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| Canker resulting from sunscald on young black ash |
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What is sunscald and why is everyone talking about it?
This is the time to talk about it because once you see it, it's too late to do anything about it. Strong, bright winter sun can heat the bark and cambium substantially above ambient air temperatures and cause some cellular activity on the sunny side of the tree, the south and southwest sides being most affected. Active cells require water which is not available to them in winter and lacking it they dry out. To further compound the problem, when the winter sun sets and temperatures plummet, the active cells are damaged. They become leaky and lose water, further drying the tissues. With the cambium and the inner bark dried out, the bark sloughs off in long, dead strips the following spring. Often only one side of the tree is affected, and the tree will survive the condition in a weakened state, since fungi and insects now have access to the interior of the plant. If the entire tree is girdled (uncommon) the tree will die.
Trees with smooth bark are more susceptible to sunscald than those with rough bark. Trees with high crowns are more susceptible than those with branches extending closer to the soil line, because, in the latter case, the lower branches provide some shade to the trunk. Shrubs are in the same boat and get enough shading from their branching canes to make sunscald a small, or nonexistent problem. Since young trees have smooth bark and often high crowns, that makes them most susceptible. Trees with dark bark are more susceptible than those with light bark, since the dark bark heats faster. However, all trees are susceptible and need protection, especially in Montana with our intensely bright winter days.
What to do?
Now is a good time to protect the trunks of your trees by wrapping them with paper tape or burlap up to the lowest branch. Both these materials are light colored and reflect the rays of the winter sun, keeping the bark cool and preventing sunscald. An alternative is to spray or paint the trunks with white, LATEX paint. DON'T USE OIL-BASED PAINT. Some people don't like their tree trunks painted white, but I think it looks pretty classy, especially along a tree lined driveway. If you use a wrap, remove it the following spring. Leaving it on the trunks can cause some trees to sprout burr knots and tiny roots beneath it and also makes a good place for insects to hide, and I believe it may interfere with the tree hardening for next winter.
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Are green-skinned potatoes poisonous?
This is the month for potato questions. Green-skinned potatoes have the potential to be toxic. As exposure of the tubers to light either before or after harvest increases, the tubers begin to manufacture chlorophyll (remember, they're shoots, not roots). Any kind of light, incandescent, fluorescent, or natural, will cause the reaction. The chlorophyll itself is not toxic but building up along with it is a bitter, toxic alkaloid called solanine. Just because a tuber is green doesn't necessarily mean that it is also toxic, but there is a pretty good correlation between chlorophyll and solanine buildup. The more intense the green, the deeper it will go into the tuber.
Solanine is also one of the toxins in the potato tops, including the SPROUTS, and is found in other solanaceous crops such as tomato, pepper, and eggplant. It's a acetylcholinesterase inhibitor and solanine poisoning is characterized by circulatory and respiratory depression, diarrhea, dilated pupils, headache, loss of sensation, paralysis, shock, stomach pain, subnormal body temperature, and vomiting. A person would have to eat, at one sitting, 4.5 pounds of "normal" potatoes to get the first symptoms of solanine poisoning—drowsiness and itchiness behind the neck. But the greener the potato, the less you have to eat to be poisoned. Don't eat green potatoes, potato sprouts, or potato tops.
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Does watering shrubs now really decrease winter damage?
It can, and you ought to do it to reduce problems next year. Most winter damage is caused by drying of the plant tissues. This is made worse by extreme cold, which freezes soil water, and by dry conditions, such as low humidity and drying winds, which increase evapotranspiration. The latter problem is especially bad on broadleaved and needled evergreens, the leaves of which can transpire all winter long. All of these conditions exist in Montana and so winter damage is very common. The ability of the plants to withstand long continued hard freezing (physiological drought) and long continued winter drought (atmospheric) depends on the supply of available moisture in the plant tissues going into winter. Therefore, water your shrubs and trees heavily AFTER the leaves have fallen but before the ground freezes. If you're dealing with evergreens, wait until leaves of nearby deciduous trees have fallen before you water. This will help insure that the plants have as much moisture as possible going into the winter.
Don't water the plants too early in the season. This could stimulate late vegetative growth that will not harden off in time for winter. It will die back and have to be pruned out next year. When the leaves have fallen you can be pretty sure that you will not stimulate any late growth.
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Should I prune in October?
It really depends upon what you are pruning, but generally no. Montana has severe winters and pruning wounds will not have a chance to heal if made in the fall. Early fall pruning can also sometimes cause vigorous late shoot growth that will not harden in time for winter, resulting in winter damage to the plant.
Some trees that "bleed" excessively, such as maple, black walnut, and birch, are often pruned in the fall when the sap is down. This is primarily for convenience so that the profuse spring sap will not stain and otherwise mess up sidewalks, driveways, parked cars, and so forth. You could prune these species now, or you could wait until spring. But for most other plants, prune in the early spring before the buds begin to swell. An exception is spring flowering shrubs (those that flower with or before Syringa vulgaris, the common lilac). Because most of these set flower buds on current season's growth and flower on one year old wood, prune them right after flowering is completed. If you prune these shrubs now, you're removing next season's flower buds!
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