Stamp out root rots

The sudden appearance of Phytophthora in greenhouse production can spell disaster for growers. The disease is most often seen during the summer months, but can get going in spring and appear late in the fall, says Ann Chase, owner of Chase Agricultural Consulting. Chase performs plant pathology research, diagnostics and consulting.

“It’s sudden and deadly, so prevention is the key to control,” she explains.

A strong preventative program should start just as hot weather hits, she says. Recycling water greatly increases the risk of Phytophthora, she adds. In the greenhouse setting, scout often and remove dead plants.

“With Phytophthora, infected plants can collapse overnight,” she says.

Pythium can also be a serious issue for all growers, “but it is the opposite of Phytophthora and many times sneaks up on growers,” she warns.

Signs of Pythium include irregular growth, wilting, yellowing — especially lower leaves — and stunting.

“Plants can recover from Pythium but rarely recover from Phytophthora,” she says.

For a soil-borne disease control program, apply broad-based fungicides like Segway O, she says.

“Many of the other fungicides labeled for Phytophthora and Pythium only work on Phytophthora,” Chase says. “But Segway O is very effective for both of these oomycete pathogens. Other very effective fungicides for Pythium and Phytophthora include FenStop and Subdue Maxx.”

Segway O contains the active ingredient cyazofamid, making it “an invaluable alternative to commonly-used fungicides where widespread resistance to the water mold diseases has developed,” says Carlos Bográn, OHP’s manager of technical services.

“As the only product from MOA 21, Segway O is an excellent choice for resistant strains of Pythium and Phythophtora on ornamentals and now greenhouse-grown vegetables and herbs,” he says.

In late July, OHP announced the expansion of the Segway O label that allows the product to be used for control of Pythium, Phythophthora and downy mildew on certain greenhouse-grown vegetables and herbs transplants.

Segway O also offers a pre-harvest interval of zero days.

The recent label expansion falls in line with growers adding food crops to their rotation. The COVID-19 pandemic and subsequent quarantine boosted the market for home-grown vegetables and herbs.

“The broadening of the greenhouse market has included many vegetables and other herbs. Large container production of crops like tomatoes and peppers has really increased in the ‘ornamental’ operations I visit,” Chase says.

Historically, herb growers have experienced problems finding products labeled for rosemary and lavender, she adds.

“It has been hard to find materials labeled for these crops even when they are produced as ornamentals,” she says.

Anyone adding basil to their production schedule will appreciate the label expansion.

“Basil downy mildew has become quite an issue in recent years and Segway O provides greenhouse herb growers another option, which is important,” Bográn says.

Even with effective products like Segway O, growers “should always use products from different chemical classes with different modes of action,” he says.

When it comes to proper chemical rotation to prevent Pythium and Phytophthora, Chase created a table for growers to reference (see above).

“If you are trying to prevent Pythium and Phytophthora you should rotate materials in the lower half of the table including FenStop, Segway O, Subdue Maxx and Terrazole (or Truban). The P07 products can do an excellent job on both pathogens, but trials have shown control of Pythium only 50% of the time. Using a rotation of two different FRAC groups is sufficient for resistance management,” she explains.