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After the Freeze: The Second Crop

By Tim Martinson

The May 22-23 spring frost that occurred in the Thousand Islands region (and in other parts of NY) killed off many primary shoots and clusters – when they were out 4-6 inches in many cases.

  1. Now, three weeks later on June 15, we see a fairly full complement of shoots, especially on Frontenac:
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Frontenac, June 15, 2015

 

  1. Vines have a mixture of the few shoots that survived the frost with clusters in the middle of bloom (right on schedule, June 15) and smaller secondary shoots, some with 1 – 2 clusters just emerging.
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Frontenac with secondary and primary shoots, June 15, 2014

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  1. The second crop: The new shoots and clusters will produce fruit, but they will be delayed in development by about 3 weeks – I project bloom to occur on these new shoots sometime late in the first week or early second week in July. They will ‘catch up’ somewhat because they will develop in warmer weather, but you can expect veraison and ripening to be delayed by 2-4 weeks. Timing of emergence ‘second crop’ clusters is variable, so you can expect some earlier and some later-developing clusters. This will complicate management.
Frontenac Variability

Flower development ranges from bloom (left) to clusters just emerging from new secondary shoots with 3-5 leaves

 

Will these grapes ripen enough to harvest late at reasonable maturity levels? Good question.   With the canopy developing a month later, will the vines produce enough leaf area to ripen the crop and lay in reserves to harden off the canes and prepare them for the winter? Another good question.

Experience from 2012. Following spring frost and early budburst in 2012, Paolo Sabbatini at Michigan State tracked Marquette clusters from both primary shoots (first crop) and secondary shoots (second crop). Although the ‘second crop’ were delayed by 3 weeks, they still reached maturity (Brix=24.4; TA= 7.59; pH=3.52). Fruit from primary shoots had higher brix (28.4), but TA was only 0.5 g/l lower at 7.0 g/l. Fruit from both was harvested on the same date (see Paolo’s article in Northern Grapes News)

Keep in mind, however, that 2012 was a very early spring, and even the second crop bloomed in early June. This year the delay puts these grapes back a month behind the warmer climate in Southwest Michigan.

Management considerations:

  1. Botrytis: Decaying shoots and the wet weather we have had over the past week means there is a lot of grey mold or Botrytis inoculum (spores) out there. Clusters at full bloom can get latent infections, generally where the stamens dry up and leave scars at the base of the berry. If it is dry later on (after veraison) this may not make a difference, but if not, these latent infections could lead to significant botrytis fruit rot after veraison. This isrobably a small risk – but if frost injury is light and there are a lot of primary shoots and clusters out there, a botryticide application could reduce the risk. Are the MN or Swenson varieties at high risk for botrytis? Data is scant, but I’d guess that La Crescent and Marquette might be at higher risk than Frontenac or many of the Swenson cultivars in extreme years like this one. But that’s just a hunch.

For the ‘Second crop’, it is far enough away from bloom that it probably won’t make a difference. Typically with a few sunny days, this tissue should dry up and eventually fall off the vine.

Botrytis frozen shoot

Botrytis spores visible on decaying shoots and clusters

 

  1. Should I remove the dead shoots? If you have the time, it won’t hurt anything to do so. But the benefit in doing so will probably be modest, at best. Secondary buds and base shoots from cordons are not inhibited by the presence of the original dead shoot. They will eventually dry up with a few sunny and warm days.
  2. Should I keep the second crop? Good question. Here’s some thoughts:

Pros: My guess is that there will be fewer shoots bearing clusters (a few preliminary counts on Frontenac suggested about 15-20 clusters on about 40 new shoots per vine), and the clusters will probably be smaller. So the clusters that are there will probably accumulate ample sugars by harvest. Having a crop will absorb any extra vigor that vines might have. If the 2 week delay in harvest pushes it back from early September or Late August to Late September/Mid October, there is still time enough to allow grapes to ‘hang’ a few weeks later. If you are already harvesting in Late September – Early October, 3 weeks could be ‘too late’.

Cons: Delayed development could result in higher titratable acidity at harvest and more malic acid. Acids drop due to normal metabolism, which is more sensitive to temperature than to crop level – so having a light crop won’t necessarily result in lower acidity at harvest. Delayed harvest, coupled with a delay in canopy development, could have an impact on cane maturation (periderm formation) and winter hardiness.

4. Spray program: Having the ‘second crop’ with delayed development will affect when the clusters are most susceptible to fruit infections by powdery mildew, downy mildew, phomopsis and possibly black rot. Scheduling one or two additional fungicide sprays (for PM, DM, BR, Ph) to protect clusters will in most cases be a prudent thing to do. Foliar phylloxera may also be more of an issue on short shoots with few mature leaves.

5. Impact on vines and crop level management: The delay in canopy and fruit development shortens the growing season, and is an additional ‘stressor’ that – along with other stressors such as previous trunk injury, disease pressure, and drought stress (doesn’t seem to be in the cards at this point) – could compromise long-term vine health.   So if you will be keeping the ‘Second crop’, or had moderate freeze injury that left a partial ‘first crop’ – be mindful of the number of clusters you leave on the vines, and how late they are developing. You may want to thin some of them off.   A couple of scenarios:

Modest frost injury, partial ‘first crop’: If you only had partial frost injury to the primary shoots, and a relatively large ‘first crop’, you may want to remove all of the second crop.

Severe frost, second crop only: If all you have is a ‘second crop’, the late bloom will stretch out to a few weeks. You may want to then remove the clusters that are last to develop.

 

Bottom Line: This was an unusually late frost event. Early frost after budburst often happens when shoots are less than 1-3 inches long, and its often only a partial loss of primary shoots. That means that the vine has more time to regenerate a canopy and ripen a crop. I’m not sure what will happen to the late ‘second crop’, but we will be monitoring it and collecting data that I hope will be useful for guiding management and knowing what to expect in future years.

Comments

3 Responses to “ After the Freeze: The Second Crop ”

  • duane

    Would a spare parts mentality in terms of having longer spurs(10-12 bud count) and additional canes folded down parallelling existing cordons be a potential “Backup northern strategy” implemented during pruning. Here of course the buds would exhibit some degree of apical dominence ultimately suppressing to some degree lower buds and thus pull a “pick” for lack of a better words when such a late season freeze occurs? Also more labor inputs in event that later freeze never happens however at least a greater potential crop and perhaps less compounded vine physiology issues like northern growers are dealing with now? This technique is used in Quebec which observe these type of northern grape phenomenas about once every decade………Any thoughts on this idea love to hear feedback on this concept? Nice to view such organized data and imagery thanks Tim to you and your crew for your efforts here. Duane

  • tem2@cornell.edu

    Thanks for the comment, Duane. Short answer is that we did leave longer spurs (4-5 buds) at pruning, and waited until shoots were out 3-6 inches to thin to about 5-6 shoots per foot of canopy. This was about 1 week before the freeze event. And yes, we laid down canes to fill in for blank spots on the cordon. But this was a very late frost, about 20 days post bud burst, and even double pruning probably wouldn’t have had much of an impact, given the time elapsed. What you described is a proven method for delaying bud burst (perhaps by a week to 10 d), and I recommend it, but with this event it probably wouldn’t have helped much in my opinion.

  • Charlie Veneros

    I grow mostly cold hardy Valiant, in 2014 after a very prolong winter I lost about 100 vines I need to either cut the trunk way back or remove all together. That year I did not harvest at all, rather let the plant recoup.
    This year with a heavy freeze after bud break and several nights of frost, plants are showing good signs of secondary shoots. being in the north will help in delaying picking maybe until middle of October.Very little sign of infection at this time. I figure that plants are about 20-30 days behind on canopy, but doing nicely.

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