Photo courtesy of IPPS Western Region

Woodburn Nursery and Azaleas in Woodburn, Ore., is one of the largest growers of floral azaleas in the U.S. I manage the Integrated Pest Management/Biological Control Program. I have been given latitude over this program that few in the industry experience. This latitude has given me a perspective that is unique and valuable to the industry.

Woodburn Nursery follows a systems approach to biological control.

On numerous occasions, I have achieved control, well below damaging thresholds, of harmful insects using an overwhelming number of beneficial insects. I can tell you through personal experience that, yes, beneficial insects work. We have two primary approaches to insect biological control. The first is augmentative and the second is conservation. Augmentative insect control is the purchase and release of beneficial natural enemies to control insect and mite pests. Conservation biological control refers to the conservation of natural enemies by avoiding practices which are harmful to natural enemies and implementing practices which benefit them.

Our biological control program extends outside of our floral azaleas department to other crops. Woodburn Nursery also grows woody ornamentals including Japanese maples and Euonymus fortunei. These crops are grown in unheated greenhouses with roll-up sides that are situated right next to each other. There is about an acre of maples and about two acres of euonymus. Each year in the early spring, the Japanese maples and the euonymus become infested with aphids. And each year native hoverflies lay their eggs among the aphids. For the last four years I have not needed to spray for aphid control on either of these crops. It takes about four to six weeks until the aphids on these crops are destroyed by the hoverflies. Of course, it’s not just the hoverflies, but a ménage of native beneficial insects, including, but not limited to, brown lacewings, lady beetles, parasitizing wasps, predatory midges, and soldier beetles. But it is the hoverflies that do the heavy lifting. Hoverflies require a pollen meal to lay eggs, so I place baskets of candytuft (Iberis) and other early flowering annuals and perennials within the crop. The candytuft is typically set out between February and March, depending on when the hoverflies appear. I also set out barley plants infested with a cereal aphid to feed the hoverflies. The cereal aphid is found only in monocots, such as barley and grass, therefore the aphids do not migrate into our crop. This combination of flowers/pollen and added aphids as food is jokingly referred to as the “Full Meal Deal.”

The late comers to the party always seem to be the lady beetles. Once I find a contingent of lady beetles, I know the end is near for the aphid infestation. I can tell you with high confidence that even though I scout our crops like a bluetick hound on a black-tailed jackrabbit’s trail, I have not found all the actors in this little drama.

Predator and prey

In our floral azaleas, I have not had the same level of success. Floral azaleas take about one to two years to grow from cuttings to finished plant. The floral azaleas are very prone to several pests including, aphids, western flower thrips, whitefly, two-spotted spider mites, echnothrip and broad mites. The broad mite is by far the hardest to control. The sprays that are most effective for control of broad mite are also the worst for any beneficial insects.

Naturally occurring native hoverflies enter the greenhouses each year to feast on aphids.
Photos by Bruce Colman

Amblyseius swirskii, a predatory mite, will easily control broad mite when applied in enough numbers. In fact, new, unharmed foliage will emerge from the A. swirskii-treated plants as quickly as on the plants that have been sprayed with long lasting, broad-spectrum insecticides.

A. swirskii is an ideal product to be used in crops that are grown under protection in warm conditions, such as floral azalea propagation. A. swirskii will consume the immature stages of western flower thrips and whitefly. A. swirskii will also consume two-spotted and broad mites. There are many low-toxicity, non-broad-spectrum, short lasting insecticides that are effective on aphids and that are soft, or sometimes even harmless, on beneficial insects. For the echnothrips, scouting and spot spraying is effective.

But to treat all of those insect pests with A. swirskii would require an overwhelming population of the predatory mite, which would be prohibitively expensive.

Besides attracting and releasing predators, we have also created two insect rearing facilities. One is heated and lighted in winter. When we find an infestation on a crop, I bring the worst plants into the insect rearing greenhouse. I am able to isolate the infected plants and apply large amounts of beneficials in a controlled environment. I am then able to monitor these trial plants. Because of my trials, I have confidence the A. swirskii predatory mites are effective on these damaging insects. The other facility is a 1,600-square-foot building where the individual rooms have independent heating/cooling and lighting. Our insect rearing facility is an in-house augmentative program.

Trial and error

This dragonfly represents just one of many beneficial insects that are found in the nursery.

A potential solution to the broad mites starting in the propagation house is to dip the floral azalea cuttings in 0.1% SuffOil-X (12.8 ounces per 100 gallons of water) prior to sticking. The purpose of the dip is to control the broad mite eggs, any live mites and thrips. The challenge is to not burn the new, tender cuttings as they root out. Be aware that although it’s standard to store the cuttings in a refrigerator for a short time before sticking, oil dips cannot be stored and must be done immediately before sticking.

We’ve also tried placing A. swirskii sachets at every fourth plant, which breed and release the swirskii over a period of four to six weeks in order to establish a population. I need to note that in propagation the pots and foliage will be touching each other, so that the predatory mites will be able to move from plant to plant. We found that the predatory mites do not drop off the propagation benches and stay on the plants. I have found eggs and adult swirskii on the floral azaleas grown on benches.

Native insects are found throughout the nursery.

We can spot spray insect growth regulators and soft insecticides for aphids and echnothrips when our scouting reveals outbreaks.

The use of beneficial insects in a growing operation complicates an already complex process. The more inputs that have to be accounted for, the more expensive and complex the process becomes. Woodburn Nursery and Azaleas strives to reduce the volume of sprays and the toxicity of the pesticides while maintaining the look and quality of our floral azaleas, without adding undue expense. It is a balancing act, and it is a process filled with some pitfalls and errors.

For more:

Bruce C. Colman is the IPM manager at Woodburn Nursery and Azaleas in Woodburn, Ore.