Jeffrey Hoy, Gravois, Kenneth | 1/9/2010 12:26:34 AM
Grow Resistant VarietiesThis is the primary rust-control measure. However, many current, even major, varieties are now susceptible, so it will not be possible to cultivate only resistant varieties. The resistance ratings of the current varieties are as follows:
Diversify Varieties Under CultivationExtensive cultivation of rust-susceptible varieties leads to more severe rust outbreaks and can adversely affect the durability of the resistant varieties.The adaptability of the brown rust pathogen that allows it to overcome varietal resistance makes this disease difficult to control. Growing a mix of varieties on the farm can reduce rust severity even in susceptible varieties and may increase the longevity of the resistant varieties.
Avoid Excess FertilityDo not exceed recommended nitrogen and phosphorus fertilization rates. High levels of these nutrients contribute to more severe disease development. Fertilization should be based on soil test results. Brown rust occurs first in the most-advanced, vigorously growing cane during the spring. Rust usually develops first in plant cane of susceptible varieties. Fertility and disease severity tend to be higher in cane growing on light-textured soils.
Remove Above-ground Green Leaf Material During WinterShredding during winter to remove green leaf material will act like a freeze and destroy rust overwintering in the living leaf tissue. However, it also can reduce crop growth potential. Rust spores can be spread by wind from neighboring fields to initiate disease, so shredding single fields may not delay rust development long. Cane should not be shredded during winter unless the growing point of shoots has been killed by a freeze. Shredding during spring is never recommended.
Apply Fungicide to Control Brown Rust
Brown rust can reduce cane yield by 3-8 tons, depending on the length of time rust is affecting the cane. Well-timed applications of fungicide can prevent this loss. During 2015, seven fungicides, Caramba, Headline, Headline Amp, Priaxor, Quadris, Quilt Xcel, and Tilt, will be available for brown rust control. Headline and Quadris are strobilurins, the fungicide type that provides the best control of brown rust. Caramba and Tilt are triazole fungicides, a type that provides inadequate brown rust control when applied alone. Headline Amp contains a mixture of Headline and Caramba; Priaxior contains a mixture of Headline and Sercadis, a carboximide-type fungicide; Quilt Xcel contains a mixture of Quadris and Tilt. The fungicide mixtures will provide good control with less chance of resistance build-up in the pathogen. The most effective options and suggested rates are shown in the table below (in alphabetical order). All can provide good brown rust control. The manufacturers have recommended applyhing the products at the low end of the rate range. In experiments conducted in Louisiana, the lowest rate of Headline has been effective. The fungicide mixtures have been more effective at higher rates. When brown rust does not appear until the end of April or the beginning of May, a single banded application may be all that is needed. In this case, using a higher rate will provide better control and a longer residual. Conditions under which fungicide should be applied to minimize yield loss due to brown rust are provided below.
Rate Range (oz. formulated product/acre)
9 - 12
|Headline Amp (BASF)||
12 - 15
5 - 7.5
|Quilt Exel (Syngenta)||
16 - 20
Conditions Likely to Result in a Brown Rust Outbreak Requiring Fungicide Application:
Fungicide Application Recommendations:It is important to consult the label for each product when making an application. During spring, application of fungicide on a 36-42 inch band will protect the young leaves and provide good rust control with reduced cost. Once the crop canopy extends to the row middle, a broadcast application will be needed. Fungicide should be applied in at least 15 gallons of water per acre with a surfactant for good coverage of leaves. Good coverage is essential. The labeled fungicides will work best when applied before extensive development of severe rust symptoms on young leaves. Fungicide will only protect against brown rust infection for 3-4 weeks. Therefore, rust epidemics beginning during March and April may require two fungicide applications. Brown rust severity diminishes naturally during summer, so application after early to mid-June will probably not provide a positive economic return.
General Brown Rust Information
Brown rust of sugarcane is caused by a fungus, Puccinia melanocephala. Severe disease can occur during spring and early summer in Louisiana. Windblown spores of the pathogen infect leaves. After the fungus colonizes the leaf tissues, reddish-brown lesions develop. Pustules containing reddish-brown spores erupt from the underside of leaves. The newly produced spores are then dispersed to cause more infection. Spores of the brown rust pathogen are not long-lived, and the organism can only live in green leaf tissue. Severe winters can therefore reduce rust severity during the following growing season. Mild winters and warm spring temperatures will result in severe epidemics in susceptible sugarcane varieties. Extensive brown rust development on young leaves will reduce photosynthesis and plant growth. The amount of yield loss is related to the length of time extensive rust is present on the young leaves. During this stage of the disease, affected fields appear reddish-brown when viewed from a distance.