HPIPM:Rust FC

Author: Howard F. Schwartz, David H. Gent, and William M. Brown, Jr.

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Pucciniomycotina
Class	Pucciniomycetes
Order	Pucciniales
Suborder	Uredinineae
Family	Pucciniaceae
Genus	Puccinia

Scientific Name

Puccinia polysora

Common Name

southern corn rust

Identification and Life Cycle

Several rust diseases occur on corn, but only common rust caused by the fungus Puccinia sorghi is found in the High Plains. In North America, windblown urediospores from tropical and subtropical environments are the primary inoculum source. Plants are infected from mid-June to mid-July when moderate temperatures (60-77ºF) and high relative humidity (greater than 95%) coincide. The pathogen overwinters on living hosts.

Plant Response and Damage

Common rust symptoms are small, reddish brown to black, linear streaks or pustules that common occur in bands on leaves. The fungus sporulates on both sides of leaves about 7 days after infection. Defoliation and plant stunting may occur. Yield losses of 3 to 8% per 10% area of the leaf area infected have been reported.

Biological Control

Practical biological control strategies have not been developed for common rust.

Cultural Control

Resistant varieties are available and should be planted. Several races of the fungus exist, so single-gene resistance needs to be matched against the prevailing rust races present. Varieties with general resistance are available that do not completely control disease, but reduce the number and size of lesions.

Chemical Control

Well-timed fungicide applications effectively control common rust, and should be applied before significant secondary inoculum develops. Fungicides are most effective when combined with varieties with general resistance.

Product List for Rust:

Pesticide	Product/Acre	Interval	Preharvest Interval, remarks
Chlorothalonil	Varies	4-7 days	Various formulations available, including Bravo Ultrex, Bravo WeatherStick, Echo 720, and Echo Zn; 7-14 day PHI
EBDC	Varies	3-10 days	Various formulations available, including Manzate, Maneb, and Dithane; Include a nonionic surfactant to improve performance; 7-40 day PHI
Propiconazole and Propiconazole/Trifloxystrobin
PropiMax	4 oz	7-14 days	Maximum of 16 ounces per season; 30 day PHI
Stratego	10-12 oz	7-14 days	Maximum of 36 ounces or three applications per season; do not make more than 2 consecutive applications before rotating to a fungicide with a different mode of action; 30 day PHI
Tilt	2-4 oz	7-14 days	Maximum of 16 ounces per season; 30 day PHI
Azoxystrobin
Amistar	2-3 oz	7-14 days	Maximum o six applications per season; rotate with a fungicide with a different mode of action; 7 day PHI
Quadris	6.2 – 9.2 oz	7-14 days	Maximum of 2.88 quarts or six applications per season; do not make more than 2 sequential applications before rotating to a fungicide with a different mode of action; 7 day PHI

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.