7904

	va1-sg19016.securesites.net

	version=3.1.8



SOUTHERN RUST, MAIZE - USA (IOWA)

*********************************



University via Cattle Network [edited]





Severe leaf blighting due to southern rust has occurred throughout 

central and southern Iowa [in early September 2007]. The last severe 

outbreak of southern rust in Iowa was in 1999. This disease was 

reported in Nebraska and Kansas earlier in the growing season; 

however, it was only in mid- to late August [2007] that we started to 

notice a few lesions in our field trials. Temperatures and 

precipitation in Iowa throughout August [2007] were well above normal 

and thus highly favorable for southern rust.



Southern rust is caused by the fungus _Puccinia polysora_. Like all 

rusts, _P. polysora_ spores are windblown to Iowa from the South. 

High humidity and warm temperatures favor the development of the 

disease. Under these conditions, new infections can occur every 7 

days, resulting in numerous new rust lesions and extensive leaf blighting.



Two types of rust occur on corn. Common rust is widespread each year 

in Iowa. Southern rust occurs less frequently. Southern rust can be 

pustules are brick red; southern rust spore pustules are bright 

on both upper and lower leaf surfaces; southern rust pustules develop 

predominantly on the upper leaf surfaces.



Southern rust can develop rapidly, resulting in severe and early 

senescence and considerable yield loss. In Iowa this year [2007], we 

"dodged the bullet." It is unlikely that this southern rust epidemic 

will affect yield noticeably since disease development started late 

in the grain-fill period. Registered fungicides are effective against 

southern rust, but with disease occurring so late in the season, an 

application was unnecessary. Fields in which a fungicide application 

was made earlier in the growing season are still at risk for southern 

rust since fungicides are only effective against foliar pathogens for 

14 to 21 days after application.



--

J. Allan Dodds





[_Puccinia polysora_ causes southern rust (also called polysora or 

tropical rust) in maize. The fungus occurs in most tropical and 

subtropical regions and can cause significant losses of over 50 

percent. Southern rust is favoured by warm, humid conditions making 

it an important disease in tropical areas.



Infection reduces the photosynthetic ability of the affected leaves 

interfering with kernel development. With heavy infections, leaves 

may die prematurely, and defoliate from the base up. Therefore 

infection before grain fill has been completed is more damaging to 

crop yield than infection late in the crop cycle. _P. polysora_ needs 

living host tissue for survival and spores are wind dispersed. No 

alternate hosts of the fungus are known. Resistant or tolerant ('slow 

rusting') varieties are being developed.



Common rust of maize is caused by the related species _Puccinia 

sorghi_. The disease is found worldwide in subtropical, temperate, 

and highland environments with cooler temperatures and high humidity. 

Rust development is much more likely in pre-tassel stage corn, 

because a large whorl provides a humid, protected environment, and 

young leaf tissue is more susceptible to infection than emerged 

leaves. Resistant maize varieties are available. This fungus can also 

affect _Oxalis_ species as alternate hosts producing light 

orange-coloured pustules, which are another stage of the same fungus.





Pictures



Links



Southern rust & ear rots, maize - USA 20070918.3096

2002

----

Puccinia polysora, southern rust, corn - Argentina 20020205.3486]

...................................dha/mj/mpp