By Boyce R. Foerman,
Extension Agent, Agriculture
The perplexing
problem of how to rejuvenate declining citrus trees has confronted most
Southern Arizona gardeners. Assuming this sometimes dubious challenge
takes determination and patience reinforced with know how and the
proverbial "green thumb."
Although citrus trees
are comparatively hardy, they're substantially weakened from prolonged
neglect, then suffer considerable injury from our scorching, desiccating
summers and occasional winter freezes. Potential for recovery depends
upon each tree's health and vigor and, of course, the extent of injury.
Late winter and early
spring are the best seasons to initiate restoration attempts, and the
base of each tree is the place to start.
Make sure the bud or
graft union, that swollen enlargement that encircles the base of the
trunk, is above the ground surface. If not, soil should be removed to
expose this critical area to the air. Occasionally trees are
transplanted too deep, or too much soil is filled in under established
trees or mounded around the base of their trunks. This condition makes
them more susceptible to Foot Rot Gumosis infection, an all too common
fungus disease of the lower trunks and roots of citrus trees.
Then, as near as
practical, extend irrigation well out to the "dripline" of each tree.
This is necessary in order that the important feeder roots which are
most prolific in the outer reaches of root zones can adequately be
supplied with water and fertilizer. These wells need only be deep enough
to confine water under the trees during irrigations, however, since the
rate of flow can usually be adjusted in accordance with the soil's rate
of absorption.
Next, closely inspect
the trunks and lower limbs of each tree. Carefully cut away any bark
that's loose, cracked, or bleeding sap. Don't remove healthy bark! And
no wood need be removed unless it's rotting. Immediately treat such
surgical wounds with a smear of Bordeaux Mixture diluted with water to a
thin paint consistency. Then, to discourage future Foot Rot Gumosis
infection, dilute three tablespoons of Bordeaux Mixture per gallon of
water and drench 3 to 5 gallons of this solution into the soil
immediately around the base of each tree trunk. Usually this drench need
not be repeated, at least for a few years.
Now, look to the
limbs and branches. Corrective pruning will probably be necessary. If
summer foliage has been sparse, sun exposed bark of branches, limbs, and
trunks will be sunburned to varying degrees. But, whatever the cause,
any dead or severely weakened twigs, branches, or limbs best be pruned
out. Then, thin out twigs of the rest of each tree to balance its
remaining branching. Treat all larger cuts with the Bordeaux Mixture
smear, then seal them with asphalt pruning paste after they dry.
Next, or at least
before the weather gets hot, white vinyl tree paint ought to be applied
to any larger branches, limbs, or trunks that are not shaded by foliage
from our summer's intense sunlight. Its white color will reflect the
sun's burning rays and prevent further burn injury.
Finally, a good
application of nitrogen fertilizer, evenly applied under each tree and
watered in by a deep, thorough irrigation, will hopefully stimulate
recovery.
The regular seasons
to fertilize citrus are early February and then again in late May, but
an additional application about the first of August will help weakened
trees recover their vigor. Nitrogen fertilizers normally suffice, but if
summer foliage develops a chlorotic (yellowing) appearance, an
application of chelated iron will green up leaves and stimulate growth.
Established citrus
trees should be irrigated 6 to 8 hours each time and about every 10 days
to 2 weeks during the summer, every 2 to 3 weeks spring and fall, but
only once each month in the winter. Those growing in sprinkler irrigated
grass lawns additionally need those prolonged 6 to 8 hour irrigations
but only about once a month to supply their deeper rooting needs.
Insect sprays are
normally not a practical necessity for landscape citrus, but don't
entirely discount the possibility. New growth produced from cut back
limbs will be particularly susceptible to thrips injury. Attentive
observation and prompt controls could save weakened trees from further
set back.
2/78
Issued in
furtherance of Cooperative Extension work, acts of May 8 and June 30,
1914, in cooperation with the U.S. Department of Agriculture, James A.
Christenson, Director. Cooperative Extension, College of Agriculture,
University of Arizona.
The University of Arizona College of Agriculture is an Equal Opportunity
employer authorized to provide research, educational information and
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without regard to sex. race , religion, color, national origin, age,
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