By BASF

A common question that comes up every season is what kind of fungicide should I use, a “preventative” or “post infection” fungicide? While there are many factors that go into this decision, understanding how disease sets in can and the differences in preventative and post infection can help.

Unlike weeds, when a fungal pathogen lands on a leaf and begins infection, it is not noticed until a lesion has formed. This period of time is known as the latent period; the disease is present in the plant, but symptoms of the disease are not yet visible. Depending on the disease organism, the latent period may last as little as a few days or as much as a few weeks. All corn and soybean diseases have a latent period and can cause destruction before you can spot a lesion. Here is a list of several diseases and their latent periods:

• • Frogeye Leaf Spot: 7-10 days
  • Target Spot: 8 days
  • Southern Rust: 7-10 days
  • Tar spot 14-20 days

However, once lesions are visible they CANNOT be removed.

“Preventative” fungicides, when applied prior to fungal spore germination, prevent the disease from penetrating the leaf. This means infection cannot begin and lesions are not formed! A planned, proactive fungicide application provides greater protection from disease than a rushed, reactive application.

If lesions are present, a “post infection” fungicide can help. These fungicides, once applied, can stop early growth of the pathogen (colonization) in the plant tissues. Post infection fungicides are only able to stop disease development within 24-72 hours after a fungal spore penetrates the leaf. At this point, the presence of disease is still not visible to the naked eye. Even though lesions might be present, the development of more lesions is stopped.

BASF Plant Health fungicides include Veltyma™ and Revytek™, which contain both preventative and post infection active ingredients. Whether you find yourself in a “preventative” or “post infection” situation, know that a BASF Plant Health product will aid in both situation in to your corn and soybeans this year.