Mar 9, 2015
Pruning, thinning advice for Pennsylvania peach growers

Prior to pruning peach trees this season, check for bud mortality from subzero winter temperatures.

We evaluated bud mortality of six varieties of peach growing in Adams County, Pennsylania, on March 3. The percent of damaged buds per shoot were calculated. Barring further winter freeze or spring frost, it appears that growers with orchards near the Penn State Fruit Research and Extension Center will need to manage the peach tree crop load in 2015 by pruning and thinning as usual.

Given the colder sub-zero temperatures experienced this winter in parts of western and northern Pennsylvania, it is likely that flower bud mortality may be higher in these regions. The following guidelines can assist you in determining the likelihood of peach flower bud damage in your orchard.

Growers can check flower bud mortality in their own orchards as follows:

1. To get a good estimate, you should examine about 150 buds of each variety per block, so collect 5 to 8 fruiting laterals – those typical of the best ones from the trees you wish to test.
2. Bring the fruiting laterals into a heated building and allow them to warm up overnight.
3. Count and record the total number of flower buds (the fat ones) on a branch.
4. Slice each bud open lengthwise with an exacto knife, single edged razor blade or scalpel. A box cutter or utility knife with a fresh blade can serve in a pinch.
5. With a magnifying glass or visor, examine the contents of each bud cross-section. Apart from the outer husk of bud scales, the contents should have a lime green color, with a yellowish green base.
6. Count the number of buds with internal tissue that is brown or black, and record these as dead.
7. Calculate the number dead and number that appear to be healthy. If, for example, you have 24 live flower buds on a fruiting lateral that should carry four peaches at harvest, then you have six times as many live flower buds as are required to have a full crop.

James Schupp, Penn State University

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