1-1/2 feet in diameter, but larger trees have required 4- or 8-pound treat- 
ments. In one test area, at Shreveport, La., large zinc-deficient trees 
that were given either 4 or 8 pounds of zinc chelate in 1954 recovered 
fully in 1955 and so far have not required further treatment. Meanwhile, 
other trees given 20 pounds of zinc sulfate have shown Similar good and 
lasting response. 3 
In alkaline soils, where pecan rosette is particularly hard to combat, 
even the 8-pound treatment with chelated zinc has not entirely corrected 
the condition, but has been more effective than 20 pounds of zinc sulfate. 
In soils where chelated zinc is effective, benefit may be relatively 
lasting. Hence, several years will elapse before it is known how fre- 
quently treatment must be renewed, and thus whether it would pay to use 
chelated zinc to replace zinc sulfate for pecans in such soils or not. 
CHELATED IRON FOR ORNAMENTAL PLANTS 
Chelated iron is being increasingly used by nurserymen and gardeners 
to combat chlorosis in azaleas, roses, rhododendrons, and other orna- 
mentals. Marked helpfulness of chelated metal treatments for such plants 
has been established in some growing situations. Where results remain 
uncertain, Some growers are making their own small-scale tests. 
ARS horticulturists have not included ornamentals in chelate research 
projects, but have gained some practical knowledge by applying chelated 
iron to ornamentals, chiefly azaleas, at the National Arboretum. The fol- 
lowing information on azaleas would apply also to rhododendrons and gives 
some indication of how chelated metal may benefit other ornamentals. 
Iron chlorosis in azaleas may be due to varied common causes: too 
much or too little water; a soil that is poorly aerated from compactness 
or lack of organic matter; a soil containing excessive lime which has 
leached from cement in a nearby building or wall;or a soil type that is by 
nature unfavorable to the acid-loving azalea plant. Azaleas normally get 
their iron requirement from moderately acid soils of 4.5 to 5.5 pH in the 
acid-alkaline scale. Azaleas grown in alkaline soils become So deficient 
in iron that remedial treatment is difficult and in calcareous soils treat- 
ment may be futile. 
If the cause of an iron deficiency of azaleas cannot be corrected by 
adjusting the water supply, mulching, or resetting plants in a more favor- 
able soil, chlorosis-susceptible azaleas can be kept supplied with iron by 
conservative treatments with chelated iron such as iron-DTPA or EDTA. 
It is essential to keep treatment conservative to avoid risk of burning 
these delicate plants. 
The safest method of applying the chelated iron to azaleas is to sprin- 
kle a mild solution--made with 1/4 to 1 pound of the chelated metal to 100 
gallons of water--on the soil around the plants. 
ato lee 
