What causes poor grape cluster?

This year I have an unusual amount of clusters of grapes that are not fully developing. Not sure if it’s poor pollination of a nutrient deficiency?
If you have experience with grapes please advise. Normally over the past 20+ years my grapes have been very good, so why this?

Kent, wa


My grapes buds were damaged/frozen by later spring frost. Second grow buds have poor clusters

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Hi Annie,
Thanks, perhaps that is the explanation, I was not paying attention but I notice that the ones with most sun exposure did well, so maybe this is the reason

Hi Dennis:

Same explanation as Annie: we got a late frost (-2,5 C) on may 27 and some clusters were damaged on many varieties: Troll, Somerset, Vanessa, Montreal Blue etc. I would say that about 20% of all clusters are fruitless or partially fruitless.


Hi Dennis.
I am from a tremendously wine-producing area (my town is Villarrobledo in Spain is one of the towns with the largest vineyard area in the world).
I know perfectly what happens to you in your vines.

This phenomenon is called in Spain "Corrimiento , Millerandaje or Filage of the grape ", and may be due to different causes.

Is this " corrimiento of raceme "


Look at this link (I’ll translate it for you).

The " corrimiento " of the vine is defined as the accident that makes perfect fruit setting impossible, resulting in dismembered bunches with few berries, reducing the productive potential of the vineyard. Sometimes what occurs are alterations in fertilization, producing smaller berries that do not have grains, these may or may not fruit set .
The main causes of " corrimiento " are:

  • Due to environmental factors: excessive rainfall, low sunshine, sudden changes in temperature.

  • Due to excess vigor: In these cases the plant grows very quickly causing a deficit fruit setting, some rootstocks such as 140Ru and 1103-P accentuate this phenomenon.

  • Lacks of some elements with iron, zinc and boron cause a bad curdling.

  • Varietals: Some varieties such as Merlot, Cabernet Sauignon and Garnacha have a tendency to this phenomenon

The solutions go through knowing the causes of the " corrimiento " , when they are due to an excess of vigor, it is due to:

  • Limit the contributions of nitrogen fertilizers.

  • Perform adecuated pruning

Make trimmings, taking into account that they must be a little before flowering and that we must not overdo it since if it is too aggressive it can cause a harmful vegetative stop with cluster emissions that will produce a detriment in quality.

The application of paclobutrazol, which is a growth regulator, limits the size of the shoots favoring good fruit set, it should be used two to three weeks before flowering and the amount to be used is very uneven, so it is advisable to be well advised .

So far the theory, now we go with empirical science, and for this I need to ask you some questions.

1st - What variety of grape is it and tell me if they are grafted on some vigorous rootstock like these (110 Ritcher, 140 Ruggeri, 1103 Paulsen), or if they are directly rooted vines

2nd- How are formed your vines , yor conduction system (Double cordon Royat, Double Guyot, etc …) , and know if you are doing short or long pruning (most likely you are doing an inappropriate pruning)

3rd- How old are the vines?

And then external factors would come, such as knowing if you have had bad weather conditions during the flowering and fruit setting period), and what type of fertilizer you make in your vines.

Most likely you have a vigorous variety and are doing short pruning .



Hi Jose,
Thanks for your thoughts.
I am inclined to think that it’s an unusual spring followed by a rain free summer (45 days without rain, and I never water or fertilize them!)
To your questions:

  1. they are directly rooted vines.

  2. I have pruned them consistently for over 20 years spur on cordons

  3. They have been in the ground since 1994.

Hi Marc,
I will pay more attention next spring as they begin to set blossom clusters, I can’t complain too much as this is my first year to see this occur since they were planted around 1994

Shot berries like this are typically caused by poor pollination. Since your vine has not done this before, it’s very likely due to cold, wet weather during bloom. I see this happen quite often on some of my grapes when it rains a lot during bloom.


I suspect you are right, Hal. The spring here was very wet with a number of freezes, I recall worrying about losing our plums. Even my cherry plum tree was only about 50% pollinated this year, so I think what you are describing is the cause.
Take care

Kent, WA excessive rainfall, low sunshine