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Healthy Fruit 2008 Vol. 16:19

Sep 9, 2008

Observations from Belchertown

Not much to say except we are picking as fast as we can. McIntosh color on 'legacy' Macs such as 'Rogers' is lacking, Gala have developed good background color, and Honeycrisp have high starch-index readings. Cooler weather forecast for the second half of this week should help color and further accelerate apple maturity. I have already detected a bit of internal browning of Honeycrisp, so I hope it does not get worse. Despite the wind and rain from Hanna, pre-harvest drop has not been too bad -- yet.

J. Clements

Apple maturity report

Below are some of my observations on apples we are harvesting in Belchertown. Nothing too unusual, except Gala seem ready plenty early, and as already mentioned, Honeycrisp are ready and being picked.

Harvest date: 05-September

apple
drop
diam. (in.)
% red skin
firmness (lbs.)
Soluble Solids
Starch Index
comments
Honeycrisp
nil
3.1
70
16.3
13.1
6
good, ready to go

Harvest date: 08-September

apple
drop
diam. (in.)
% red skin
firmness (lbs.)
Soluble Solids
Starch Index
comments
Blondie (MO-1040)
few
3.0
yellow
19.6
13.9
6
fruity, banana-like flavor
Rogers McIntosh
few
3.1
50
15.5
11
3.6
lacking good color; wait a week to pick
Silken
nil
3.0
yellow
16.1
13
5
just about perfect, this is an excellent eating apple, but bruises easily; recommended
Buckeye Gala
none
3.0
98
20
14.2
5.7
mostly ready for 1st-pick based on size and background color; some fruit already getting slightly greasy

Jmcextman blog posts

TUESDAY, September 2, 2008 Slender-axis Lindamac McIntosh

Why apples may need a fungicide spray during September

by Dave Rosenberger, Cornell's Hudson Valley Lab, Highland, NY (reprinted from Scaffolds Fruit Journal, September 2, 2008)

Thirty years ago, most apple growers in New York State applied their last fungicide spray to apple trees during the first half of August. After that, they could focus on harvest issues and forget about fungicides until the apple scab season started the following spring. In recent years, many growers have found that a September fungicide spray is essential for controlling sooty blotch and flyspeck (SBFS) that would otherwise reduce pack-outs of late-maturing apple varieties. This is especially true in years when heavy rains in late August or early September remove fungicide residues and wet weather thereafter allows flyspeck to appear before fruit are harvested.

Our current understanding of flyspeck development was previously explained in an article in Scaffolds Fruit Journal (Vol. 15, no. 15, 26 June 2006), and details will not be repeated here. Based on our current understanding of flyspeck, three factors come into play when deciding if late-maturing apple cultivars should be sprayed during September:

1 - All of the summer fungicides (except captan when it is used alone) will protect fruit for at least 21 days or through two inches of accumulated rainfall if the fungicides are applied at recommended rates. Fungicide residues on fruit are depleted after fruit have been exposed to two inches of rain.

2 - Flyspeck appears on apples prior to harvest only after fruit accumulate roughly 270 hours of wetting in the absence of fungicide residues. To estimate when flyspeck might appear on fruit in autumn, wetting hours that occurred during fungicide protection gaps in July and August (as determined using rule #1 to calculate fungicide depletion) must be added to wetting hours that accumulate after fungicide residues are depleted prior to harvest.

3 - The wettest harvest season in my records occurred in 2006, when heavy rains during the last few days of August removed fungicide protection and we then accumulated an additional 270 hr of wetting during the first 26 days of September. Using that season as a worst-case scenario, one can assume that any cultivars that will be harvested within 25 days from the time of fungicide depletion should not need a September fungicide spray because flyspeck will not have time to appear on fruit before harvest. The exception would be fruit that were previously exposed to extended fungicide protection gaps during summer as described in the preceding paragraph.

After combining these factors with other observations, we have concluded that flyspeck will rarely be a problem in Hudson Valley orchards that received regular fungicide sprays during summer, so long as the final fungicide spray was applied near or after mid-August, and fruit are harvested prior to 20 September. If late August and early September are unusually wet, then a September spray may be needed for fruit that will be harvested between 20 and 30 September. A September spray is often required to protect fruit harvested after 1 October. Of course, these are generalized rules that may need to be adjusted for other geographic areas and/or for inoculum density in the orchard perimeter. Furthermore, these rules apply only if fungicides are applied in such a way that residues actually last as long as predicted based on our small plot studies.

Why have September fungicide sprays become important for late-maturing apple varieties, whereas they were almost never used 30 years ago? I doubt that anyone can provide a definitive answer to this question, but some of the changes in our apple production system may have made it more difficult to control SBFS on apples.

Ag statistics show that apple production in New York increased from about 24 million (1977–79) to 28.5 million (2005–07) bushels of utilized production, despite a decrease of more than 40% in apple acreage over that same time period (1980–2006). In fact, the average yield per acre in New York State has roughly doubled over the past 30 years, largely due to the conversion of orchards to high-density planting systems.

While average production per acre was doubling, average tree height was decreasing. Given a doubling of productivity per acre combined with a 50% reduction in tree height, it might be fair to estimate that apple production per cubic foot of tree canopy has almost quadrupled over the past 30 years. In short, apples today are spaced much closer together within the tree canopy than they were 30 years ago. This dense fruit spacing makes it difficult to achieve complete coverage of the fruit surfaces when fungicides are applied during late summer and fall. The clustered fruit on productive limbs also dry more slowly, thereby fostering growth of the SBFS fungi.

Furthermore, because of the narrow row spacing in high-density orchards, a tractor and sprayer must be driven at least twice as far now as compared to 30 years ago if a grower wishes to spray each side of every row. Frequently, growers opt to spray only alternate rows in high-density systems, but that decision further reduces the likelihood of achieving complete fungicide coverage of fruit surfaces during late summer.

When late-season sprays do not contact all fruit surfaces, then control of SBFS on the unsprayed surfaces is dependent on redistribution of fungicide residues during subsequent wetting periods. One can assume that controlling SBFS via rain-dependent redistribution of fungicide residues will require a higher initial fungicide dose than would be necessary if the sprayer was capable of providing even fungicide coverage of all fruit surfaces. An increasing dependence on fungicide coverage via redistribution may help to explain why growers and private consultants are reporting that they must use Topsin M at rates of 1 lb/A in late summer, whereas 30 years ago rates of 6–9 oz/A provided adequate control of SBFS. In fact, rates of 6–9 oz/A of Topsin M still provide good control of SBFS in my small plot trials where trees are sprayed to drip using a high-pressure handgun. Thus, it appears that the fungicide is still as effective as it ever was, but fruit spacing in modern orchards has made it more difficult to cover 100 percent of the fruit surfaces with fungicide when sprays are applied with airblast sprayers.

Orchard fertility is another factor that may affect the incidence of SBFS in modern orchards. Russ Holze, an experienced apple grower and private consultant in the Hudson Valley, recently noted that apple growers today pay much more attention to orchard fertility than they did 30 years ago. Most farmers today expect to see healthy green foliage on their apple trees throughout the harvest season.

Researchers reported many years ago that huge quantities of carbohydrates and minerals are leached out of apple leaves during late summer rains. In fact, in one study published in 1956, researchers estimated that carbohydrates leached from apple tree canopies might total more than 700 lb/A/year (Tukey 1971). Newly formed leaves are relatively resistant to leaching, but leaves become more "leaky" as they age. So far as I know, no one has attempted to determine whether higher fertility levels and modern pest management tools have affected the quantities of carbohydrates and minerals that are leached from apple tree canopies. However, one might assume that higher fertility would result in increased levels of carbohydrate leaching.

Carbohydrates leached from leaves might affect development of SBFS if the growth of sooty blotch and flyspeck on fruit surfaces is at least partially sustained by external nutrients deposited on fruit surfaces. No one has proven that leached nutrients directly affect SBFS, but several lines of evidence support that possibility. In the fall of 2007, late-season SBFS infections appeared primarily on the upper hemisphere of Golden Delicious fruit in a research plot where fruit were well separated (and therefore were hanging vertically from the stem). The half of the fruit toward the calyx was nearly disease free. This distribution of SBFS is consistent with the hypothesis that growth of the SBFS colonies was fostered by leached nutrients released from leaves above the affected fruit. (Of course, other hypotheses might also explain this distribution.) A second line of evidence comes from an apple grower who, after the Alar scare in the early 1990s, attempted to control SBFS with a "fungicide alternative" that contained various sugars. This grower reported that the sugar solution enhanced growth of SBFS and that his black apples were not very marketable despite their lack of fungicide residues.

To summarize, no one has yet documented (via scientific trials) that either fruit density within trees or changing fertility practices within orchards are contributing factors for the SBFS problems that have plagued many growers in recent years. However, it may be easier to accept the fact that a September fungicide spray will sometimes be needed in modern orchards if we see this change in fungicide strategy as a normal consequence of doubling our production per acre. In fact, if one considers that 30 years ago NY apple growers had to spray two acres to get the production that now comes from one acre, then adding a September fungicide spray to control SBFS on late-maturing varieties is a small price to pay for the season-long savings that accrue from spraying and maintaining only half as many acres throughout the rest of the year!

Literature cited Tukey, H.B. Jr. 1971. Leaching of substances from plants. Pages 67–80 in: Ecology of Leaf Surface Micro-organisms, T.F. Preece and C.H. Dickinson, eds. Academic Press, NY.

Unusually severe cherry leaf spot disease may put next year's crop at risk

(reprinted from Penn State Fruit Times, Vol. 27, No. 8, August 26, 2008.)

From a plant pathology perspective, this has been an excellent year for development of many fungal diseases that affect plant foliage. The frequent rains in May and early June when leaves for many plants were tender provided the ideal conditions for infection and disease development. Not surprising therefore, we have an unusually high levels of cherry leaf spot disease in our orchards. Many of you may have noticed that cherry leaves turned yellow in late July to early August. At this time, most trees have already shed more than a half of their leaves---which is too early compared to 2006 and 2007 when most leaves were shed in mid to late September. A close inspection of the yellow leaves will reveal numerous spots caused by the cherry leaf spot fungus Blumeriella jaapii. Why should we be concerned? There are two main reasons why we should be concerned about severe cherry leaf spot this year. First, everything being equal, we can expect more inoculum to overwinter and as a result a higher disease pressure next year. Blumeriella jaapii overwinters in infected leaf litter on the orchard floor. The more infected leave there are that overwinter, and the more severe the levels of infection on those the leave, the more the spores to be produced early next spring. Secondly, early defoliation is likely to affect the return yield in 2009. My own research and that of others indicates that defoliation occurring too early will not only limit the number of flower buds formed, it may predispose trees to winter injury. Within Pennsylvania, defoliation occurring any time in July leads to significant negative effects on return yield of tart cherries the following year. Defoliation before mid July can result in partial die-back of affect shoots. So what can we do about the situation? Obviously, the time to stem this year's epidemic is well past. However, I will let you into a little secret…I made an application of Indar on July, 2 which was soon after harvest; the treated trees still look green and have lost less than 10% of the leaves to date. It's about the best evidence I have for utility of post-harvest fungicide applications for this disease. Even if you did not make a post-harvest fungicide application, there are several sanitation practices that should help reduce overwintering inoculum. This include, removal of leaf litter through raking and shredding, and application of 2.5 to 5% urea in the fall to facilitate decomposition of the infected leaves thereby denying the fungus a refuge. This is about the time to think and start preparing yourself for such practices. (Submitted by: Dr. Henry K. Ngugi, Penn State University, FREC)