Southern Rust Is On The Scene
GREG PFEFFER
DEXTER, MO.
A grower told me the other day that this year he just had to throw the book out of the window because nothing went according to plan. Surprisingly, there are some good looking crops out there despite all of the various issues. There are also plenty of things to look out for, including southern rust.
Southern rust has shown up in corn from Louisiana all the way to the northern part of the delta in Southeast Missouri. It seems that the crop is a couple of weeks behind normal, so a disease of this nature could potentially have a greater impact upon the crop than normal in the north delta.
Southern rust is characterized by the small bright orange pustules that colonize the upper part of the leaf. Southern rust pustules will primarily be limited to the upper side of the leaf, while common rust lesions will extend through to the bottom side of the leaf.
Southern rust is favored by frequent leaf wetting and higher temperatures. Given the right conditions, southern rust has been known to kill corn within days of infection, and can cause yield losses due to decreased grain fill or lodging.
Scouting for the amount of field infection can be difficult but I do recommend scouting as opposed to making blanket applications in most situations. I recommend looking in various places in the field after a “hot spot” area of rust has been found. If another “hot spot” is located, then there likely will be other areas of spore deposition in the field and thus the field would need to be treated with a fungicide.
The consensus of the DuPont Pioneer agronomists in the delta for treatment of southern rust in corn is that corn should be protected with a fungicide until 50 percent milk line if the grower plans to harvest early and grain dry the corn. Any corn fields that growers plan to let field dry would need to be treated until 75 percent milk line. Most of the yield loss prevention past 50 percent milk line would result from better harvestability due to decreased lodging. ∆
GREG PFEFFER: Agronomist for Pioneer, Dexter, Missouri