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Crucifer Insect Pest Control and New Resources

By Dr. Ayanava Majumdar, Extension Entomologist,

James Miles, Regional Extension Agent

It is true that insect pests never sleep in Alabama! Temperature fluctuations with an occasional rain during spring are great for insect pests like caterpillars and aphids on crucifer crops. With the mass popularity of high tunnels in Alabama, we now not only have crop season extension but we have also successfully extended the life and feeding duration of insect pests that overwinter inside the tunnels. This article will focus on crucifer crops since many producers have one or more varieties on their farm for direct sale to customers. Our crucifer IPM project has been funded by the USDA Organic Agriculture Research and Education Initiative and Sustainable Agriculture Research and Education Grants.

The major problem with crucifers is that pests directly attack and contaminate marketable produce. So, pest prevention is the key strategy for all producers – big or small, organic or conventional, open or closed cropping systems. Consider the case of the beautiful cabbage butterfly that zips around in your field or garden amazing you with its energetic flight. But look closely…that beautiful yellow butterfly landing on your cabbage is actually a female laying small elliptical eggs on the leaf surface. The eggs will hatch into tiny velvety green caterpillars that start munching on cabbage leaves and fatten themselves. Interestingly, a few days of cold weather may cause the medium-sized caterpillars to move into the developing cabbage head in order to survive temperature fluctuations. Producers and gardeners who do not act timely may wrongly think that the caterpillar has disappeared, when in actuality, the insect has moved into the inner cupped leaves where it cannot be destroyed by insecticide sprays. We have experienced outbreaks of cabbage butterfly or imported cabbageworm in fields where the crop looks grazed due to extensive feeding. Cabbage butterflies are usually seen munching along with their cousins, like the striped cabbageworm, diamondback moth, and cabbage looper. Again, prevention is better than the cure for the caterpillar complex!

Scouting of these pests involve weekly checking of crops, counting larval size and numbers, and calculating the economic threshold for maximizing spray effectiveness. For details about the caterpillar pests and scouting methods, visit the Alabama Vegetable IPM website (www.aces.edu/vegetableipm) for Extension bulletins and look for the crucifer pest scouting sheet to learn calculation of larval units.

Organic or small farm approach for caterpillar control is to use insect netting or screens for deterring large moths and butterflies. A properly sealed high tunnel with netting around the sides can keep large insects at bay but may not stop aphids and other small pests from getting in. This is called the High Tunnel Pest Exclusion (HTPE) system and even shade cloths can be used under the rolled up side walls to permanently block insect pests (Will Mastin’s Local Appetite Growers in Silverhill, AL, is a perfect place to see this technology in action). HTPE system can be designed to keep out insect pests but allow beneficial insects to colonize high tunnel crops. Watch pest exclusion videos on Alabama Vegetable IPM website for more information.

Caterpillars on the crops can also be stopped by using consistent weekly spray of products like Bt (Bacillus thuringiensis or Xentari), spinosad (Entrust) or pyrethrin (PyGanic) (Figure 1). Bt product (Xentari) alone can be quite effective on cabbage butterflies if the coverage is uniform and thorough as we have seen in our test plots. So, Bt becomes “preventive spray” if you farm in a high caterpillar pressure area. Bt can also be tank-mixed with Pyganic for higher pest pressure conditions. Remember to remove infested or unwanted vegetation to prevent these insects from building up (sanitation).

Conventional cabbage producers not only have the option to start out with Bt (to protect natural enemies that do a great service in this case), but also could use some reduced-risk foliar insecticides include flubendiamide (Belt – a selective feeding inhibitor), spinetoram (Radiant), and novaluron (Rimon – an insect growth regulator). Belt and Radiant are very effective caterpillar control products that have been tested extensively in Alabama. Chorantraniliprole or Coragen is also a great preventive insecticide suitable for application through the drip irrigation system. Pymetrozine (Fulfill) is a unique selective insecticide for aphid control and whitefly suppression with minimal side effects. A number of synthetic pyrethroids are also cheap alternatives for caterpillar and aphid control during mid-season but they wipe out beneficial insects as well. We recommend using pyrethroids for cooler weather for quick kill of insect pests while incorporating some selective insecticides for long term benefit. Always remember to check the label (especially when using generics) and rotate insecticides because insecticide resistance can happen rapidly with uncontrolled pesticide use.

Watch for the Yellow-margined leaf beetles! These 5-mm long beetles have brown forewings and a yellow margin along the edge. The larvae are black with three pairs of legs behind the head and much body hair. Adult beetles and larvae completely devour turnips and napa cabbage, especially on organic farms. If you suspect this insect to be present, then call the main author (251-331-8416) for possible solutions or visit the IPM website (www.aces.edu/vegetableipm). Subscribe to the Alabama IPM Communicator newsletter (www.aces.edu/ipmcommunicator) and stay informed about the latest agricultural innovations and training events statewide!

New Extension Resources for Small Producers

We are excited to inform high tunnel producers about the availability of the New Producer Handbook for High Tunnel Crops. This is a must-have book for beginning farmers! This book has chapters on basic high tunnel cropping system and agronomics, several chapters on integrated pest management and statewide resources. The Alternative Vegetable IPM Slide Charts are also available to small farmers and transitioning producers that provide information about the three-tiered IPM approach to insect pest management. These publications have been supported by grants from USDA National Institute of Food and Agriculture, SARE Program, and the Wallace Center at Winrock International. Industry donations have also supported publications. Contact James Miles (Regional Extension Agent) at 574-8445 for details or attend a crop production training meeting to receive your copy. The New Producer Handbook for High Tunnel Crops is also available on iBooks.

Announcement: AFVGA Annual Conference and Tradeshow this fall

The Alabama Fruit and Vegetable Conference and Tradeshow is set on November 19-21, 2015 at a new location. The Fall conference will be held at the Clanton Conference and Performing Arts Center near Jeff State Community College. The conference will include several farm or field tours and hands-on workshops on a range of topics suitable for producers and gardeners. Watch for more information at www.afvg.aces.edu.