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Section 26.5.5: Common Rust

Puccinia sorghi

Time for concern: Whorl through tassel
Key characteristics: Rust appears in the field as oval to elongated cinnamon-brown pustules scattered over the surface of the leaves. 

Management Option Guideline
Scouting/thresholds

Scouting should begin at the early whorl stage and continue through to the tassel stage. Sample 120 plants. Record the number of leaves with any rust pustules. Make a ten plant sample of the field and count the number of leaves on each plant. Calculate an average number of leaves per plant for the field. Calculate the percentage of infected leaves using the following formula:

% of infected leaves = total # of leaves with rust x 100 / average # of leaves per plant x 100

Spray when 80 percent of the leaves are infected. For best results, all fungicide applications should be made prior to tassel. The threshold is not valid for highly susceptible varieties such as Silver Queen, Sweet Sue, Florida Staysweet, Candy Bar, Crisp N Sweet 711, Sweet Belle, Sweetie 70, Candy Bar II, Crisp N Sweet 730, and Super Sweet 8002. 

Resistant varieties Plant resistant varieties whenever possible. See Section 26.1 Recommended Varieties.
Crop rotation Avoid sequential plantings in close proximity. The staggered planting schedules result in high concentrations of fungal spores from earlier plantings that easily infect young, susceptible plants.
Site selection Avoid fields with poor air drainage.
Seed selection/treatment,
Postharvest, and
Sanitation
These are not currently viable management options.
Pesticides Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production