Thin stalks with large heads — it’s a challenging combination for grain sorghum farmers, like Nick Zenger, embarking on the long-awaited fall harvest.
With great anticipation in his heart, yet sharp eyes on the pivotal season of rapidly changing weather on the high plains, the 60-year old Zenger of Cuba, Kan., is daily monitoring his field of autumn-red grain sorghum, also known as milo.
However, Zenger and many other grain sorghum farmers are also currently mulling over a double concern — noticing some of the sorghum leaning, or falling over, known as “lodging,” yet also anxious to let their sorghum sit a few extra days for greater drying.
“It is falling over in places,” acknowledged Zenger, who also shared his greater concern. “If we happen to get the wrong kind of weather — too much wind or even ice — it’d break over.”
It’s recommended that farmers harvest their grain sorghum as soon as possible, since it’s reported to be lodging, which, in many cases is also due to stalk rot.
“Yes, we suggest getting it out of the fields, as soon as it dries down enough to harvest,” said Kim Larson, a Kansas State University crop production extension agent, with the River Valley Extension District in Concordia, Kan. “Although the issue of grain sorghum lodging is spotty in fields now, as time goes on — more sorghum plants will likely lodge. It’s not necessarily the whole region, but when I’ve gone out to examine fields in my area (north central Kansas), any fields that had lodging issues, have stalk rot.”
Stalk rot causes yield loss, because it causes the plant to die prematurely. This reduces grain fill time.
Estimates are that at least five-percent of the sorghum crop is lost each year to stalk rot. The incidence of stalk rot in individual fields may possibly reach higher percentages. There may also be yield losses which may not be noticed.
Early maturing hybrids are generally more susceptible than full-season hybrids.
Experts say stalk rot is a stress-related disease, and that any stress on a crop can increase both the occurrence and intensity of stalk rot.
Larson points to research that indicates, that when the carbohydrates used to fill the grain become unavailable due to a soil nutrient shortage — or other issues occur, such as drought stress, leaf loss from insects, hail, disease or reduced sunlight — the plant then uses nitrogen and carbohydrate reserves, which are stored in the stalk, to conduct the grain fill.
This loss of nitrogen and carbohydrate reserve then weakens stalk tissues and results in increased stalk rot susceptibility.
“This year — we had that hot, dry period early in the summer, and that weakened the plant’s defense against the disease,” said Larson. “Drought doesn’t cause it, but it needs rain or irrigation. So, when you get periods of dry weather, it weakens the plant’s defense against the disease. In my area of north central Kansas, we are seeing potentially good sorghum yields. However, due to the poor growing season during vegetative growth early on, we’re seeing weaker and smaller stalks. And, our stalk strength is likely having a difficult time supporting those heavier heads anyway. If we get high winds or a heavy rain, I project that more will be falling over.”
“It’s disappointing, that although we have good sorghum yields, the combines may have a difficult time picking it up and getting the grain out of the field due to severe lodging in some areas,” Larson added. “So, we may not get the yield that we should’ve gotten, because we just can’t get it out of the field, if it’s lodging.”
Zenger, who’s been farming since he was in grade school, drove three miles north on a dirt road to examine his vast grain sorghum field. As he surveyed his 70 acres of sorghum, the Kansas farmer noted, he plants the crop about every other year. Zenger also farms an extensive field of corn, as well as wheat, some soybeans, and has a cow-calf herd in north central Kansas.
“In drier weather, grain sorghum can last a little longer than corn,” observed Zenger, “Although as far as spraying, we’re able to spray shattercane in the corn more than milo. In corn, you can spray it, but in milo, you can’t.”
Checking the Grain Sorghum
“If your stalks are still standing, and you squeeze the bottom of your stalk and it’s squishy, there is likely stalk rot, and you want to get it out of the field as soon as possible, to prevent the issue of lodging,” Larson recommends. “If they’re firm, then switch your harvest priority to any fields that do have stalk rot. Harvest fields with stalk rot issues first.”
She says stalk rot may affect grain yields to some extent, since plants with stalk rot would probably die about two weeks earlier than expected.
How To Check Grain Sorghum
“In your fields, take a knife and split the grain sorghum open at the base of the stem. If it has stalk rot, the inside of the stalk will appear shredded. The most characteristic symptom of stalk rot is the shredding of the internal tissue in the lowest internodes of the stalk.”
Colors of Stalk Rot
This shredded tissue may be tan colored (Fusarium stalk rots), or red or salmon-color, (Fusarium and Gibberrella stalk rots), or grayish-black (Charcoal rot.) The inner stalk might be gray or black discoloration; caused by the reproductive structures of the fungus.
Regarding each of these rots, if there are dry conditions early in the season, and poor nutrient uptake by the plant (nutrients being pulled up into the plant,) Larson attributes these factors to the stress that increases the chance of stalk rot.
“That’s what we had here this year,” Larson acknowledged. “The rain that we did have came fast and hard, and potentially leached the nitrogen out of the soil.”
Future Planning and Planting
“There are not any hybrids out there that have complete immunity to these pathogens, so when you’re selecting your milo or sorghum hybrids, look for those that not only have good yields, but also good stability in what’s called “stay green” characteristics,” Larson suggested. “If stalk rot does get into that stalk, the plant will have a lower chance to lodge quickly, because it would have a stronger stalk.”
Larson says the disease is likely present in some fields, but suggests you can rotate the fields, so it doesn’t have a host (field) every year.
“Crop rotation is good to reduce the severity of stalk rot,” she recommended.
Experts also advise that a good insect control program is a must to limit any losses to stalk rot. Pathogens may enter stalks or roots through wounds created by insects.
Another recommendation is nutrient management. Larson emphasizes the importance of having a solid nutrient management program in place.
Zenger, meanwhile, is watching his field of dreams ... like a hawk.
“Just as soon as the moisture drops, we’ll start harvesting the milo. Hopefully within the next two weeks,” said Zenger. “Then, as soon as corn is dry, that’s next.” ❖