Late blight is one of the most devastating diseases for potato growers. One infected plant in a field is enough to spark an epidemic. If left uncontrolled, and weather conditions favour disease development, late blight can devastate a potato field in one week or less.

Late blight typically arrives after flowering when the weather shifts toward cooler mornings, heavy dews, and prolonged leaf wetness. Making two preventative applications of Orondis^® Ultra fungicide after flowering can help prevent late blight and protect new growth.

How Orondis Ultra works

Orondis Ultra brings two highly effective modes of action together for powerful residual control. It combines mandipropamid (FRAC Group 40) with oxathiapiprolin (FRAC Group 49), a unique active ingredient that delivers highly effective residual protection against all known strains of late blight (Phytophthora infestans).

Once applied, Orondis Ultra provides translaminar and acropetal activity, meaning that it moves across the leaf surface as well as upwards into new growth via the plant’s xylem, or water-conducting vessels. Both modes of action work in tandem to protect the plant – even while it’s actively growing.

Mandipropamid and oxathiapiprolin both bind tightly to the waxy layer of the leaf surface (1) and flow steadily into the leaf tissue (2), where they provide disease protection on the upper and lower leaf surfaces.

Oxathiapiprolin moves through the xylem (3) – the plant’s water conducting vessels – and moves upward and outward (4) to protect the plant as it grows.

Control throughout the disease cycle

Orondis Ultra prevents the release and germination of zoospores and sporangia. It inhibits late blight infection by targeting a binding protein that’s essential to fungal development.

The diagram below shows where oxathiapiprolin (purple) and mandipropamid (blue) work on preventing late blight infection.

Because Orondis Ultra is taken up in the plant, it will not wash off in the event of a rainfall. This rainfastness, combined with the length of control, provide excellent application flexibility when less-than-ideal weather is an issue.

Application tips

Orondis Ultra must be applied preventatively, prior to late blight infection in the field, for highly effective protection at low use rates. If you see disease in your field, do not use Orondis Ultra.

Other considerations include:

• Begin applications prior to disease development and continue on a seven- to 14-day spray schedule.
• To manage resistance, apply a maximum of one Orondis Ultra treatment for every three applications targeting late blight in your potatoes. Do not apply back-to-back sprays of Orondis Ultra or follow an Orondis Ultra application with an application of Revus^® or any other Group 40 fungicide.
• Apply 400-600 mL/ha (162-243 mL/ac). At the mid-rate (200 mL/ac), one case of Orondis Ultra will treat 75 acres.
• Use a higher rate and shorter interval when disease pressure is high.
• Orondis Ultra has a 14-day pre-harvest application interval.

Remember: Orondis Ultra must be applied preventively. If late blight is present, do not apply Orondis Ultra; use an alternate solution.