Downy mildew of sunflower

Symptoms

• Main signs: the plants are dwarfed, the stem is thickened, and the leaves are crinkled and light in colour.
• If plants are infected at the seedling stage, no heads form. With later infection, heads do form, but they are small and upright, and the seeds in them are shrivelled.
• On the leaves of plants infected later, large irregular spots appear along the veins.

Signs of the pathogen

On the underside, the spots are covered with a powdery greyish-white coating.

When to look

• In the field, the disease begins to show at the second leaf pair stage.
• The disease appears at the seedling stage (primary infection) and develops throughout the growing season (secondary infection).
• The second assessment is carried out at the 3–4 pairs of true leaves stage. At this time, pay particular attention to downy mildew infection of the plants.
• During the third assessment, at flowering, downy mildew is recorded along with other diseases.
• Before harvest, the crops are surveyed for, among other things, downy mildew.

How to count

When assessing downy mildew infection, record the number of systemically infected plants and the number of plants that have died.

No rate and no spray timing here: both come from the label and the register.

Source of infection

The pathogen persists in seed, in infected plant residues and in the soil, where its reserve is considerable.

Favourable conditions

Intensive development and spread of the disease in all growing zones are favoured by an air temperature of 15–18 °C and excessive moisture during the sunflower growing season.

Every fact rests on a quote from its source, and each quote was checked against the page it is printed on.

1. EPPO Global Database · European and Mediterranean Plant Protection Organization
2. Станкевич С. В., Положенець В. М., Немерицька Л. В., Журавська І. А., «Моніторинг хвороб сільськогосподарських культур», навчальний посібник, 301 с. · Інститут біоенергетичних культур і цукрових буряків НААН, Державний біотехнологічний університет; Житомир: Рута, 2022 · p. 175, 176, 177, 178
3. Прогноз фітосанітарного стану агроценозів України та рекомендації щодо захисту рослин у 2025 році · Держпродспоживслужба, НААН, НАН · p. 111
4. Photos: Tom Gulya, iNaturalist, CC0 1.0 · Senna Bryce Robeson, iNaturalist, CC BY 4.0