Agronomic Crop Diseases

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Corn
Gray leaf spot was identified this week from an irrigated field in Sussex County. The lesions were on the lowest leaves and not very numerous but a cause for concern since it is relatively early for this diseases to be showing up. The corn was just beginning to tassel so this field is a good candidate for a yield response from a fungicide application. If strobilurin fungicides (Quadris, Headline, Stratego) are used on corn be sure to wait until tassel emergence, there have been some problems in the Midwest with early fungicide applications causing some strange symptoms on corn especially “beer can ears”.

 

Early symptoms of gray leafspot – note rectangular lesions

Soybean Rust Update
Things are slow on the soybean rust front. However there was more rain last week in northern Florida and south Georgia so we may see some activity this coming week. Let’s hope not.

Soybean rust was confirmed in Taylor County, Florida, on kudzu on June 20th. This is the first find in that county in 2008. Since the beginning of 2008, soybean rust has been reported on kudzu in one county in Alabama; eleven counties in Florida (two of these counties had reports on coral bean and snap bean, and one county had a report on soybean); three counties in Louisiana; one county in Mississippi, and three counties in Texas. Reported infected kudzu sites in many counties have been destroyed. Rust was also reported in three states (5 municipalities) in Mexico on yam bean and soybean. These too have been destroyed or are no longer active, except for the find in Chiapas.

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