Brett Alldredge is the pest management supervisor at Greenleaf Nursery in Texas. He handles pest and disease control for 450 acres of ornamental crops. His biggest problem these days is chilli thrips, followed by mealybugs and scale.
Alldredge says chilli thrips start in April and continue to be a problem through October, peaking in the hot summer months. They attack plants with new growth on the foliage, and deform and at times discolor foliage. Chilli thrips are much smaller than the western flower thrip, so they are very hard to see when you’re scouting.
“Those are a real challenge because they fly in in waves and they attack anything that flushes,” he says. “In cooler weather they aren’t a problem. You just don’t see them. Usually April is early, but with mild winter, you see them.”
In addition to the chilli thrips, the warmer winter has also increased pressure from other pests, particularly scale and mealybugs.
“Mealybugs are also a huge struggle,” he says. “This year is worse than most because of the warmer winter.”
Alldredge says those are two of the hardest to kill insects in his nursery.
Michael Roe, vice president of production with Windmill Nursery, has also been fighting chilli thrips and scale, but at his Louisiana nursery, the red headed flea beetle is public enemy no. 1.
“Believe it or not, they eat everything,” Roe says. “They have been on every crop we have.”
The indicator crops include hydrangea paniculata, roses, weigela, and crape myrtle. Roe says the pest will show up there first. It’s been an issue for three years. His scouts know to watch for a hatch at the beginning of July.
“You’ll see the beetles or you’ll see the damage,” he says.
“You’ve got to look at your target pests,” Alldredge says. “If you’re targeting a scale, it should be told that neonics are as good as there is in the industry for scale control or even mealybugs.”
Alldredge says there are several new chemistries that have real advantages and valid applications, but at a very high cost to the grower. Their use has to be highly specific on something that is very challenging for it to make financial sense.
Many growers have difficulty with western flower thrips, a common species that feeds on more than 300 plant types. These pests do direct damage by feeding on foliage and flowers, but their indirect damage as a vector for disease can be even more dangerous.
Raymond Cloyd, professor and extension specialist in Horticulture Entomology with Kansas State University, says contact insecticides are effective as long as applications are timed when the most susceptible life stages are present, including nymphs and adults; thorough coverage of all plant parts (leaves and flowers) is obtained; and frequent applications are made to kill nymphs and/or adults that were previously eggs and/or pupae.
Cloyd says translaminar insecticides may be most effective against western flower thrips because the material enters plant tissues, which increases the probability that thrips concealed in the flowers actually ingest the toxins. When applied as a drench or granule to the growing medium, systemic insecticides tend to be less effective because the active ingredient is not readily transported into floral tissues.
If pollinator health is a factor, growers should consider acetamiprid, or TriStar. When used at its labeled rates, it is much less toxic to bees than other neonicotinoid insecticides. It also has been EPA classified as a reduced risk insecticide, is compatible with many fungicides and miticides, and can be used as an effective resistance management tool.
Jill Calabro, research and science programs director for AmericanHort, says acetamiprid is not as water soluable as dinotefuran or imidacloprid, but it is still systemic.
“Due to the properties and contact activity of acetamiprid, TriStar is well-suited as a foliar spray and is effective at controlling a variety of greenhouse pests, such as aphids or mealybugs,” she says.
Resistance is one of the biggest barriers to successful regulation of thrips. It is important to rotate insecticides with different modes of action to mitigate or delay resistance. One mode of action should be used within a generation (two to three weeks) before switching to another insecticide with a different mode of action.
“You always need to rotate,” Alldredge says. “You can’t just keep putting the same chemical on a plant to treat a certain insect without expecting some resistance to develop.”
Cloyd recommends an eight-week rotation program using four different modes of action. One for weeks one and two, second mode of action for weeks three and four, third mode of action for five and six and fourth mode of action for weeks seven and eight.
Scout it out
Aphids are another challenge for Greenleaf Nursery, and like thrips, scouting is an important part of the control plan. Greenleaf grows about 25 acres of Rhaphiolepis indica (Indian hawthorn), and when the aphid pressure starts to pick up, Alldredge sees it in his scouting reports. He has five fulltime scouts that cover 450 acres, 40 hours a week.
At Greenleaf Nursery, scouting reports are categorized 1 through 5, with one being some observance of the problem and five being a disaster. Once the 3 threshold is reached, the area needs to be sprayed immediately. The alternative is a major detriment to the crop. However, Alldredge doesn’t usually wait to see a 3 in his reports to take action.
“I’ll see it as a 1 or a 2 in several locations and I’m not even going to think twice,” he says. “I’m going to start putting chemicals on the plants before they reach my threshold, which is a 3. But if there are already 1s and 2s on eight locations out of 15 locations, it’s only a matter of time until they reach that point.”
Scouting isn’t all there is, of course. Alldredge does a lot of preventative sprays on key crops, especially for scale insects. He sprays for scale once a month. He’s also using tank mixes on the front end, before a problem occurs. aphids or whiteflies. It’s a matter of seeing the cycles, something he’s getting better at each year.
“Rather than waiting for a report to come through, I start putting something with locally systemic activity into a plant that’s about to have some really high pest pressure develop,” he says.
It’s still not an easy task. If you’re in the middle of shipping in the busiest season of the year, hand spraying and thoroughly treating these problems is very challenging. It’s usually windy, you’ll get some rainy days. Generally, the weather doesn't cooperate and even if it does, you may not have the labor you need. Alldredge usually has eight employees spraying, but he says there’s just not enough man hours in a day, even with adequate weather.
Alldredge recommends taking some time to learn about your pests. Understanding which pests affect what varieties will help you develop a program that works for you. Then you can start to recognize how best to handle each situation as they develop.
“Any time you can stay ahead of a problem in this game, you’ll be so much better off,” he says.