Every so often a usually innocuous disease like common rust on corn lets farmers know that it still is around, just waiting for the right conditions to multiply. It did that year over much of Indiana, although not everywhere.
"We've seen it in many places, but there are pockets without it," says Dave Nanda, Bird Hybrids, LLC., a long-time plant breeder. "Where weather was warmer, such as in southwestern Indiana, there are fields where you can't find it. However, there you find other things that are far more serious for yield impact, such as gray leaf spot. You find them especially in corn after corn fields."
Common rust typically won't hurt yields in commercial corn. However, it can set fields up for secondary infections of stalk rot later in the season. Those diseases become most serious when plants have been stressed earlier in the ear,. Stalk rots can cause economic yield losses if they cause enough lodging to affect harvest losses. Before the season, the best option is to work with your seedsman and pick hybrids with good diseases protection packages, including protection against major stalk rots. The best remedy for stalk rots at this point in the season is to carefully scout fields, and mark those with an increasing amount of stalk rot for early harvest. That's likely to be at higher moisture contents than you like, given the high cost of fuel. But the trade-off this year will boil down to leaving valuable corn in the field, or paying more to dry more bushels that you can save by harvesting early. Ag engineers say that one normal ear every 175 feet of row left behind on the ground can amount to one bushel of lost yield per acre. So just one ear could mean $5 or more, depending upon what price you contracted corn fro during this marketing season for the '08 crop.
Rust is more of a problem in seed fields. Those fields are usually hit with fungicides in many years, and are a good testing ground for various fungicides. This year rust is one of the disease organisms that seedsmen needed to control.
"Sweet corn is also very susceptible to rust," Nanda says. "It's so susceptible that when I was doing active breeding work, I would often grow sweet corn as a trap crop to attract rust.
"I've been in sweet corn patches already this year where the rust is so intense that the leaves literally look rusty. Some varieties of sweet corn are much more susceptible to rust than others."
Fortunately, he notes, rust on sweet corn doesn't affect one's ability to harvest the ears for use. "And it doesn't affect the taste at all," he quips. Word is it doesn't ward off raccoons either!