Any enterprise that involves living things can be full of surprises. Christmas trees are no exception.
Some years, conditions are perfect for growing, with mild temperatures and ideal amounts of sun and rainfall each week. Those years, we treasure. But weather isn’t always made to order.
Extended droughts, in particular, can wipe out entire new plantings. Even those who can afford to irrigate might not find enough water available.
Winter cold by itself seldom bothers conifer species that are suitable for the area, but ice storms can damage even the hardiest. Pines, especially, can be badly damaged when a hard frozen crust forms on top of deep snow, then settles as the snow melts from beneath. The crust rips limbs from tree trunks as it sinks. Alternate freezing and thawing in years with little or no snow cover can heave young trees of any species out of the ground, drying out their roots.
Winter burn — browning of needles — occurs when winter winds evaporate water from the trees’ needles faster than it can be replaced by the roots, especially when the ground is frozen for long periods or when the trees are growing on poor soil that tends to be dry. Minor damage disappears as it becomes covered with new growth, but severe windburn may deform or even kill trees.
Along with winter burn, another culprit is salt. Once it was only trees planted near the seashore that were damaged, but now those growing close to highways where traffic kicks up road salt in winter can suffer, also. The fact that wind carries this salty spray for considerable distances is strikingly obvious along heavily traveled northern highways every spring. Evergreens can also be damaged when salt-laden snow melts and drains onto their roots. These conditions are difficult to control in vulnerable areas, so it is wise not to plant trees where salt damage is likely.
Spring doesn’t end the weather problems. Late-spring frosts are a common complaint of tree growers nearly everywhere. As often occurs, a few warm days stimulate the trees to start growing, and then a freezing night comes along and all the tender new growth is killed. The tree will live, but all new growth for that season is lost, and the next year a major shearing may be necessary to get the tree back in shape. It helps to avoid planting in pockets where cold air is likely to settle, but your best insurance is to plant only species that break bud late, hopefully after the last spring frost has struck.
Like humans, plants suffer from stress. Weather extremes make them more susceptible to attacks by insects and disease. Trees sometimes appear to have survived flood, drought, or cold, and then succumb a few weeks later. They have simply become too weakened to absorb the needed nutrients and convert them to plant tissue.
Stress can be caused by circumstances other than weather. Heavy rainfall can weaken trees, as can too much competition from weeds. Certain soil conditions also contribute to stress: excessive wetness, acidity, or alkalinity; deficiency in necessary trace elements; or an excess of aluminum. Damage to the bark caused by deer, rabbits, mice, or mowers can be devastating. Stress can also be caused by too much or too little fertilizer, improperly used herbicides or insecticides, or pruning off mature branches during the spring when the trees tend to bleed badly.
It may be tempting to reach for a chemical solution immediately at the first sign of a sickly looking plant, but don’t load up the sprayer unless you know for sure what’s wrong. Rather, follow an Integrated Pest Management (IPM) approach, which means first taking the time to determine what is causing those dead needles or drooping new growth. Many tree disorders are physiological, and rather than indicating the presence of a serious disease or insect pest, the condition could be a symptom of stress caused by any of the factors described previously. When you are certain it is not an environmental problem, look for tiny eggs or larvae of insects, or the fruiting bodies of disease (spores, rust, molds), to positively identify the culprit(s). Only then can you decide on the course of action.
To help in your identification, invest in a good quality hand lens and a comprehensive identification guide (or online Extension website) with good, clear photos in order to confirm exactly what you’re seeing. Consult an expert when in doubt. Elsewhere in this book we have listed the more common diseases and insects that affect trees, but literally dozens more could appear. Some are widespread, but others are specific to certain areas. Some affect many different trees species, while others come only in cycles, say every seven years. Fortunately there are plenty of Extension service websites and other online resources to help you pinpoint the problem and understand treatment options if necessary. The last step is to determine if the level of damage is something you can tolerate, of whether it crosses a threshold where control is required.
As with herbicides, there are too many insecticides and fungicides on the market to review them all here. Some of these products are also restricted use and require a license in order to apply. Read all pesticide labels carefully before buying them to be sure that the product is safe to use on trees and recommended for the pest affecting your planting. For example, some fungicides control only certain diseases but not others. And insecticides that kill weevils are not always effective on mites.
Buyers will not be interested in your trees unless they look healthy. Unfortunately, trees that have been green all spring and summer sometimes mysteriously turn yellow just before sales season, even when there are no insects or diseases present. This condition may be the result of natural fall coloring, as is common with some strains of Scotch pine. It can also be a result of nutrient deficiency when a tree runs short of food just when it should be storing it up for winter. A rainy summer may leach away the fertilizer, or heavy weed growth in late summer may also rob the trees of nutrients. Some growers will apply a little extra nitrogen to only those trees that will be cut that year in the fall. The color should improve by harvest time.
If fertilizing doesn’t help, it may be necessary to spray a tree colorant a few weeks before harvest. These green dyes are especially formulated to be absorbed into the needles of evergreens. They look natural and will not wash off. Colorants are available from most Christmas tree suppliers and can be applied with almost any type of sprayer. Follow the manufacturer’s application instructions for best results.