Asian soybean rust was found in southwest Arkansas' Little River County on July 22. Six days later, the disease was discovered in Hope, Ark., in Hempstead County.
“It's still confined to southwest Arkansas,” said Jeremy Ross, Arkansas Extension soybean specialist, on July 28. “The Arkansas River Valley appears to be clean, so far. We ran scouts through there this week and found nothing — and that's after increasing the number of locations we'd been checking.”
At the Hope find (in a sentinel plot on the Southwest Research and Extension Center) “leaves were pulled yesterday and incubated overnight. We put the microscope on them this morning and soybean rust is definitely apparent.”
The infestation was light: 3 to 5 percent on lower leaves with severity of less than 1 percent. That isn't much comfort, however, because when scouts returned to check ASR finds in Little River County, the disease had tightened its grip. The infected fields there are now at 25 percent to 35 percent incidence.
The disease was first found in Arkansas “about 25 miles northwest of Texarkana and 10 miles east of Ogden,” said Cliff Coker, Arkansas Extension plant pathologist on July 23. “We only found it (July 22) and had it under a microscope this morning.” The rust was at very low levels and was low in the canopy on new leaves.
Coker and colleagues also checked Miller County and Lafayette County and found no rust. However, they did find additional ASR just across the border north of Hooks, Texas, in Bowie County.
“A farmer alerted us to a possible find there and we checked it out. That should give an indication on how quickly word of mouth is on this. That Hooks field was sprayed with a fungicide yesterday.”
Ross said the southwest Arkansas finds are “certainly of concern. Wheat beans could be especially vulnerable. We're not recommending any spraying prior to R-1. Earlier than that is pointless and farmers could be looking at multiple applications. The window for application is R-1 to R-6.”
The fungicide recommendation is only for soybeans in southwest Arkansas. “Soybeans from west of El Dorado, Ark., to the Louisiana, Texas and Oklahoma lines at R-1 to R-6 (flowering to pod-fill) should receive a combination of strobilurin and triazole fungicides,” said Coker. “The recommendation is for both a curative and a preventive.
“Farmers in the rest of the state should hold off. As we've done all season, we'll continue to scout all over and quickly let everyone know if we find anything of concern.”
Meanwhile, ASR continues its Texas migration. On July 27, the disease was confirmed in more Dallas-area commercial soybeans. According to the USDA ASR Web site, the malady is now in “three additional counties south and east of Dallas. The incidence was very low: less than 1 percent of leaves in the lower canopy, with less than 0.1 percent of leaf area. This adds to recent finds in commercial soybean fields in that area of the state. The disease is widespread in this part of the state. This area is still receiving isolated, heavy thundershowers.
“Fields in the Upper Coast counties, including Calhoun, Victoria, Jackson, Wharton, Colorado, and Fort Bend, are at high risk for rust development and a preventative fungicide application is advised if these fields are not at R-6.
“Fields in central and east Texas that are R-1 to R-4 are at risk and a preventive fungicide application is recommended. Fields that are at R-5, but less than two weeks from R-6, do not need a fungicide.
“Soybeans in the High Plains that are in the vegetative stage do not need a fungicide at this time.”
To access the toll-free ASR hotline call (866) 641-1847.