by Elizabeth A. Tomlin
Got aphids?
Look again. See any tiny white casings of discarded skin? Or maybe some sticky, yellowish “honeydew” droplets? And if you do discover the critters, can you identify them? And why would that be important?
The answer to these and many other questions were investigated at a hands-on, sustainable pest management integrated pest management (IPM) workshop, sponsored by Cornell Cooperative Extension’s Capital Area Agriculture and Horticulture Program, and featuring speakers IPM Award winning Professor of entomology, John Sanderson of Cornell University; NYS IPM ornamental plant specialist Dr. Elizabeth Lamb; IPM Specialist Dr. Lily Calderwood; and Grad Student Erica Hernandez.
Beneficial and detrimental greenhouse insects — and how changes in environmental conditions affect them — were discussed in depth. Various plant diseases were also investigated.
Participants were encouraged to look at specimens under microscopes and growers are advised to have a hand held magnifying glass available at all times to examine specimens found on their own premises for diagnosis.
Sanderson’s presentation of ‘Biological Warfare for Aphids’ included examining species of aphids for identification.
Aphids are cool weather greenhouse and high tunnel pests that top many growers’ lists of pests to control — with over 20 species of aphids found infesting greenhouses.
Many folks don’t realize that some aphids are born pregnant and do not need to mate to reproduce; thus, given the right temperatures of 70–75 degrees, they will soon infest your greenhouse or high tunnel. Females give birth to more females, which develop into reproducing adults in 5–12 days, with each in-turn producing another 50–250 offspring.
“Aphid populations can explode.” emphasized Sanderson during his presentation. “If you see them, don’t ignore them.”
In a 2017 Spring survey taken in New York and Massachusetts, it was determined that Green Peach Aphids are most frequently the culprits and were found in 53 percent of samples taken. Foxglove Aphids were found in 28 percent of samples, Melon Aphids were discovered at 6 percent, and Potato Aphids numbered 4 percent of samples.
Identifying the pests is not easy, even with a hand held scope.
“Aphids are all generally small (1-3 mm) and soft bodied and have a pair of unique structures that resemble ‘tailpipes’ near the end of their abdomen, called cornicles,” Sanderson explained. “Adults may or may not have wings.”
Green Peach Aphids vary in color from a light green to pinkish hue, with cornicle color the same as the body, except for dark tips. A noticeable indentation between their antennae is a characterizing feature.
Foxglove aphids (aka “Glasshouse Potato Aphid”) attack a broad host of plants, and are frequently found on ivy, zonal geraniums, salvia, and cineraria, and many other crops, in the northeastern U.S. They are like green peach aphid in appearance, but are shiny, with a darker base of the cornicles.
“Foxglove Aphids do not do well in high temperatures and are definitely cool weather pests.”
Melon Aphids are very small, with light yellow to very dark green bodies, which may appear nearly black. They have no pronounced indentation between their antennae and their cornicles are always black.
Scouting for aphids is critical to your production.
“If possible, quarantine newly-arrived plants and inspect thoroughly before moving them into production areas,” advised Sanderson, who also advises not planting aphid susceptible cultivars near doorways or vents, where they may be infected from outside sources. “Yellow sticky cards can monitor when winged aphids are active and may detect a migration of aphids into the greenhouse.”
Lamb pointed out that yellowed, dying leaves on plants may also attract aphids, once they are present.
Experiments have been done with fertilization effects on aphid populations, and Lamb reported findings of those studies, noting that the effect of fertilization differed between tests on pansies and tests on pepper plants.
“Aphids are looking for a nitrogen source,” she confirmed. “It is a possibility that you will have an increase in insect population if you have too much nitrogen. It’s something to keep in mind when you are looking at fertility.”
Sanderson advocates the use of bio control when confronted with aphids, which makes identification crucial, as all bio control does not affect each species effectively. The natural enemy you use depends on the aphid species you have.
“Bio controls are organisms whose sole purpose in life is eating others — in this case eating pests that attack greenhouse crops,” explained Lamb. “Do not wait to put in your aphid biological control until you think the population is high enough. It’s always higher than you think.”
Sanderson exhibited species of parasitic wasps and habitats designed to produce them.
“Commercially available natural enemies for aphids include ladybird beetles, lacewings, parasitic wasps (e.g. Aphidius colemani), predaceous midges (Aphidoletes aphidomyza) and insect-pathogenic fungi (Beauveria bassiana),” he reported.
Once wasps are in place, it is important to know what parasitized aphids (mummies) look like.
“Parasitized aphids should not be crushed or removed from plants,” explained Sanderson. “Parasitoid wasps will emerge from these cases to continue parasitizing aphids.”
Biological control of thrips is also being studied.
Dr. Lamb also conducted a session on identifying and treating greenhouse mildews. Sanitation is huge. Management is crucial.
Debris inside the greenhouse or high tunnel should be removed promptly. Disease resistant varieties of cultivars should be considered for use and rotation of plants is advised. Fungicides should also be rotated and overlap should be managed.
“Reduce potential for developing resistance,” Lamb reminded attendees. “Cultural control is the most effective.”
Lighting during hours of darkness has been found to reduce the spreading of spores when mildew and fungal conditions are present. “Manage humidity.” advised Lamb.
Experiments with lighting in high tunnels and greenhouses were reported on by Hernandez.
A variety of lighting techniques were displayed and reports on different colors used at different stages of growth were explored.
“Different colored lights produce different results,” reported Hernandez. “LED lighting gives you a lot of control.”
Blue lights produced shorter, fuller plants in studies, and also produced best results with seedlings.
“Lighting can also be used to control insects,” commented Hernandez. “Colors may be attractive at low light intensity, but repellent at high light intensity.”
Studies show that brightly colored, reflective mulch can help to repel insects from lower leaves on plants.
Nighttime lighting with a UV-B for 5–10 minutes has also been shown to have a negative effect on mildew. This is best when applied in the dark or with a red light. Less control was shown with a blue or UV-A light.
Cost of lighting should be considered when planning, including initial cost of fixtures, installation, operation, lifespan and bulb replacement. Hernandez recommends investigating grants and rebates before making a decision on lighting for your facility.
For more information on lighting your greenhouse or high tunnel contact Cornell Associate Professor Neil Mattson at