Aphids can be one of the most damaging and hard to control pests during the winter months in high tunnels. The first step to managing aphids is to develop a scouting plan. Aphids reproduce clonally and develop quickly leading to very large population build-up in a short period of time. Therefore scouting is recommended at least three times a week. When examining plants be sure to look at the growing point and underside of leaves, where aphids prefer to colonize (Figure 1). Outbreaks commonly begin on the outer rows or the start of the row so these are places to be sure to include when scouting.
Figure 1. Aphids on kale crop. Photos courtesy Liz Maynard.
In the summer months, successful control has been achieved using a soap/mineral oil spray consisting of 1.5% castile soap and 0.25% mineral oil. Cornell University also reports grower success using the biopesticides Mycotrol O and BotaniGard. These are commercially available formulations of the aphid-attacking fungus Beauveria bassianal. All three of these methods require that applications directly contact the aphids. Plant spacing and anatomy can affect the rate of application and efficacy.
Biological control is another approach that can have lasting control. During production times in high tunnels when the sides are open, it has been difficult to retain predators. These problem will be alleviated by having the sides closed and with the addition of row covers which will trap the predators closer to the crop. Lady beetles have been reported as effective, offering control throughout the colder months, according to Cornell University. Control was achieved using a release rate of 9 adult lady beetles per square foot. In early fall green lacewing larvae (Chrysoperla carnea) may be an additional option for controlling populations. Releasing eggs is not recommended at this time because the cooler temperatures increase the time to hatch, delaying control. Larvae will begin eating aphids when they are released. The cold tolerance of green lacewings has not been examined but we have conducted experiments showing that adults are active and still lay eggs at 11C (51.8˚F). Parasitoid effectiveness declines under cooler temperatures and growers have expressed concerns regarding removing aphid mummies from the vegetables and therefore are not recommended.
Some important cultural considerations to keep in mind is starting with clean plants, whether that be transplants or removing infested crops from summer production before seeding winter greens. It is also very easy for aphids to hitch hike on workers so knowing where infestations are happening and working in those areas last can prevent movement among crops or tunnels. Adhering to suggested plant spacing can make application of oils and biopesticides more effective. Lastly, controlling weeds, which can serve as alternative hosts to the aphid pests will lessen problems with re-infestation.
A combination of the practices described above can lead to the successful control of aphids in winter green production in high tunnels in Indiana. Frequent scouting and quick responses may be key to preventing large infestations. Combining predators and biopesticides in an integrated program can offer natural controls for aphid management.
See this link for the information from Cornell: http://rvpadmin.cce.cornell.edu/uploads/doc_197.pdf.