Independent Grape Growers - Paso Robles Area
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September Blog – Biological Soil Fertility & Late Season Botrytis

Special Blog Post on Fall Concerns





Cristy Christie
Black Diamond VermiCompost
Post Harvest Biological Soil Fertility


Grape growers around the globe are recognizing the need to add nutrients to their vineyards after harvest.  In-season tissue analysis determines post-harvest soil and foliar applications of nutrients to help the vines build and store the carbohydrates and sugars. These nutritional needs have been well documented by universities and growers alike from South Africa to Australia New York to here on the West Coast.  As grapes enter dormancy, the maximum crop potential for the next growing season has most likely already been determined.

What else can growers do to add value to their pocketbook next year? Not only is early season growth potential determined by the nutritional reserves that have been built up prior to leaf drop (photosynthesis), root activity is also largest immediately post-harvest. But what is it that makes the root systems active and vigorous? A large part of the answer is found in the soil life.  Call it productive soil, healthy soil, microbial soil life or the soil food web, it’s all the same. Plants have amazing communication skills. The vast majority of soil microbes have yet to be identified, but what we do know is when a large variety are added to soil, the entire plant, including fruit, above and below ground, benefit.

[Excerpt] Extensive communication occurs between plants and microorganisms during different stages of plant development in which signaling molecules from the two partners play an important role. Fungal and bacterial species are able to detect the plant host and initiate their colonization strategies in the rhizosphere by producing plant growth-regulating substances such as auxins or cytokinins. On the other hand, plants are able to recognize microbe-derived compounds and adjust their defense and growth responses according to the type of microorganism encountered. You may want to re-read that a time or two to begin to realize how complex and fascinating the conversation is that takes place between soil microbiology and a plant’s root system. Minerals and microbes must both be present for the cycle to be effective.  If you want to learn more, the entire article can be found here.

There are dozens of studies and abstracts on the value of healthy soil microbiology, but suffice it to say that it’s just good farming practice to add a good dose of it with post harvest nutrients.  By adding teas and/or extracts, nutrients stored in the bodies of the microbial life are not lost through irrigation to contaminate ground water. Hair-thin fungal hyphae, or tentacles, wrap around soil particles in their search for food, forming aggregates that create great soil texture. Both the fungi and soluble organic matter are held in the soil. Bacteria release a sticky mucous that enable them to cling to solid particles of mineral and organic matter, ensuring they too remain in the soil and, like the fungi, aid in the formation of aggregates.

Properly made compost teas and extracts, when using vermicompost as the base, adds a plethora of soluble plant nutrients and growth compounds, a diverse microbial population, and organic matter that provide an ongoing supply of nutrients. The plant receives a consistent and reliable food source when bacteria and fungi feed on the organic matter. This below ground surface microbial activity releases some of the nutrients to the soil and retains others for their own energy and reproduction. When nematodes and protozoa in turn feed upon them, the nutrients stored in the bacterial and fungal cell walls are released to the soil in a highly soluble plant available form. When we feed the soil, the soil feeds nutrients to the plant.

You can learn the differences between aerated compost teas and extracts here. Supply the minerals and nutrients your vines need, add tea or extract to that solution and let nature go to work while you take a short break from the vineyards task list.

Since you have read this far…(thank you!)…I hope you will take advantage of the offer that follows. It’s a substantial discount, and we are confident that your vines will wake up next year with healthy vigor and a stronger immune system.



Dr. Lowell Zelinski
IGGPRA President

As we move into fall, most diseases of grapes, especially Powdery Mildew are no longer an issue. This assumes it has been prevented and/or controlled in the past and is not a concern right now.

But we are not out of the woods yet. There is another fungal disease of grapes which commonly occurs in the fall, but may be a pest all season long, namely Botrytis. This article will discuss the ecology and control of Botrytis in wine grapes in the Paso Robles area.

The botany of Botrytis is complex and is not really worth going into in this article. It has two different names, one for the sexual stage, which is rare and one for the asexual stage which is very common. Botrytis can infect almost all dicots (broad leaf plants) and many monocots (grasses). If you have any weeds in your vineyard they are probably a host for Botrytis. This includes the Oak trees that occur throughout Paso.

Botrytis can also survive in the soil for many years. Basically, there is no way to avoid the inoculum, it is everywhere, all the time. If this is the case, how does it not cause major problems all of the time? The answer is that it is the environmental conditions plus plant conditions that allows Botrytis to thrive. Other than on grape flowers and ripe “damaged” fruit Botrytis will not reproduce unless environmental conditions are sufficient for its growth. Botrytis needs a source of nutrients on which to feed. Flowers and damaged berries provide that source of nutrients. The environmental conditions where Botrytis can grow and thrive are fairly broad, temperature can go almost down to freezing and as high as 85 and it will do just fine. Botrytis also likes high humidity’s and even free water (like rain and heavy dew). The high humidity will most likely occur inside clusters, where after a fall rain event water will accumulate and is very difficult to get rid of.

Condition that do not favor Botrytis are dry weather, open clusters, open canopies, windy weather, low humidity, intact fruit (no damage to berry walls by birds and/or wasps).

Botrytis infected fruit is a problem on the wine making side also. Which is why so many wineries will not accept fruit with high levels of Botrytis. One the issues on the winery side is that Botrytis will convert many of the simple sugars (glucose and fructose) to more complex forms which can not be fermented. This cause fermentation to stop before the desired level of alcohol is reached. Additionally, Botrytis can release a chemical that actually kills the fermentation yeasts, which can cause stuck fermentations, further exacerbating the low alcohol problem. It also causes problems in color stability and in white varieties it can lead to browning of the juice/wine. Finally, off flavors and aromas can results in wines made from grapes high in Botrytis.

How is Botrytis controlled in the Paso area? I know this all sounds like doom and glum but actually Botrytis is only a minor problem in Paso. A major reason is our variety selection. Pinot noir can easily get Botrytis because of its thin skin characteristic (actually, the movie Sideways was right here). We also have fairly dry harvest seasons. Recall, that Botrytis need either free water or high humidity to really become a problem. The only times I’ve had an issue is when the zinfandel grapes would not sugar up and harvest was delayed until mid-November. Of course, it rained enough a few weeks before harvest that the inside of the cluster got wet and didn’t dry out. This caused two problems, the free water needed for Botrytis was available, and the berries swelled and, especially on the insides of the cluster the berry skin ruptured and therefore the fruit was no longer intact.

Finally, I have found that a fungicide spray just prior to berry closure (the time when the berries begin to touch each other) with a material that has efficacy against Botrytis has been beneficial. This has to planned month ahead of potential problems but in my experience it has been worthwhile.