“The last couple of years have been interesting in terms of watching the problems with target spot develop in soybeans,” says Jason McGee from his combine cab. Around Weiner, says the northeast Arkansas farmer and consultant “it hurt a number of fields last year. This year, some growers started picking it up around mid-July.”
McGee and fellow consultants began asking questions. “It’s kind of weird because most of the data out of university literature kind of brushes it off, says its impact isn’t that great. But a lot of that work was done back in the 1960s and 1970s and I don’t know how relevant it is for today.”
Consultant Rick Thompson also works the northeast part of the state – predominantly the counties of Poinsett, Cross, Craighead and Mississippi. The problems with target spot “seem to be worse on the west side of Crowley’s Ridge but I think that probably has more to do with planting date.”
At first, Thompson thought finding so much target spot was a fluke. “Cotton producers have been seeing it show up and they’ve seen an uptick. You can just drive down the road and see some of these cotton and soybean fields that have lost their skirt. If it’s early enough in the year, of course, that points to problems.”
The men have seen target spot for years “but it always was in the same category as brown spot and never seemed to be a big problem,” says Thompson. About three years ago, “it began moving a little but not an alarming amount. Last year, though, a few fields were hurt with it – maybe a hit of 15 bushels, or so -- and that was a precursor to some serious problems this year.”
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Where is it most likely to occur? “The well-managed fields watered down the row, May plantings, are the ones that seemed to be harmed most,” says Thompson. “We saw it this season on flood-irrigated fields, as well. Add rainfall on top of the canopy and that seemed to encourage the disease.
“Last year, I didn’t see it on furrow-irrigated fields and we don’t have much pivot-irrigated so can’t comment on that.”
McGee agrees that as the disease progressed rapidly through July it seemed to be worse the more intensely a field was managed. “If you watered aggressively, especially down the row, it seemed to set the fire to defoliate the crop from the bottom up. That really worried some of us.
“We chose to spray a lot of the fields (with a fungicide) relatively early. In hindsight, I’m glad we did.
“It’s just very aggressive in some of the Group 4s. I don’t fully understand all the factors in play. Our crop management practices are a little different than they used to be. That could be a factor along with a degree of susceptibility in some of the lines that we underestimated. If you coupled a susceptible variety with intense management, it jumped up quickly.”
During a hot summer, “guys like me who water down the middles may be irrigating every week or eight days,” says McGee. “Well, if you look at the old data sets they say you need periods of high humidity to make target spot go. I feel we may be creating that environment for the disease. That may be why it was a bit underestimated this season. You had high humidity naturally and then bring in the extra humidity from intense irrigations.”
Thompson readily admits observation is the only factor in his belief but “from what I’ve seen there are varietal differences. If it continues to be a problem, I think we may need to consider some shorter-type varieties. There may be some taller varieties that show some resistance – if so, great.
“Let me make it clear that I’m not an expert but am just asking questions. I do think there is some susceptibility in some varieties just like there is with sheath blight in rice. It reminds me a lot of sheath blight where it starts at the bottom of rice plants and then blows out the top.”
Many growers don’t even know they have target spot in their soybeans, says Thompson. “But some fields got bad enough that you could see it climbing up the crop. You have to be paying attention and sometimes that isn’t as easy as it sounds. It’s amazing how fast target spot can move in a week’s time. If it gets going at the right time, then rain falls and stays cloudy, it’ll go wild.”
Target spot has “really hurt” a lot of acres, says McGee. “For affected fields, I think it probably took out 10 bushels for the April plantings. Get to May and June planting dates and yields may have been cut in half – some losses have been very severe.”
In many cases, the April plantings “kind of outran” the target spot. “If you didn’t get the crop in until later, you might have paid a heavy price,” says McGee. “I’m very aware of fields that should have cut 70 and 80 bushels and didn’t cut but 55 bushels. There are also may-planted fields that should have cut 65 bushels that are, unfortunately, cutting in the 30s, or below.”
McGee, who works predominantly in southern Poinsett County and the Cross County area, is on board with those saying there are “definitely varietal differences with target spot. Guys in the field weekly are seeing some varieties that tolerate target spot better than others. Now, of course, that’s just eye-balling the situation for a year. It’s just hard to get a firm grip on it and I’m not saying this has been measured in a scientific manner. I know what I saw, though.”
No rock chucking
Next year, there are some varieties McGee will shy away from. “Guys in certain circles are saying the same thing, making notes about how certain varieties did. I’m not chucking rocks but there are definitely varietal differences with regard to target spot. We’ve turned something loose in some of these Group 4s.
The good news, says McGee, is “based on what I saw this year, target spot is a controllable disease. (BASF fungicide) Priaxor shut it down but it has to be applied early enough.
“I was called into a lot of fields late. So, if you plant susceptible lines, you need to be scouting around R3. Make the fungicide decision early and realize you’ll probably get about three weeks of protection. You may need to put another fungicide out, especially where irrigation wells are being fired up frequently.”