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Volume 6, No. 5 April 29, 1998

• Scab protection
• Petal-fall thinning

It's Pink and Bloom

With today's warm temperatures, a number of areas will be in full bloom just in time for some wet weather. This is a particularly dangerous time for scab, so plan to treat accordingly. It's also time to plan for petal fall thinning. So it looks like a week of heavy sprayer use.

Normally, bloom is a May 10 affair at the HRC, give or take a few days. While it has slowed a bit, bloom is as advanced as we have seen in the last 10 years.

McIntosh growth stages for various locations:

• Ashfield very early pink
• Belchertown full pink
• Northboro early bloom
• Sterling full pink
• Wilbraham early bloom

Scab Still Scarce

The good news is that apparently Massachusetts has not been hit with early scab, at least not to the extent seen in the Hudson Valley. Dave Rosenberger reported in this week's "Scaffolds" that there is quite a bit of early scab in commercial orchards in the Hudson Valley growing region. A spot check in Massachusetts, including non-sprayed trees, indicates that there isn't any scab yet. Apparently conditions were just enough delayed and/or slower that the wetting of April 1-2 did not cause the level of infections seen further south in New York.

The bad news is that we are entering a very high risk period for apple scab. As of this writing, it appears that we are in store for several days of showers, starting tomorrow (April 30). This, the amount of scab inoculum mature and available (20 to 40%), and the amount of sensitive tissue make this a high risk period for scab. Don't take chances with fungicide programs now.

Dave Rosenberger also points out that of the protectant fungicides, against scab, captan has an edge over Dithane or Polyram. This may not appear at the full rates of these fungicides, that is, 2 lbs./100 gal. for captan 50WP, Dithane 75DF or Polyram 80DF. However, when these are cut in half to 1 lb/100 gal., Dave has shown significantly better scab control with captan. The down side, of course, is that captan is not compatible with oil. For the few folks that need to pay attention to rust, captan is very weak on that disease. 

Wet Bloom Weather Can Bring Rust

Cedar-apple rust is active now. The galls on junipers are shooting out bright orange spikes when they get wet. In Massachusetts, the problems with cedar-apple rust are usually minimal, by which I mean we hardly ever see any symptoms in commercial orchards. However, there are a few orchards which are, unfortunately, close to a large number of red junipers. Occaisionally, these orchards will have either leaf or fruit symptoms of rust. If an orchard is close to a large number of junipers, and these junipers produce brightly colored around apple bloom, consider using a scab fungicide that will also control rust. Fortunately, there are a number of them.

All of the EBDCs (Polyram, Dithane, Penncozeb, Manzate, etc.) do an excellent job stopping rust. So do the sterol inhibitors (Nova, Rubigan, Procure). However, captan, Benlate, Topsin-M and Syllit are either ineffective, or have very little effect on rust.

It is hard to believe, but we are very near the beginning of the chemical-thinning season for apples. Chemical thinning is probably the most important practice that you can undertake as an orchardist. A good job of thinning will net you more money than any other single practice, and a poor job of thinning will lose you more money than any other single practice. It is important for you to become a careful but aggressive chemical thinner, with a goal of producing all 96-count apples (at least for McIntosh). Anything smaller costs you money (that is, if you pick it).

At the upcoming twilight meetings (May 5-7), a revised set of thinning recommendations will be presented. As in the last couple of seasons, we recommend a multiple approach to thinning, beginning with a petal-fall spray, a second treatment when fruit are between 8 and 12 mm in diameter, and under appropriate conditions (the lack of response or the lack enough warm temperatures), a third treatment when fruit are about 15 mm in diameter.

At petal fall, or soon thereafter, a spray of Sevin (1 quart Sevin XLR/100 gal) should begin the thinning process, forcing early differentiation among fruit and early allocation to fruit that will stay until harvest. Early thinning will result in larger fruit at harvest. This treatment can be used on all trees that require thinning. If more severe thinning is desired, a combination of Sevin plus NAA (5-10 ppm) can be used at petal fall, but avoid using Accel, since it is less effective at this time.

So far this season, only a handful of orchards have had high enough captures of tarnished plant bug on monitoring traps to warrant a pre-bloom treatment. However, this does not mean that TPB are finished for the year. Spotty warm weather over the past several weeks has inspired some activity, but with a few successive warm days during bloom, TPB can still cause significant damage to the fruit. Damage inflicted during bloom looks less like the dimpling of the fruit typical of TPB injury, and has more of a scabbed-over appearance, similar to plum curculio damage.

We are approaching the time of year when white rectangle traps begin to lose their effectiveness as a monitoring tool. Once white tissue starts to show in the blossom clusters, the huge amount of white in the canopy competes with the visual stimulus of the monitoring traps. Because of this, we do not consider these traps a good indicator of TPB populations after mid-pink.

Growers who traditionally have problems with dimpling and scabbing of fruit by TPB should visually inspect blossom clusters at late pink and into bloom in order to determine whether or not there is a level of damage which warrants a petal fall insecticide application.

This year has held pretty true to last year in that there are many orchards that are far exceeding treatment thresholds for leafminer. In a couple of monitored orchards, trap captures have exceeded 100 LM per trunk trap, which is a sure sign that some action should occur at petal fall or soon after. General recommendations for LM management appear in the last two weeks' issues of Healthy Fruit; a more lengthy discussion appears in the March Message.

Like tarnished plant bug, European apple sawfly has been a relatively low-impact pest in Massachusetts and other northeastern states for the past couple of years. That notwithstanding, EAS have already been captured in low numbers in orchards at full pink. Now (mid- to late pink) is the time to hang white sticky rectangle traps for monitoring sawfly activity. These traps should be hung as high as you can reach on the south side of the canopy, clear of any waving branches.

A few leafroller/bud moth larvae have been seen in the past week feeding in blossom clusters. Although present most seasons, populations do not generally develop to large enough numbers to cause significant damage. Usually, these blossom feeders are controlled very well by pre-bloom insecticide applications. Even if no pre-bloom insecticide is used, the petal fall plum curculio spray should offer good control.

Red mite eggs have hatched in orchards which have reached early to mid-pink. Although an oil application made in the early stages of egg hatch will still be effective against the remaining eggs, the benefits of oil applications alone against mites begin to decrease substantially after egg hatch has begun.

In orchard block that did not receive a full oil program, psylla nymphs have begun to build in blossom clusters. Growers observing large numbers of nymphs in clusters should be prepared for a post-bloom insecticide application. Of the post-bloom treatment options, Agrimek has shown good control of psylla when applied about 10 days after petal fall. Provado is labeled for use on pears and has shown promise in reducing high populations, but the limited residual control makes it best suited for a late season application. With proper timing, Mitac is also effective as a post-bloom treatment for psylla. For growers who are considering a treatment of Mitac, New York recommends back-to-back sprays after petal fall, with one application about two weeks after petal fall and the second application 7-10 days later. For a more complete discussion of recommendations for psylla management, refer to this year's issue of the March Message.

More good news/bad news. The good news is that there were few critical factual changes needed in the New England Apple Pest Management Guide this year. The bad news is that you won't be seeing them, or any of the other improvements to the Guide any time soon. Here's the news from Glen Koehler, the editor in Maine. Grab your pen and go correct that dog-eared copy of the Guide!

"PEST GUIDE DELAY. There have been production problems in getting the new edition of the New England Apple Pest Guide. The most recent estimate is that it could be late May before you have a copy in your hands. The process is out of our hands at this point, so all we can do is make the best of it. Fortunately, the 96-97 edition needed few factual corrections. Almost all of the changes made for the 98-99 edition are improvements or clarifications, not corrections or other discrete changes.

Pg. 23. Before Postharvest Rots, insert new entry:

MOLDY CORE. This disease causes a rot with visible fungal growth in the seed cavity and core of some apple cultivars, particularly Delicious and McIntosh. In storage, the rot may spread into the flesh of the fruit. While Alternaria is commonly isolated from moldy core apples, other fungi are also associated with the disease. Sometimes, moldy core disease will cause fruit to redden during July or August. More frequently, fruit don‚t show symptoms, and are harvested. In storage, the rot may worsen. The infection is believed to move into the calyx when it remains open and prolonged wetting occurs. Presumably, fungicides applied in the weeks just after petal fall reduce or eliminate the problem.

Page 49, Table 10

In the metiram Polyram entry, change the reentry interval from 24 hours to 12 hours.

In the triflumizole Procure entry, change the reentry interval from 24 hours to 12 hours.

Page 50 (Table 10)-

-Add as 1st entry (above azadirachtin) the following: abamectin Agri-Mek 12 hours 28 days.

-carbaryl entry. Change preharvest interval from 1 day to 1 or 3 days.

-permethrin line - Change restricted entry interval from 24 hours to 12 hours.

-pyrethrin & rotenone line- Change preharvest interval from 0 days to 12 hours.

-Add above rotenone line, pyridaben Pyramite 12 hours 25 days.

Page 62. Add following entry for Agri-mek before Ambush. This will be first entry under Notes on Insecticides & Miticides (after changing & moving Align entry).

Agri-Mek (abamectin): 0.15EC. 2.5 fl. ozs./100 gals. Higher rate on label is for use on pear trees. Effective against leafminers (eggs and sap-feeding larvae), European red mites, and two-spotted spider mites. Apply in combination with horticultural summer spray oil or with a suitable adjuvant. Oil rate should be minimum of 1 qrt. oil / 100 gals. dilute. Penetrants such as LI700 or Regulaid, or organosilicone surfactants such as Silwet, Sylgard or Kinetic may be substituted, but efficacy may not be quite as good as with oil. Effective application requires at least 40 gals. water per acre. Optimum timing for control of both leafminers and mites is at petal fall. Applications made after two weeks past petal fall will likely result in less leaf absorption and less residual efficacy. Leaf surface toxicity typically lost within six hours of application. Toxic action on pest species is due to translaminar movement of abamectin into leaf tissue. Hence, Agri-Mek has long residual activity even under high rainfall. Highly toxic to bees. Do not apply while bloom remains on trees. Do not exceed 2 applications per season. See Mite Management section for additional information. Restricted entry interval 12 hours. Preharvest interval 28 days.

Page 64 (upper, right) - Kelthane - Change 35% WP (1-1.33 lbs./100 gals.); 50% WP (3/4-1 lb./100 gals.). to 35% WP (3 lbs./100 gals.); 50% WP (2 lbs./100 gals.).

Page 72- Add following information for Agri-Mek as first entry in Table 18 (before Benlate):

Agri-Mek in combination with horticultural spray oil may cause fruit injury to certain varieties of apples, e.g. russetting on light-skinned varieties such as Golden Delicious, when used alone, or when other products are applied sequentially. Carefully follow the Directions for Use and Precautions on horticultural spray oil labels when combining with Agri-Mek.

Next week, on May 5, May 6 and May 7 the Fruit Team will hold the second series of 1998 Twilight Meetings. Please remember that we are charging $10 per farm to use on farm expenses at the HRC.

The meetings will be on

• May 5, 5 PM, Dana Clark's, Apple Valley Road, Ashfield, MA.
• May 6, 5 PM, Westward Orchard (Don Greene), Harvard, MA
• May 7, 1:30 PM, Harold Fine's, Rehobeth, MA

For details, contact Karen Haushchild:

hauschild@umext.umass.edu
or
413-545-5304

Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Please cite this source if reprinting information.