Trying to control pests effectively on a wide variety of crops is a major undertaking. Delray Plants in Venus, Fla., has been using biological controls as a part of its pest control program for more than 10 years. It operates 300 acres, which includes covered structures and 7 acres of outdoor field production. The company initially began as a foliage plant grower, but has expanded to produce a diverse mix of crops. Although foliage still accounts for 70 percent of its total production, the company grows an assortment of ornamental flowering plants It has also started an edibles program with containerized berries.
Reducing Spider Mite Pressure
Bill Lewis, grower manager at Delray Plants, says the company’s biological controls program was already in place when he joined the company in 2007.
“With the way that we grow and because of our large production area, trying to achieve adequate spray coverage is very difficult with blow sprayers,” he says. “And the operation is just too big to treat with hand sprayers.”
Delray Plants releases the predatory mites Phytoseiulus persimilis and Neoseiulus californicus for spider mite control.
“Two-spotted spider mite is the biggest issue with the type of plants that we are growing,” Lewis says. “For whatever reasons, under our conditions, P. persimilis works well throughout the year as far as controlling two-spotted spider mite.”
Two-spotted spider mites are particular about their food source, and Delray Plants uses the predators a lot on Croton, one of its biggest crops, as well as on several different palms, including Chamaedorea cataractarum, Ravenea rivularis and Dypsis lutescens.
“Those species make up a third or more of the nursery,” Lewis says. “These plants are brutal about getting two-spotted spider mite. We have found the predators to be the best way to control spider mites, which can be absolutely devastating. They can damage the plants to the point that they are unsalable.”
Predatory mites are usually released every two weeks at the operation, distributed at a rate of one per square foot of production area in those crops that are most susceptible to two-spotted spider mite.
“Our first choice is to always use P. persimilis,” Lewis says. “We also use this predator on Hibiscus, which is a year-round crop, depending on demand. We release P. persimilis in up to 40 percent of the nursery.”
Lewis constantly monitors the weather because it can have a major impact on spider mite populations.
“There may be a window in the year when we can skip a week of releasing the predatory mites because the weather has been cool, like during the winter months,” he says. “Two-spotted spider mites thrive in dry and warm conditions. April and May are typically the highest pressure months for two-spotted spider mites. They are also more active during October and early November when it is warm. During the heart of the winter when the greenhouses are covered up, typically we don’t have as much pressure because it’s cooler and more humid.”
Getting Tough On Mealybug
After spider mites, mealybug is the next pest that can have an impact on plants, and Delray Plants has tried various controls for the pest.
“We are currently using the OMRI-listed SuffOil-X horticultural oil as a spray,” Lewis says. “It has a four-hour re-entry period. Since it’s nonselective, it will kill what’s on the plants, so we have to time its spraying in sequence with the release of the beneficials.”
Preventing Banana Moth Infestations
Delray Plants applies the beneficial nematode Steinernema carpocapsae (Millenium) on its Dracaena crops, including D. fragrans ‘Massangeana’ canes and D. marginata. This beneficial nematode is applied specifically for the control of Opogona sacchari (banana moth/rotten sugar cane borer).
“There is no evidence of the pest until the damage starts to appear a couple of months into the crop,” Lewis says. “We apply the nematodes preventively so they are there when the eggs hatch, and they will attack the larvae. It’s very difficult to control the larvae once they bore inside the dracaena canes. The most susceptible time for the canes is after we receive them, whether they are brought in from offshore or area propagators. We treat all of the canes whenever we do new plantings.
Once the canes are rooted in and established, there is a minimal chance that they are going to be infested with Opogona sacchari.
When applying nematodes, as long as the growing medium stays moist, they can live for months, and they’ll remain dormant until they detect that a food source is present, Lewis says.
Attacking Fungus Gnats Early
The beneficial nematode Steinernema feltiae (Nemasys) is used to control fungus gnat larvae. Lewis says fungus gnats are usually a problem in moist environments like the mist propagation house.
“The fungus gnat larvae can cause root damage to propagation material,” he says “We monitor the plants to see if we are having any issues. The damage caused by the larvae can open the door for disease pathogens to come in.”
Delray Plants uses the nematodes on a variety of crops, including palm seeds that are germinated in the mist house, Lewis says.
“We propagate these during the cool season using bench heating to accelerate the germination time and to increase the germination percentage,” he says. “That environment is perfect for fungus gnats.”
Alternative Controls To Beneficial Insects
Delray Plants’ philosophy is to use beneficial insects or mites as the first control tool depending on the pest.
“Our second choice would be a biological-based pesticide, something like Dipel or Botanigard,” he says. “Sometimes we do have to use traditional insecticides. We rotate the modes of action and use those products as sparingly as possible. These are used only when we are trying to control something else outside of two-spotted spider mites.”
Scouting Is Critical
Being in a humid, subtropical climate, Lewis says Delray Plants also has to deal with a variety of pests.
“The biological controls are effective and this program works very well for us, he says. “There was quite a long learning curve using the biologicals. Since we can have problems with other pests, we have to be very careful about any of the control products we use in the P. persimilis release areas. We have learned through trial and error what those products are that can be harmful to the beneficials.”
Delray Plants does not use calendar sprays applying at specific time intervals throughout the year. Lewis says pest treatments are tailored to a specific crop and production area.
“We try to group plantings together for a couple of reasons. One is for the light levels. Another is for the growing conditions, whether the plants are in a year-round covered house, in a shade house or outside in the sun. This helps us to monitor an area looking for specific pests. It’s also more efficient for treatments and irrigation.”
The nursery is scouted on a weekly basis. Specific threshold guidelines have been established for the pests and crops.
“We determine when the pest numbers require something actionable,” Lewis says. “There are other beneficials around here like hunter flies (Coenosia attenuata) that are now established in our houses. We try to protect the good bugs. Our goal is to have quality plants with a minimal impact on the environment and on our employees.”