WITH THE positive identification of Asian soybean rust (ASR) on soybean plant tissue in Iowa in March, Midwest growers are on alert and in the market for fungicides.

Fortunately, a new fungicide, plus label changes on existing fungicides, will give growers more choices for controlling ASR and other soybean diseases this season.

The new fungicide, Topguard, a member of the triazole family of chemistry, has a strong track record for ASR control in South America, according to Cheminova, its manufacturer.

In addition, it is expected that the labels of four fungicides will be upgraded from Section 18 to Section 3 status: Domark, which is marketed by Valent; Laredo EC, from Dow AgroSciences; and Folicur and Stratego, from Bayer CropScience.

A Section 18 label is an emergency label granted in individual states. It allows use of unregistered pesticides for emergency purposes, in this case for control of ASR. A Section 3 label signifies that the EPA has granted a full registration, which may include a broader range of uses than allowed under a Section 18 label.

The pending label changes, assuming they are granted, will allow some of the fungicides to be used for control of soybean diseases other than ASR, assuming these uses were requested and are included on the approved label. The changes also will allow more flexible application timing for control of ASR, since under Section 18 emergency labels, the fungicides could not be applied until the threat of ASR was imminent.

Topguard

Topguard joins a list of about 20 fungicides that have a Section 3 or Section 18 label for control of ASR in the U.S. Its active ingredient, flutriafol, is the first proprietary chemistry to be marketed in the U.S. by Denmark-based Cheminova, which has focused to date on generic products such as its Glyfos brand glyphosate in the U.S. market. Cheminova purchased the chemistry from Syngenta in 2001.

The fungicide received Section 18 approvals in late 2006 in Minnesota and South Dakota, which have taken the lead in recommending Section 18 labels for ASR control since the disease was discovered in the U.S. Section 18 approvals are expected in other key soybean states by the use season, according to Jim Barrentine, Topguard technical director.

As with other triazoles, Topguard has both curative and preventative or protective activity, he says.

To date, in university and company field trials in the U.S., Topguard has performed at the top of the pack among triazoles, Barrentine says. However, he acknowledges, “we haven't had an outbreak severity to separate out the relative performance of the triazole products,” so control from various products tends to be similar, statistically.

Like other triazoles, Topguard has a relatively low recommended use rate, 7 oz./acre. Two applications are allowed, with a recommended spray interval of 21 days. That's longer than recommended for some triazoles, several of which have recommended spray intervals of up to 14 days, although some have a recommended interval of up to 21 days.

Cheminova says that Topguard has excellent safety to the crop. “We have not had any phytotoxicity at all, no leaf burn, cupping, or any other symptoms,” Barrentine says.

The fungicide will be labeled for mixing with other fungicides, as well as herbicides and insecticides, unless specifically prohibited on the mix partner's label. Use recommendations are similar to those of other fungicides: a carrier volume of at least 10 gal./acre by ground and 5 gal./acre by air, and nozzles that produce medium-sized droplets to maximize coverage. Expect the price of Topguard to be “competitive,” Barrentine adds.

Section 3 labels

Both Bayer CropScience and Valent plan to promote their fungicides for control of a range of diseases, as well as for general improved plant health, if Section 3 labels are granted, as anticipated. Dow AgroSciences will continue to promote its Laredo fungicide solely to control ASR.

Although both Folicur and Stratego control a range of diseases, and not just ASR, Stratego provides especially broad disease-control activity that “usually leads to yield increases in the absence of ASR,” says Randy Myers, fungicide product manager for Bayer CropScience.

Myers notes that Stratego, a combination product, contains a strobilurin, a fungicide class that has been shown to have physiological effects on plants apart from fungicide performance. Headline fungicide, which BASF has promoted for improving general plant health, also contains a strobilurin.

Once its Section 3 label is in hand, Valent plans to emphasize Domark fungicide's ability to control a broad spectrum of diseases, including ASR, frogeye, purple seed stain and brownspot, as well as for maximizing yield, according to Valent's Jamie Nielson.

Janice Smith of Dow AgroSciences notes that a Section 3 label will provide growers more flexibility in how they use the company's Laredo fungicide. Technically, under a Section 18 label, growers are not allowed to make applications until the disease has been identified in an area, or is an imminent threat.

“Our recommendation is the same as in the past, to rely on the sentinel plot system and recommendations from local extension service experts to make a treatment decision,” Smith says. It is too late to prevent yield loss after you visually identify ASR in a field, she adds.

Dow AgroSciences will not be promoting use of Laredo to improve general plant health in the heart of the soybean belt. “In the southern U.S., where diseases other than ASR are routinely prevalent, a planned disease-control program has shown that it pays a dividend,” Smith says. “I call that good integrated pest management. In the north, the jury is still out whether there is an economically significant level of diseases on a regular basis to justify routine fungicide applications.”