Photo courtesy Becky JacobsonSpring rains, winds and warmer temperatures can cause some symptoms on trees that often get landowners’ attention. Some of them do not cause any significant damage to the trees and do not require any action, while others can be damaging and should be treated. Some of the more common problems that we are seeing this spring are mostly on juniper, aspen, chokecherry and ponderosa pine.
Rust fungus on juniper
Juniper trees and shrubs are susceptible to a fungal disease called Gymnosporangium, an interesting disease that requires two different plant species to complete its lifecycle. Symptoms on the primary host, juniper (Juniperus scopulorum, or Juniperus virginiana) look very different from symptoms on the alternate host — hawthorn, mountain ash, apple and crabapple.
Juniper or cedar trees infected with rust develop chocolate-colored, kidney-shaped galls on the upper or inner foliage surface. When mature, the galls may range from one-sixteenth inch to more than 2 inches and are covered with small, circular depressions. The rust galls become active following rainy spring weather, when an orange gelatinous material exudes out of the pocket-like depressions on the galls. These horn-like structures eject billions of spores that are carried by the wind to the alternate host.
The fungus that causes this rust spends 18 to 20 months of its life on the juniper. Juniper leaves are infected between June and September by spores blown from leaf spots on the alternate hosts. The juniper galls that result from the initial infection do not mature until the following spring. After rainy weather, the gelatinous orange spore horns extrude from the galls. In Colorado, these usually are produced sometime in May and early June, depending on weather conditions.
The rust depends on two hosts to complete its life cycle. It cannot survive in the absence of one of the hosts; however, the rust spores can travel great distances in our strong winds. Where practical, locate the house or a dense hedge between junipers and alternate hosts. Remove juniper galls in late winter or early spring by pruning them out. To break the disease cycle, remove galls before the gelatinous spore horns emerge. Chemical control usually is not necessary on juniper. However, if fungicide control is desired, application to juniper would occur from July through September at two-week intervals to protect the junipers from spores being blown from the alternate host.
For more information on this fungal problem, download Fact Sheet No. 2.904 Juniper-Hawthorn Rust, written by L.P. Pottorff and W.M. Brown Jr. from the CSU Extension website at www.ext.colostate.edu.
Tent-making caterpillars
Several kinds of caterpillars form silken shelters or tents on various trees and shrubs and are beginning to draw attention in the area. Most common in spring are various types of tent caterpillars (Malacosoma species), which can infest aspen, mountain-mahogany, fruit trees, gambel oak and cottonwoods. A few other tent-producing insects also infest trees in Colorado, including the uglynest caterpillars (Archips cerasivornana) thatinfest chokecherry, where they produce a messy nest of silk mixed with bits of leaves and insect frass.
Tent caterpillars spend the winter in egg masses glued to twigs of the host plant. Prior to winter, the insects transform to caterpillars and emerge from the eggs shortly after bud break. The newly emerged caterpillars move to crotches of branches and begin to produce a mass of dense silk. This silken tent is used by the developing insects for rest and shelter during the day. Most often, the caterpillars leave the silk shelter to feed at night, returning by daylight, although they sometimes feed during daylight hours as well. The tent is gradually enlarged as the caterpillars grow.
Many natural enemies attack all of the tent-making caterpillars, including birds, predaceous bugs, various hunting wasps and viruses. Because of these biological controls, serious outbreaks rarely last more than a single season. The microbial insecticide Bacillus thuringiensis can be an effective, selective control of all the tent-making caterpillars. Several contact insecticides also are effective including Sevin (carbaryl) and various pyrethroids such as permethrin, cyfluthrin and esfenvalerate.
If accessible, tents may also be pulled out and removed. More severe measures such as pruning or burning are not recommended because they can cause more injury than the insects. Often there is no need to control these insects except where there are sustained, high levels of defoliation over several years.
For more information on this topic, visit the Colorado Extension website at www.ext.colostate.edu and download Fact Sheet No. 5.583 Tent-Making Caterpillars.
Drought-stressed trees
Most of Archuleta County has been experiencing prolonged, strong winds. The soil moisture from last fall, light winter snowpack and May rains is quickly drying up and some of our trees are starting to show symptoms of drought stress.
Symptoms of drought injury to trees can be sudden or may take up to two years to be revealed. Drought injury symptoms on tree leaves include wilting, curling at the edges and yellowing. On evergreen trees such as ponderosa pines, needles may turn yellow, red or purple. They may also turn brown at the tips of the needles and browning may progress through the needle towards the twig. Oftentimes, drought stress may not kill a tree outright, but set it up for more serious secondary insect and disease infestations in following years.
To help combat drought stress, begin adding supplemental watering to landscape plants, particularly evergreen trees that have been subjected to strong, drying winds this spring. When watering, water deeply to a depth of 12 inches below the soil surface. Saturate the soil around the tree within the “dripline” (the outer edges of the tree’s branches) and continue watering 3 to 5 feet beyond the dripline on all sides of the tree. The objective is to water slowly, dispersing the flow of water to get the water deep down to the tree roots. Watering for short periods of time only encourages shallow rooting, which can lead to more drought damage.
Don’t dig holes in the ground in an effort to water deeply as this dries out roots even more. A soil needle/deep root feeder attached to a hose is acceptable to insert into the ground if your soil is not too hard and compact. Overhead spraying of tree leaves is inefficient and should be avoided during drought conditions. How much water your tree should receive depends upon the size of the tree. A general rule of thumb is to use approximately 10 gallons of water per inch of trunk diameter for each watering. Measure trunk diameter at knee height. General formula: Tree diameter x five minutes = total watering time.
Free wildfire mitigation workshops
An on-site defensible space workshop will be held June 19 from 10 a.m.-noon. This on-site workshop will take you through the steps to create a wildfire defensible space around your home and structures. A location in Archuleta County will be identified.
An on-site oak brush management workshop is set for June 26 from 10 a.m.-noon. Gambel oak is one of our most common and prolific shrubs. Learn how to manage this shrub for greater wildfire prevention. A location within the county will be identified for this hands-on training.
CPR and first aid
CPR and first aid certification classes are now being offered monthly by the CSU Extension office on the second Monday and Wednesday of each month from 6-10 p.m. Anyone needing to receive or renew certification can register by calling the Extension office at 264-5931. We will also schedule classes on additional dates with five or more registrations.
Cost for the classes is $80 for combined CPR/first aid, $55 for individual CPR or first aid and $35 for recertification with proof of current certification. The type of first aid information provided will vary by the needs of the audience.
