For many foliar diseases, growers take a see-it-and-spray approach. But when it comes to target spot, they can’t afford to wait. As soon as they see signs the disease is coming, they should head to the sprayer.
And with confirmed reports of target spot in northeastern Arkansas this season, growers should already be thinking ahead to next year to prevent the disease from appearing again.
Because target spot can devastate fields in just weeks, waiting to find the signature circular lesions could mean it’s too late to stop the disease from progressing.
Proactive planning and fungicide applications have been the most effective ways of controlling target spot as it spread throughout Delta cotton and soybean fields during the last five years.
Four points to take into account:
#1. Timing is critical.
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 time frame of when the disease is likely to emerge.
Target spot overwinters in soil and crop debris, and it 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 in which there was no sustained cold to kill the disease. Continuous soybeans or cotton can also increase inoculum in a field.
#2. Keep an eye on current weather and environmental conditions.
Another reason the disease can be such a problem is that 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 frequently or on less ground to try and slow disease progression.
Depending on the weather, the disease typically shows up mid-to-late growing season. The disease thrives in hot, wet conditions; the higher the humidity, the higher the chance of target spot.
# 3. Don’t underestimate the importance of scouting.
For the best scouting approach, out into the middle of a field, where there’s little airflow and humidity is greatest. That’s the recommendation of Ryan Bane, BASF Innovation Specialist in Arkansas.
Also, 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.
#4. Consider a fungicide application.
Timing is critical, but making a good application can go a long way toward improving control. On both soybeans and cotton, Bane suggests making one application with the company’s fungicide, Priaxor.
On soybeans, a rate of four fluid ounces per acre delivers protection until the plants stop vegetative growth, Bane notes. But since cotton plants keep growing and producing, he has increased the rate to six fluid ounces per acre to help extend control.
If the disease persists, growers can follow up with a second application. He also advises using 15 to 20 gallons of water per acre when spraying. “The more water, the more penetration, because we can only protect the leaves that we get the fungicide on,” he emphasizes.
“Among most of the growers I work with now, we proactively spray,” says Bane, who has seen great results. BASF studies have shown that Priaxor can help control target spot and prevent yield losses. And target spot can do a number on yield, wiping out 15-20 bu/acre in soybeans and as much as 400 lb/acre of lint yield in cotton.
The fungicide delivers additional plant health benefits, he adds, including increased photosynthesis, increased nitrogen use efficiency and improved stress tolerance, helping crops keep producing yield while withstanding the stresses disease can impose.
