Back to top

Healthy Fruit 2010 Vol. 18:16

Aug 10, 2010

Orchard Radar preliminary McIntosh harvest date forecasts (for Belchertown)

Begin measuring actual McIntosh starch-iodine index no later than Wednesday, August 18

The Michigan formula estimate for standard (i.e. non-spur) McIntosh starch index 4.0 and beginning of optimum McIntosh harvest for CA storage is Wednesday, August 25. Estimate adjusted to lessen influence of unusual bloom date is Tuesday, August 31

Cornell Bulletin 221 provides formulas for different locations to estimate date when non-spur McIntosh reach starch index 6.0 and the end of optimum harvest for CA storage. Using the Hudson Valley formula, the estimated end of McIntosh CA harvest for Belchertown MA is Wednesday, September 15

The way I see it

All signs still point to an early harvest. Paulared apples are being harvested by some this week, a good 1-2 weeks ahead of average: fruit diameter, 3.1 inches; 65% red skin color; flesh firmness 14.5 lb; soluble solids 10.5%; starch index 3.8 (2-7 range); fruit have some watercore (results from Belchertown, MA). I am expecting to see above-average pre-harvest drop given the early season and hot/dry weather we are having. It is not too late to apply ReTain to McIntosh and other later-harvested varieties, but only in blocks that are not particularly stressed. Expect to see a flush of apple maggot fly activity with a little rain after this dry spell, so keep some insecticide coverage in place for the next few weeks. Ditto for summer diseases and rots, although with the dry conditions, summer disease pressure has not been high. A return to more frequent rain will change that though, and sometimes we get caught short on fungicide coverage during this very late summer period and end up with more sooty blotch/flyspeck than we would like at harvest. I will start apple maturity testing in earnest next week and will report any unusual ripening or pre-harvest drop issues as they arise. JC

Still time to collect leaves for foliar analysis

It's not too late to collect leaves for foliar (plant tissue) analysis to determine nutrient status. (But I would do it this week.) Foliar/leaf analysis is the best way to get a snapshot of the nutrient content of your trees, and thus tailor fertilizer programs to address deficiencies or excess of nutrients as indicated by the leaf analysis results. Complete directions for collecting and submitting the leaves are available at theSoil and Plant Nutrient Testing Laboratory. Consider sampling every block every three years so you can best address the nutrient needs of your trees. Note that analysis can be done for apples, peaches, pears, cherries, etc.

Painless and efficient maturity testing

Win Cowgill, County Agricultural Agent, Rutgers Cooperative Extension; Jon Clements, Extension Tree Fruit Specialist, University of Massachusetts; Jeremy Compton, North Jersey Tree Fruit Technician, Rutgers University

UMass Extension Fruit Program, Clements Corner

Our observation has been that few growers utilize the Starch Index (SI) method of determining harvest maturity. Perhaps SI testing is perceived as time consuming and difficult to properly judge. We contend, however, that SI testing is the best and easiest indicator of apple maturity that a grower can use to plan their harvest and storage regimes.

Why is it important to perform SI testing? First, as mentioned, the SI method is probably the best way to judge fruit maturity without expensive equipment. The Sl technique, wherein the starch to sugar ratio is measured, is correlated with ethylene evolution. In fact, ethylene synthesis occurs as fruit ripens. Therefore, the SI index is an inexpensive way to assess the degree to which fruit has converted starch to sugar, and is indicative of the onset and progress of ethylene production.

Secondly, because SI is a reliable indicator of relative fruit maturity, SI testing can help you determine if harvested fruit should be placed in early CA, late CA, or regular cold storage. Remember that, as a rule, fruit with SI readings of 3-4 are suitable for late CA, apples measuring 4-6 on the SI scale are best for early CA, and any fruit reading 6 or above should be placed in regular cold storage or marketed immediately. Of course, reliability in using the SI method for determining apple maturity is predicated on good sampling techniques, i.e.; looking at fruit that has sufficient size and color. Or, in other words, sample apples that you expect are approaching harvest readiness. (Note: Apples going into late CA (available in April-June, etc.) should not average less than 15 lbs. flesh firmness.)

Dr. George Green, Pennsylvania State University, has more details on harvest maturity in the Pennsylavania Tree Fruit Production Guide. He also offers the following: "Over the years charts have been developed for many varieties but some charts went from 1 to 5 while others went from 1 to 7.There was much confusion so the postharvest physiologists at Cornell University have developed a more universally accepted chart that is useful for all varieties. It is being used by researchers in over 20 states in the national apple cultivar-testing program. Cornell has an excellent publication available to help you use the starch-iodine test and to develop an apple maturity program. The publication also contains a laminated starch iodine chart to aid in interpreting the tests. I strongly suggest that anyone seriously interested in harvesting high quality apples with good storage potential download a copy of this publication, 'Predicting Harvest Date Windows for Apples (1992)' Information Bulletin 221." Full-color plates show how to use and interpret the starch-iodine test for determining maturity and the best harvest dates for quality, especially important for apples going into storage. Covers McIntosh, Cortland, Empire, Delicious, Mutsu/Crispin, and Idared; dates for other varieties can be interpreted from the information presented.

Specific starch charts have also been developed for Gala, Liberty, Cortland, and Mutsu.

Having tested tens of thousands of apples over the years, per numerous experimental protocols, we can now suggest a simple, quick and efficient method for evaluating orchard by orchard or block by block SI apple samples. Here is our quick and simple testing technique:

  • Equipment consists of a one quart hand-operated spray bottle filled with SI solution, a pocketknife, and a Starch Index chart. It's most important to just use the chart and begin sampling and testing the fruit two weeks before anticipated harvest to get a baseline on the maturity.
  • The procedure is simple -- pick a sample of apples that appear ready to harvest, based on size, color, days after full bloom, and taste. Spray the SI solution on longitudinally halved fruit, wait one to one and one-half minutes, and make your readings based on the SI chart. The whole process is portable, quick, simple, and saves Sl solution compared to dipping individual apples in a solution filled pan.
  • It is important to keep good records on your maturity determinations by cultivar and block. You will start to build a good database of harvest maturity information for your orchard.

Although the SI is a reliable gauge of many cultivars, such as McIntosh, Empire, Jonathan, Red and Golden Delicious and Macoun, some cultivars do not respond as well to the SI test. Examples include Gala, Honeycrisp, and Fuji, which do not respond well to the SI rating, and should be gauged using background color, soluble solids content, and flesh firmness.

Background color is a very good maturity indicator on Gala and will provide the grower with an accurate maturity gauge. Red color, flesh firmness and soluble solids are not as reliable an indicator of maturity as is background color on this cultivar. Fruit should be harvested for optimum long-term storage quality when the background color of the fruit is changing from a green to yellow color. After that, the background color changes from yellow to cream. It is at this stage that the fruit is ready for immediate sales or short-term storage. Galas will require multiple pickings for optimum fruit quality. Background color is also one of the best indicators of maturity for Fuji cultivars.

Here are some additional resources on fruit maturity testing and for purchasing/making supplies for doing the SI test, including SI Test solution and charts. Also, contact Win Cowgill or Jon Clements if you have further questions or need more information.

From the Ontario Ministry of Agriculture, Food, and Rural Affairs, two publications on using the SI test, including directions for making the solution and charts for McIntosh, Delicious, Empire, Idared, and Spartan

For purchasing SI Test solution and charts

Cascade Analytical, 800-545-4206, Wilson Irrigation, 1-800-232-1174,

Guest article

POTENTIAL NON-TARGET EFFECTS OF GLYPHOSATE ON APPLES Dave Rosenberger [Plant Pathology, Highland], Mario Miranda Sazo, Craig Kahlke, Hannah Mathers, and Chris Watkins Reprinted from Scaffolds Fruit Journal, Volume 19, Number 20, August 2, 2010.

Note: this is an excerpt from the full article. Please read the full article to understand background for these recommendations. JC

Generalized rules for minimizing adverse, non-target effects of glyphosate on apples:

  1. Never apply glyphosate to Macoun apples. Macoun trees seem uniquely susceptible to damage if glyphosate hits the tree trunks near the soil line.
  2. Avoid using glyphosate for sucker control on apples because doing so will probably reduce winter hardiness and may increase the probability of internal browning (at least on Empire). Nor should glyphosate be applied immediately after suckers are cut because glyphosate is readily absorbed by freshly cut stems.
  3. We suspect that early summer applications of glyphosate are less likely to create problems than are late summer applications. However, Mather's group in Ohio has shown that glyphosate exposure in spring can result in elevated levels of shikimic acid for at least a full year following the exposure.
  4. Whenever glyphosate is applied, a drift inhibitor should be included in the spray tank to minimize the number of small droplets that are produced.
  5. After the Roundup patent expired in 2000, generic brands appeared. They include Touch- down, Jury, Makaze, Cornerstone, Roundup Original Max, Roundup Pro, Roundup Weathermax, and others. Each of these products incorporates various surfactants at varying doses. Read the label and only add a surfactant if that is suggested on the label. High concentrations of surfactants may increase uptake through tree bark, so cheaper products that do not contain as much surfactant may actually be safer around trees.
  6. Some growers and consultants believe that protecting trunks with white latex after planting can reduce the potential for herbicide injury, but this claim needs verification in replicated trials.
  7. The pressure on herbicide sprayers should be kept as low as possible (e.g. 20–30 psi) to mini- mize the generation of small droplets. (Conside using air-induction nozzles too. JC)
  8. Where possible, a hooded boom sprayer should be used to apply glyphosate to tree fruits to minimize the bounce-back from bare soil that can sometimes appear as a haze of small droplets that circle upward into trees.
  9. NEVER apply glyphosate with controlled-droplet applicators that disperse concentrated glyphosate from a spinning disk. The fine droplets produced by these CDAs can remain airborne for a long time and will almost certainly drift onto trees.

Useful links

UMass Extension Fruit Program

Scaffolds Fruit Journal

Follow me on Twitter and Facebook