Chill hours are important to tree
and vine crops during dormancy. This is the timeframe when the plant rejuvenates.
This time is critical. Trees and vines, just like you and me, have to take a “vacation”
from the busyness of the growing and producing stages. These hours are the time
or opportunity for the plant to rest up for the next crop. It’s a vacation
period for trees and vines to get rested. In California’s San Joaquin valley,
this usually occurs when kids get excited because its foggy day schedule weather and shortened school days. It’s wet and
cold and there is not a lot of sunshine. But this is perfect weather for
permanent crops like pistachio, almond, peach or grapevines.
Without adequate rest or “chill”,
the plant works from an “energy deficit” position. This is a problem. It is the
monetary equivalent of drawing money from your savings account because the
interest earned isn’t enough to live on. You can’t do this for very long
without dire consequences and the same is true with your crops.
When you get enough rest, you wake
up ready to go better. The same goes for trees. When they get enough rest, they
wake up ready to grow better. When
trees do not get enough rest, they will have delayed canopy development. This
is an important detail because without leaves the plant cannot feed itself
effectively. The more efficiently a tree can start growing leaves and a healthy
canopy the sooner it can begin taking in sunlight, water, and carbon dioxide so
that through photosynthesis glucose production kicks into gear and provides
food for the plant and developing crop to feed on.
On a year with short chill hours, the
problem becomes an issue of how to make the most of a bad situation. For
instance, in January you find that you have 400 hours or less of chill accrued
to date. Historically by this time, we have between 700-800 hours. This is a
harbinger and we need to pay attention because it’s telling us to be prepared
for “what” the outcome of this can potentially be. This is important because
some crops use an awakening agent to help crops rouse themselves, in order to harvest
earlier. The problem with this is, when you apply a product to awaken a plant
that has not gotten enough chill hours you induce an extreme stress condition or
worse actually damage the plant’s fruit buds. That can have a long-term adverse
effect. Think of how trees grow fruit buds. It usually develops on 2nd
year wood. So, if you hurt your tree badly, it could take two to three years to
recover, assuming there are no other major stressors that occur to limit
recovery. Growers should consider the tradeoffs carefully before proceeding with
a “dormancy-breaker” spray for their trees especially those that have not
gotten the proper amount of chill hours. We cannot merely wish good seasonal
weather on our crops. If our crops don’t get enough chill, the plants
themselves will be underdeveloped and this ultimately affects profitability.
Keeping energy in mind as you go through dormancy is important.
Dormant plant energy comes from carbohydrate reserves. This becomes a high
demand on heavy crop load years. As fall passes, the plant behaves much like a
bear before going into hibernation. It eats and stores up food to carry it
through winter until awakening in the spring. The difference with a plant is
that, while it does its best to make and store up food reserves with both
photosynthesis and the fall root-flush, it often falls short due to outside
influences such as drought, large crop load stress, heightened insect pressure,
imbalanced nutrition, etc. The bottom line: If you go to bed hungry, you will
awaken very hungry and nutrient deficient.
As a grower, you decide what nutrition your crops
receive. Therefore, if you want to ensure your crops are well fed for dormancy,
feed them well BEFORE dormancy with next bloom in mind, as the goal. Remember good
intentions don’t equal good actions. More to the point don’t apply materials
because your neighbor is or it was a “good deal”. You should be testing your
soil and tissues in the fall or before harvest, in order to determine what “got
in” and what “ran short”. These are an annual progress report of your field’s
health. If your adviser doesn’t offer these services, look around for one that
does. After all, it’s your asset and investment. This information will help
guide you to make more accurate decisions on what should be applied and at what
rates. If you aren’t sure what should be applied, ask your crop adviser for
counsel. If they aren’t experienced with your crop or soil type, get a second
opinion. But, don’t fall prey to “analysis-paralysis” or information overload.
If you trust your adviser (and you need to), because of their experience,
success or approach, go forth with confidence.
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| Photo by Marc Suderman from Traver, CA |
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