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34 W i n e s & V i n e s A P R i L 2 0 1 4 reflected heat and keeps down dust. Con- trol weeds beneath the vine with either cul- tivation or herbicides. Consider chemical mowing early with low doses of glyphosate when weeds are small. Rates as low as one quart per acre are effective when weeds are less than 3 inches in height. Bloom and fruit set Irrigate well as you see flower clusters start to expand and increase in size. Be sure that you have moisture at least 2 feet into the soil beneath the emitters. If you have no moisture at this point, it is unlikely that you will set a crop. Further bad news: You will most likely not have a crop the next year either, since flower bud initiation for the following season hap- pens at bloom during the current season. Fruit set to véraison Once the crop is set, hold back on irrigation so that you don't encourage excessive can- opy growth. Practice regulated deficit irri- gation (RDI) so that you devigorate the vine and produce loose clusters that color well but still keep the vine from becoming so stressed that it stops photosynthesizing. (Note: For an excellent guide to RDI, download "Wine Grape Irrigation Schedul- ing Using Deficit Irrigation Techniques" by Terry Prichard.) Canes that are about 3.5 feet long with eight healthy leaves and two clusters are the goal as an indicator of a balanced vine. If the shoots are more like 24-30 inches long, you should leave only one cluster. This is the time to be very careful with your water. You want to irrigate enough to keep the foliage on the vine in healthy condition, but not a drop more. Adjust your fruit load. Ripening fruit takes water, so if you have no water at this point, it is advisable to remove fruit to minimize permanent damage to the vines. If you have a limited amount of water, thin your crop early to give it the best chance of ripening normally without dehydrating and raisining. Véraison to harvest Hopefully you have saved enough water to irrigate for the last part of the season. You want to ripen your crop with actively photosynthesizing green leaves. If the leaves start to fall off, you may end up ripening your crop by dehydration. Fruit may reach desired sugar levels, but acidity will almost certainly be high, pH will be low, and winemaking may become a chal- lenge. Yeasts do not like to grow under high acid/low pH conditions, and com- bined with high sugars in the must, stuck fermentations are a real possibility. Apply your irrigations so that they are g R A P E g R O W I N g availablE WatEr-holding CaPaCity PEr foot of Soil texture Water inches / 1 foot Soil Water inches / 3 feet Soil Water inches / 4 feet Soil Water inches / 6 feet Soil Sand <0.6 1.8 2.4 3.6 Sandy loam 0.8 2.4 3.2 4.8 loam 1.5 4.5 6.0 9.0 Clay >2.0 6.0 8.0 12.0