PREVENTION WORK ON ASPENS IN THE FALL CAN HELP PREVENT BLIGHT IN THE SPRING
FUNGUS: THERE'S LITTLE YOU CAN DO TO CONTROL THE PROBLEM ONCE SPOTS HAVE BEEN SPOTTED.The old gag of "do you see spots before your eyes?" used in many cartoons and situation comedies isn't nearly as funny if those spots are on the leaves of your aspen trees. The aggravating part of seeing spots appear on aspen leaves is that there is little, if anything, that can be done to control the problem.
Aspens and all other poplars are subject to various foliage diseases. They are caused by a number of different organisms, but the most common one in our area is aspen leaf spot from the Marssonina fungus. Aspen leaf spot generally shows as dark-brown flecks that sometimes have a yellow halo around the spots. Severely infected leaves have spots that grow together to form large, black, dead patches and black leaves. Infections may develop on the leaf petioles and succulent new shoots.Like all foliage diseases, the primary damage is reduced aesthetic beauty. When infections occur early in the season, the tree may send out a second set of leaves. Defoliation later in the summer reduces the tree's ability to harden off during winter and also reduces the amount of energy the tree can store to begin growth the following spring. Increased damage from frost, reduced growth and predisposing the tree to other insects and diseases are side effects of aspen leaf spot.
Control of aspen leaf spot begins in the fall. The organism survives the winter on fallen leaves that were infected the previous year. Warm, wet, spring weather allows the fungus to produce microscopic spores that are carried by wind to infect newly emerging leaves. If the weather remains moist, spores from these infections cause widespread secondary infections. This causes the blackening and defoliation later on in the season.
Other aspen diseases include leaf and shoot blight. These are caused by a different fungus and produce different symptoms. The symptoms become visible on shoots that were infected the previous season. Brown or black irregular-shaped areas spread through the leaves, causing them to become distorted and dry out. The fungus spreads down through the succulent new shoots, which blacken and curl to resemble a shepherd's crook. Death of these new shoots causes distorted, shrub-like growth on the aspen trees.
In higher mountain areas, such as Park City, ink spot of aspen also appears. This does not occur in the valleys along the Wasatch Front. Ink spot produces dark, discolored ring patterns on the leaves and raised black bodies with a black, velvety appearance on the leaves. These spots are about a quarter of an inch in diameter and are very distinctive. It is rarely a serious problem because the fungus only completes one life cycle per year.
Managing these diseases of aspens takes effort and persistence. Fall removal of infected leaves, twigs and branches removes the source of infection for the next year. Raking infected leaves and pruning off infected shoots and destroying them will aid in this process. Leaves should be kept as dry as possible to reduce the incidence of leaf spot. Generally avoid sprinklers wetting the tree. If that is not possible, water early in the morning to reduce humidity.
Fungicides applied in the early spring can prevent foliage diseases. Spraying only prevents new infections, it does not cure leaves that are already damaged. Trees that are valuable from an aesthetic standpoint, or young trees, should be sprayed at bud break and repeated at 12- to 14-day intervals as the moist spring weather subsides. Products that can be used to spray aspens include Daconil (chlorathalonil) or copper. Benomyl (Benlate) was previously a recommended spray for control of aspen leaf spot but is no longer being sold as an ornamental fungicide. Existing products that you have or stocks still in the garden center can be purchased and used. The infections must be controlled now. Spraying later this season when the black spots have "appeared before your eyes" is a waste of time and money.
- RED BUTTE GARDENS HORTICULTURAL CLASSES, 290 Wakara Way, instructor Larry Sagers, USU Extension horticulturist. Preregistration is required, call 581-5322.
- Rose care: Wednesday, April 1, 5-7 p.m. Red Butte Gardens.
- Pruning trees: Wednesday, April 15, 5-7 p.m. Red Butte Amphitheater.
- Pruning shrubs, vines and ground covers: Wednesday, April 22, 5-7 p.m. Red Butte Amphitheater.
- A PUBLIC LECTURE ON WATER GARDENING will be given at 7:30 p.m. Thursday, April 2, in the Sugar House Park Garden Center, 2100 S. 1602 East. Sterling Herriman will present the free lecture, which is open to the public.
The session will cover fountains and ponds for the back yard and patio, water plants and maintenance. There will be an open forum following the meeting to answer individual questions. For additional information, call Herriman at 561-8177.