Editor’s note: Ronald Valentin is the Technical Lead & Business Development Manager for North America at Bioline Agrosciences, a producer of biological control agents.
Greenhouse Management: What types of beneficials are useful during the propagation stage of plant production? Which pests and diseases are they effective against?
Ronald Valentin: In propagation, all kinds of biological control agents (BCAs) can be used.
The following is an outline of some products, along with a few preliminary recommendations:
- Amblyseius cucumeris for thrips and broad mites. This small predatory mite feeds primarily on larval stage thrips, but also feeds on broad mites. They can be released either through weekly broadcast introductions at 10 mites per square foot or with one mini sachet on a stick per plug tray. Research, and my experience, show that sachets produce a higher number of mites on plants compared to broadcasting. The sachets are water resistant and do well in propagation. It is important to know that these mites have limited mobility, so one sachet per plug tray is highly recommended.
- Hypoaspis miles and Atheta coriaria for fungus gnat, shore fly and thrips pupa. Both of these predators are soil-dwelling and are considered generalist. They live in the top layer of soil, feeding on fungus gnat and shorefly larva and thrips pupa, as this is where thrips pupates. Release rates are one application of 10 mites and 0.2 rove beetles per square foot and typically another half rate application after transplanting the plug into the final pot or hanging basket.
- Nematodes (Steinernema feltiae). More and more growers are using this as a cutting dip. Nematodes and products containing the active fungus Beauveria bassiana, work well, but conditions play a vital role. First of all, contact is required for it to work. No contact leads to no results, which is why dipping creates higher efficacy than spraying over top after sticking cuttings. The second condition is humidity, which you always have during propagation. For these products, the best possible time for them to work is during propagation.
- Aphidiusspp. For preventive control of aphids, it is best to release wasps weekly or to have a banker plant system in place. As these wasps are host-specific, there is now a mix of three different wasp species available to take the guesswork out of the equation. Aphidius colemani, Aphidius ervi and Aphelinus abdominalis combat all four major aphid species found in greenhouses.
GM: Which crops would most benefit from the use of beneficials during propagation?
RV: I believe all crops would benefit from beneficials during propagation.
GM: Why should a grower use beneficials versus other control methods during propagation?
RV: Historically, many cutting producers would spray a lot to try and reach zero tolerance. It is more and more understood that zero tolerance is impossible, and by trying to reach that goal, the overuse of insecticides has contributed to resistance development.
Conversely, the use of BCAs is an excellent resistance management tool by taking the pressure off excessive applications. It also has shown to be very effective and the integrated pest management (IPM) approach is becoming more and more common.
Additionally, regulations in Europe surrounding residue of pesticides that are no longer registered in the European Union has resulted in limitations of what can be used on stock plant farms around the world. The other positive aspect of using BCAs in an IPM approach is that with less long-term residual pesticides on the cuttings, BCAs start working once cuttings arrive at growers, and root and sell locations in North America and elsewhere around the world.
GM: How do beneficials fit into an IPM program?
RV: Ideally BCAs are used as a first line of defense. Nowadays, there are more compatible products available than 20 years ago. Back in those days, growers either were completely on BCAs or completely on chemistries, but very [few were using] an IPM approach. It is important to make a clear choice, though, as too many compatible products or applications can still be a problem in programs that work with multiple BCAs. The best results are achieved when this is carefully considered.
GM: What tips can you share with growers about how to get the most out of their beneficials?
RV: It is also important not to just ‘try’ BCAs. Commitment is important. I often have seen people fail when they say they use BCAs in one or two sections. This strategy can get complicated, especially if products used in the other sections are not BCA-friendly and have a vapor effect.
Further, leftover solution in the spray tank can cause trouble in the BCA areas when the tank is used again, and other chemistries are added that are not compatible. For example, 5 percent of a spray solution with Orthene or Talstar insecticide residues can cause a lot of problems with BCAs when the tank is filled up to 100 percent and other, noncompatible product is added.
GM: How might BCA programs change for different crops and growing times? Can you use a BCA program with short growing times?
RV: Growing times are not a problem for the BCAs mentioned above. There are other BCAs that require a long time to get established, such as Orius and Dicyphus. In many ornamental operations, these BCAs would only make sense when banker plant or habitat plants are used, such as ornamental pepper plants (Purple Flash) for Orius and mullein plants (Verbaskum thapsus) for Dicyphus. This way, a resident population stays in the greenhouse when there is a high turnover of crops that are grown, including propagation.
This interview has been edited for clarity, space and editorial style.