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Tomatoes 2008
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Fungi and Other Conifer Problems Parasites and Mistletoes Arceuthobium spp. and Phoradendron spp. Mistletoes are parasitic plants that injure and may eventually kill their woody hosts by stealing water and essential nutrients. Both dwarf mistletoe and true mistletoes occur in New Mexico. Dwarf mistletoes live only on conifers, while true mistletoes occur on conifer and hardwood trees and shrubs. In New Mexico, dwarf mistletoes attack ponderosa pine, Southwestern white pine, pinyon, Douglas-fir, Englemann spruce, and blue spruce, while true mistletoes are found on several species of juniper, numerous species of oak, and other hardwoods. Mistletoe plants vary in color from yellow to green to red-green. Dwarf mistletoe plants vary in size from an inconspicuous bud structure protruding through the tree bark as found on Douglas-fir to shoots nearly a foot long on ponderosa pine. True mistletoe plants vary in length from a few inches to several feet. Symptoms of mistletoe infection include swelling at infection sites and formation of witches’ brooms. BIOLOGY: Dwarf mistletoes spread by shooting seeds from explosive berries a distance of 20 to 30 feet. True mistletoes are spread by birds that eat mistletoe berries. Seeds pass through the birds unharmed and are spread in their feces. CONTROL: Branch infections on trees attacked by mistletoe can be pruned out to reduce damage and to reduce further spread of the parasite. If the infection is on or close to the trunk of the tree, it cannot be removed. Witches broom caused by dwarf mistletoe.
In dwarf mistletoe infested forests, favor non-host trees to leave when removing trees from the site. Infested stands can also be under planted with other tree species. Young regeneration can be protected from infection by removing older infected trees.
True mistletoe on juniper. Infection on trunk. Fungi that affect Conifers White Pine Blister Rust Cronartium ribicola White pine blister rust is a disease of white pines that was introduced to North America in the early 1900’s. The disease has devastated forests of eastern white pine, western white pine, sugar pine and white bark pine in other parts of the continent. The disease was discovered on Southwestern white pine in the Sacramento Mountains of southern New Mexico in 1990. It appears that a high percentage of this native tree may be killed by this disease over the next few decades. Also, the disease has the potential to infect limber pine which occurs in mountain forests Statewide and bristlecone pine which is found at high elevations in the Sangre De Cristo mountains in the northern part of the State. BIOLOGY: White pine blister rust requires the presence of currant or gooseberry shrubs (genus Ribes) to complete its life cycle. Five different types of spores are produced through the year: three on Ribes and two on pines. In the late summer or fall, spores produced on Ribes leaves are windblown to pine needles. At the time of infection, almost 100 percent humidity is necessary for the fungus to successfully invade a tree. The fungus enters through stomata on the needles and grows slowly to the stem where it eventually forms a swollen canker. Several years after infection, the canker will produce spores that infect Ribes leaves. The canker on pines is perennial and the stem is eventually girdled and killed. Trees die when the main stem becomes infected from attached branches. On small trees, trunk infection usually occurs directly from needles. Spores on Ribes Stem canker with blisters
CONTROL: No effective controls are available to stop the spread of the disease in the Sacramento Mountains of southern New Mexico. Also, once a forest tree is infected, little can be done to save it. For ornamental trees, pruning branches with cankers that are at least six inches from the main stem may prolong the life of the tree. It appears that some Southwestern white pines may be resistant to the disease, but it will take many years to confirm this observation. To avoid spread of the disease, white pines and Ribes shrubs from the Sacramento Mountains should not be transplanted elsewhere in the State.
Gymnosporangium Stem Rusts of Junipers Gymnosprangium spp. Several species of stem rusts occur in New Mexico on junipers. All produce orange to brown fruiting structures or spore sacs that gelatinize during spring rains. Swellings, distortions, and witches brooms often occur on junipers, but alternate host plants can be more seriously affected by these fungi. C. bethe!ii causes knobby galls or tapered swellings, and the alternate host are hawthorns (Crataegus spp.). C. nelsonli causes globe-shaped galls on juniper and has alternate host species in the genus Amelanchier or service-berry. C. speciosum causes tapered swellings on woody tissue and is the showiest of the various species due to the red-orange structures. Its alternate hosts are in the saxifrage family, which include currants and gooseberries. An eastern species, the cedar-apple rust, C. juniperivirginiana, has been found in the Albuquerque area. This rust can cause significant damage to apple trees.
BIOLOGY: All Gymnosporangium rusts require two hosts to complete their life cycle. The gelatinous structures are produced following spring or summer rains and they produce spores that infect the alternate host. Yellow to orange lesions occur on the alternate host and they produce another type of spore that are dispersed by the wind to junipers where infection causes galls or swellings. The fungus over winters on junipers. CONTROL: Other than branch dieback, the native species of Cymnosporangium in New Mexico cause little damage to junipers and their alternate hosts and control is usually unwarranted. However, fungicides have shown to be effective against the cedar-apple rust to protect apple crops. Gelatinous fruiting structure.
Broom Rusts Chrysomyxa spp. Melampsore!!a caiyophyllacearum Broom rusts are primarily a forest problem. Infections cause growth loss, top-kill, and occasionally tree mortality. Trunk infections may provide entrance for decay fungi.
Two species of broom rust are important in New Mexico—spruce broom rust, which attacks Engelmann spruce and blue spruce, and fir broom rust, which attacks white fir and sub alpine fir. Infections are characterized by conspicuous, dense masses of branches called witches’ brooms. Witches’ brooms are large and yellow.
BIOLOGY: Broom rust fungi require the presence of an alternate host to complete their life cycle and successfully spread. Kinnikinnick is the alternate host for spruce broom rust and chickweed the alternate host for fir broom rust. Needles on brooms are often stunted and drop off each fall. Other fungi and disease organisms may cause formation of witches’ brooms, but only broom rust causes annual drop of needles.
CONTROL: On trees with only a few branch infections, witches’ brooms can be pruned out if the infection is not too close to the trunk of the tree. Trunk infections are characterized by trunk swelling and cracks in the bark at infection sites. There are no chemical or biological controls available for broom rust. Broom rust on white fir.
Branch and Shoot Dieback on Spruce Cytospora Canker of Spruce Cytospora kunzei Sacc. Sirococcus Shoot Blight of Spruce Sirococcus strobilinus Cytospora canker and Sirococcus shoot blight are primarily fungal diseases of Colorado blue spruce, although other ornamental spruce and Douglas-fir may be attacked.
Cytospora canker causes death of lower branches followed by progressive dying of branches up the tree. Trees are occasionally killed, but more often damaged by loss of symmetry. Cytospora cankers are inconspicuous and may or may not cause bark deformation. Any part of the branch is susceptible to girdling except for very small twigs. Typically infected areas are marked by a heavy, clear amber pitch flow that later dries and covers the cankered area with a hard, crusty, white pitch coat. Pitch exuded will also drip down and cover branches below the infection. Needles on infected branches fade and eventually turn brown. Needles may stay on the branch for up to a year after infection. Sirococcus shoot blight is indicated by fading, drying needles at the ends of branches. Needles eventually drop, leaving the last 2 to 12 inches of branches bare by summer’s end. It is usually seen after heavy rainfall and high humidity. BIOLOGY: Tiny black fruiting bodies of Cytospora canker can be seen by scraping away bark in the transition area of diseased and healthy tissue. Spores ooze from fruiting bodies in wet spring and summer weather and spread to the same or other trees by splashing rain, wind, insects, birds, and man. Spores must land on freshly wounded wood to infect the tree. Small fruiting structures of Sirococcus shoot blight can be seen with a hand lens on bud scales and other parts of dying shoots. A canker also forms as the fungus grows within the succulent stem; it rarely invades older wood. Spores are produced by fruiting structures during wet periods and are spread by splashing rain and irrigation water. CONTROL: Trees under environmental stress, especially during drought, appear most susceptible to infection. Fertilizing and watering during dry periods aids tree vigor, but will probably not control the disease. Cytospora—Early detection and removal of infected branches can reduce continued development of the disease. Prune infected branches close to the trunk. Cankers will continue to produce spores even after pruning so promptly destroy (burn of bury) cut branches. Prune only in dry weather to avoid spreading spores to healthy branches. After pruning, watch for development of new cankers. No chemical sprays adequately control Cytospora on spruce. Sirococcus—Remove diseased shoots to reduce sources of infection and improve the tree’s appearance. Fungicide sprays may help reduce infection if applied before summer rains and periods of high humidity. Root Rots
Root diseases are difficult to diagnose since symptoms above the ground can
resemble symptoms caused by many other problems. In ornamental situations, root
problems frequently develop in response to unfavorable soil conditions, such as
an impenetrable hardpan or abnormally high or low moisture content. In forests,
two frequently encountered root diseases are shoestring root rot and annosus
root rot. Both of these diseases occur in expanding pockets, often with
mortality at the center. The entire crown of infected saplings usually turns
reddish brown all at once. Dieback, thinning foliage, or yellowing of the crown
is characteristic in older trees. Forest trees are predisposed to root disease
when stressed by fire, drought, poor sites, or insect injury. Shoestring Root Rot aka. Oak Root Fungus
Armillaria mellea. Annosus Root Rot Heterobasidion annosum BIOLOGY: Shoestring root rot often produces white, fan-shaped mats beneath the bark on the lower surface of infected boles and shoestring-like black rhizomorphs in the soil. Outer bark at the root collar is often covered with resin. The disease spreads over long distances by means of spores or locally by rhizomorphs. When the fungus contacts the tree’s root or root collar, it penetrates the bark and enters the living tissue. It then spreads and penetrates the wood. Cellulose is consumed, leaving the root light-colored and causing the tree’s butt to rot. The fungus produces small (less than 1 in.), white to buff-colored conks under the bark or larger (6 - 8 in.) shelf-like conks flat against the soil or in litter. CONTROL: Maintain trees in vigorous condition. Avoid planting pines on old hardwood sites that contain shoestring root rot infected stumps. In areas infected with annosus root rot, avoid thinning stands during cool, wet periods when spores are being produced and germination of the spores can occur. The spores are air borne and can remain dormant during dry weather, but will germinate when moisture is available. Mycorhizzial Symbiosis Many other fungi have symbiotic relationships with trees and do not cause diseases. Many of the edible fungi collected by the mycologists for food or for identification purposes benefit both the trees and other plants. For a discussion on some of these go to Mushrooms . Needle Diseases In New Mexico, relatively dry conditions help limit the incidence of foliage diseases in conifers. Many non-insect foliage problems are due to environmental factors rather than disease. However, there are a few needle diseases that may occur. Lophodermella spp.—This fungus is an occasional problem primarily for ponderosa pine in New Mexico at elevations above 7,000 feet. During outbreaks of the disease, nearly all of the second-year foliage in the lower half of the crown may be lost. If conditions allow for successive years of infection, only the current year’s needles will be left on the tree. Airborne spores of the fungus settle and germinate on developing needles in spring. The following spring, infected needles turn reddish brown and small, fruiting structures develop that are difficult to detect. Needles dry and fall from the tree shortly after the fruiting structures mature. Elytroderma deformans— Elytroderma needle cast is widespread and infects pinyon and ponderosa pine in New Mexico. It is particularly damaging because it invades twigs and branches and persists for several years. Symptoms occur in spring when all of the year-old needles on an infected twig simultaneously turn red brown 6 -12mm from the needle bases. Infected needles persist on the tree until fall or winter. Fortunately, incidence of the disease is low because weather conditions favoring its development are rare. Local outbreaks generally start in sheltered humid places, such as bottoms of deep arroyos, sapling thickets, and on low branches on north sides of trees pole-sized and larger. Dothistroma pini—Dothistroma needle cast (red band disease or red banded needle blight) may infect ponderosa, pinyon, and Austrian pines in New Mexico. Symptoms first appear as yellow or tan bands around the needles. Bands later turn red. Both old and new needles may be infected, but infection periods differ. Old needles are infected in spring and usually turn brown by fall. New needles are infected in mid-summer and turn brown in late summer the following year. Initial infection occurs on the lower portion of the tree and progresses upwards. Spores are released during rainy weather and spread by splashing rain. Rhabdocline pseudotsugae— Rhabdocline needle cast on Douglas-fir is an occasional problem in New Mexico. The most recent outbreak was seen in 1989 in and around the Lincoln National Forest and on Mescalero Apache lands. This conspicuous fungus disease causes mottling and premature shedding of needles over a year old. It occurs during long, rainy periods while new needles are growing. The disease is not usually serious since conditions favoring infection rarely occur over successive years. Natural Environmental Stresses Cold Injury—Injury from cold temperatures can usually be categorized as frost damage or winter damage. Frost damage most often occurs in the spring after shoots have begun to grow. Trees most frequently injured are those growing at the northern limit of their species range. Young conifers are more susceptible to injury than are older trees. Frost damage to spring shoots may resemble damage from shoot borers such as pine tip moth. Winter injury generally occurs in midwinter to early spring. Most often, the entire tree above the snow line is affected. Cold winds dry the foliage but because the ground is frozen, the tree can’t replace lost moisture so foliage dies and turns red. Protect ornamental conifers by covering them or buffering them from dry, cold winds. Heat Injury—Tree tissues may be injured by unusually high temperatures. Sunscald results from overheating and drying of bark and is characterized by reddening bark, followed by canker formation. Leaf scorch or needle scorch, a heat injury found more frequently on hardwoods but also on young conifers, results when a tree loses more water through transpiration than it can absorb through the roots. Water Injury—Lack of water can cause foliage to dry from the tips back and eventually foliage and twigs may die. Drought injury is indicated when foliage yellows or browns and needles are prematurely cast. Flooding or a dramatic increase in the water table can suffocate tree roots, resulting in above-ground symptoms of discolored foliage and spongy bark. Soil Deficiencies—A shortage of available nutrients can injure or kill conifers. New Mexico soils are often deficient in iron and zinc and have a pH level that ties up many nutrients in compounds the tree can’t use. Nutrient abnormalities are indicated by foliage discoloration and often by distorted needles and twigs. Heavy clays commonly encountered in New Mexico are difficult for roots to penetrate and can significantly limit tree growth. Storm Injury—High winds can break branches, limbs, or trunks. Shallow rooted trees are often uprooted. Heavy snows may break limbs. Hailstorms can wound or kill buds, foliage, twigs, and branches. Damage varies with time of year, size of hailstones, and intensity of the storm. Younger stems with tender bark and trees with developing foliage are most seriously damaged. Animal Injury—Mice and other small rodents seriously damage trees by feeding on bark at the root collar of young conifers, particularly in plantations. Damage usually occurs in winter when snows are deep, food scarce, and where there is plenty of grass or weed cover around the trees’ base. Trees are often completely girdled although symptoms of injury may not appear until the following summer or fall. Sapsuckers also commonly injure and kill trees. These birds drill holes, often in a characteristic pattern, and drink the sap. Bark in heavily drilled areas may die. Occasionally, the tree or its top is completely girdled. Forest trees may be browsed on by deer and damaged by deer or elk rubbing antlers against tender bark. Small ornamental trees and shrubs around the home may be injured by dog urine and by cats sharpening their claws on thin bark. Human-Caused Stresses Soil Compaction—Soil trampled by confined animals or compacted by machine traffic is less aerated and resists water penetration and drainage. Injury to tree roots during soil compaction results in yellowing foliage, premature leaf drop, and often death of the tree. Mechanical Injury—Frequent wounding of ornamental trees occurs from lawn mowers and trimmers hitting the base of the tree. Mechanical injuries can occur from anything scraping against the bark. Poor pruning jobs can seriously wound trees. Excavation around trees can hurt the root system. Air Pollution-Trees can be injured or even killed by air pollutants. Symptoms of air pollution injury generally include discolored, spotted, or blotched foliage. Most damaging pollutants are produced from industrial emissions and vehicle exhausts. Oxidants produced by internal combustion engines are concentrated in urban areas but may be windborne to rural areas. Ozone injury may occur anywhere from ozone created by lightning. Industrial emissions such as sulfur dioxide and fluorides, usually only cause injury in areas immediately downwind of the pollution generator. Salt Injury—De-icing salt applied to roads, walks, and driveways can seriously injure trees. Most of the damage occurs on foliage but eventually roots may be killed. Salt-injured trees may have yellow, red, or brown needles. Frequently, only the road side of the tree shows symptoms resulting from salt spray from passing vehicles. Calcium-based salts are less damaging than sodium salts; unfortunately these are infrequently used. Salt-injured trees also appear more susceptible to winter injury. Herbicide Injury—Conifers are very susceptible to herbicides and herbicide drift. The concentration and type of herbicide reaching the tree, the type of tree, and weather conditions all affect severity of injury. Frequently, foliage and twigs will be distorted. Ornamental trees can be damaged by over application of lawn weed killers, which usually contain 2,4-D . |