Zinc Foliar Trials 2001
Thor Lindstrom and James Frisby
Department of Plants, Soils and Biometeorology
Utah State University


Introduction:
Zinc deficiencies are widespread in areas of high pH calcareous soils, like those found in Utah. Many fruit trees grown in Utah are deficient of zinc. Characteristic symptoms of zinc deficiency include the "little leaf" and "rosette" of fruit tree shoots. Severe deficiencies exhibit shoot die back, defoliation and chlorosis. Leaf analysis results from trees grown at Kaysville have consistently shown low levels of zinc, despite annual zinc applications. This year, we decided to compare the standard dormant zinc sulfate spray with a summer chelate spray.

Materials and Methods:
Trees included: 'Golden Delicious' apple on EMLA 26 rootstocks, 'Redhaven' peach on Lovell rootstocks, and 'Montmorency' tart cherry on Maheleb rootstocks. The apple and peach trees were planted in the spring of 1995. The tart cherry trees were planted in the spring of 1988. Apple and peach trees were irrigated with a micro- sprinkler system. A solid-set under-tree impact sprinkler system was used to irrigate the tart cherry trees.
Treatments included: the control or check trees, trees sprayed with zinc sulfate (Nutra Spray Zinc 50), and trees sprayed with chelated zinc (Zinc Metalosate from Albion Laboratories). The zinc sulfate treatment (10 lbs/acre at 100gal/acre) occurred on April 11. Floral bud stages on April 11 were as follows: apple at ½ inch green, peach at calyx red, tart cherry between green tip and tight cluster. Chelated zinc was sprayed twice (1 qt/acre at 50 gal/acre) on May 7 and June 6. Floral bud stages on May 7 were as follows: apple at full petal fall, peach and tart cherry between shuck to shuck-split. The June 6 spray occurred some five days before the first codling moth cover spray on apples; one week before the first peach twig borer cover spray on peaches, and tart cherry fruit was at first pink. Total cost for the sprays is about $13 for the zinc sulfate and $16 for both applications of chelated zinc, not counting application cost.
Treatments were set up in a completely randomized block design. Two trees were used for each replication. A sample of leaves from both trees was collected on July 20 and analyzed for zinc content by Albion Labs. Samples were submitted to Albion Labs with a number and no indication of treatment applied. Individual completely randomized ANOVA statistical analysis were run for each tree type using the CoStat program. Means were compared using the Student-Newman-Keuls method at 0.05%.

Results and Discussion:
Leaves from the control trees were just marginally better than deficient (<15 mg/kg). Leaf zinc levels from trees sprayed with zinc sulfate were not significantly better than the controls. Leaves from the chelated zinc treatment had significantly higher zinc for both apple and tart cherry but not peach (Table 1).
Chelated zinc appears to be most effective in increasing foliar concentrations of zinc in apple and tart cherry, especially during the growing season. Zinc sulfate in not normally applied during the growing season because it can be phytotoxic.


Table 1. Zinc Concentrations in Leaves after Various Treatments

Tree

Treatment

Zinc Foliar Levels (ppm)

Significance

Apple

Check

16.3 b

 
 

Nutra-Spray Zinc 50

15.4 b

 
 

Zinc Metalosate

23.1 a

 
         

.0000 ***

Tart Cherry

Check

19.5 b

 
 

Nutra-Spray Zinc 50

19.2 b

 
 

Zinc Metalosate

26.3 a

 
         

.0003 ***

Peach

Check

15.6 a

 
 

Nutra-Spray Zinc 50

16.0 a

 
 

Zinc Metalosate

21.6 a

 
         

.1581 (ns)