1a.Objectives (from AD-416)
1. Determine if sap flow (‘bleeding’) is a prerequisite for budbreak and canopy development.
2. Test if spring shoot vigor and fruit set are related to soil moisture before or during budbreak.
3. Develop practical recommendations for early-season irrigation management.
1b.Approach (from AD-416)
We propose to investigate with pot and field experiments designed to vary soil moisture before and during budbreak. The resulting differences in grapevine vigor will be assessed by measuring shoot length and final pruning weight. Measurements of bleeding sap volume and composition will enable us to determine whether spring shoot vigor is related to the bleeding rate and/or content. Such measurements will be supplemented with estimates of fruit set, yield formation and fruit composition. We will then use the knowledge gained from these experiments to develop practical recommendations for early-season vineyard management. Documents Grant with Washington State University
There is reason to believe that the stunted shoot growth and poor fruit set observed in unirrigated inland Northwest vineyards after the dry winter of 2004/05 (23-45% of normal precipitation) may have been caused by the vines’ inability to initiate sufficient sap flow (‘bleeding’) before budbreak. This may have led to failure of their hydraulic system, leading to inadequate water supply to the developing canopy. We began investigating these questions in the spring of 2011, using pot experiments designed to vary soil moisture before and during budbreak. The resulting differences in budbreak and grapevine vigor were assessed by measuring shoot length. Bleeding sap was collected to determine whether spring shoot vigor is related to the bleeding rate and/or content. All data collected to date point to the existence of a soil moisture threshold below which bleeding cannot be initiated by grapevine roots. This appears to be associated with an inability of buds to break. Under severe drought stress, vines died. But under moderate stress, budbreak was possible albeit followed by stunted shoot growth and abortion of clusters.
Methods of project monitoring included meetings, e-mail, and phone calls.