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Arkansas soybean rust/spraying update

Following the confirmation of Asian soybean rust in 11 Arkansas counties, fungicide recommendations have been tweaked. On Sept. 2, a rust update and “conditional” fungicide spraying advisory was released by Scott Monfort and Cliff Coker, both Arkansas Extension plant pathologists.

The release reads:

“Soybean rust has been confirmed in eleven counties (Arkansas, Ashley, Chicot, Desha, Drew, Jefferson, Lee, Lincoln, Lonoke, Monroe and Phillips) in Arkansas. Until this week, the disease had only been confirmed on R6 to R7 soybeans. We are now finding low levels in R5 soybeans.

“Although, the disease has increased in both incidence and severity in confirmed fields over the last week due to the unseasonable cool conditions, we don’t expect this disease to spread from field to field under the current dry conditions. It is estimated that these locations were infected two to three weeks ago and are just reaching detectable levels.

“The bad news is that we have the potential for rain in the near future which would give soybean rust the chance it needs to increase inoculum and spread.

“In addition, the recent increase of confirmed fields and development of soybean rust in Lee, Jefferson and Phillips counties in Arkansas, northwestern Mississippi, and northeastern Louisiana has prompted this change concerning the management of soybean rust in Arkansas. “With this in mind, we are issuing a fungicide spray advisory for the eastern soybean production areas in Arkansas. This is a conditional spray advisory not an automatic spray recommendation for all soybeans nor is this a rust spray warning.

“So what do we recommend?

“We are not recommending a blanket application of a rust fungicide for the state.

“At this time, the southeast and east central part of the state is more at risk and should be the primary area of concern when considering applying a fungicide. This could change in the next few days as we continue to scout and receive samples from county agents from the other regions of the state and/or if weather conditions change.

“Please scout your soybeans and send in samples if you have suspicious fields. Before you apply a fungicide, we recommend you consider a few things first:

1. Are you within a couple of counties from the confirmed locations?

• If yes, your crop is at a higher risk.

• If no, you have a little more time to make a decision.

2. Have you scouted your soybeans?

3. What growth stage are your soybeans?

• R1 to Mid R5 are more at risk.

• Late R5 to R8 means you will more than likely outrun yield impacts.

4. Yield potential of your soybean crop?

• SBR control may not be economical if yield potential is less than 25 bushels per acre (depends on what you have in your crop to date).

5. What fungicide/fungicide combination do I use if I need to make an application?

• Soybean fields at R1 to mid-R4 should be sprayed with a combination of a strobilurin and a triazole fungicide.

• If soybeans are currently between late R4 to mid-R5, an application of a triazole alone should be applied.

• Soybean fields that are currently at, or beyond, R6 are no longer vulnerable and should not be sprayed.

“We will revisit the confirmed locations along with other eastern counties to determine if the disease is continuing to develop and/or beginning to spread. We will continue to scout kudzu patches, soybean sentinel plots, and soybean fields throughout the state and will update everyone as soon as we have new information.

“We also need your help over the next few weeks! County Extension agents should be sending in samples to the Lonoke Diagnostic Lab or the Monticello Lab. I would also encourage consultants and growers to send in samples (at least 100 leaves) if you think you have soybean rust.”

The toll-free soybean rust hotline can be accessed at (866) 641-1847.

For more on soybean rust, see

TAGS: Soybean
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