Tar spot has already been confirmed in nine Iowa counties, and crop protection specialists say its early appearance should have corn growers thinking about disease management well before symptoms become widespread. While much of Iowa’s corn crop has benefited from favorable growing conditions this season, those same conditions have also created an environment where fungal diseases like tar spot can establish themselves early.
According to Nate Quam, Technical Service Representative with BASF, this year’s first detections came at nearly the same time as last year, continuing a trend of earlier disease development. That means growers should already be evaluating their fungicide plans rather than waiting until visible symptoms become widespread across their fields.
One of the challenges with tar spot is that infections often begin well before growers realize the disease is present. By the time the familiar black lesions appear on corn leaves, the fungus has already been developing inside the plant for weeks. That makes routine scouting and monitoring disease reports especially valuable during the early part of the season.
Quam recommends growers keep a close eye on regional disease reports, including the Crop Protection Network’s disease tracking maps and reports from university plant pathologists. Those resources can help producers understand where tar spot is being confirmed and provide another tool when making fungicide decisions.
While every field presents different levels of disease risk, having a treatment plan in place before tasseling can help producers avoid delays if disease pressure increases quickly. Fungicide applications are generally most effective when made at the proper growth stage rather than after significant disease symptoms are already widespread.
Quam says growers considering more intensive disease management programs should work closely with their local agronomist or BASF representative to determine the most effective application strategy for their individual fields.
