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Nibblers & Killers
Ever heard of nibblers and killers? Anyone who has heard Wayne Pedersen, retired Extension plant pathologist from the University of Illinois, discuss corn and soybean diseases, sure has. He talked about them at a Syngenta Seed Care field day earlier this month in Brookings, South Dakota.
Nibblers in corn and soybeans include diseases like Pythium, Rhizoctonia, and Fusarium. Pedersen’s moniker for these is correct. These diseases feed, or nibble on root tips.
Nibblers have more of an impact now than decades ago. “In the 1980s, when you had 160 bushel (per acre) corn, nibblers were not as important,” says Pedersen. Now, with farmers pushing for 250 bushel per acre-plus acres, every root and root hair is important in maxing out those yields, he notes.
“Killers” are those diseases that, well, kill plants quickly. They include phytophthora in soybeans and Pythium in corn and soybeans.
So how do you deal with them? Since Pythium thrives in wet soils, tiling is a good start, says Pedersen. Seed treatments that deter early-season diseases also are key to reducing its incidence. No known resistance to Pythium in soybean varieties yet exists, says Pedersen.
Rhizoctonia root rot tends to be more common under warm, dry conditions. It doubles both as a nibbler and killer. “It reduces root hairs and fine roots, and reduces water uptake by the plant,” says Pedersen. “It may also kill seedlings under severe disease pressure.” Like Pythium, resistance in seed does not yet exist. Seed treatments can curb it, though.
Fusarium is a nibbler, reducing water uptake by attacking root hairs and small roots. Be on the lookout for it following small grains and corn, especially under no-till. There are no known sources of seed resistance. Seed treatments can curb it, though.
Seed treatments work well with early planted soybeans, according to 1997-2009 trials, says Pedersen. Soybeans treated with Maxim and Apron XL planted on April 15-28 had populations and yields of 141,190 plants per acre (ppa) and 60.2 bushels per acre. The populations and yields of untreated soybeans paled to treated ones at 105,490 ppa and 49.9 bushels per acre.
The seed treatment edge narrowed with soybeans planted May 15-22, though, notes Pedersen. Treated soybeans had a population of 165,320 ppa and 51.1 bushels per acre yields. The control group had a population of 160,180 ppa and 51.1 bushels per acre yield.