For a lot of foliar diseases, growers take a see-it-and-spray approach. When it comes to target spot, they can’t afford to wait — as soon as they see signs the disease is coming, they should be in the sprayer.
With a disease that can devastate fields in just weeks, waiting to find the signature circular lesions could be too late. Proactive planning and fungicide applications have been the most effective ways of controlling the disease as it has spread throughout Delta cotton and soybean fields during the last five years.
“Most of the growers I work with now, we proactively spray,” says Ryan Bane, BASF Innovation Specialist in Arkansas.
Bane has seen great results with Priaxor® fungicide. Studies have shown Priaxor fungicide can help control target spot and prevent yield losses. And target spot can do a number on yield, wiping out 15–20 bu/A in soybeans or as much as 400 lb/A of lint yield in cotton. The fungicide delivers additional BASF Plant Health benefits, like increased photosynthesis, increased nitrogen use efficiency and improved stress tolerance that help crops keep producing yield while withstanding the stresses disease can bring.
Knowing when to spray before a disease appears can be tricky, but as target spot has spread, so has the understanding of it. Growers now have telltale signs to scout for, environmental conditions to watch for and a general timeframe of when the disease is likely to emerge.
Target spot overwinters in the soil and crop debris and can survive several years in fallow fields, so areas that have had problems with it in the past are at a higher risk for another infection. That’s especially true after warm winters where there was no sustained cold to kill the disease. Continuous cotton can also increase inoculum in a field.
One other reason the disease can be such a problem is the conditions that are best for growing cotton and soybeans are also best for the disease. Highly irrigated and well-fertilized crops create the perfect environment for target spot. Some growers are watering less often or on less ground to try and slow the disease down.
The disease typically shows up on healthy crops in early July, though that timing can shift depending on weather. The disease thrives in hot, wet conditions; the higher the humidity, the higher the chance of target spot.
“Once we get to the first week of July, if there’s a 10-day forecast and seven of the days it’s going to rain, it’s time to start looking for it and proactively start treating it,” Bane says. That’s usually around first bloom in cotton and R2–R3 in soybeans.
For the best scouting, Bane recommends getting out into the middle of a field where there’s little airflow and humidity is greatest. Growers should make sure to scout deep in the canopy as lesions begin on the low canopy and spread upward, becoming larger as they go. Soybeans can also have lesions on pods, stems and petioles.
Timing is critical, but making a good application can go a long way to improving control as well. If the disease persists, growers can follow with a second application around the third or fourth week of bloom.
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