William Peacock, Tulare County farm advisor of University of California Cooperative Extension has been researching the application of foliar K during fruit ripening and has assessed that the nutrient has a positive affect on advancing fruit maturity. Peacock has been evaluating the application of foliar K for the past three seasons in several Tulare County vineyards.

His findings over the three year study show:

• K was not applied to correct deficiency but rather to increase K in fruit during a period of high demand. He noted that growers should test the viability of applying foliar K to their vineyards before adopting it as a standard practice.
• He noted that foliar K should be applied late during ripening when fruit reaches 14 degrees to 18 degrees Brix. "Sprays applied earlier than this were not as affective," he said.
• Potassium sprays should be applied at 1 to 1.5 pound K per acre. Peacock noted that applying less than 1 pound may not be effective, and applying more than 1.5 pounds of K per acre does not improve the maturity response.
• There was no difference in maturity response between the four materials tested: Albion K metalosate, K sorbate, K phosphate, or K phosphite.
• The K material can be applied with either a concentrate or dilute spray, however, it is very important that clusters are contacted by the spray.