Frequently Asked Questions About Flint

Over the past few weeks there have been a lot of questions about FlintÒ (trifloxystrobin), a new strobilurin fungicide from Bayer Crop Sciences that just received registration in apples for scab, powdery mildew, fly speck, sooty blotch and cedar apple rust. Flint is in the same chemical family as Sovran and should be used in rotation with other chemistries such as EBDC's (Ferbam, Zineb, Dithane, Manzate, Polyram, Penncozeb), sterol inhibitors or demethylation Inhibitors (Nova and Nustar), and phthalimides (Supra Captan and Maestro).

Like Sovran, Flint is absorbed and retained in the waxy cuticle of leaves and fruit. These products redistribute well within a leaf or fruit; however, they do not move systemically through the leaf or the plant via the sap stream. There is some redistribution of Flint on the leaf surface following an application; however as the leaf grows, the leaf surface that is not covered by Flint will not be protected from diseases. Also, leaf tissue that expands after Flint has been applied will not be protected either.

Flint is rainfast after just 2 hours. No pH adjustment is necessary if the spray is applied immediately. However, if the product is left in the tank for a few hours, the spray mixture should be buffered to pH 7. The buffering must be done at the time the spray mixture is prepared.

Unlike the SI fungicides (Nova and Nustar), the strobilurin fungicides are excellent inhibitors of spore germination and therefore they are excellent proctectant fungicides. Flint has good kick-back activity on apple scab, but no kick-back activity on the other diseases on the label. For apples, the labeled 175 g/ha rate allows for up to 72 hours kick-back under moderate to heavy disease pressure and up to 96 hours kick-back under light disease pressure. For curative applications, a disease forecasting system should be used, and a second application is required within 7 to 10 days. The kick-back activity period starts at the beginning of the infection period.

FLINT works best preventively; however, if curative applications are necessary, they should be made soon after an infection period when the leaves are mostly dry.

Researchers in the US have shown that in orchards where DMI (Nova, Nustar) resistant scab is present, strobilurin fungicides lose their kick-back activity on apple scab. Although loss of control of apple scab due to increased DMI resistance has not been documented in Ontario, growers should be following resistance management strategies to avoid the development of DMI resistant scab. These strategies include rotating chemistries, preventative application of fungicides, use of full label rates and excellent coverage of leaves and fruit.

OMAFRA Pub. 360 recommends that Flint should be applied preventatively at 140 g/ha at 7-10 day intervals, depending on the weather and disease pressure. The label rate ranges from 140 to 210 g/ha, depending on the pest. Under high disease pressure or for kick-back activity (scab) the higher label rate should be used. Reports from New England researchers suggest that both Flint and Sovran are rated as only "fair" in terms of efficacy against cedar apple rust. If you have susceptible cultivars, moderate to high inoculum pressure, and conditions favorable for cedar apple rust and quince rust infection, you should not rely on the strobilurin fungicides for rust control. If you do use Flint for cedar apple rust (or powdery mildew), the label states that you should alternate it (every other application) with a sterol inhibitor fungicide. (from Disease Management Update to 2000-2001 New England Apple Pest Management Guide, L. P. Berkett and T. Bradshaw, University of Vermont.)

Flint should not be applied using tree-row-volume. Remember that alternating between Flint and Sovran is not rotating at all. To prevent resistance, strobilurin fungicides (Flint or Sovran) should not be used more that 4 times per season and no more than 2 applications in a row.

Unlike other strobilurins, Flint is not phytotoxic to cherries.

Related Links

• Disease Management Update to 2000-2001 New England Apple Pest Management Guide