Increase the Effectiveness of Your Biocontrol Program Using Banker Plants

Banker plants are plants that are grown together in the same zone as your primary crop. Also known as habitat plants, they assist in establishing, supporting and maintaining a population of one or more biological control agents that are released on the banker plants. Banker plants support the biological control agents (BCA’s) by providing food, such as pollen. Banker plants can also support a host pest, which does not affect the primary crop grown, like the aphid banker plant system. Here we discuss three distinct types of banker plant systems.

Aphid Banker Plants

The aphid banker plant system introduces Bird Cherry Oat Aphids (Rhopalosiphum padi), a type of cereal aphid into the growing environment on cereal plants, such as barley.

Bird Cherry Oat Aphids only reproduce on monocotyledonous plants (like grasses). These aphids serve as a food source for the parasitic wasp, Aphidius colemani, which reproduces by parasitizing these cereal aphids. Cannabis sp. is a dicot, so it is impossible for the Bird Cherry Oat Aphid to establish and feed on your crop.

"Chris Freeman understands our crop and our culture. He designed a biocontrol program that helped us start clean and stay clean in our new production facility."

- Josh D.

For the aphid banker plant system to be most effective, the banker plants need to be introduced as early in the crop as possible before aphids appear. Contact Harrell's to learn about our supply of aphid banker plants to get you started!

Keys to Success with Aphid Banker Plants

• Take a proactive approach. Start the aphid banker plant system as early as possible in the crop cycle. Once the first banker plants are out in the growing environment and populated with A. colemani, it takes 4 weeks for the first A. colemani to hatch from the parasitized cereal aphids.
• Be consistent. Introduce a minimum of one banker plant per compartment or acre per week or two every other week.The system is only successful when new banker plants are regularly introduced into the growing environment. In this way you will have continuous production of A. colemani. 
• The more the merrier. Having more banker plants doesn’t hurt. Many growers use higher rates to ensure a high population of Aphidius during peak seasons for aphids, like in spring.
• Give it time to work. Do not remove older banker plants until they start to die off. Barley plants can last up to 10 weeks.
• Banker plants need love too. Monitor the banker plants and make sure they are watered. Drip irrigation works best. Overhead watering can reduce the life of the banker plant and / or wash the cereal aphids off the leaves.
• Know your target pests. When using banker plants, it is important to identify the species of aphid pests to match the right BCA to your target pest. A. colemani is an excellent parasite for green peach aphid (Myzus persicae) and black melon aphid (Aphis gossypii).

Orius banker plants

Orius insidiosus (minute pirate bug) is employed extensively as a generalist predator to control thrips.  Orius is an aggressive hunter. It can kill up to 80 thrips per day, even though it only feeds on a few. As a generalist, it also preys on other pests such as spider mites and moth eggs. It can feed and establish itself on plant pollen. Sunflower and pepper pollen are favorite food sources.

Orius has five stages of nymphs and completes its life cycle from egg to adult in one month to 35 days. After its release, it takes eight to 10 weeks (2 generations) before the Orius population is high enough to have an impact on a thrips population. Once Orius is established, the thrips population quickly decreases.

Under short-day conditions, Orius diapauses (a period of suspended development) and becomes inactive.

We recommend two varieties of ornamental plants for Orius banker plants. The ornamental pepper ‘Purple Flash’ (Pan American Seed Company) works well because it flowers continuously. Other ornamental peppers require the added labor of harvesting fruit to sustain flower production. Since pepper plants germinate and grow slowly, plants need to be started well in advance to be used as banker plants. Its many flowers provide pollen for Orius to feed on in the absence of thrips. More recently, the ornamental sunflower ‘Sunfinity’ (Syngenta Flowers) has proven effective as a banker plant for Orius.

After Orius is released on banker plants, nymphs can usually be found within four weeks. Once established in the growing environment, it is not unusual to count dozens of Orius on yellow sticky cards each week and few, if any thrips.

Dicyphus hesperus is another generalist predator. It attacks many of the same pests as Orius. Rather than a pollen source, Dicyphus requires a plant it can drink water from where it can complete its lifecycle. We use common mullein (Verbascum thapsus), a biennial, for this purpose.

Dicyphus was initially developed as a generalist biocontrol for tomatoes, a hairy, sticky plant. While Orius can get stuck in trichomes, Dicyphus has longer legs and can more easily maneuver through sticky plants. Additionally, unlike Orius, Dicyphus does not diapause under short days. For these reasons, we recommend Orius as a great generalist for vegetative plants and Dicyphus as your go to for plants in flower.

We recommend supplemental feeding with Ephestia eggs for both Orius and Dicyphus. These frozen moth eggs provide food for these generalist predators and increase fecundity (the ability to produce an abundance of offspring). Weekly supplemental feeding will help you achieve optimal predator populations in the shortest time possible.

Banker plants give the grower a standing army of biocontrol agents, regardless of whether there are pests present. They help avoid the peaks and troughs of pest populations, where the grower detects an infestation, introduces the BCA to control the pest, then the pest population disappears and along with it the BCA, until a new infestation is detected and the cycle begins anew. In many cases, your predators on the banker plant system will detect and eradicate a pest invader before your scouting even revealed its presence!

These banker plants systems have been used successfully with a variety of commercial crops. Most suppliers do not talk about banker plants. Their rationale is, “We sell bugs in a bottle. If we teach them how to use banker plants they might not buy as much from us.” 

At Harrell’s we are most concerned with your success as a grower and are committed to giving you all the education and tools necessary to achieve your goals.