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ALERT: Horry County, SC, positive for rust, despite extended drought
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10/04/2005 3:45 p.m. CDT -- South Carolina officials confirmed soybean rust today on a sample from a Horry County sentinel plot. Horry County is on the border with North Carolina on the very eastern coast of South Carolina, making this both the northern-most and eastern-most discovery of soybean-rust infection this year.
Soybean specialists there say they believe if the drought had not been so severe this year, soybean rust would have been at yield-reducing levels in unsprayed fields.
This fourth positive county in the state was turned red this afternoon on www.sbrusa.net, and South Carolina officials there had the following to say in an e-mail rust newsletter and the state commentary today:
South Carolina Soybean Rust Note -- October 4, 2005
From John Mueller, Extension Soybean Pathologist, Clemson University; and David Howle, Assistant Director, Regulatory Services, Clemson University.
"Rust seems to be a little tougher than most of us had guessed. Despite our recent hot dry weather, it appears to have not only survived, but done well in a few areas. Today I received a sample from Bruce Johnson, Horry County Ag Agent, that contained rust. The sample was from Bruce’s early planted monitoring plot near Conway, which contained Deltapine 5634 RR planted on April 26. The plots had started to drop leaves.
"Bruce found five leaves out of 30 with rust. Three of the leaves had only two or three pustules per leaf, but the other two leaves had well over 100 pustules per leaf.
"Last week we found rust in the monitoring plots at the Edisto Research and Education Center. Once again, it was early planted Deltapine 5634 RR that had almost shed all of their leaves. In this field, the rust was present on about 30 percent of the leaves and typically had 15 to 30 pustules per leaf. Also at the Edisto R.E.C., the field where we originally found rust has defoliated in part due to rust and to a large part due to extreme drought.
"In the Calhoun County field where rust was detected three weeks ago, the rust has progressed slightly. In samples taken by Calhoun County Ag Agent Charles Davis, rust was now present on about 20 percent of the leaves, but still only a few pustules per leaf. This field is currently R-6.
"Charles Davis also has our first find of rust on kudzu. This patch was within the St. Matthews city limits. The infestation is relatively light: one leaf out of 20 with only one pustule."
Spray recommendations for South Carolina growers:
"Most of South Carolina is still undergoing a drought. Yields have been cut severely, and in some fields, many plants have dried up. All of the rust we are finding is on soybeans that would normally be senescing. Unless in spite of the drought you have young, healthy soybeans, spraying for rust is not warranted. It should only be considered if your young, healthy beans are next to or near a field where rust has been identified.
"I do not believe that rust is causing yield losses in the fields where we have seen it. However, it is evident that rust was capable of moving into South Carolina and spreading. If we had not had this severe, extended drought, I believe we would have had numerous fields in which, if left unsprayed, rust would have developed and caused yield losses."
On the SC state commentary today, Moeller added that as of October 4, most of the crop is within two to three weeks of leaf drop. This process has been greatly accelerated by the drought, he said, which has occurred almost statewide since September 1.
Sources: www.sbrusa.net and the South Carolina Soybean Rust Note e-mail from Clemson University, October 4, 2005.
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