8/13/2019 Fusarium Stalk Rot21

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Fusarium stalk rot

Fusarium stalk rot - red internal discoloration of sorghum stalks infected by Fusarium species

General information

During a La Nina summer, sorghum crops are at an increased risk from fusarium stalk rot. The

mild wet weather is conducive to root infection from the soil borne Fusarium species, which in

turn can result in increased stalk rot. limatic stress during late grain fill, or after pre-harvestspraying, can lead to rapid development of stalk rot and may result in lodging.

The

pathogens

 Fusarium species and Macrophomina phaseolina are the main causes of sorghum

stalk rot. !n "ueensland, fusarium stalk rot is caused predominantly by two

species, Fusarium thapsinum and Fusarium andiyazi. These species do not causefusarium wilt of cotton, fusarium head blight of winter cereals, or fusarium cob rot

of mai#e.

Biology

$oth F. thapsinum and F. andiyazi survive in infected sorghum residues. !nfectionnormally occurs during the early stages of plant growth. The pathogen enters

through the roots, and can cause significant root death during prolonged mild, wet

weather.

%ther root rotting fungi such as Pythium species, also common during this

weather, can e&acerbate the damage. The Fusarium fungus then invades the

crown, where it remains dormant until a period of stress after flowering. !nvasionof the stalk may then follow.

Symptoms Lodging is often the first obvious sign of fusarium stalk rot in sorghum plants, but

the diagnostic symptoms of the disease are usually not evident until the plants arestressed. 'hen a stalk infected by Fusarium is split lengthwise, a pink-red

discoloration is evident from ground level up the stem.

(talks can be infected by Fusarium but not lodge - this depends on the strength ofthe stalk, and on the speed at which Fusarium invades the stalk. The latter is

influenced by the severity of the stress and perhaps by the tolerance of the hybrid.

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 Fusarium or other stalk rotting pathogens may not be the sole cause of crop

lodging) physiological *non-biotic+ stress factors can often be the cause.

The issue

The prolonged wet weather over much of southern and entral "ueensland andflooding in many localities has provided ideal conditions for the development of

fusarium root rot in grain sorghum. onseuently, the risk of sorghum stalk rot

developing in these crops is likely to be higher in // crops than in other years.

0re-harvest spraying of grain sorghum crops with glyphosate to assist inharvesting and grain dry down can result in the rapid development of fusarium

stalk rot. 'hether or not infected plants then lodge depends mainly on the weather

conditions and on the time to harvest.

!n general, crops sprayed before harvest with glyphosate are at greater risk from

fusarium stalk rot and lodging than those which are not sprayed. The predicted

 persistence of the La Nina weather pattern until 1utumn means that pre-harvest

desiccation of sorghum crops is likely to be a common practice.

Management

2nfortunately there is nothing that can be done after planting to control fusariumstalk rot. 0lants may or may not display symptoms of fusarium stalk rot inside the

stem at the time of a pre-harvest glyphosate spray, so it is difficult to determinethe potential risk of lodging in these situations. Timely harvest of crops at grain

maturity and particularly after desiccation by glyphosate can reduce losses from

lodging.http://www.daff.qld.gov.au/26_19945.htm