Friday, February 1, 2008

Greenhouse - Using Banker Plants for Aphid Control

The following is an article on using banker plants as an IPM strategy to control aphids in greenhouses from the University of Maryland.

Using Banker Plants in Greenhouses for Aphid Control

On greenhouse crops in general, the two most common species by far are the green peach aphid, Myzus persicae, and the melon aphid (also known as the cotton aphid), Aphis gossypii. Aphids feed by inserting their stylet mouthparts through plant tissue directly into the phloem and sucking on plant sap. Their feeding can cause plant stunting and leaf deformities. Large numbers of aphids can remove enough nutrients from a plant that its vigor is affected. The population may be small in January but will rapidly build as we move into mid-winter.

Under greenhouse conditions, aphids reproduce parthenogenically, that is, all insects present are females, and each female gives birth to more females without the need to mate. In the greenhouse, aphids are viviparous, wherein females do not lay eggs, but give birth to living nymphs. In fact, in some species, an unborn aphid already contains a complement of developing nymphs, a phenomenon known as paedogenesis.

Aphids can vary in their preference for host plants. We are finding aphids on Easter lily, pansy, and ranunculus at this time of year. These photos show the aphids and their cast skins clustered on the tip growth and at the base of the Easter lily stems. Note: By January 27, 2008 Easter lily shoots should be 15 inches long. It is recommended that the first Fascination application be made at this stage.

How about using banker plants as a way to biologically control aphids? Everyone is looking for ways to be sustainable and banker plants fit this mold. The idea behind banker plants is to grow a plant that you can infest with insect species that only feeds on the host (banker plant). These host specific insects will not move over to greenhouse ornamental crops. Once you have a good population of an insect species specific to the banker plant you can introduce your favorite parasite or parasitoid. Let the parasite or parasitoid lay eggs in or on the insects feeding on the banker plants. Using this method you are building up the population of beneficials and ending up with healthy, fresh parasites or parasitoids that emerge from the dead bodies (mummies) of the aphids and will then search throughout a greenhouse looking for aphids in your greenhouse growing area.

How we used banker plants We started barley seed purchased from a local farm supply store in 288 trays and then transplanted the seeding into six inch pots (three per pot). Banker plants (barley plugs with bird cherry oat aphids) were purchased from IPM Labs. Banker plant plugs cost $15 for a tray of 16. IPM Labs recommends that you apply 500 or less Aphidius colemani for every four banker plants. The wasps cost $24 for a container of 500. We ordered 1,500 Aphidius and released one container of 500 in each of the three treated bays.

Can you do this? Here are the steps for aphid control if you want to try
1. Determine your crops with the highest aphid pressure.
2. Purchase barley seed from your local farm supply store.
3. Start barley seedlings in 288 (or a similar size) plug trays.
4. Transplant three barley plugs into six inch pots.
5. Purchase banker plants from a beneficial supplier.
6. Plant one banker plant in the center of each pot.
7. Wait for bird cherry oat aphid populations to build.
8. Place four of the pots in each 10,000 square foot area.
9. Apply 500 or less Aphidius for every four banker plants.
10. Monitor your crops for both live and parasitized aphids.

Adapted from "Banking and Investing on Aphid Control in Greenhouses" in the January 25, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension.

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