Know your mites

 Appearing from seemingly out of nowhere, broad mites descended this year upon Casa Verde Growers in Columbia Station, Ohio, resulting in what section grower Jen Kolenc calls “broad mite apocalypse 2017.”

“By and large, I don’t see mites in here, and I certainly haven’t seen broad mites to this extent in my entire tenure,” she says. “I spent four springs here at Casa Verde, and then I did three years over at Heartland Growers in Indiana. I never saw broad mites like this.” Usually, Kolenc doesn’t spray miticides, but that has changed this year.

Broad mites and other tarsonemid mites, such as cyclamen mites, wreak havoc on growers all over, as do spider mites. However, their attributes and the problems they present differ.

Tarsonemids are microscopic — less than one-one hundredth of a millimeter — and require a microscope to be seen, says Dr. Raymond Cloyd, professor and extension specialist in horticultural entomology and plant protection at Kansas State University. Two-spotted spider mites, within the tetranychid family, are roughly two to four millimeters in size and can be seen with the naked eye.

The two mite types often feed on the same crops — such as gerbera daisies — but they feed on different parts of plants, Cloyd says. “The spider mites are feeding on the leaves because they need the chlorophyll,” he says. “Broad mites feed on the terminal growth of the leaves.”

Despite their differences, prevention and control of the two mite families are comparable. Because mites can't fly, growers will not be able to catch them on yellow sticky cards, so they should monitor their plants individually, Cloyd says. “The control is always going to be good sanitation and throwing away plants that are heavily infested,” he says. “That’s probably the best thing. But it takes also preventative action — scouting, looking for damage — and if you see it, determining if it’s broad mite. If it is, you may have to spray with a miticide — and the same for spider mites — there are a number of miticides that you can spray for both.”

One of those miticides is Akari, a contact miticide from SePRO, which contains the active ingredient fenpyroximate. In addition to controlling tarsonemids and tetranychids, Akari also controls eriophyid mites, and suppresses mealybugs and whiteflies.

Several years ago, Cloyd tested Akari on tetranychids, and he was pleased. “We did get some positive results with high mortality of two-spotted spider mites,” Cloyd says.

Spider mites

This year, Julian Figueroa, facility manager and grower at one of Riverview Flower Farm’s three locations in Seffner, Fla., has sprayed Akari to successfully control spider mites. “So far, we don’t see any insect population growing after the spray,” Figueroa says. “We were trying to control some whiteflies and a few mites that we have in some areas, and after the spray, we didn’t see anything.”

Figueroa has worked at Riverview, which has about 12 acres of undercover space, for one year, but he has worked in other greenhouses and says mites are consistently an issue. At Riverview, the mites appear mainly on pentas and lantana, but also on others, such as Cuban Gold.

In a mist blower with a three-gallon capacity, Figueroa says he uses three ounces of Akari, and sprays it over about one acre of production space. He uses Akari in a rotation with chemicals from different IRAC groups. So far this year, he has sprayed the miticide in the first week of February and the first week of June.

Almost every day, the growers at Riverview’s Seffner location scout for insect damage on the greenhouse’s crops, Figueroa says. “They know the insects and everything, so if they see something that I don’t see, they just tell me right away and we figure out right away how we’re going to treat it,” he says.

Broad mites

At Casa Verde Growers, which has about 24 acres under plastic and glass, employees walk through the greenhouse two or three times a day to look for insects, Kolenc says. She recalls stumbling across spider mites spinning webs on eggplants. “I’m like, ‘Oh, you jerks! You jerks!’ Kolenc says. “I was like, ‘All right, go get the miticides.’”

Despite run-ins with spider mites, much of Kolenc’s pest control in 2017 has been focused on broad mites. She sprays Akari in a rotation with four other miticides from different IRAC groups. “Usually, earlier in the spring, I’m spraying for sucking insects about once a week, and then when we get into this time of year when things are little bit more serious, the pest population is a little higher, I’ll go two times a week,” she says. “Now it’s just adding miticide.”

Graphic information courtesy of Raymond Cloyd

Casa Verde Growers’ propagation department frequently tank-mixes many miticides, insecticides and fungicides and sprays their plugs and cuttings, so everything is pretty clean by the time it comes to the finished grower side of the business, Kolenc says.

“I would say with the Akari and with the rotation, we’re starting to see them knock back now,” Kolenc says. The dahlias seem to be the main target. “Between when we saw damage, cut them back, sprayed them — I would say it probably took three to four weeks before we saw a complete recovery where we went from absolutely not saleable to mostly salable,” she says.

—Patrick Williams

Main image: Two-spotted spider mite damage on a clematis leaf; Photo: Raymond Cloyd