The second most important factor is to understand how you fit in in the puzzle. Am I a mildew enabler? In the first post on this topic we talked about the things that the viticulturist must know but, cannot control. Today we will talk about the things that the viticulturist can control. Much of this for the seasoned viticulturist may seem like a review of items they've heard before. So, I will be taking the vocabulary that I have outlined and applying it to the decision making process I used in the 2016 season to add context.
Canopy management is important.
In our area we have full water control, that means if we don’t water the plant, it will die. This could be a tactic to reduce mildew but, may not help you meet your business goals. Canopy management is achieved by our cultural processes, water management, pruning/thinning and nitrogen management. If our canopy stays relatively open and we have adequate air flow and sunlight penetration we will be less prone to infections. A slight rain will dry out quicker and be less of a risk. The vapor pressure created by the canopy microclimate will be less beneficial to harboring mildew and botrytis spores because the boundary layer is weaker on a whole plant basis. This effect is achieved by early season shoot/cane thinning and by correctly applying water as to not over grow the canopies in the vineyard. Only give the plant as much as it needs and you will avoid a ton of issues down the road. In addition to creating the correct canopy size, water stress post-bloom will help the plant build up physical and ontogenic resistance to disease. This state can be achieved by the first week of July in nearly any Washington season. I say nearly because we are dealing with nature and there will always be an exception. To backward plan a little if we have a bloom date near the first of June or a little before my goal is to have the canopy shut down by the 20th-25th of June each year.
If you know the rules of the game the opportunities will stick out!
I want to make a second note on water management, many people presume that water management occurs after the plant has set fruit. This is a fallacy. Water management lasts all season long. From the irrigations at the end of the season to the early season irrigations and in this case, management in May. I believe May is one of the most important times to understand your water in the vineyard for the highest quality fruit. Just because the plants need plenty of water during this time doesn’t mean that we give them so much water they could never use it all. The amount of water over what you need in the soil will come back to bite you in June when you are trying to shut down the canopy and maximize phenolic potential at harvest. The optimum is even and controlled growth during this period. Enough water but, not too much. Remember you can put water in the soil but, only the plant and the environment can remove it.
Tweet: "The amount of water over what you need in the soil will come back... ...maximize phenolic potential at harvest."
If I get my canopy set, the water right and the canes are turning brown are there any other risk factors to think about? Yes, there are. Again mildew needs live plant material. It likes young and tender leaves especially well. The tenderness of a leaf is created in large part by three main factors. Age of plant material, remember even if your main canopy is old enough and hardy enough to discourage growth of mildew you may have laterals that are not. Have they been removed? Are they excessive in the canopy? The second is nitrogen, any block that has received a large amount of nitrogen in that season may be more susceptible to infection. Nitrogen elongates cells and growth making them an easier target for mildew to attack. Water management is the third, again which we’ve already covered.
Those are the rules of the game now let’s talk about timing.
A note on human nature, we are part of the problem.
Admit it and get on with it. When we don’t quite understand something or we rely on someone else as an authority humans have a tendency to build safer margins. In the spraying game that is as easy as listening to your consulting chemical company who gives you recommendations for your spray program. Many of these representatives have never managed a vineyard and although they may be able to keep one safe, they rarely understand the economics completely. Between these two factors you end up spraying earlier than needed and later than needed consistently. Those margins are where you can save money and meet the goals you intended for. Nothing is more frustrating than spending money to find out it didn't work right.
When starting your program in the Spring wait until all your canopies are consistently long enough to get the first spray on.If that means 3-4 inches on one variety and 8-10 inches on another. You are still ok. Make it easy on yourself, the first spray is usually during a cooler period than optimal growth for both botrytis and mildew, drag your feet a little keeping your timing goals in mind for the season. My main goal for the early season management is estimating bloom time. I want to be able to save a pass in the vineyard by tank mixing my bloom nutrients with the second spray for the season and have that land within 7-10 days of bloom. So, I work backwards from my estimated window. This usually requires me to stretch 3-4 days on an early season oil spray that only lasts 10-14 days. You can readjust and stretch or shorten that interval in the two weeks after that spray with more information on how the season is progressing.
When the second spray comes up you can decide on whether you would like a chemical that lasts 14 days or 21 days. This gives you further control on where your next spray lands. I like to time it so that I am not spraying the plants while they are in the middle of bloom, which could cause problems with set. The third spray of the season I always ask for a 21 day chemical. This is important. That 21 days gives me enough time to shut the plant down by holding back water. If I have done my May irrigation correctly. The goal is to shut the plant down in that window and near the end you might start to see the effects of cane browning and ontogenic resistance building up in the plant. We base the next spray on what we think our level of risk is to infection. Is the temperature hot enough to retard mildew growth? (95 degrees and above). Has there been any rain/humidity? Is there any rain in the future? Does the forecast say we will have a week of 100 degree weather? All these factors play into whether you can stretch the window a little or whether you need to spray.
That was the preface, here is the context.
Here are the most important factor as I saw it for the 2016 season.
Bud Break and Canopy Development. Looking at Agweathernet on 3-3-16 soil temperatures were much higher than normal running at 45-49 degrees Fahrenheit. This is warm enough to start bringing some varieties out of dormancy. Had we stayed on this schedule we would have seen an even earlier bud break date than we did. Unfortunately, this early heat did have an effect on the canopies that developed later. My personal feeling is that some of the buds on a plant came out of dormancy and some did not. This created a about a week delay within canopy that showed up in the early part of the season and stayed with the canopy for the remainder of the year. I do not believe that it ultimately affected the final fruit quality negatively though because it was such a long season. The main way this heat affected the growers was in some phenological overlap during the flowering stage. This made for some difficult decisions. We still needed to push our canopies for length, where some canes were already long enough. In addition flowering began right in the middle of this causing a dual sink scenario.
Soil water baseline. The 2015 Winter was a wet one... actually normal, we just hadn't had a normal year in a long time. But, there was plenty of soil moisture heading into the growing season and I think that many growers did not account for this moisture correctly. We trenched two locations in the vineyard this Spring (middle of the row). Normally what we had been seeing was a lighter colored soil as you get to the 3.5 to 4ft level just above the caliche for our soils. There was no such change in soil moisture this year. It was nice and dark all the way to the bottom. We needed to account for this information in our management. We did not do any Spring watering until later to mid April. Which allowed us to dig into the deeper bucket and start using some of that extra moisture.
Tweet: "When dealing with nature a bird in the hand is better than none in the bush... and that is exactly what happened."
Air Temperature. The one caveat I spoke to those I came in contact with between the 2015 and the 2016 season was the temperature between the two vintages. Even though 2015 was a hot season, the Spring was not. Looking at any of the seasonal comparison temperature graphs you can see a small crossover in the beginning of the season where 2015 was much cooler for the first 3 weeks than the last 4-5 seasons. I remember this vividly because the grass was not growing in the pastures and we had to feed hay to the sheep for a couple extra weeks during this period. So, the caveat was that if the 2016 Spring was warmer than 2015 then we could see an even earlier season than the last. Not a far stretch based on the recent seasonal averages. In terms of soil water management, I am always wary of irrigation during early season warm periods. Especially those at the later part of May and early June. During this period we did not irrigate. We stayed on the schedule. When dealing with nature a bird in the hand is better than none in the bush... and that is exactly what happened. No sooner than bloom had finished and the soil water was used up did El Nino break. The high pressure ridge that had been holding back all the Western weather from our area broke and we saw low moderate temperatures for several weeks post bloom. We had at that time just finished getting all the excess water out of our soils from the Winter and were about to put back what we wanted but, there was no reason to. The plants looked great and even though the soil was drier than I had ever grown on, there was no stress. We held the plants in this state for nearly 4 weeks by doing only 6 hours of irrigation per week. When eliciting a biological response such as phenolic development, berry size and physiological maturation it is important to understand the time that takes. Water stress on one day does not make a plant shift gears. You need to hit the stress level and hold the plant in that state for 2 to 3 weeks for a full shift in development. These shifts are differentiated, meaning once you have applied enough stress the plant cannot go back into an earlier state, such as active growth. The plant, in colloquial terms, is on to bigger and better things by then.
Nitrogen. Everyone has their normal replacement rates of nitrogen on a year to year basis and we are no different. For our property that is about 36 lbs per year. We split that into two additions typically, 18 lbs at active shoot growth and 18 lbs post-bloom. There are exceptions around the property based on soil types, varieties and block goals. Aside from normal replacement values there are other places where nitrogen can become an influence during the season. Increased soil volume access to the plant. Having a wetter than current average Winter puts water in the 3-4ft depth of soil that may not have been as accessible by the plant in previous years. So, in essence your plant has more soil to mine for nitrogen because nitrogen is movable by water. Adjusting management in light of these facts we cut our nitrogen by half in most blocks. In others we used a foliar nitrogen spray post-bloom to keep from adding water to the soil yet, get nitrogen into the canopy that was needed. Even with this reduced nitrogen utilization I saw several ETS reports post crush from our vineyards and others that were identical in terms of YAN (yeast assumable nitrogen). The seasonal average being higher than normal at 120-140ppm early season and declining to 50-75ppm in later harvested fruit.
Let's put the season together and see where the management decisions fall.
The first spray fell during the last 7 days of April this year. This being an oil spray with a limit of 2 weeks effectiveness. The recommendation was to put that spray on 4-5 days earlier around the 20th of April, however this would have made my next spray land during the first week of May. If I could get a few more days I would be in the 14th range for the 2nd spray. This in conjunction with the fact that canopies were more uneven than normal for some varieties based on the early soil temperatures recorded in March we stretched that window out until the last week of April. By the time we had arrived at the second spray we were already seeing indication of bloom occurring within a week of May 10th to 15th. So, we decided to utilize a tank mix of bloom nutrients at that time along with a 21 day chemical that would get us past that period and place our third spray in the first week of June. When the first week of June had arrived bloom was complete as predicted and we had just entered a period of moderate temperatures with a decent amount of humidity. The third spray was a second 21 day chemical which moved the end of our next window to the end of June. By the 18th of June the canopy was completely shut down and we were in a holding pattern looking to the future for when the first week of heat would return for the year. Holding the canopy in this state until the end of June and our spray window we noticed that the plants had already begun the cane browning process which tells me that ontogenic resistance and physical resistance has been built up. During this time we had already removed all the laterals from the vineyards so there was no young plant material to act as a source of infection that might come back to bite us later. We stretched the window a week going into the beginning of July. We finally caught a break after that first week and the heat returned increasing my comfort level with the decisions we had made. Did we see anything show up later in the year after harvest and during the October timeframe after rain had begun again. No. We did see a cluster here and there in the canopy on tight cluttered varieties but, the threshold was low to normal. 1-2 clusters per 5-10 plants.
In closing, I am aware that this year by many has been regarded as a "bad" year for botrytis and mildew in general. I disagree. The largest driving factor to the degree in which people were affected this year was canopy size and environment. Plain and simple less heat existed this season so, it wasn't as forgiving. On the canopy size, still completely controllable. Berry size as well, for those quality aficionados. The easiest thing to overlook is that which we cannot see or measure and soil usually meets both of those factors. Not accounting for the increased deep soil moisture and the increased nitrogen availability especially on deeper soils kept the canopies growing creating an environment that was counter intuitive to our goals.