Timely Viticulture Updates

May

Timely Viticulture Updates: Bloom
Tissue Sampling & Early Season Disease Management

As usual, we have experienced diverse weather conditions across the state. We have had both cool and hot, as well as dry and wet periods. Shoots continue to develop very quickly, and clusters are in various stages of development, depending on cultivar and location. The growth period from 2 weeks pre-bloom until 3 to 4 weeks post-bloom is the most critical for protecting foliage, especially flowers and newly set fruit, from black rot , Phomopsis, powdery mildew, Downy mildew, and Botrytis bunch rot infections.

As each disease has a specific set of temperature and moisture requirements and specific infection timing, growers should apply a series of fungicides to protect the susceptible young tissue before the diseases become established. Proper attention to disease management during this period will make management considerably easier the rest of the season. Conversely, stretching or skipping applications during this period may result in an increase in the inoculum and early infections, making management very difficult for the remainder of the season. As always, close attention should be paid to maintaining proper shoot density and an open canopy, which will decrease disease pressure.

For more information on Disease Management, please visit the Timely Viticulture website.

• Pre-Bloom To Post-Bloom Disease Management https://extension.umd.edu/resource/pre-bloompost- bloom-disease-management
• Early Season Disease Management https://extension.umd.edu/resource/earlyseason- disease-management/

The bloom period is a very important time for disease and pest management, but it is also critical for nutrient management. From bud break -through bloom, the grapevine relies on nitrogen from its storage reserves, but then switches to uptake from the soil. However, nitrogen status is best evaluated with tissue sampling, not through soil sampling. Spring/bloom tissue sampling is recommended, as deficiencies can be corrected in the current growing season. Veraison samples are good for verifying and monitoring long-term nutrient status. Remember all vineyards with income of >$2500 per year MUST have an approved nutrient management plan.

For information about taking samples and a list of labs to analyze samples, go to https:// extension.umd.edu/resource/tissue-sampling.