- Author: Chris M. Webb
Today Ventura County Cooperative Extension Farm Advisor, Ben Faber shares some of his knowledge of avocados with us.
The only treatment that should be done rapidly after a freeze is whitewashing. Often the most severe damage following a freeze results from sunburn of exposed twigs and branches after defoliation. Temperatures do not have to be extremely high to cause sunburn. A white latex paint that has been diluted with water so that it can be sprayed is the easiest way to whitewash. The whitewash needs to be white on the tree, so don’t add too much water.
Pruning should be carried out to prevent secondary pathogens and wood decay organisms from slowing tree recovery. Again, however, there should be no rush to prune. Premature pruning, at the very least, may have to be repeated and, at the worst, it can slow tree rehabilitation. It should be remembered that when pruning, all cuts should be made into living wood. Try to cut flush with existing branches at crotches. Do not leave branch stubs or uneven surfaces. Tools should be disinfected in bleach or other fungicide before moving on to the next tree.
Irrigate carefully! Remember that when leaves are lost, obviously evaporation from leaves is greatly reduced, and, therefore the amount of water required is also greatly reduced. A frost-damaged tree will use the same amount of water as a much younger or smaller tree. Over irrigation will not result in rapid recovery. Instead, it may induce root damage and encourage growth of root rotting organisms. This is particularly true for avocados. Irrigation should be less frequent, and smaller amounts of water should be applied until trees have regained their normal foliage development.
Fertilization of freeze-damaged trees should be carefully considered. There is no evidence to indicate that frozen trees respond to any special fertilizer that is supposed to stimulate growth. If trees are severely injured-with large limbs or even parts of the trunk killed-nitrogen fertilizer applications should be greatly reduced, until the structure and balance of the tree become re-established. Trees should be watched for evidence of deficiencies of minor elements. Deficiencies of zinc, manganese, copper, and iron are most likely to develop.
- Author: Chris M. Webb
Today Ventura County Cooperative Extension Farm Advisor, Ben Faber shares some of his knowledge of citrus with us.
Citrus leaves appear wilted or flaccid during periods of low temperature. This is a natural protective response to freezing temperatures and does not mean the leaves have been frozen. Leaves will be firm and brittle and often curled when frozen. Leaves become flaccid after thawing, and if the injury is not too great, they gradually regain turgor and recover, leaving however, dark flecks on the leaves. Seriously frozen leaves collapse, dry out, and remain on the tree. Foliage form recent flushes are most susceptible to this damage. If twigs or wood have been seriously damaged, the frozen leaves may remain on the tree for several weeks. If the twigs and wood have not been damaged severely, the leaves are rapidly shed. Trees losing their leaves rapidly is often a good sign and is not, as many growers believe a sign of extensive damage.
Cold damage to the twigs appears as water soaking or discoloration. In older branches and trunks it appears as splitting or loosening of bark where the cambium has been killed. Bark may curl and dry with many small cracks. Dead patches of bark may occur in various locations on limbs and trunk. Sensitivity to frost is dependent upon many variables. In general, mandarins are the most cold hardy followed by sweet orange and grapefruit. Lemons are very frost sensitive with Eureka decidedly more sensitive than Lisbon. Limes are the least cold hardy. Healthy trees are more tolerant than stressed ones. The rootstock also imparts sensitivity onto the scion. Injury to the foliage and to young trees may be immediately recognizable but the true extent of the damage to larger branches, trunks, and rootstocks may not appear for on to four months following the freeze. No attempt should be made to prune or even assess damage from the frost until spring when new growth appears.
- Author: Chris M. Webb
Today Ventura County Cooperative Extension Farm Advisor, Ben Faber shares some of his knowledge of avocados with us.
Avocado leaves appear wilted or flaccid during periods of low temperature. This is a natural protective response to freezing temperatures and does not mean the leaves have been frozen. Leaves will be firm and brittle and often curled when frozen. Leaves become flaccid after thawing, and if the injury is not too great, they gradually regain turgor and recover, leaving however, dark flecks on the leaves. Seriously frozen leaves collapse, dry out, and remain on the tree. Foliage form recent flushes are most susceptible to this damage.
If twigs or wood have been seriously damaged, the frozen leaves may remain on the tree for several weeks. If the twigs and wood have not been damaged severely, the leaves are rapidly shed. Trees losing their leaves rapidly is often a good sign and is not, as many growers believe a sign of extensive damage.
Cold damage to the twigs appears as water soaking or discoloration. In older branches and trunks it appears as splitting or loosening of bark where the cambium has been killed. Bark may curl and dry with many small cracks. Dead patches of bark may occur in various locations on limbs and trunk.
Sensitivity to frost is dependent upon many variables. For avocados, Hass is about as cold tolerant as lemons, while Bacon is more cold tolerant. Healthy trees are more tolerant than stressed ones. The rootstock also imparts sensitivity to the scion.
Injury to the foliage and to young trees may be immediately recognizable but the true extent of the damage to larger branches, trunks, and rootstocks may not appear for up to four months following the freeze. No attempt should be made to prune or even assess damage from the frost until spring when new growth appears.
- Author: Chris M. Webb
Today Ventura County Cooperative Extension Farm Advisor, Ben Faber shares some of his knowledge of citrus with us.
The only treatment that should be done rapidly after a freeze is whitewashing. Often the most severe damage following a freeze results from sunburn of exposed twigs and branches after defoliation. Temperatures do not have to be extremely high to cause sunburn. A white latex paint that has been diluted with water so that it can be sprayed is the easiest way to whitewash. The whitewash needs to be white on the tree, so don’t add too much water.
Pruning should be carried out to prevent secondary pathogens and wood decay organisms from slowing tree recovery. Again, however, there should be no rush to prune. Premature pruning, at the very least, may have to be repeated and, at the worst, it can slow tree rehabilitation. It should be remembered that when pruning, all cuts should be made into living wood. Try to cut flush with existing branches at crotches. Do not leave branchstubs or uneven surfaces. Tools should be disinfected in bleach or other fungicide before moving on to the next tree.
Irrigate carefully! Remember that when leaves are lost, obviously evaporation from leaves is greatly reduced, and, therefore the amount of water required is also greatly reduced. A frost-damaged tree will use the same amount of water as a much younger or smaller tree. Over irrigation will not result in rapid recovery. Instead, it may induce root damage and encourage growth of root rotting organisms. Irrigation should be less frequent, and smaller amounts of water should be applied until trees have regained their normal foliage development.
Fertilization of freeze-damaged trees should be carefully considered. There is no evidence to indicate that frozen trees respond to any special fertilizer that is supposed to stimulate growth. If trees are severely injured-with large limbs or even parts of the trunk killed-nitrogen fertilizer applications should be greatly reduced, until the structure and balance of the tree become re-established.
Trees should be watched for evidence of deficiencies of minor elements. Deficiencies of zinc, manganese, copper, and iron are most likely to develop. For citrus, these materials should be applied as sprays, and they should be used as often as symptoms are observed. Two or more applications may be required the first year.
- Author: Chris M. Webb
Today Ventura County Cooperative Extension Farm Advisor, Ben Faber shares some of his knowledge of avocados with us.
Avocados in general are very frost sensitive, however backyards tend to be warmer than open fields and homeowners can often grow trees with less concern than growers. All young trees are more susceptible to freeze damage than a tree that has a full canopy down to the ground. The canopy traps heat and keeps the tree warmer than the surrounding air.
When trees are young they are small enough that frost cloth can be framed around the young tree. This usually provides at least 5 degrees of protection. Just a blanket can be used, as well as long as a structure is built to keep it off the tree. When trees get older and are too large to cover, homeowners have used a sting of lights in the canopy to generate heat. Make sure they are lights designed for the outdoors.
There are differences in how much cold a tree will take. ‘Hass’ and ‘Holiday’ are very sensitive, while ‘Stewart’ and ‘Zutano’ are much more cold tolerant. Here is a comparative chart of the different varieties
Variety Frost Resistance |
||
Race |
Typical varieties |
Critical temperature below which fruit and/or trees are subject to damage |
Mexican |
Duke, Topa topa, Mexicola, Zutano, Bacon |
25 Degrees F |
Hybrids |
Fuerte, Puebla |
28 Degrees F |
|
Ryan, Hass, MacArthur, Nabal, Endranol, Rincon |
29 Degrees F |
Guatemalan (Very Tender) |
|
30 Degrees F |