Ministry of Agriculture and Land
Can Biocontrol and IPM Work for Floriculture?
David Flood
Floriculture Development Officer
British Columbia Ministry of Agriculture and Lands
About 15 years ago, the B.C. greenhouse vegetable industry started using biological controls for insect pests. The industry was quick to realize the benefits of reducing their reliance on sprays in an era of increasing resistance to pesticides, a shrinking arsenal of materials to choose from, and growing public concern surrounding the use of chemicals in agriculture. Today, nearly every insect pest problem in vegetable greenhouses can be managed with the help of beneficial insects and organisms. They have become a model for the rest of the world in the adoption and refinement of biological pest control methods.
It hasn't always been an easy transition. It has taken many years for growers and their pest control advisors and suppliers to develop the expertise in monitoring and managing the appropriate pest/predator levels needed to maintain lasting control at a level below the threshold of economic damage.
So why hasn't this worked as well for floriculture? Well first, it has and continues to work in some instances, but the overall adoption of biological pest control methods in floriculture has been slow, and for good reason. Biocontrol methods have succeeded for greenhouse vegetables, since in most cases, it is only the fruit that must be marketable. Most greenhouse pests tend to inflict their damage on the leaves of the plants leaving the fruit relatively untouched. However, this is not always the case, as in cucumbers, where severe losses have resulted due Western flower thrips damage to developing fruit. This has made the WFT more difficult to control than some other insects since relatively low numbers can inflict serious damage.
Unfortunately, we face similar problems in trying to adapt the use of biologicals to floriculture crops. In most cases, the entire plant, or a good portion of it must be marketable. Flowers are an aesthetic item, bought for their perfection and beauty. While many biocontrol agents can eventually achieve some form of control and population reduction in greenhouse settings, they do not always succeed before pest levels have soared astronomically, causing significant damage. Even if the pests and predators are in perfect balance on the plants, they simply cannot be tolerated if they or the injuries they inflict are noticeable and unsightly. Therefore, the wholesale adoption of biological insect controls for floriculture requires a new level of sophistication in pest management. We will need to achieve control at very low numbers in order to minimize visible damage.
A few years ago, we thought we had a good prospect for controlling greenhouse whiteflies on poinsettias with tiny parasitic wasps. Encarsia formosa was doing very well in trials and we were able to produce test crops from start to finish without any other pest control applications. Then, just as we were about to expand the use of Encarsia commercially, along came the Sweet Potato Whitefly which is somewhat more immune to Encarsia. We found that the wasps would parasitize the scales of SPF, but few if any of these would develop into mature Encarsia. The parasites failed to cycle and the whiteflies remained out of control. So it's back to the drawing board for poinsettias. However, Encarsia still remains a viable alternative for crops which are infested only with the greenhouse whitefly. The secret is to start the introductions immediately upon receipt of your cuttings to establish a good balance early in the crop.
At the BCMAL we have also tried IPM or integrated pest management methods on roses. Unlike potted crops, roses are a long term, multi-year crop with periodic insect pest cycles. It has been noted in previous attempts to introduce biological agents into commercial rose houses that the populations often failed to take hold and thrive, even in the midst of plenty of prey. One explanation was that the standard preventative and curative spray programs carried out on these operations may have resulted in a buildup of chemical residues on the plants or the greenhouse structures to a level where they were inhibiting the normal development of beneficial insect introductions. As a rule, insect biocontrol agents tend to be highly susceptible to conventional pesticides since they have not had the decades of pesticide "battle hardening" that our greenhouse pests have survived. If this is the case, then it would seem more likely for your bio-control program to succeed if you begin when your plants are young, or if you time the introductions so as to leave as long a period as possible between pest control sprays and the introduction of beneficials.
We started with a new crop of roses at our test greenhouse In Abbotsford. From the beginning we used an integrated approach to pest control. That is, we used biological controls whenever possible, and if a spray was necessary, we tried to select one which was as benign to the beneficial insect population as possible.
For the first six months our spray/insect release calender looks like this:
March 27 - planted
March 28 - applied pirimor for green peach aphids
April 7 - introduced P. persimilis (predator mites) to control two-spotted mites. ( 2 predators per plant)
April 15 - applied meltatox for powdery mildew
April 20 - started burning sulphur for mildew (continued 4 hrs/night with good control)
May 5 - introduced Amblyseius cucumeris, a predator mite for thrips control.
May 12 - introduced persimilis (6 predators per plant)
June 20 - introduced aphidoletes for aphid control (6 per plant). Population did not hatch, probably due to high temperatures
June 26 - applied pirimor again for aphids - pirimor does not affect beneficials. Some Aphidius parasites (gold mummies) were now naturally present in the crop - a bonus that often happens with spray reductions. They had flown in from outside.
July 15 - introduced Orius tristicolor (pirate bugs) for thrips control.
July 24 - second introduction of Orius (pirate bugs were never seen again. They can fly and evidently did - right out the vents!)
Sept 4 - applied pirimor again for another aphid outbreak (we had a heavily infested crop of peppers in the next compartment.)
Sept 28 - dipel applied for a looper outbreak. Good control.
From the log it is evident we have had some successes and some failures with our biocontrol program alone, but when this was integrated with selected chemicals we were able to substantially reduce the amount of sprays which we would normally have needed for a typical young crop of roses had we relied on chemicals alone. We had particularly good success with the predator mites, with season long control from just two introductions. The Western flower thrips population never increased to economic levels, although we were unable to determine if the Cucumeris or Orius introductions were of benefit. We still have to calculate the economics of IPM, both the successful and not so successful introductions, but the first objective was to see if we can just get it to work.
Obviously, the fewer sprays applied, the less likely they are to harm the biologicals. Even if they aren't killed by the pesticides, spray applications can interfere with biocontrol agents by destroying all their food. For example, Vendex won't kill the persimilis spider mite predators, but if the spray is thorough and effective enough, there will still be a crash in the persimilis population due to simple starvation.
Certainly, our early results in roses are promising. Even though we were somewhat unsuccessful in controlling aphids without chemicals, we were at least able to preserve the other benficial insects. In the years to come there remains much work and discovery before full biological control programs can meet all the pest challenges in the floriculture industry. Until then, the IPM or integrated approach offers the best possibility of reducing our dependence on dwindling chemical alternatives and paving the way towards more innovative answers to pest control.
