Alfalfa:Diagnostics

ALFALFA AND HAY PESTS AND NUTRITIONAL DISORDERS

ACROCALYMMA ROOT AND CROWN ROT (ACROCALYMMA MEDICAGINIS)

‘‘‘Acrocalymma Root and Crown Rot (Acrocalymma medicaginis) ‘‘‘ The disease is characterized by red-flecked cortical and woody tissues at the end of a wedge-shaped lesion, beginning in the crown branches and extending into the taproot. The bark of infected regions is often cracked. No current information is available on resistance to the pathogen or control measures. (Fungal Disease That Principally Occur on Crowns and Roots)

AIR POLLUTION INJURY

‘‘‘Air Pollution Injury:’‘‘ Symptoms resulting from exposure to different outdoor gases can appear quite similar to each other and to those induced by other weather conditions, nutritional disorders, diseases, insects, and pesticides. (Noninfectious Disease -- Caused by Abiotic Agents)

ALFALFA CHLORINE DEFICIENCY

‘‘‘Alfalfa chlorine deficiency:’‘‘ Symptoms are small, thickened leaflets with a slit at the tip, along the midvein. Plants may also appear to be limp and nonturgid. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

ALFALFA ENATION (AEV)

‘‘‘Alfalfa Enation (AEV) ‘‘‘ The disease is primarily characterized by crinkled leaves. The diseased plants may reach normal size but will have an erect, bushy posture. The flowers become deformed and cannot be pollinated by insects; therefore, seed production is reduced and possibly eliminated. Infected plants die prematurely. Control measures have not been established. (Disease Caused by Viruses and Viruses Infectious to Alfalfa)

ALFALFA MOSAIC (AMV)

‘‘‘Alfalfa Mosaic (AMV) ‘‘‘ This disease is characterized by leaves marked with light green or yellow spots, shoot stunting, and leaf or petiole distortion. Alfalfa mosaic is most likely to appear during cool spring and autumn conditions. It should be noted that the symptoms are typically inconspicuous in summer foliage. The disease can be controlled by minimizing localized aphid-transmission of Alfalfa Mosaic Virus. This is possible by using aphid-resistant cultivars. (Disease Caused by Viruses and Viruses Infectious to Alfalfa)

ALFALFA STEM NEMATODE (DITYLENCHUS DIPSACI)

‘‘‘Alfalfa Stem Nematode (Ditylenchus dipsaci) ‘‘‘ Plants infected with this disease have swollen nodes on the stems, greatly shortened internodes, and are usually discolored. In warm, humid weather leaves may become curled and distorted or turn white. Planting resistant cultivars is the only practical method of controlling the stem nematode. (Disease Caused by Nematodes)

ALUMINUM

‘‘‘Aluminum:’‘‘ Plants affected by aluminum are stunted and unusually, dark green. In high-aluminum soils, roots are restricted and stubby. Yellow spots may develop on the lower leaves. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

ANTHRACNOSE (COLLETOTRICHUM TRIFOLII)

‘‘‘Anthracnose (Colletotrichum trifolii) ‘‘‘ Symptoms of this disease vary from a few small, irregularly shaped blackened areas on resistant stems to large, sunken, oval to diamond-shaped lesions on stems of susceptible plants. If not prevented, blueish black crown rot may develop, which is the most serious expression of the disease. This symptom is often observed when killed stems are broken off at the crown. Planting resistant cultivars and using clean equipment are the most practical forms of control. (Fungal Disease That Principally Occur on Lower Stems and Crowns)

APHANOMYCES ROOT ROT (APHANOMYCES EUTEICHES)

‘‘‘Aphanomyces Root Rot (Aphanomyces euteiches) ‘‘‘ This disease is characterized by plants that are often slow or may fail to resume growth following harvest or winter dormancy. Roots and hypocotyls initially appear gray and water-soaked, but develop a light to dark brown color. Infected seedlings are yellow and express chlorotic, yellowish cotyledons followed by yellowing of foliar tissues. Resistant cultivars are being developed. Soil and water management practices that improve soil drainage can reduce the risk of Aphanomyces root rot. (Fungal Disease That Principally Occur on Seeds and Seedlings)

BACTERIA-INDUCED CROWN AND ROOT ROT

‘‘‘Bacteria-Induced Crown and Root Rot:’‘‘ The symptoms of bacteria-induced crown and root rot are very similar in nature to those induced by random fungal agents. However, they are more destructive in connection with other organisms. To determine the actual causal agent, isolations must be made. Good management practices, such as proper plant nutrition, good soil drainage, and proper timing of harvest may be the best forms of control. (Caused by Bacteria and Mycoplasmalike Organisms)

BACTERIAL LEAF SPOT (XANTHOMONAS CAMPESTRIS PV ALFALFAE)

‘‘‘Bacterial Leaf Spot (Xanthomonas campestris pv alfalfae) ‘‘‘ This disease is characterized by leaves that develop yellow areas within which tiny, circular, water-soaked spots may emerge. Lesions that begin on the stem are tiny, water-soaked greasy spots which enlarge and often group together. These grouped lesions then form elongated lesions, sometimes extending for several internodes. At this time, resistant cultivars offer the most practical means of control. (Caused by Bacteria and Mycoplasmalike Organisms)

BACTERIAL SPROUT ROT (ERWINIA CHRYSANTHEMI PV CHRYSANTHEMI)

‘‘‘Bacterial Sprout Rot (Erwinia chrysanthemi pv chrysanthemi) ‘‘‘ The first symptom associated with bacterial sprout rot is a translucent yellowish coloring of the radicles as they emerge from the seed. Within 48 hours, the sprouts stop growing and turn into a yellowish, strong smelling substance containing numerous visible bacteria. Sanitization of equipment between crops using sodium hypochlorite effectively controls bacterial rot if all residual sprouts are eliminated. (Caused by Bacteria and Mycoplasmalike Organisms)

BACTERIAL STEM BLIGHT (PSEUDOMONAS SYRINGAE PV SYRINGAE)

‘‘‘Bacterial Stem Blight (Pseudomonas syringae pv syringae) ‘‘‘ Symptoms associated with bacterial stem blight include overall stunted growth and shorter, spindly, brittle stems. The stems initially begin showing symptoms as they develop water-soaked, yellowish to olive green lesions. These lesions are visible where the leaf attaches to the stem and then extends down one side of the stem for one to three internodes. In severe cases, the first harvest cutting should be done as soon as the danger of late frost is past. This removes the infected material and the regrowth will likely be healthy. (Caused by Bacteria and Mycoplasmalike Organisms)

BACTERIAL WILT (CLAVIBACTER MICHIGANENSE PV INSIDIOSUM)

‘‘‘Bacterial Wilt (Clavibacter michiganense pv insidiosum) ‘‘‘ This disease is characterized by leaves that show a yellow-green color and plants that have shown stunted growth. Mild symptoms consist of leaf mottling, slight cupping or upward curling of the leaflets, and some reduction in plant height. Many resistant cultivars are available which is the best form of control. (Caused by Bacteria and Mycoplasmalike Organisms)

BEAN LEAF ROLL (BLRV)

‘‘‘Bean Leaf Roll (BLRV) ‘‘‘ There are few indications that bean leaf roll may present a problem; however, an occasional mid transient yellowing of older leaves was noticed on some bean leaf roll virus infected alfalfa plants. Reducing the spread of the virus to other crops, especially pea or lentil seed crops, may be the only incentive for controlling bean leaf roll virus in alfalfa. (Disease Caused by Viruses and Viruses Infectious to Alfalfa)

BORON

‘‘‘Boron:’‘‘ The key characteristics of this deficiency are the leaves become yellow or reddish yellow, and plant tops are bunched. Yellowing is usually followed by the development of purplish to rose pink color on leaflet margins and on the undersides of the youngest fully developed leaves. Later, the chlorosis, or yellowing, extends to the interveinal tissues and the upper leaf surface yellows and then turns red or reddish yellow. The lower leaves maintain a healthy green color. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

BROWN ROOT ROT (PHOMA SCLEROTIOIDES)

‘‘‘Brown Root Rot (Phoma sclerotioides) ‘‘‘ The characteristic symptom associated with this disease is a brown taproot lesion with a blackish border. Younger lesions that develop on the taproot are roughly circular, slightly sunken, and drain with ooze. As the lesions grow and mature they become darker and more irregular. The dead roots become shrunken, grayish, brittle, and dotted with numerous lesions that develop short beaks. Control measures for this disease would include using cultivars that show resistance three years of annual crops should be planted before a second crop of alfalfa is planted in the same field. (Fungal Disease That Principally Occur on Crowns and Roots)

CALCIUM

‘‘‘Calcium:’‘‘ If plants where calcium is a deficiency, root growth is significantly impaired, and rotting may occur in the roots before the tops are affected. In young plants, the first visual symptom is a sudden collapse of the petioles of the youngest fully developed leaves. Marginal deadened tissue develops on immature leaves, sometimes preceded by the yellowing of the tissue. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

COMMON LEAF SPOT (PSEUDOPEZIZA MEDICAGINIS)

‘‘‘Common Leaf Spot (Pseudopeziza medicaginis) ‘‘‘ Common leaf spot is characterized by small, circular, brown to black spots that develop on the leaflets. Most of the disease will form on the upper leaf surface where it can be easily detected. Infected leaves turn yellow and drop as the disease progresses through the plant. Some cultivars have been developed which show moderate resistance and should be used in connection with fungicidal sprays, if possible. (Fungal Disease That Principally Occur on Leaves and Stems)

COPPER

‘‘‘Copper:’‘‘ Plants suffering from copper deficiency appear necrotic. Pale gray or green or white spots appear on the silted leaves, either on the margins or, more often, about one half to one fourth the distance toward the base of each leaflet. Soon after the growing point dies, the leaflets and petioles also die. Plants may appear to be drought stressed. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

CORKY ROOT ROT (XYLARIA SPP)

‘‘‘Corky Root Rot (Xylaria spp.) ‘‘‘ This disease is characterized by thinning stands and lack of recovery after cutting. The initial penetrating agent first destroys the lateral roots and then produces a dry, brown, sunken canker on the taproot. The fungus progresses slowly in root tissues, but it eventually invades the entire root, and the plant dies. Unfortunately, no control measures are available at this time. (Fungal Disease That Principally Occur on Crowns and Roots)

CROWN AND ROOT ROT COMPLEXES (FUSARIUM SPP)

‘‘‘Crown and Root Rot Complexes (Fusarium spp.) ‘‘‘ This disease is characterized by brown, necrotic areas which are often restricted to the crown or root cortex. As more of the root system rots and dies, plant vigor declines. Plants with advanced stages of rot are stunted and eventually wilt and die. Crown rot often causes plants to develop asymmetrically, which may be a key characteristic in identifying the disease. Using sound management practices to minimize losses and planting adapted cultivars are the best forms of control. (Fungal Disease That Principally Occur on Crowns and Roots)

CROWN GALL (AGROBACTERIUM TUMEFACIENS)

‘‘‘Crown Gall (Agrobacterium tumefaciens)’‘‘ The disease is characterized by irregularly shaped, twisted galls that appear on the crown branches at or slightly below the soil line. Affected plants may show some loss of vigor and slowly die. No information on control of the disease on alfalfa is available; however, it is unlikely that the disease will be a major problem. (Caused by Bacteria and Mycoplasmalike Organisms)

CROWN WART (PHYSODERMA ALFALFAE)

‘‘‘Crown Wart (Physoderma alfalfae) ‘‘‘ This disease is characterized by galls which develop from infected young crown buds. In most cases, the galls are white when they are young and immature and turn gray to brown as they dry and decay in midsummer. The best form of control is to provide good drainage and avoid excessive irrigation. (Fungal Disease That Principally Occur on Lower Stems and Crowns)

CYLINDROCARPON ROOT ROT (CYLINDROCARPON EHRENBERGII)

‘‘‘Cylindrocarpon Root Rot (Cylindrocarpon ehrenbergii) ‘‘‘ This disease is characterized by a water-soaked appearance on the root just below the crown. This area soon turns light brown and then develops into a dark brown color. At this time, no resistant alfalfa cultivars have been developed. Rotating alfalfa crops with plants not of the legume family to minimize the buildup of pathogen populations is recommended. (Fungal Disease That Principally Occur on Crowns and Roots)

CYLINDROCLADIUM ROOT AND CROWN ROT (CYLINDROCLADIUM CROTALARIAE)

‘‘‘Cylindrocladium Root and Crown Rot (Cylindrocladium crotalariae) ‘‘‘ Characteristics of this disease include seedlings that have brown, necrotic lesions that girdle the hypocotyls and extend upward to the cotyledons on the plant. Seedling blight also results from a black deadening of tissue that develops in the young roots. Later infections, which begin in established plants, are identified by the collapse of leaves and death of shoots due to extensive dark brown decay of the crowns. Control measures would include following careful rotation programs because resistant cultivars are not yet available. (Fungal Disease That Principally Occur on Crowns and Roots)

DISEASES CAUSED BY RHIZOCTONIA (RHIZOCTONIA SOLANI)

‘‘‘Diseases Caused by Rhizoctonia (Rhizoctonia solani) ‘‘‘ There are several characteristics that can be identified with Rhizoctonia diseases. In the root canker phase, the fungus can be seen on the taproot near the area where lateral roots emerge. These cankers exhibit an oval sunken shape and are tan to buff in color. As the disease spreads to the outer margins, the cankers develop a darker and more vivid color. If the disease extends to the crown of the plant, brown lesions will first appear on the buds and young shoots at and below ground level. Sunken whitish to brown lesions also develop near the base of a stem. At this time, no control measures are known. (Fungal Disease That Principally Occur on Lower Stems and Crowns)

DODDER (CUSCUTA SPP)

‘‘‘Dodder (Cuscuta spp.) ‘‘‘ The first signs of the parasite are fine, inconspicuous, orange to yellow, leafless seedlings that emerge from seed in or on the soil. Seedlings attach to the host plant and produce abundant fine, orange to yellow strands that grow and intertwine, suffocating the aboveground parts of the plants. Dodder is extremely invasive and difficult to completely destroy. Begin by using certified seed that is free of dodder. When dodder occurs in patches, destroy all dodder and the host by flaming or by cutting plants below the ground and burning the residue. Rotate to a nonsusceptible crop like a grass for at least 2 years. (Parasitic Flowering Plants)

DOWNY MILDEW (PERONOSPORA TRIFOLIORUM)

‘‘‘Downy Mildew (Peronospora trifoliorum) ‘‘‘ This disease is characterized by yellowing tissues in localized areas on leaflets but may also include the entire leaves or shoots if the whole plants becomes infected. The diseased tissue usually turns yellow and the infected leaves become twisted and their margins curl down. Cultivars highly resistant to downy mildew are available for most alfalfa varieties and provide the most economical means of control. (Fungal Disease That Principally Occur on Leaves and Stems)

DWARF (XYELLA FASTIDIOSA)

‘‘‘Dwarf (Xyella fastidiosa) ‘‘‘ Plants that suffer from stunting have shortened stems and a slight reduction in leaf size. Leaves may appear darker green than normal and have rounded apices. Dwarfed plants may be flower late or may not flower at all. The roots of dwarfed plants show a slight yellow vascular discoloration. The best form of control is to use resistant cultivars. (Caused by Bacteria and Mycoplasmalike Organisms)

FOLIAR FREEZE INJURY

‘‘‘Foliar Freeze Injury:’‘‘ Characteristics of foliar freeze injury include tissue that appears water-soaked and the outer layer separates itself from the underlying tissue that can be easily torn away. If the entire shoots become frozen, the first harvest may be delayed and reduced. It should be noted that freeze-damaged tissue is more prone to diseases of all kinds than non-frozen tissue. (Noninfectious Disease -- Caused by Abiotic Agents)

FUSARIUM WILT (FUSARIUM OXYSPORUM PV MEDICAGINIS)

‘‘‘Fusarium Wilt (Fusarium oxysporum pv medicaginis) ‘‘‘ The first indication of Fusarium wilt is shoots show signs of wilting. In early stages, leaves may wilt during the day and regain turgidity at night. As the plant and disease mature the leaves and stems become bleached and a reddish tinge often develops in the leaves. Because the pathogen persists in the soil for several years, the only practical control is the use of resistant cultivars. (Fungal Disease That Principally Occur on Crowns and Roots)

HIGH-TEMPERATURE FLOODING INJURY

‘‘‘High-Temperature Flooding Injury:’‘‘ Plants suffering from high-temperature flooding injury will fade to a light green and wilt even though the soil is wet. Roots of some plants completely rot and, when removed from the soil, have a putrid odor. Proper water management is the best control. Flooding for short periods when temperatures are high reduces the likelihood of injury; however, some soils remain saturated long after irrigation because of the soil type, the slope of the land, and the length of the irrigation run. Therefore, flooding for short periods should be closely monitored. (Noninfectious Disease -- Caused by Abiotic Agents)

HYDROGEN FLUORIDE

‘‘‘Hydrogen Fluoride:’‘‘ Hydrogen fluoride characteristically causes marginal deadening of the tissue. This symptom may resemble sulfur dioxide damage. (Noninfectious Disease -- Caused by Abiotic Agents)

INEFFECTIVE NODULATION

‘‘‘Ineffective Nodulation:’‘‘ Plants with ineffective nodules are stunted, spindly, and yellow. Ineffective nodules are similar in size and number as effective nodules but are pale pink, smaller but more numerous than effective nodules, and are large, creamy white, popcorn-shaped, tumorlike structures that contain no leghemoglobin. Inoculation is an inexpensive form of insurance for providing adequate nodulation. (Noninfectious Disease)

IRON

‘‘‘Iron:’‘‘ In iron-deficient plants, areas between the veins of the youngest leaves first become chlorotic and yellow and then gradually turn from yellowish green to bleached yellow. As the deficiency becomes more severe and mature, the veins will also turn yellow, and finally the leaves will become almost white. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

LEAF-VEINED CLEARING CAUSED BY THE SPOTTED ALFALFA APHID (THERIOAPHIS MACULATA)

‘‘‘Leaf-Veined Clearing Caused by the Spotted Alfalfa Aphid (Therioaphis maculata) ‘‘‘ Characteristics associated with this disease causes yellowing of the veins in leaves, which are similar to symptoms associated with some virus diseases. There are numerous cultivars that are resistant to the spotted alfalfa aphid. Insecticides are required for susceptible cultivars when aphid damage exceeds economic thresholds. Biological control of the aphid by fungal and insect parasites is effective in many situations. (Noninfectious Disease -- Insect Injuries)

LEPTOSPHAERULINA LEAF SPOT (LEPTOSPHAERULINA BRIOSIANA)

‘‘‘Leptosphaerulina Leaf Spot (Leptosphaerulina briosiana) ‘‘‘ This disease primarily affects young leaves but also attacks petioles and older leaves. Lesions often start as small, black spots with light brown to tan centers. The centers then develop darker brown borders and are often surrounded by a chlorotic, yellow area. Unfortunately, resistant cultivars are not available. However, harvest should be done on schedule to prevent significant leaf loss and inoculum accumulation. (Fungal Disease That Principally Occur on Leaves and Stems)

LUCERNE TRANSIENT STREAK (LTSV)

‘‘‘Lucerne Transient Streak (LTSV) ‘‘‘ This disease is primarily characterized by visible yellowing in the leaf veins, yellow vein banding that spreads to all tissues located near the veins, and leaf distortion in the spring-growth foliage of infected alfalfa plants. Summer-growth foliage tends to be free of symptoms. At this time, no control measures are available. (Disease Caused by Viruses and Viruses Infectious to Alfalfa)

MAGNESIUM

‘‘‘Magnesium:’‘‘ Plants that exhibit magnesium deficiency show yellowing between the veins beginning with the lower leaves of the plant and progressing upwards. The margins initially remain green but later become yellow, and the leaves die. The center of the blade of the leaf develops a red color which eventually spreads though out the leaf until only a small inverted V-shaped area of green tissue remains around the base of the midrib. The affected leaves finally die and fall off the plant. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

MANGANESE

‘‘‘Manganese:’‘‘ The initial symptom connected with manganese deficiency is reduced growth, associated with strong yellowing between the veins, limiting only the very youngest leaves. Yellowing occurs first in the tissues between the veins, while the veins remain green. Later, small, light brown dead areas, which are initially visible on the upper surface, develop in the yellowing leaves. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

MOLYBDENUM

‘‘‘Molybdenum:’‘‘ Plants that are suffering from molybdenum deficiency are pale green and stunted, and the lower leaves may drop off prematurely. If not treated and the deficiency matures, the leaflets may show white notching between the veins extending to the tips and centers of the leaves. The plants usually will not flower. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

MYCOLEPTODISCUS CROWN AND ROOT ROT (MYCOLEPTODISCUS TERRESTRIS)

‘‘‘Mycoleptodiscus Crown and Root Rot (Mycoleptodiscus terrestris) ‘‘‘ This disease is characterized by a black rot of the lateral roots and taproot and decay of the crown and interior of the taproot on mature plants. Reddish brown lesions develop on the stems and small leaf spots are produced when foliage and stems are inoculated with a spore suspension. At this time, no control measures are available. (Fungal Disease That Principally Occur on Crowns and Roots)

NITROGEN

‘‘‘Nitrogen:’‘‘ Plants showing signs of nitrogen deficiency are usually dwarfed and spindly, with light green or somewhat yellow leaves. These leaves soon yellow, die, and may drop off. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

OZONE

‘‘‘Ozone:’‘‘ Plants affects by ozone usually show some yellowing on the leaves. However, the main symptom occurs between the veins of injured leaves and is exhibited by small, isolated dead areas or intense brown lesions. (Noninfectious Disease -- Caused by Abiotic Agents)

PHOSPHORUS

‘‘‘Phosphorus:’‘‘ Plants that are suffering from phosphorus deficiency have light brown roots which are restricted in growth. The plant above the ground is also stunted in growth and is also stiff and erect. The leaves on the plant are usually small and sometimes abnormally dark or bluish green. The leaflets often fold together and the undersides and stems may develop a red or purplish color. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

PHYMATOTRICHUM ROOT ROT (PHYMATOTRICHUM OMNIVORUM)

‘‘‘Phymatotrichum Root Rot (Phymatotrichum omnivorum) ‘‘‘ This disease is often characterized by growing in a fairy ring pattern. The plants in the center of the circle die due to the invasion of the disease and these plants are replaced by grasses that are unaffected by the disease. As the fungus spreads outward from the inner circle core, it kills the remaining alfalfa and forms the fairy ring. Presently, no methods for disease control have been used successfully in commercial plantings of alfalfa. (Fungal Disease That Principally Occur on Crowns and Roots)

PHYTOPHTHORA ROOT ROT (PHYTOPHTHORA MEGASPERMA PV MEDICAGINIS)

‘‘‘Phytophthora Root Rot (Phytophthora megasperma pv medicaginis) ‘‘‘ Plants that carry this disease show signs of wilting as the plants become larger and more mature and the foliage, usually the lower leaves, becomes yellow to reddish brown. After the alfalfa has been cut, the regrowth of diseased plants is often slow. Many taproots develop lesions with radiating margins that are tan to brown. These lesions usually begin where a lateral root emerges. Soil and water management is the most important control measure. Combining these practices with the use of resistant cultivars has been extremely successful in controlling Phytophthora root rot. (Fungal Disease That Principally Occur on Crowns and Roots)

POTASSIUM

‘‘‘Potassium:’‘‘ Potassium deficiency is perhaps the most common and most easily recognized nutrient imbalance. Plants showing signs of potassium deficiency will develop small white spots at the margins of the lower leaflets. As the deficiency progresses, the areas between the spots turn yellow and die, and the spotting progresses up the plant. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

POTATO LEAFHOPPER BURN (EMPOASCA FABAE)

‘‘‘Potato Leafhopper Burn (Empoasca fabae) ‘‘‘ Characteristics of this disease would include stunted plants with characteristic V-shaped yellowing. The yellowing is usually followed by reddening and purpling, beginning at the tip and progressing toward the base of the leaflet. Symptoms of leafhopper burn are very similar to those caused by boron deficiency. Leafhoppers are best controlled by timely applications of appropriate insecticides. (Noninfectious Disease -- Insect Injuries)

PYTHIUM SEED ROT, DAMPING-OFF, AND ROOT ROT (PYTHIUM SPP)

‘‘‘Pythium Seed Rot, Damping-Off, and Root Rot (Pythium spp.) ‘‘‘ This disease can be easily detected within a few days of planting. The infected seedlings fall over or may become stunted and die within a few days. They also develop small, very dark green cotyledons. The best form of control is seed protectant fungicides which are effective both in the greenhouse and in the field. (Fungal Disease That Principally Occur on Seeds and Seedlings)

RED CLOVER VEIN MOSAIC (RCVMV)

‘‘‘Red Clover Vein Mosaic (RCVMV) ‘‘‘ Symptoms of alfalfa plants infected with this disease include a yellow vein mosaic and yellowing at the edges of the leaf. As the disease matures and spreads throughout the plant these tissues die and fall off. Foliage deadening also appears regularly in areas between the veins and often results in premature death of infected plants. At this time, no control methods have been developed. (Disease Caused by Viruses and Viruses Infectious to Alfalfa)

RHIZOPUS SPROUT ROT (RHIZOPUS STOLONIFER)

‘‘‘Rhizopus Sprout Rot (Rhizopus stolonifer) ‘‘‘ This disease is characterized by many visible symptoms. Sprouts that have become rotted form in pockets rather than uniformly through out the plant. Tissues that are decayed are soft and translucent but firmer than tissues rotted by bacteria. In the areas that have become rotted, coarse, gray to brown, cottony mycelium develops with large, visible black sporangia. The best form of control is good sanitation practices and avoiding plant injuries. (Fungal Disease That Principally Occur on Seeds and Seedlings)

ROOT-KNOT NEMATODES (MELOIDOGYNE SPP)

‘‘‘Root-Knot Nematodes (Meloidogyne spp.) ‘‘‘ This disease is characterized by plants that have become stunted and infected root systems branch excessively and have developed galls. Some galls are small and inconspicuous and may be missed if the roots are not examined carefully. Resistant cultivars provide the most practical control method as chemical control is not economically feasible. (Disease Caused by Nematodes)

ROOT-LESION NEMATODES (PRATYLENCHUS PENETRANS)

‘‘‘Root-Lesion Nematodes (Pratylenchus penetrans) ‘‘‘ The most characteristic symptom associated with root-lesion nematodes is nematode feeding on the roots usually causes dark brown or black lesions. These lesions may fuse together leaving the entire root with a brown color and reduced growth. Infected plants also experience stunted top growth when the nematode numbers are high. At this time, no complete control measures are available. (Disease Caused by Nematodes)

RUST (UROMYCES STRIATUS)

‘‘‘Rust (Uromyces striatus) ‘‘‘ Symptoms associated with rust are easily recognized by the small, reddish brown, circular pockets of spores that rupture the epidermis on the surfaces of leaflets and on petioles. When abundant, rust pustules cause the leaves to shrivel and fall prematurely. Resistant cultivars offer the most practical means of controlling rust, but few are currently available. (Fungal Disease That Principally Occur on Leaves and Stems)

SCLEROTINIA CROWN AND STEM ROT (SCLEROTINIA SPP)

‘‘‘Sclerotinia Crown and Stem Rot (Sclerotinia spp.) ‘‘‘ There are many visible symptoms that are associated with this disease. In the early stages of rot, the crown tissue develops a yellow-brown color that eventually turns dark brown and soft. As the disease progresses, the infection spreads and produces webs of mycelium that grow across the soil surface and then from one plant to another. The individual plants suffer as the stems crack, turn brown, become soft and mushy, and totally disintegrate. Because resistant cultivars are not available, the best form of control is early spring planting. (Fungal Disease That Principally Occur on Lower Stems and Crowns)

SCLEROTINIA ROT (SCLEROTINIA SCLEROTIORUM)

‘‘‘Sclerotinia Rot (Sclerotinia sclerotiorum) ‘‘‘ This disease is characterized by white fluffy mold that grown on dying leaves and stems. It usually occurs in the spring when the weather is cool and moist. Eventually as they mature, the white masses of mold develop into heard black masses.

SCLEROTIUM OR SOUTHERN BLIGHT (SCLEROTIUM ROLFSII)

‘‘‘Sclerotium or Southern Blight (Sclerotium rolfsii) ‘‘‘ The symptoms associated with this disease include plants that appear water stressed, collapse, and turn light brown or tan. When the plant eventually dies, there is no indication of green color in the tissues. During warm, wet periods, thick, white mycelium develops at the base of affected plants and on debris on the soil surface. Most alfalfa cultivars appear relatively resistant to southern blight. (Fungal Disease That Principally Occur on Lower Stems and Crowns)

SOUTHERN ANTHRACNOSE (COLLETOTRICHUM TRIFOLII)

‘‘‘Southern Anthracnose (Colletotrichum trifolii) ‘‘‘ This disease is characterized by young shoots and stems that are bleached and bent. Stem lesions that develop are salmon colored and diamond shaped causing the young tissues to die. Sometimes crown infections can be identified by a dry, rotting, blue-black stem which turns brick red as it develops into the roots. Stems can become blue in color and very brittle.

SPRING BLACK STEM AND LEAF SPOT (PHOMA MEDICAGINIS)

‘‘‘Spring Black Stem and Leaf Spot (Phoma medicaginis) ‘‘‘ The characteristics for this disease develop in the early spring as several small, dark brown to black spots on the lower leaves, petioles, and stems. As the disease matures, irregularly shaped lesions develop on the leaves and increase in size and group together. The leaves turn yellow and often wither and dry out before falling. Unfortunately, there are no highly resistant cultivars available at this time. The best form of control would be foliar fungicides which effectively reduce the severity of the disease. (Fungal Disease That Principally Occur on Leaves and Stems)

STAGONOSPORA LEAF SPOT AND ROOT ROT (STAGONOSPORA MELILOTI)

‘‘‘Stagonospora Leaf Spot and Root Rot (Stagonospora meliloti) ‘‘‘ This disease is characterized by a diffuse margin with a bleached center. The infected leaves will drop soon after the lesions form. Stem and leaf spots are similar in appearance and will develop black spots in the infected tissue. There are no resistant cultivars known at this time. (Fungal Disease That Principally Occur on Crowns and Roots)

STEM GIRDLE (STICTOCEPHALA FESTINA)

‘‘‘Stem Girdle (Stictocephala festina) ‘‘‘ This disease is a problem due to a three-cornered alfalfa hopper which causes girdling of the lower stems of alfalfa and other plants in irrigated desert valleys. There is no known control at this time. (Noninfectious Disease -- Insect Injuries)

STEMPHYLIUM LEAF SPOT (STEMPHYLIUM SPP)

‘‘‘Stemphylium Leaf Spot (Stemphylium spp.) ‘‘‘ The characteristics associated with this disease differ in warm and cool temperatures. Plants growing in warm temperatures develop oval, slightly sunken, light brown lesions. These lesions have a dispersed, dark brown border often surrounded by a light yellow halo. Under severe disease conditions, the lesions may ultimately cause the leaflet to yellow and fall prematurely. Plants growing in cool temperatures produce slightly irregular lesions with a light tan color that has a sharply defined dark brown border. The cool temperature plants rarely experience premature defoliation, but the quality of the forage may decline. Low to moderate levels of resistance exist in some cultivars for both warm and cool temperature isolates. If severe weather or severe disease threatens a crop, the most recommended solution is harvesting early to avoid total leaf loss. (Fungal Disease That Principally Occur on Leaves and Stems)

SULFUR

‘‘‘Sulfur:’‘‘ Symptoms of sulfur deficiency are somewhat similar to those of nitrogen deficiency in that the plant, including the veins, becomes pale green to yellow. Plants tend to be small, stunted, and lack forage. Yellowing of the plants is more evident on younger leaves or over the whole plant, whereas yellowing associated with nitrogen deficiency may be more concentrated on the lower leaves. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)

SULFUR DIOXIDE

‘‘‘Sulfur Dioxide:’‘‘ Symptoms associated with sulfur dioxide include dead cells that extend to various tissues with the plant. Sulfur dioxide deficiency is rarely the primary problem in plants that are not properly developing. Where there is a problem of isolated dead tissues, there is often symptoms of other diseases or deficiencies present. (Noninfectious Disease -- Caused by Abiotic Agents)

SUMMER BLACK STEM AND LEAF SPOT (CERCOSPORA MEDICAGINIS)

‘‘‘Summer Black Stem and Leaf Spot (Cercospora medicaginis) ‘‘‘ This disease is characterized by defoliation of the plant beginning with the lower leaves and progressing up the stem. Leaf spots develop before stem lesions. Stem infection causes reddish brown to chocolate brown, elongated lesions, which may enlarge and unite to discolor most of the stems. The best form of control at this time is to harvest alfalfa early, as this minimizes overall losses. Unfortunately, cultivars differ in resistance, and presently none are very resistant. (Fungal Disease That Principally Occur on Leaves and Stems)

VERTICILLIUM WILT (VERTICILLIUM ALBO-ATRUM)

‘‘‘Verticillium Wilt (Verticillium albo-atrum) ‘‘‘ This disease is characterized by a V-shaped yellowing of the leaflet tips and a narrowing and upward longitudinal rolling of some apical leaflets. As the disease matures and progresses, leaflets become completely dry and fall off, frequently leaving stiffened, yellow petioles attached to the green stem. Infections located in the crown progress slowly and as the pathogen spreads within the crown, new stems become diseased, and eventually the entire plant wilts and dies. The best form of control is the use of resistant cultivars and should be grown in areas where the disease is a problem. (Fungal Disease That Principally Occur on Crowns and Roots)

VIOLET ROOT ROT (RHIZOCTONIA CROCORUM)

‘‘‘Violet Root Rot (Rhizoctonia crocorum) ‘‘‘ This disease is characterized by a tight felt cloak of mycelium that has a bright violet to cinnamon color. Aboveground parts of infected plants turn yellow, then turn brown, and finally die. This starts in small, circular to irregular patches that enlarge as the disease progresses. Crop rotation is the most effective control. Plants of the grass family are highly resistant and can be grown safely where the disease is a problem. Sanitation and good drainage have been suggested as additional control measures. (Fungal Disease That Principally Occur on Crowns and Roots)

WINTER CROWN ROT (COPRINUS PSYCHROMORBIDUS)

‘‘‘Winter Crown Rot (Coprinus psychromorbidus) ‘‘‘ A key characteristic of this disease is that is can be identified from year to year in the field by patches of dead plants that continue to expand. Rotted parts are dark brown at first but then become blackish and soft. Younger plants may be rotted off where the crown and taproot join together, leaving an apparently sound taproot topped by a watery, brown soft rot caused by invasion of secondary organisms. The best control measures would include using resistant cultivars where available and rotating alfalfa with annual crops for at least 3 years, as this greatly reduces the inoculum and is beneficial for at least 3 years in the succeeding alfalfa crop. (Fungal Disease That Principally Occur on Crowns and Roots)

WITCHES'-BROOM

‘‘‘Witches' Broom:’‘‘ The disease is characterized by excessive development of short, spindly shoots from all parts of the crown and from axillary buds along the stems. The plants often have a yellowish cast due to the marginal yellowing of the small, rounded, often puckered leaves and the pale green color associated with the tiny succulent stems. No practical direct methods of control are known, but good cultural controls are recommended. (Caused by Bacteria and Mycoplasmalike Organisms)

YELLOW LEAF BLOTCH (LEPTOTROCHILA MEDICAGINIS)

‘‘‘Yellow Leaf Blotch (Leptotrochila medicaginis) ‘‘‘ The key characteristic associated with this disease is blotching which occurs most often on leaves rather than petioles or stems. This blotching usually begins first as small yellow spots on the upper surface which develop into numerous small, dark, openings on the outer layer of the upper leaf surface. The only practical measure of control would be to harvest early to reduce the buildup of infected leaves. (Fungal Disease That Principally Occur on Leaves and Stems)

ZINC

‘‘‘Zinc:’‘‘ Plants suffering from zinc deficiency begin by exhibiting a reduction in size and upward curling of the youngest leaves. Later, brown to bronze spots appear on the upper leaf surface around the margins of the top leaves of the plant. Areas between the veins may show dead tissue. (Noninfectious Disease -- Caused by Abiotic Agents: Nutrient Deficiencies and Toxicities)