Issue: May 25, 1998

Effect of forest fire smoke on garden

With all the smoke from the fires in Central America and Mexico, should I be worried about my plants? I've never seen such smokey days for so long a time.

Your garden may actually benefit from the smoke. New Mexico has extremely bright sunlight levels, to the point that we suffer sunscald on our plants. The smoke diffuses and attenuates the light which is to the benefit of the plants. By diffusing the light, the light seems to come from more directions, so the shadows under the top leaves of plants are less intense and the lower leaves are more effective at producing food for the plant. Normally, the shaded leaves become more consumer than producer of food.

By attenuating the light, the intensity of the direct sunlight is reduced and the incidence of burning is reduced a little.

There are concerns about greenhouse gases. Carbon dioxide is actually a benefit to the plants. A plant uses carbon dioxide to make sugar and other foods for itself and us. Any increased carbon dioxide levels around the plants would be carbon dioxide fertilization for the plants. I have not seen any numbers regarding increased carbon dioxide levels at the elevation our plants are grown; however, at our distance from the fires, we may not see much of an increase. So, there may be little carbon dioxide fertilization effect. I can't address what is happening in the upper atmosphere and the effects of carbon dioxide at that level.

To summarize - the smoke, by altering light intensity and any potential carbon dioxide increase, may be beneficial to our gardens. Large scale climatic effects may be another story, but the environmental scientists have considerable research to do before they will be able to determine the large scale effects with certainty.

Cherry fruit drop

My cherry tree blossomed well and began to develop a bumper crop of small cherries. Then when the weather warmed, and most of the cherries dried up and dropped from the tree. What happened?

I can only guess at the source of the problem. One likely cause is a late, spotty frost. This did happen in Albuquerque this spring. Some people still have a bumper cherry crop and others describe what you have experienced. Many of our trees seem to exhibit some minor frost damage. This probably occurred after a period of warm weather when the plants had begun to grow. Through the winter the buds and bark of the trees had been quite hardy, but to grow they lost this hardiness. Our quick drop to moderately cold temperatures could then cause injury. Because of our topography, slopes and hills, pockets of slightly colder air formed in some areas. While some areas were just warm enough not to cause damage, these pockets of cold air were just cold enough to damage the flowers. The damage was so slight that while the weather remained cool, the damage was not evident. When the weather warmed and the demand for water increased, the damage became apparent and the cherries dropped.

There are other things which could also have contributed to the problem you described. Watch for evidence of peach tree borer (yes, even in cherries) at the base of the tree. You will observe a dark sawdust material and a gummy exudation. If this is observed, ask your local nursery or Cooperative Extension Service office for a product labeled for peach tree borer control in cherry trees.

Another problem to watch for is crown gall. Crown gall is a disorder caused by bacteria that enters through wounds and causes the formation of a gall, or tumor, on the base of the tree, branches, and underground roots. It is observed as a crusty, bark-covered swelling. If the roots are affected, you will often see suckers (stems) emerging from the ground above the roots where they formed. There is no cure for this disorder. Just care for the tree as long as it is attractive and productive. Once it is no longer worth keeping, replace it with another tree, but select one that is resistant to crown gall. That means you will not plant a cherry tree at the same site.