What's eating my sunflower?

Sunflowers are targeted by birds eating seeds and seedlings, squirrels and deer eating seed heads, cutworms severing stems at soil level, aphids on stems, and sunflower moth caterpillars in seed heads. Birds and squirrels raiding seed heads are the most disruptive problem, particularly as flowers mature; they can strip a seed head in a single visit.

Birds systematically peck out developing seeds from maturing flower heads; squirrels break stems to knock heads down or chew through the centre of the seed head to extract seeds. Loosely wrap maturing seed heads in paper bags or horticultural fleece; install bird netting over the crop; stake stems firmly so squirrels cannot tip them; harvest heads as soon as seeds mature.

Fat grey or brown caterpillars sever seedling stems at soil level overnight, leaving the plant lying cut on the ground; damage appears suddenly with no warning. Apply Steinernema carpocapsae nematodes to moist soil around seedlings; place cardboard or foil collars around stem bases; cultivate soil before planting to expose and destroy pupae.

Dense yellowish or grey colonies encrust stems from mid-season, causing sap loss; heavy infestations can stress plants and prevent seeds from filling properly. Encourage natural enemies (ladybirds, parasitic wasps, hoverflies); knock off with water; apply insecticidal soap if populations are very high; a moderate infestation late in the season rarely needs treatment.

Caterpillars web and feed inside the seed head, consuming developing seeds and leaving silk-bound masses of frass; discovered only when heads are opened at harvest. Apply Bt (Bacillus thuringiensis) or spinosad spray to open flowers when moths are active (July–August); plant early-maturing varieties to escape peak moth flight period.