at petal fall are equally effective in controlling LM. If trap captures, egg counts, or mine surveys indicate that treatment is warranted, growers should avoid overuse of one material; consider switching to SpinTor or Agri-Mek if Provado was used as the last LM treatment.
Hatch of European red mite eggs has progressed rapidly through the hot spell of the past week. Growers who are not confident in the efficacy of oil applications may benefit from a petal fall sample of interior fruit cluster leaves for presence of motile ERM nymphs. Experience in New York suggests that if 30% of clusters have nymphs present, a petal fall miticide treatment may be in order. Currently, the petal fall mite management tools are Apollo, Savey, and Agri-Mek—each of which has shown good to excellent ERM control. Each of these materials should be used with some caution toward resistance management; if annual treatments are necessary, the best approach is to alternate between use of Agri-Mek and Apollo/Savey. Combined data indicate that petal fall is indeed the optimal timing for use of Apollo or Savey; Agri-Mek (with an adjuvant) can be effectively used up to two weeks after petal fall.
At this point, inspection of terminal growth offers the best indication as to whether treatment against pear psylla is necessary. If 10% or more terminals are found infested (at fruit set), then there are several options for treatment. Data from New York suggest that an application of Provado (20 oz. per acre) followed by a second application within 2-4 weeks will offer control of low to moderate populations; Agri-Mek in conjunction with horticultural oil applied 1-2 weeks after petal fall provides 4-6 weeks of protection; and back-to-back sprays of Mitac have shown an acceptable level of control (though the effects of this strategy may be diminishing), with the first application 2 weeks after petal fall and the second 7-10 days later. Pyramite is also an option for use against psylla (at 10-13.2 oz. per acre), and recent studies in Massachusetts and New York showed that a dual application (10 and 21 days after petal fall) gave excellent psylla control.
We have roared right through bloom in the East and are already at early petal fall in some locations. In the West, most orchards are still in full bloom. The bloom period is being compressed to a few days in many areas due to the extreme heat!
Thanks to Polaris Orchard Management (POM) and New England Fruit Consultants (NEFCON) we have
timely fire blight warnings for you. POM ran the Maryblite program and found that infection conditions were present from yesterday onward where there was rain. Calculations were based on a green tip date of April 1 and pink date of May 1. NEFCON notes that fire blight pressure is very high in orchards where fire blight has been present during the last three years. Degree accumulations are very high, and last night's thunderstorms provided ample wetting to wash the bacteria into the apple blossom nectaries. In orchards which have been clean in the past the nagging question is, where will new infections pop up?
Scab pressure is very high. Spore maturity is approximately 60 % in Amherst and exceeds 40 % in higher orchards to the West. Day degree accumulations reached 443 by Monday morning in Sterling, MA. These 2 facts put central and eastern MA right in the middle of the accelerated phase of ascospore maturation, and western orchards are not far behind. The good news is that we didn't have any infection periods there (Sterling) or elsewhere (NEFCON report) during the period from last week's Healthy Fruit through yesterday mid-day. The bad news is that last night's rainfall may have been long enough to cause an infection period. We don't have that data yet and the storm seems to have been patchily distributed across the region.
NEFCON reports that pears are at petal fall, and that most pears were past peak bloom when fire blight risk began, but late cultivars and late areas have significant risk if fresh blossoms are present. Peaches are also at petal fall and brown rot risk is currently high.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, and Duane Greene except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
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