Ask an Organic Specialist: Season Extension Answers
Aphids are sucking insects that weaken plants by sucking up sugars and other fluids from crops. They are not easy to see, since they are the same color as the plant stem and generally like to feed on stems, buds, and underneath leaves.
Step one for control is to monitor your crops on a regular basis. Infested plants are often stunted and can be a lighter green or yellow. Look closely at the stems under the leaves for aphids. A magnifying glass or loop can help. A good approach that saves time is to flag “sentinel” plants. Mark plants in a grid pattern and only monitor those specific plants on at least a weekly basis. If you find significant numbers of aphids on these plants, you know it is time for control options. Yellow sticky cards are another good monitoring device. Adult female aphids have wings and are strongly attracted to the color yellow, which mimics the color of sickly plants. The cards are coated in sticky glue, which traps them. Check cards at least weekly for signs of adult aphids. Sticky cards need to be replaced frequently to work well. Fortunately they are cheap and available through any greenhouse supply company.
If you have any infested plants in a greenhouse or high tunnel, you should begin control options since their numbers can explode quickly.
Here are your options as an organic farmer:
There are a number of predators and parasites available for purchase and release. Ladybug larvae are the most familiar, but there are parasitic wasps, lacewings and others available now as well. Biological controls work best to keep aphid levels down, but may not give good control if you already have a problem. They simply cannot reproduce as quickly as aphids (which can actually reproduce without males- females give birth to clone daughters). Beneficial insects work best as preventative controls. A number of companies sell beneficial insects, including:
Soapy water will kill aphids. The soap strips away their waxy cuticle and they die of dehydration. In order for this to work, they must be directly sprayed with the soapy water. Use a sprayer and mix one tablespoon of liquid soap per gallon of water. (Dr. Bronner’s is pure soap. Be careful not to use soaps with perfumes, dyes or other synthetic additives.) There are also many ready-to-use brands that are OMRI listed including the common Safer Insecticidal Soap.
Allowed Chemical Sprays
Remember that all insecticides approved for organic use are “restricted use” products. You can use them only when your other control options have failed, and you must notify your certifier if you intend to use a new product and the reason you must use it. Pyrethrum/pyrethrin-based sprays will work on aphids, but have a very short residual effect and must come in contact with the aphids. The product Pyganic works well, since it is pyrethrin mixed with oil, which coats and kills aphids and many other insects. Your certifier should be able to provide a list of approved pyrethrum/pyrethrin sprays or check the OMRI website for a list: www.omri.org.
Aphids also love plants that are over-fertilized with nitrogen. If they are a constant problem despite other control efforts, you might be adding too much nitrogen to your potting mix or through fertilizer applications. A tissue test to determine nitrogen levels may be in order if you are having ongoing issues with aphids and other sucking pests.
As always, crop rotation and good sanitation practices can help control aphids in the long run.
- Cold Climate Greenhouse Resource (9 MB PDF)
This guidebook highlights the successes and lessons learned by growers across the Midwest who have designed and built cold-climate greenhouses to grow produce during the winter with minimal reliance on fossil fuel-based heat. Univ. of Minn. Southeast Regional Sustainable Development Partnership, Univ. of Minn. Center for Sustainable Building Research, Eagle Bluff Environmental Learning Center, Univ. of Minn. Center for Urban and Regional Affairs
- High Tunnels Manual (2.5 MB PDF)
A manual describing how to use low-cost technology to increase yields, improve quality and extend the season. Written by Ted Blomgren and Tracy Frisch. Cornell University and Regional Farm and Food Project
- High Tunnel Raspberries and Blackberries (1.3 MB PDF)
Work composed of research results generated from ongoing bramble (raspberry and blackberry) high tunnel projects throughout the northeast region. Information in this guide comprises current thought on all aspects of bramble high tunnel production. Cornell University
- Minnesota High Tunnels
Learn more about the statewide high tunnel conference, a new case study, high tunnel basics, structures, management, crops, economics and marketing, news and events, and resources. University of Minnesota
- Minnesota High Tunnel Production Manual For Commercial Growers
Published in 2010 and updated in 2012. University of Minnesota Extension
- Season Extension: An Overview
Don’t know a hoop house from a greenhouse? Learn the basic ABC’s of season extension. Sustainable Agriculture Research & Education
- Season Extension Techniques for Market Gardeners
This publication describes season extension techniques and provides sources for equipment, supplies, and further information. ATTRA
- Season Extension Tools & Techniques (1 MB PDF)
Information and tips on marketing and market outlook, specific tools and techniques, and economic considerations. University of Kentucky
- Sustainable Pest Management in Greenhouses and High Tunnels (1.37 MB)
Growers using greenhouses in which temperature, light and relative humidity are controlled have relied for many years on releases of natural enemies to manage aphids, thrips and two-stopped spider mites. This fact sheet provides detailed advice on how growers can use natural enemies to manage insect pests in minimally heated greenhouses and unheated high tunnels. Sustainable Agriculture Research & Education
- Thermal Banking Greenhouses
Thermal banking is the storage of heat that accumulates during the daytime and can then be used to keep the greenhouse beds warm during cold periods. Sustainable Agriculture Research & Education
- The Hoophouse Blog
Learn about hoophouse construction and find information about other season extension techniques like row covers, quickhoops, low tunnels, and 3-season high tunnels. Michigan State University
- Natural pest management in New York high tunnel and greenhouse vegetables
A three year project by the Cornell Vegetable Program researched and promoted natural pest management in greenhouse and high tunnel vegetables. Sustainable Agriculture Research & Education
- Tunnels to tables: High tunnel production and distribution model for produce
High tunnel facilities offer a production alternative for specialty crop farmers, but also require a new set of management skills and tactics. Leopold Center for Sustainable Agriculture
- Season Extension Small Potatoes Farm
Practical Farmers of Iowa
- Season Extension in a Wood-Heated Structure
Practical Farmers of Iowa
- The Hoophouse Handbook
- The Northlands Winter Greenhouse Manual
Carol Ford and Chuck Waibel
- The Winter Harvest Handbook
- Walking to Spring
Paul and Alison Weidiger
- Four Season Tools
- Gothic Arch Greenhouses
- Hightunnels.org Supplier Directory
- Rimol Greenhouse Systems
From the Organic Broadcaster:
High tunnels allow vegetable farmers to extend the growing season, but often require supplemental heat to protect plants during spring and fall cold spikes. Read more.
With the changing climate delivering hotter, drier summers, many farmers are seeking solutions by irrigating crops. Read more.
Availability of locally grown strawberries is extremely limited in the Upper Midwest, primarily due to the short growing season. Read more.