I heard from someone at HOS that they had to be careful about spraying trees in the daytime because of the water acting as a magnifying glass and burning the apples. Just a thought.
Watering foliage during hot days doesn't scorch it, so I wonder about the likelihood of fruits being affected in this way. http://www.puyallup.wsu.edu/~Linda Chalker-Scott/Horticultural Myths_files/Myths/Leaf scorch.pdf
Watering foliage during hot days doesn't scorch it It surely can if there are salts in the water. Also, high levels of lime in the water and once allowed to dry in hot weather will burn foliage. I thought I had referenced the original article Preventing Sunburn on Apples in a former post of mine in this forum in regards to overhead watering but I have not found it. I think there are some interesting points brought out in the article. I like the whole idea of using an overhead watering system to ward off specific diseases and certain insects but once we initiate a program to water for long periods of the day we will be married to doing it. Years ago I proposed a ground and overhead watering system for Plums, Apples, some Citrus, Pears and Cherries to which my brethren in Fruit Trees could not see the economic importance of having a dual watering method until several years later. I agree with the premise in the article but I am at a loss to explain how the core temperature can prevent sun burning or sun scald of the skin of Apples. We grow Fujis here and sun scald is not prevalent even with ground based watering practices only. We do see some incidence of sun burning on Granny Smith's however and from what I've seen canopy management and the effect of over pruning does indeed play a role in how much sun burning we will see on Granny Smith Apples. I'll even take it a step further by stating that from our experience certain dwarfing rootstock have led to a higher frequency rate of the number of Apples in the outer portion of the tree facing the sun for the longer portions of the day can burn, as opposed to Granny Smith Apples grafted on standard rootstock will. I think we will find if we study it closer that where the sun burning has occurred we will likely find a higher degree of ethylene build up in the flesh tissue, right underneath the skin, depending on the variety of Apple as some Apples will scald easier than others will. If the skin is allowed to remain a relative, constant temperature then I believe the premise is correct in that we will have less incidence of sunburn no matter what rootstock we are using and how much intense sunlight we get. For the Apples that get tissue breakdown right under the discolored skin that used to be thought of as being a physiological disorder. What I especially like in the article is the effect of timing our waterings, not so much to save water as that notion has not been adequately estimated but was thrown in to help secure the funding of the study but if areas are using overhead watering from dawn to dusk then if we only water from noon to dusk to achieve maximum protection then we will have some water savings in certain areas of the Apple growing country but there was no mention of a ground based watering program to coincide with the overhead watering. Overhead watering alone will not leach the salts out of the soil in the root zone but can help yield a higher level of concentration of salt build up instead. The mist overhead waterings seems to work best on trellised Apples rather than standard row planted non trellised Apples. Jim
Hi Jim If you look at the article I linked to it mentions salts and chlorine scorching foliage. The water is not causing the damage, these are. Water that does not contain them in sufficient amounts will not scorch.
I do not believe there was any mention of alkaline water as applied onto foliage and the effects thereof in the The Myth of Hot-Weather Watering article. I believe the chlorine and sodium mentioned were not derived, as referenced, from the water itself at all but from other ground based and foliar applied sources. All I did was point out that salts present in alkaline water can indeed help cause wet leaves to sunburn. Yes, we do have areas here that have alkaline water, even to the extent that rainfall in those areas can be saline to alkaline. I agree pure water will not cause a sun burning but elements intermixed in the water can scorch leaves. Even a topographically applied acid water can aid in the burning of leaves in hot sun and we've seen that happen on Conifers in the form of acid rain in warm weather conditions here as opposed to acid rain in cool weather. The generalization that wet leaves will not sunburn is not totally true as a result of naturally occurring, existing conditions in some areas here in California. My argument is not with you Ron. Many people never have had to deal with alkaline water to better know how it can adversely affect the leaves of various plants. A higher degree of sun burning is one of the more noticeable effects some nurseries and homeowners near here have had to learn to live with arising from overhead sprinkler irrigation. Jim
Hi Jim The mythical magnifying glass effect was the idea first put forward here, which is what I was responding to.
Hi Ron: Yes, the so-called prism effect of the interaction of water, sunlight and leaf surfaces was the issue you responded to and the article was correct, for now, to call the leaf burn a myth based on what we know so far. I knew what you meant Ron. My objection was to the wet leaves will not sunburn as I've seen what can happen before and after and have helped work on solutions for people, around here and also around the central to mid-upper, Oregon coast on plantation grown Conifers. I agree with the salt issue in the article but no one wants to talk about topographical salts and lime build up on the leaves and how the interaction of water and direct sunlight can yield a scalding effect on leaves with the right temperate conditions. It was because of what happened to plots of fruit trees with overhead sprinkler irrigation only at a nearby UC Experimental Station is what led some of us to propose the dual watering methods (sprinklers and groundwater) for fruit trees and some Citrus back in the late 70's. It was the ground based salt build up is what lead to the eventual demise of the trees long since gone and removed and replanted with Kiwis back in the early 80's. Jim
