Banded Chlorosis (physiological – cold injury): Symptoms are horizontal areas of light green to white tissue that extends in a narrow (2-4 inch) band across the leaf. Within a field, the banded chlorosis symptoms will be seen on leaves of different plants about the same height from the ground. It occurs as a result of cold damage to portions of unrolled leaves within the spindle. The damage is visible weeks later, when the leaves grow out. This damage does not significantly affect the plant.
Herbicide Injury: Paraquat injury on leaves resembles fungal leafspots. Clomazone injury causes white areas on leaves. Misapplication of pendimethalin on plant cane results in poor germination and growth. Roots have a stubbiness that resembles root pruning caused by Pythium spp. or certain nematodes.
Mosaic (sugarcane mosaic virus): On leaves, scattered areas of lighter green coloration are seen. The chlorosis is most visible on young leaves, particularly near the base.The virus is spread via aphids and the use of infected plant cane. It also infects sorghum. The disease is controlled through the use of resistant varieties. In south Texas, it causes significant disease on CP72-1210 and NCo 310, but no yield reduction has been noticed with NCo 310. CP70-321 is resistant.
Ratoon Stunting Disease (bacterium – Clavibacter xyli subsp. xyli): The external symptoms are stunting and poor growth, which might not be noticed if most plants in a field are affected, or might be attributed to other causes. Yield losses become more pronounced with the age of ratoons. In some varieties, there is reddening of the internal tissue of the stalk, near the node. The discoloration is in the lower part of the node, where the leaf traces are. The disease is reliably diagnosed using phase-contrast microscopy or serological techniques.
Depending upon the variety grown, the yield loss can be substantial. In south Texas, it is economically important on CP70-321. In contrast, although NCo 310 is susceptible to infection, no apparent yield reduction has been seen with this variety.
The disease is established within a field by the use of infected plant cane. The pathogen is further spread via cutting implements such as cane knives and harvesters that contaminate the cut surfaces of healthy plants. To cure or prevent introduction of the pathogen, cane should be immersed in hot water (122 degrees F) for two hours before planting. Implements should be cleaned and chemically disinfected before being moved to different fields.
Smut (fungus – Ustilago scitaminea): The earliest symptom is the grass-like appearance of shoots, which have small and narrow leaves. Later, long, black whip-like structures appear at the stalk tip. Longer whips will curve downwards.
The whips contain the spores of the fungus which are spread by wind to other plants. It can also be spread by planting infected seed pieces. The disease is controlled through the use of resistant varieties. NCo 310 is the only susceptible variety grown in Texas. The hot water treatment used for ratoon stunting disease control will also eliminate smut infection in plant cane, but plants can become re-infected in the field as a result of airborne spores.
Chimera: A chimera is a plant with distinctly different portions that arise as a result of a mutation. In sugarcane, chimeras are seen as white stripes in leaves. The stripes are straight, clearly defined and run to the tip of the leaf blade. Yield is seldom affected.
Interveinal Chlorosis (physiological – iron deficiency): Iron deficiency is seen on young leaves. There is an interveinal chlorosis (i.e. alternating light and dark green stripes on leaves). The entire plant may be affected. Symptomatic plants may be found next to healthy plants. Plants may later recover. This is a common problem in south Texas because of the high alkalinity of soils. Foliar applications of iron sulfate are sometimes used to alleviate symptoms. A non-uniform application of iron will partially restore leaf color and excessive amounts of iron can cause necrotic spots on the leaf.
Pineapple Disease (fungus – Ceratocystis paradoxa): Cane seed pieces (setts) are infected at the cut ends shortly after planting. The tissue is reddened at first, then the sett becomes hollowed and blackened. Setts do not germinate or shoots may die back shortly after emergence. Conditions that delay germination, such as delayed irrigation or cold temperatures, favor disease development. This is a minor disease in Texas and no control is warranted.
Red Rot (fungus – Glomerella tucamanensis): On leaves, there is a reddish streak on the midrib. Internal tissues of the stalk have a red coloration which is interrupted by elongated white patches. This is a minor disease in Texas. Resistant varieties are used to control the disease in other areas where it is important.
Yellow Leaf Syndrome (virus): Symptoms occur first on older leaves. The leaf midrib yellows and the yellowing extends to the rest of the leaf. Eventually, the affected leaf dies. The incidence of this disease has been low in Texas. It has been seen in CP86-1644, CP72-1210, CP66-315 and CP65-657. As yet, there has been no measureable yield loss attributed to this disease in Texas. There are no control recommendations.
Freeze Damage: The degree of damage caused by temperatures below freezing is a function of how low the temperature is and its duration. A light freeze can result in mosaic-like symptoms on leaves. When the stalk is cut open, browning indicates damage to the whorl, terminal bud and nodes.
Leaf Scald (bacterium – Xanthomonas albilineans): The initial characteristic symptom is a white streak (“pencil-line”) 1-2 mm wide on the leaf which follows the direction of the main veins (see illustration). The streaks may later become more enlarged and the affected leaf becomes wilted and necrotic. The white pencil line may also be visible on the leaf sheaths. Symptoms of this phase are seen after ratooning or in young shoots growing from infected plant cane. Later, these symtoms may disappear, although plants remain infected. Alternatively, plants may be infected, but grow without showing any symptoms. Mature stalks may suddenly wilt and die, sometimes without the previous appearance of other symptoms.
In south Texas, other agents can cause symptoms that resemble leaf scald. These include: cold injury, iron deficiency, clomazone injury, insect injury, or chimera.
The bacterium is transmitted by infected cuttings and by implements used to cut stalks. There is evidence for soil and water transmission, as well.
The disease is kept out of production areas through the quarantine of varieties introduced from other growing areas. In areas where the disease is endemic, resistance is used to manage the disease. Additionally, cane should undergo a cold soak/hot water treatment before planting.
Pokkah Boeng (fungi – Fusarium moniliforme and F. subglutinans): One of the symptoms is chlorosis near the base of the leaf. Leaves are crumpled, stunted and twisted, and the stem may be malformed. In advanced stages of the disease, there is a top rot; the growing point is killed and the plant dies. However, plants can also recover from symptoms. This is a minor disease in Texas and no control is warranted.
Rust (fungus – Puccinia melanocephala): Early symptoms are tiny, elongated spots, light green to yellow. Later, the spots enlarge and turn orange to reddish-brown. Reddish spores are producedon the lower leaf surface, which come off as a fine powder when lesions are touched. Plants with heavy infection take on a reddish color. Rust is controlled through the use of resistant varieties. In south Texas, it can cause significant disease on CP70-321 and CP72-1210.