The effects early spring had on Michigan juice grapes

You cannot farm for the exceptions, but be aware they exist.

A few years ago at the Grand Rapids fruit and vegetable expo, Tom Davenport, former director of viticulture at National Grape Co-op Welch’s, told me “You cannot farm for the exceptions, but be aware that exceptions exist.” Sadly, this is so incredible true for spring 2012. By looking at Figure 1, 2012 (red line) started as the year of the “exceptions” and negatively “exceptional.”

Figure 1. Growing degree days (GDD) calculated from March 1 at the Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor, Mich. Mean GDD accumulation 2000-2011 on April 15 was 101; this year (2012) is 294, almost three times the mean. The minimum GDD accumulation was 2008 (40 GDD) and the maximum 2010 (185.1 GDD). The year 2010 was, unfortunately, a frost year for our Michigan juice grape growers. Concord bud break happens at 200 GDD, and this year during the third week of March (20 days ahead of normal).
GDD calculations

Figure 1 shows pretty clearly the exceptional effect of the early spring in 2012 on heat accumulation and consequently vine phenology. The red line (2012) is at 300 GDD the second week of April, while 2010 (warm year and frost year) was at the same level of GDD accumulation only the second week of May. The year 2001 (a cool year) reached 300 GDD at the end of May, six weeks later that 2012. This is the negatively “exceptional” 2012 and this is what caused, accordingly to National Grape Co-op viticulturist Jon Jasper, the loss of 95 percent of the juice grapes in southwest Michigan, following last week’s frost occurrence. Concord bud break begin approximately at 200 to 220 GDD; this threshold was reached very early this year so that bud break occurred 20 to 30 days ahead compared to an average year.  

Unfortunately, spring freeze is a common hazard in our climate. Crop protection technologies utilizing overhead irrigation are available and used at SWMREC in our experimental blocks.

Concord vines
Photo 1
. Concord vines at SWMREC in Benton Harbor, Mich., are protected
with overhead irrigation. Photo credit: Jenny Schoonmaker-Wells.

However, economic considerations in juice grape production limit their application. Most growers know well that the best tool is the selection of vineyard site that has low susceptibility to freezes. That is no consolation for any Michigan grower who repeatedly experienced large crop losses from several spring freezes (just two years ago in 2010 and now this year again). Fortunately, there are some viticultural tools, with moderate cost, that can be used on frost-vulnerable vineyard sites. These include:

Vineyard row middle management. The best row middle management to reduce the risk of a spring freeze is to create a firm, dark soil surface achievable with row cultivation early in the spring. Cultivating just prior to a freeze event is counter-productive because it aerates the soil and instantaneously releases soil heat, too quickly to be used for protecting the vines. A grass sod is less capable of capturing solar radiant than bare soil. A grass sod should be mowed short prior to freeze episodes as this will keep the lowest temperatures during a radiation freeze closer to the ground and further away from the fruiting zone of the vine.

Vineyard fans. Cold air is heavier than warm air and it will settle and form layers with the coldest air near the ground. If the site is flat, or worse, if it is in a low spot with high ground around it, the cold air will settle or flow there – vineyard fans could help. Fans move very cold air at the ground and mix it with warmer air above 20 feet. This system works down to about 28 or 29 degrees. Below this temperature there is no warmer air to mix.

Long cane pruning. Buds along a grape cane progressively break bud from the tip of cane to its base. Long cane pruning can help to slow down bud break of buds near the base of a cane and this may help to avoid freeze damage. In highly hazardous “frost pocket” areas, delaying pruning until late in the spring can be an effective strategy for avoiding freeze damage.  

However, we had major damages in juice grape production this year and probably for the grape loss it could be not be cost-effective for several juice grape growers to harvest the 2012 crop. Early estimations from Welch’s are indicating that grape loss could cost farmers $22 million this year. However, no one has better knowledge of the level of damage that the frosts we experienced in the last few weeks made on the vines than the growers. Freeze damages vary significantly between and within vineyards (i.e., location, altitude, extent of low temperatures and phenological stage of the vines). Moreover, grapevines have mechanisms to compensate for freeze damage. Secondary buds can restore some of the vine’s fruitfulness that was lost with primary bud loss (Photo 2).

Primary bud in Concord
Photo 2
. Primary bud in Concord killed by
spring frost and secondary bud pushing and
not damaged.Photo credit: Mark Longstroth, MSUE.

How much do these secondary buds produce? If we consider that a primary bud has the capacity to produce 100 percent of a crop at that node, then the secondary bud (for Concord and Niagara) could produce about 35 to 40 percent of a crop. Only if both primary and secondary buds are killed by several spring frost events, then a tertiary bud will produce a fruitless shoot for the next year’s crop. This is why it is important to remember that it is premature to forget this year’s crop.

Further, vines have this ability to compensate. When such losses occur, vines may compensate for reduced cluster number by increasing the number of berries set per cluster and compensate for reduced berry number by increasing berry size. All compensations are going in the direction of increasing yield per acre, which will partially recover the expected economical losses.

Concord cane
Photo 3
. Concord cane with a “double push,” a primary and secondary
bud growing simultaneously. Note the angles of insertion of the future
shoots in the cane; the primary bud is less than 45 degrees from the cane
axis, while the secondary bud is less than 90 degrees from the cane axis.
Secondary buds are fertile in native and hybrid varieties, but not in vinifera.

An important thing to remember is that this season’s potential secondary crop (from secondary buds) is based on last season’s vine performance. A balanced vine – not over-cropped in 2011 – with a good summer canopy management (mainly shoot positioning) had the opportunity to develop fruitful secondary buds last year, setting the potential for good productivity in any vineyard where the spring frost killed the primary buds. However, a vine that was over-cropped last season, with over-shaded canopy, may not have been able to develop fruitful secondary buds. The bottom line is that it won’t be possible to make a reasonable estimate of the crop level in a vineyard with spring freeze damage until after bloom and fruit set.

Canopy management this summer (mechanical shoot positioning) may be more important than in a normal year for vineyards that experienced a spring freeze. Sunlight penetration to the portions of shoots near the cordon that will be next year’s fruiting canes is important for flower bud initiation for the 2013 crop. When grapevines carry a reduced crop, they tend to become over-vegetative, increasing shade in the fruit zone. Balanced nutrition will also play an important role. Therefore, a reduction or elimination of nitrogen fertilization could be appropriate for the 2012 season (see “Pest management considerations for frost-damaged vineyards” by MSU’s Rufus Isaacs and Annemiek Schilder).

However, nitrogen applications should be specific for each block or section of the vineyards; 2012 may be an opportunity to build larger vine size in blocks with weak vines. But, frost damages are very different between location, vineyards and in the same vineyard different between varieties and vines. Microclimate can play a huge role in damaging vines in different location of the vineyard. In particular, labrusca varieties (Concord and Niagara) developed physiological systems during their evolution to dodge the frequent frost of our cool climate; they compensate to some extent for primary bud loss producing fertile secondary buds (Photo 3). This is the reason why I believe that it is really premature to forget this year’s crop from a viticulture view point. Unfortunately, because of the potential of the loss, it could not be cost-effective for our juice grape growers to harvest the 2012 crop.

How could we estimate a potential crop, or the amount of damage, in a specific vineyard? This question has to be answered individually by each grower. Growers will see portions of their vineyards that have too poor of crop (few un-damaged clusters) to justify expenses of spraying or harvest, while other parts of the vineyard will have economic potential. A representative number of nodes could be collected (blind nodes, live primaries, and live secondaries) to estimate the potential crop. While the frosts we experienced were terrible, it may not be a total disaster yet – at least, it is still too early to know.

Dr. Sabbatini’s work is funded in part by MSU’s AgBioResearch.

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