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R5.1 – R6 Insect & Disease Concerns/Insect & Disease Concerns During Sunflower Bloom Stages

Growth Stages NSAC Page 1

Figure 1. Stages of Sunflower Development

Manitoba’s sunflower crop is currently staged from about R4 – R6 on some field edges. It has been a tough summer for staging the crop accurately with regards to insecticide and fungicide applications. There are fields that have plants that range from R4 – R6, which makes is seemingly impossible to achieve the best results from a pesticide application. When this is the case and an application needs to be made, we recommend assessing the whole field and apply based on the majority of the crop. When insect pressure is strong enough to require an insecticide, spraying at the R5.1 provides the best results for potential yield. It isn’t always possible to spray that early and pests may not be present in economical amounts to warrant an application at that time, which makes it even more important to be checking the crop often for new developments. As soon as insects get close to that threshold number, schedule an insecticide application and know that you can call it off if numbers remain at bay.

Fungicide applications are a little different. We can prevent Sclerotinia Head Rot with the use of a fungicide, and applications should begin at R5.1 stage, and again 7 – 10 days later if disease persists or environmental conditions support sclerotia development. Note that fungicides are preventative and not curative for sclerotinia, which is why it is essential to apply early. The best method of prevention for sclerotinia is crop rotation and to not plant sunflowers following another sclerotia-susceptible crop for 3+ years, where possible.

Sunflower rust is still important to be scouting for before the crop reaches R6 (full bloom). According to the NDSU Plant Pathology department, If rust reaches approximately 1% disease severity on the upper four fully expanded leaves at or before bloom (R5), a fungicide application should be considered. At R6 or later (after bloom) fungicide applications have not had an impact on yield in our trials.” See full article on sunflower rust here.

Sunflower rust

Figure 2. Sunflower rust severity assessment (NDSU)

Lygus bugs remain an insect of concern through to seed hardening and the economic threshold is 1 lygus bug per 9 plants. Generally, lygus bugs are not a great concern in oilseeds but can cause major quality issues in confection sunflowers. Producers of confections will normally make one insecticide application at R5.1, and potentially follow up with a second treatment 7 days later.

Insects Affecting Sunflowers

Sunflower Rust ID Card

Sunflower Insect Card

Banded sunflower moths have been increasing in traps in North Dakota over the past weeks, which means that producers in Manitoba need to be scouting diligently for them as well. Typical control timing is at R5.1, as with other insects, to get maximum control.

Other Resources:

Sunflower Growing Season Calendar

Making the Grade for Sunflowers

Article written by Morgan Cott, Agronomy Extension Specialist (Special Crops) with Manitoba Crop Alliance