|Ayars, James - Jim|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/19/2004
Publication Date: 3/28/2005
Citation: Williams, L.E., Ayars, J.E. 2005. Water use of thompson seedless grapevines as affected by the application of gibberellic acid (ga3) and trunk girdling - practices to increase berry size.. Agricultural and Forest Meteorology. Interpretive Summary: Interpretative Summary: Girdling and gibberellic acid (GA3) sprays are routinely used to manage berry size in the production of Thompson Seedless grapes. How these practices affect water use and irrigation scheduling for grapevines is not well understood. A project was completed to develop answers for these questions. The results indicate that water use of vineyards used for table grape production, where only girdling is employed, can be reduced for the period of time the girdle remains open. This will also affect the Kc. However, seasonal water use for these vineyards may only be minimally affected compared to those in which this practice is not used. The lack of an actual decrease in either water use or constant Kc when the vines were girdled in combination with an application of GA3 indicates that GA3 may possibly mitigate the depressing effect of girdling on gas exchange and subsequently whole vine water use. Additional studies are required to determine if this is the case. In this study the Kc did not decrease after harvest or later as long as the vines were continually irrigated and that the foliage remained functional due to the season long control of insect pests. This was independent of whether the grapevines were farmed for use as table grapes or for the production of natural Thompson Seedless grapes used for raisins or crushed for juice or concentrate. Therefore, the decrease in the crop coefficient after the mid-season plateau for grapevines given in several publications may not be appropriate where irrigation continues through harvest and later in the season and the canopy remains fully functional, such as is the case for commercial table grape vineyards in the Coachella and San Joaquin Valleys of California.
Technical Abstract: Seasonal water use of Vitis vinifera L (cv. Thompson Seedless, clone 2A) was determined with a large weighing lysimeter in the San Joaquin Valley of California from 1994 to 1996. The first year of the study, the vines growing within the lysimeter were treated as would be done to produce fruit for use as table grape; the application of Gibberellic Acid (GA3) and trunk girdling at berry set (approximately two weeks after anthesis). Both practices will increase berry size of this seedless cultivar. In 1995, the vines in the lysimeter were only girdled at berry set, no application of GA3 at that time. Reference crop evapotranspiration (ETo) between March 15th and the end of October averaged 1124 mm across the three years. Water use shortly after the vines were girdled in 1994 increased as would be expected for non-girdled grapevines while in 1995 water use after girdling decreased for a period of approximately four weeks. Once the girdles healed (callused over) in 1995 water use increased to values similar to those of the previous year. The crop coefficient (Kc) subsequent to girdling in 1994 remained constant for a period of four weeks while the Kc decreased after girdling in 1995. The Kc increased after the girdles healed both years ad remained at a value of approximately 0.9 until the end of October. In 1996, the vines in the lysimeter received none of the treatments used in the previous two years. The seasonal water use and maximum daily water use in 1996 of the vines in the lysimeter were greater than in 1994 and 1995. Water use of the vines was equivalent to 838, 708, and 936 mm from March 15 until the end of October while that of ETo was 1136, 1060, and 1176 during the same period in 1994, 1995, and 1996, respectively. At full canopy in 1996 the Kc leveled off at a value of 1.1 and remained such until the end of October. The results indicate that girdling the trunks of grapevines can affect water use when compared to non-girdled grapevines. Additionally the Kc of this perennial horticultural crop does not decrease after harvest or later in the season if the vines are fully irrigated and insect pests are controlled.