Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate

Committee Chair(s)

Gaylen L. Ashcroft


Gaylen L. Ashcroft


Gene Woodridge


Schuyler Seeley


Ricahrd Griffin


In the spring, apple orchards are susceptible to freeze damage. Various approaches to orchard protection have been used in the past. Overhead sprinkling for bloom delay has been effective in extending to a later period in the spring the freeze hardiness of apple buds. Thus, protection against a late spring freeze is obtained. Previous research has not been conducted to determine optimum sprinkling times in the spring, the most effective threshold temperature, the amount of water needed to provide adequate bud protection, and the daily length of sprinkling time.

A 2-year investigation was conducted with the objective of obtaining basic information to help in system design and the operational aspects of overhead sprinkling. The experiment was designed to determine the effectiveness of a system sprinkling beginning at the end of rest and at Celsius growing degree hour accumulations relating to stages bud development. The evaluation of limited and unlimited water use and the relation to bloom delay was obtained.

The two sprinkler types studied were umbrella and impact. On the umbrella sprinklers, four cycling times (1/2, 1/3, 1/4, and 1/6 time) and three threshold temperatures (7, 10, and 13 C) were tested. On the impact sprinkler, three nozzle sizes (4.0, 3.6, and 2.8 mm) were evaluated.

The investigation answered many questions, the most important of which were: (1) when only limited bloom delay is needed, more freeze protection can be obtained by sprinkling in the early spring than in the late spring; (2) bloom delay can be regulated by terminating sprinkling at different stages of bud development; (3) to obtain maximum delay, sprinkling should begin at the end of rest and a low threshold temperature for sprinkling should be used for sprinkler initiation; (4) when limited delay is required, greater efficiency of water use can be obtained by lowering the threshold temperature and lowering the application rate.



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