by Jerome L. Frecon, Gloucester County Agricultural Agent
 

Many studies in eastern peach producing areas show that the bark and cambium

temperatures on a peach tree are considerably higher than the air temperatures. For

example, Dr. Earl Rip Savage of the University of Georgia showed that the

temperature on the south side of a peach trunk may reach 96 degrees F., while the

air temperature at the same time was only 55 degrees F. Retired Agricultural Agent,

Les Miller, and former Rutgers Agricultural Meteorologist, Clarence Sakamoto,

reported on this differential in New Jersey Horticultural News in the late 1950’s on

some orchards in the Hammonton area.
 

Using thermocouples attached to a recording thermometer, Miller and Sakamoto

recorded the wide variation in temperatures from November through February on

bare trees and trees treated with a reflective covering, like white paint. On clear

days, temperatures varied greatly between treated and untreated trees. For example

on February 8, the highest temperature of a trunk was recorded at 84.5 degrees F.

for untreated trunks, and 52 degrees F. for trunks treated with white coverings; the

surrounding air temperature was 39 degrees F. On that same day, the trunk

temperature on untreated trees dropped 70 degrees by 1 am to 14.5 degrees. Many

days during the winter, temperatures on the southwest side rose above 32 degrees

F. It was not uncommon on the clear days during January and February to see a

differential of 25 to 40 degrees on trees not treated with a white covering material.

Peach trees treated with a white coating were always 10 degrees to 32 degrees

cooler and no more than 13 degrees higher than the air temperature. While it was

not clear in this experiment when the chilling requirement of these trees was

satisfied, it is not uncommon in New Jersey to have the chilling requirement met in

mid-January on Redhaven Peach Trees. After this rest period is completed, peach

trees are more sensitive to low temperatures after high fluctuations.

An additional factor to consider is that many of our peach trees are grown on loamy

sands and sandy loam soils. While the centers of orchard rows are covered with sod,

the strip under the trees is bare. Sandy soils heat up more quickly than heavier soils

on a bright sunny day and also lose this heat more quickly on a cold clear night. The

deep drop in soil temperature of a sandy soil may add to the problem of increasing

the low temperature sensitivity of the tree during the winter.

Many growers have gotten away from the practice of painting trees with white paint

to protect them during the winter months. The practice of painting trees has a far

greater impact on protecting the tree from damage by low temperatures than piling

soil around the trunks.
 

Painting trees has a far greater impact on protecting the tree from damage by low

temperatures than piling soil around the trunks.

 

The best coating is an interior, water- based, white latex paint covering the trunk

and lower scaffold branches, as experience over the years has shown. Some growers

find it beneficial to put repellents and other pest management protectants in the

paint. Diluting the paint at least 50% with water is probably cost effective in terms

of increasing coverage and still maintaining good residual coverage. If we want to

continue to keep our orchards living and increase yields we must protect trees

during the winter, particularly some of the newer varieties that may be more

sensitive to low winter temperatures.