aphids in greenhouse - Ask Extension
I have been battling aphid infestations in my greenhouse for the past three seasons. I have tried many different things(garlic spray, lures, releasing...
Knowledgebase
aphids in greenhouse #876089
Asked July 06, 2024, 11:37 AM EDT
I have been battling aphid infestations in my greenhouse for the past three seasons. I have tried many different things(garlic spray, lures, releasing beneficial insects targeting aphids, diatomaceous earth, and finally, fogging the entire greenhouse with a pyrethrum aerosol) and nothing has helped. They are on my peppers, carrots, crespedia, and snapdragons.
Orange County Vermont
Expert Response
Meg
Thanks so much for reaching out to the Extension Master Gardener Volunteer Program!
It sounds like you’ve tried just about everything to rid your greenhouse of aphids, but perhaps not in the right order? I can hear your frustration and I’m right there with you. The photos tell the sad story. Let’s hope we can provide you with the guidance you need to master these pests.
The article excerpt below is from UMASS Amherst and it has some great information about monitoring, biological controls, and prevention. I’m also going to provide you with a few other informative links. I’m hoping there is something in the article that rings true that you haven’t yet tried. Pay particular attention to the “preventative strategies” section.
Detection and Monitoring
Sanitation is an important part of aphid control. To prevent the introduction of new aphid species into your greenhouse, carefully inspect all new plants before placing them in the growing areas.
Eliminating all weeds in or near the greenhouse can be useful because it will help suppress potential reservoirs from which aphids might enter the crop. Winged aphids can easily move from the outdoors into greenhouses through open vents and establish on crop plants. To detect aphids early, several plants on each bench throughout the greenhouse should be checked on a weekly basis, particularly those species of plants that most often host aphids. Inspect the young growing tips, stems and buds of aphid prone plants and note which cultivars are the most susceptible. Signs of an aphid infestation include the presence of white cast (molted) skins, honeydew, and black sooty mold fungi. Yellow sticky cards can capture winged aphids that have entered the greenhouse from outdoors, particularly during spring and early summer. Since most aphids are wingless, the use of yellow sticky cards is not a reliable indicator of the population levels of aphids within the greenhouse. Direct visual inspection of the crop is required.
Young aphids of some species may reside between scales of leaf buds or in flowers. This reduces their contact with non-systemic pesticides and repeated applications may be needed for control. Pest control materials (insecticides) with contact, translaminar, or systemic activity can be used to control aphids. Translaminar means that after application the material penetrates leaf tissues and forms a reservoir of active ingredient within the leaf. This provides extended residual activity even after spray residues dissipate. It is important to rotate insecticides with different modes of action to delay the onset of resistance. Insecticide applications must be initiated early in the cropping cycle, when plants are small.
Coverage of plant parts with wettable or soluble powder formulations may be improved by the use of surfactants. In some instances, insecticidal soaps and/or horticultural oils may provide control of aphids, particularly when populations are low. However, since these insecticides kill exclusively by contact and have minimal residual activity, thorough coverage is essential. Insect growth regulators and pyrethroid-based insecticides may also provide control of aphids.
For information on specific pesticides labeled for controlling aphids in greenhouses, please see the New England Greenhouse Floriculture Guide.
Preventive Strategies
• Practice good sanitation, such as removing discarded plant material and eliminating weeds around plant production areas. Weed host plants often serve as reservoirs for migrating or ant-carried aphids.
• Avoid excessive amounts of nitrogen fertilizer, which promote soft plant tissue. An abundance of new, soft plant tissue promotes higher aphid populations.
• Use physical control methods if appropriate. These include screens or other barriers. Screens are especially important in stock plant production areas to reduce the threat of virus transmission.
• Thoroughly inspect all incoming plant material and spot treat if necessary.
Biological Control
Aphids have many natural enemies, and several are commercially available for release in greenhouses. Some are predators, which hunt and feed on aphids. Others are parasitoids, which lay their eggs inside of the aphid. When the eggs hatch, the larvae consume the aphid.
Aphid predators include ladybird beetles, lacewings, and predatory midges. In general, predators are not as effective in maintaining aphid populations at acceptably low populations, with the possible exception of the predatory midge, Aphidoletes aphidimyza; however, this predatory midge is not effective during short-day conditions.
It is important to realize that not all of the commercially available natural enemies reduce aphid populations to non-damaging levels when used alone. This is especially true when aphid numbers are abundant due to their rapid rate of development and reproduction. If high aphid populations are present in localized hot spots within the greenhouse or present on only a few plants, then apply an alternative pest control material. The use of alternative pest control materials may not disrupt already established biological control programs for aphids.
Furthermore, if aphids are abundant and widespread, scattered throughout the greenhouse, then it will be essential to apply an alternative pest control material in order to reduce the population before releasing any natural enemies. In general, alternative pest control materials do not leave toxic residues that negatively affect aphid parasitoids and/or predators.
[Read more about pesticide spraying by clicking the link above or the “UCONN” article below. It has good advice on what and how to spray. We ask that you to use the upmost caution when applying all pesticides. Follow directions and wear all the protective gear required.]
Thanks so much for reaching out to the Extension Master Gardener Volunteer Program!
It sounds like you’ve tried just about everything to rid your greenhouse of aphids, but perhaps not in the right order? I can hear your frustration and I’m right there with you. The photos tell the sad story. Let’s hope we can provide you with the guidance you need to master these pests.
The article excerpt below is from UMASS Amherst and it has some great information about monitoring, biological controls, and prevention. I’m also going to provide you with a few other informative links. I’m hoping there is something in the article that rings true that you haven’t yet tried. Pay particular attention to the “preventative strategies” section.
Detection and Monitoring
Sanitation is an important part of aphid control. To prevent the introduction of new aphid species into your greenhouse, carefully inspect all new plants before placing them in the growing areas.
Eliminating all weeds in or near the greenhouse can be useful because it will help suppress potential reservoirs from which aphids might enter the crop. Winged aphids can easily move from the outdoors into greenhouses through open vents and establish on crop plants. To detect aphids early, several plants on each bench throughout the greenhouse should be checked on a weekly basis, particularly those species of plants that most often host aphids. Inspect the young growing tips, stems and buds of aphid prone plants and note which cultivars are the most susceptible. Signs of an aphid infestation include the presence of white cast (molted) skins, honeydew, and black sooty mold fungi. Yellow sticky cards can capture winged aphids that have entered the greenhouse from outdoors, particularly during spring and early summer. Since most aphids are wingless, the use of yellow sticky cards is not a reliable indicator of the population levels of aphids within the greenhouse. Direct visual inspection of the crop is required.
Young aphids of some species may reside between scales of leaf buds or in flowers. This reduces their contact with non-systemic pesticides and repeated applications may be needed for control. Pest control materials (insecticides) with contact, translaminar, or systemic activity can be used to control aphids. Translaminar means that after application the material penetrates leaf tissues and forms a reservoir of active ingredient within the leaf. This provides extended residual activity even after spray residues dissipate. It is important to rotate insecticides with different modes of action to delay the onset of resistance. Insecticide applications must be initiated early in the cropping cycle, when plants are small.
Coverage of plant parts with wettable or soluble powder formulations may be improved by the use of surfactants. In some instances, insecticidal soaps and/or horticultural oils may provide control of aphids, particularly when populations are low. However, since these insecticides kill exclusively by contact and have minimal residual activity, thorough coverage is essential. Insect growth regulators and pyrethroid-based insecticides may also provide control of aphids.
For information on specific pesticides labeled for controlling aphids in greenhouses, please see the New England Greenhouse Floriculture Guide.
Preventive Strategies
• Practice good sanitation, such as removing discarded plant material and eliminating weeds around plant production areas. Weed host plants often serve as reservoirs for migrating or ant-carried aphids.
• Avoid excessive amounts of nitrogen fertilizer, which promote soft plant tissue. An abundance of new, soft plant tissue promotes higher aphid populations.
• Use physical control methods if appropriate. These include screens or other barriers. Screens are especially important in stock plant production areas to reduce the threat of virus transmission.
• Thoroughly inspect all incoming plant material and spot treat if necessary.
Biological Control
Aphids have many natural enemies, and several are commercially available for release in greenhouses. Some are predators, which hunt and feed on aphids. Others are parasitoids, which lay their eggs inside of the aphid. When the eggs hatch, the larvae consume the aphid.
Aphid predators include ladybird beetles, lacewings, and predatory midges. In general, predators are not as effective in maintaining aphid populations at acceptably low populations, with the possible exception of the predatory midge, Aphidoletes aphidimyza; however, this predatory midge is not effective during short-day conditions.
It is important to realize that not all of the commercially available natural enemies reduce aphid populations to non-damaging levels when used alone. This is especially true when aphid numbers are abundant due to their rapid rate of development and reproduction. If high aphid populations are present in localized hot spots within the greenhouse or present on only a few plants, then apply an alternative pest control material. The use of alternative pest control materials may not disrupt already established biological control programs for aphids.
Furthermore, if aphids are abundant and widespread, scattered throughout the greenhouse, then it will be essential to apply an alternative pest control material in order to reduce the population before releasing any natural enemies. In general, alternative pest control materials do not leave toxic residues that negatively affect aphid parasitoids and/or predators.
[Read more about pesticide spraying by clicking the link above or the “UCONN” article below. It has good advice on what and how to spray. We ask that you to use the upmost caution when applying all pesticides. Follow directions and wear all the protective gear required.]
Other excellent resources:
2019managingaphidsinthegreenhousefinal3-1.pdf (uconn.edu)
Greenhouse Aphid Management (cornell.edu)
Greenhouse Aphids [fact sheet] | Extension (unh.edu)
Managing Aphids in Greenhouses – Wisconsin Horticulture
I do hope this is helpful!
