Fusarium Head Blight Updates

Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu

Wheat is at or very near anthesis (Feekes 10.5.1) for much of the region. With the frequent rain events, we remain at high risk for Fusarium Head Blight (Figure 1) and fungicide applications are recommended for wheat that is flowering or within 4-5 days of flowering.

FHB risk model for May 7 2020

Figure 1. FHB Risk Model for May 7, 2020 (wheatscab.psu.edu)

Look for yellow anthers in the center of the wheat head to signal that flowering has begun (Figure 2). Once wheat is flowering, fungicides should be applied within a 4-5 day window. Anthers can remain attached after flowering, but become a pale white. Fungicide products should be applied at the manufacturers recommended rate with nozzles that are angled 30-45° from horizontal (30 degrees is better than 45). Nozzles angled both forward and backward or twinjet nozzles that spray in two directions give better contact with the head and increase fungicide efficacy. For ground sprays, fungicides should be applied in at least 10-15 gallons of water per acre; aerial applications are recommended at 5 gallons per acre.

Wheat at flowering (Feekes 10.5.1) with yellow anthers present

Figure 2. Wheat at flowering (Feekes 10.5.1) with yellow anthers present

Once wheat has flowered, symptoms of FHB are typically visible in 18-24 days; cool weather can slow symptom development. Heads with FHB will have bleached florets or bleached sections of the head (Figure 3) and may have pink growth on spikelets. Last week, we mentioned twisting and heads stuck in the boot due to freeze damage. This week we have also observed cases of head freeze damage; these symptoms usually take 5-10 days to appear. The freeze associated bleaching of heads we are observing is occurring prior to flowering and should not be confused with symptoms from FHB (Figure 4).

Wheat with bleached florets from FHB

Figure 3. Wheat with bleached florets from FHB

Freeze damage on wheat heads

Figure 4. Freeze damage on wheat heads

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