The Ultra Gro Agronomy Letter

Welcome to the Ultra Gro Agronomy Letter!

Welcome to September! Labor Day marks the end of summer and the middle of harvest for many of us. With that in mind, some growers have been seeing low sugar levels in their grapes, so we asked Ultra Gro Agronomist, Robert Smith, to pen a few words about brix, grapes and post-harvest importance. Thank you, Robert…

Have Your Grapes Stalled Out?

By Robert Smith, Agronomist

Weather patterns this year have been very inconsistent. Ranging from the wet cool spring to summer heat and then rain from a tropical storm. As we enter veraison, problems are surfacing: stalled maturity and potassium deficiency that can threaten grapes and result in many vineyards stalled in developing maturity. The weather has caused the vines to run up to three weeks behind normal schedule and many can’t make sugar.

Harvest determination is often a tricky subject here in California. Ripening grapes encompasses many different variables that change year to year depending on the weather and location. California grape growing areas are so large and diverse that the difference in harvest date can vary by months between specific regions. These unique challenges require close monitoring by producers on a year-to-year basis.

Grape berry development is typically characterized by three distinct stages of growth: the first stage of growth, beginning at berry set, results primarily from cell division. During this stage, organic acids accumulate (in addition to other compounds) that make the berries unpalatable and unattractive to animals. During the second stage, known as lag phase, the seeds inside berries mature and become viable. Otherwise, berry growth is not visible. The final stage (stage III) of growth, ripening, begins with veraison.

Veraison typically refers to berries in a cluster, shoot, vine, row, block, or vineyard where 50% of the berries have changed color. In addition to berries changing color, several other physiological processes take place during the ripening period including:

Berry softening and expansion.
Sugar accumulation
Acidity variation
Color change in the skin
Flavor and aroma compound development

Berry softening and sugar accumulation begin simultaneously at the onset of ripening, followed by berry expansion and skin color development. Green chlorophyll molecules in the skin degrade and anthocyanin (color pigments) levels and berry pH increase during the ripening process. Seeds change color from green to brown, and a multitude of different flavor and aroma compounds are synthesized and transformed, all prior to harvest.

One of the major physiological changes that occurs at veraison is the increase in sugar accumulation in the berry. Additionally, this affects the efficiency in the change in the primary transport path of water, carbohydrates, and nutrients from the xylem to the phloem. The phloem is responsible for moving carbohydrate energy produced by the leaves around. With this change, the phloem transport allows for the greater accumulation of amino acids and carbohydrates. Glucose and fructose are the two principal sugars in grape berries, making up 95 to 99% of the sugar present in the berries. The amount of sugar stored at harvest is proportional to potential alcohol.

As the berries begin to ripen the seed itself becomes mature, and the grape is starting to use the berry contents for cellular respiration. Energy is generated through the respiration process and that energy is used to move the sugars against a concentration gradient from phloem into the berry.

Because sugar is essential to grape maturity, growers want to support the development and movement of sugars into the fruit. The grapes are also beginning to take on their green or red color. The rise of sugar and dropping off of acid must be supported.

Potassium aids the vines in pushing the sugars into the fruit by resetting or activating the processes that move the nutrients into the berry cells. Ultra Gro Quick-K and Sweet 34 foliar potassium products are designed to effectively move potassium into the berries and surrounding tissues to get this job done.

Around 19 brix, the crop has entered the post-Veraison phase and is entering harvest. Ultra Gro Quick-K and Sweet 34 support the process by delivering the right amount of potassium to the crop. As the brix continues to rise, the crop needs to support the movement of these sugars and potassium can help with this.

The ripening process of grapes in California is complex. It has many different moving parts, and all are influenced in a multitude of different ways by a variety of factors that change on a yearly basis. Every year, as the grapes mature, the berries undergo multiple changes both physically and chemically. However, this complex process can be accurately monitored with effective sampling and monitoring techniques.

“Foliar feeding is one way you can make up for some of this by not leaving the crop to its own discretion, and instead, stimulating and re-stimulating the vines, pushing them on and keeping them going,” says Shafer. University studies have demonstrated that foliar feeding is six to 30 times more efficient than applying nutrition amendments to the soil, and at this time of year, every day is important.

Ultra Gro’s Sweet 34 is a maltodextrin saccharide complex potassium, it is derived from potassium acetate. Ultra Gro’s Sweet 34 potassium product that can quickly penetrate plant tissue – leaves, buds, and fruit skin. Nutrient uptake happens directly through the cell walls. Once inside the cell, the potassium acetate/polysaccharide molecule is easily metabolized and mobilized by the plant system.

Growers that need to pick up an extra point or two to get into harvest often use these products. Though results vary from vineyard to vineyard, it usually works. Thank you.

Post-Harvest Nutrients and Irrigation

by Robert Smith, Agronomist

It’s always nice to finish the harvest, but the work is not yet done. At one time, after harvest, we would forget about it. But we’ve learned that you must prepare those vines for the coming winter and spring. The stressed grapevines will need nutritional recharge before the leaves yield to the change of seasons. If you put them to bed healthy in the fall and winter, you will have a good start in the spring. So, fall moisture and post-harvest nutrition will be very important.

Although it may seem like nothing is happening with the grapevines after the grapes are harvested, the reality is different. After the harvest, vines continue to allocate/distribute resources; from the soil, grapevines are taking up nutrients and minerals, and with the process of photosynthesis they create carbohydrate reserves and store them in permanent wood structures – roots and trunks. Therefore, the post-harvest period is one of the most important periods for nutrient uptake, as those carbohydrate reserves are used by vines for respiration during the dormancy, and for fueling new growth in the following season. Specifically, a supply of carbohydrates from stored reserves supports new root and shoot growth in spring, these carbohydrates are stored as starch, glucose, fructose, and sucrose. Starch is the main storage carbohydrate in the roots at all growth stages.

Post-harvest nutrition needs have been documented by university and grower research from South Africa to Australia, and New York to the upper Midwest and on out West. As grapes enter dormancy, “the maximum crop potential for the next growing season has already been determined”, notes a Cornell University Extension horticulture bulletin on bud fruitfulness and yield.

Tissue samples at veraison tell us about the deficiencies in nutrients that need to be corrected for next year. In-season tissue samples are an important guide in providing the vines’ adequate nutrition and planning for next year’s crop. To make an effective fertilization program, a combination of soil analysis and tissue analysis should be done on a regular basis, depending on soil texture and characteristics, crop load, climate, as well as previous fertilization. Some suggest two to three weeks after the harvest, but it really all depends on the soil and climate. Timing is important.

Fertilizer can be applied to the soil or as a foliar application, depending on the circumstances in the individual vineyard. Apart from nitrogen (N), phosphorus (P), and potassium (K), the fertilizer can commonly include calcium (Ca), zinc (Zn) and boron (B), depending on the analysis results.

As early nutrient demand in spring cannot be met by root uptake alone, storage of nutrient reserves prior to dormancy is required to support shoot growth in the following season. The cycling of nutrients, and thus the vine’s ability to store them and remobilize them again in spring, depends on nutrient mobility within the plant. This is high for the macronutrients: nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and magnesium (Mg), but low for calcium (Ca). Apart from manganese (Mn), which also has low mobility, the micronutrients iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo) and boron (B) have intermediate mobility. Studies with whole mature vines have shown that about 50% of N and P in the new season’s canopy comes from stored reserves. Around 15% of the demand for K is met by reserves, and 5% of that for Mg and Ca.

High carbohydrate and nutrient reserves will generally encourage strong spring shoot growth and promote reproductive development; if the aim is to promote strong early canopy development, or to enhance the productivity of run-down vines, then maximizing the storage of carbohydrate and nutrient reserves will assist with this process.

And don’t forget to irrigate…for the vines to get all the necessary nutrients and minerals from the soil, sufficient soil moisture should be provided, therefore post-harvest irrigation may be necessary, depending on the climate, weather and soil texture. In the SJV hot climate, a post-harvest irrigation is often a must, especially if we run into a dry winter. Issues such as uneven growth patterns in the spring, delayed spring growth, poor and uneven bud-break, stunted growth, smaller flower clusters, etc., can show up in the spring.

One final word…the principles I have outlined in this article apply to virtually any permanent crop grown in the SJV (and elsewhere). As always, take care of your plants and they will take care of you. Thank you.

DID YOU KNOW?

Labor Day was declared a national holiday in 1894 and is observed on the first Monday in September. The roots of Labor Day grew out of violent clashes between labor and police during the Haymarket Riot in 1886, when thousands of workers in Chicago took to the streets to demand an eight-hour workday.

Please call your Ultra Gro Crop Advisor if you have any questions.

Thank you!