The intricacies of edibles

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As our ornamental industry continues to evolve, an already-complicated situation grows more complex. Interest in production of greenhouse edible crops has been growing, especially vegetables and herbs. This includes plants produced as plugs or transplants to be grown on to 6 packs and quarts for sale to homeowners, or for food production in greenhouses or high tunnels. This is a great way to expand our market and season, but it has also increased the types of pests and diseases we encounter. It has also changed the tools we can use to manage them.

Very few ornamental plant-use products are also labeled for edible crops grown in greenhouses. Even those labeled for vegetables and herbs in greenhouses are usually not compatible with organic production. Depending on your market, organic certification may be a critical feature that enhances crop value and is sought out by a portion of the public. Some growers have decided to grow using organic methods as a personal choice.

Determining what commercial practices and products are acceptable for food production, and particularly for organic production, can be a challenge. USDA’s National Organic Program (NOP) is the overriding authority in this area. While it doesn’t provide a list of all organic-acceptable products, growers may want to first consult the NOP’s National List of Allowed and Prohibited Substances (www.ams.usda.gov/AMSv1.0/NOPPetitionedSubstancesDatabase). Here you’ll find synthetic materials permitted for pest and disease management such as horticultural oils, insecticidal soaps and copper hydroxide.

Many growers at least recognize the acronym OMRI (Organic Materials Review Institute). OMRI reviews products’ inert and active ingredients to assess compatibility for organic production. Those meeting criteria can use the OMRI logo on packaging. Since OMRI doesn’t review all possible products for pest and disease management, growers will need to consult their preferred NOP-authorized certifying authority for more details, particularly when marketing a product as ‘certified organic’ with the NOP logo. Of course, any EPA-registered product must also be approved in the grower’s state.

Bacterial speck on tomato. Courtesy of Ann Chase.

It is our understanding that EPA considers pesticides labeled for use on outdoor food crops to be acceptable for use in greenhouses, unless labels prohibit such use. The good news is that this may provide greenhouse food-crop growers with more options, after first verifying their state’s pesticide regulatory position. This naturally raises some important questions on use rates (outdoor-use labels typically express use on a per-acre basis), personal protective equipment, re-entry intervals, plant safety, use in high tunnels, and more. Under no circumstances should growers violate label directions.

To help address these and other questions, Cornell staff members are working on a new Pest Management Guide for greenhouse food crops. It is expected later this year. Some well-known fungicides like Heritage are being labeled for certain uses on edible crops grown in greenhouses.

Note that some of these products are only for use on greenhouse-grown “transplants.” The most current Heritage label says, “Heritage may be applied to plants used for food in production nurseries, gardens and landscapes to control certain diseases. Follow the pre-harvest interval following applications prior to consuming fruits, nuts, or other produce from those treated areas.” The specific wording must be carefully read and understood. If you are not clear on a particular use, contact your local extension service or the manufacturer directly.

Some products that might be legal and useful on diseases of greenhouse-grown edibles are shown in Table 1, including some approved for organic production.

RootShield Plus is the newest product from BioWorks. It does have OMRI listing, a 0-hour REI and a broader range of activity than RootShield. The new product is a combination of Trichoderma harzianum T-22 (FRAC group 44) and Trichoderma virens G41 (not classified). It is somewhat variable in its efficacy, which is a characteristic of biological control agents. It is labeled for Pythium, Phytophthora, Fusarium and Rhizoctonia root diseases and must be used preventively.

Regalia is an OMRI-listed product that has been brought to market by Marrone Bio Innovations and is labeled for just about anything. It is primarily marketed as “a plant extract to boost the plants’ natural defense mechanisms to protect against certain fungal and bacterial diseases, and to improve plant health.” In our trials with Regalia alone, we have seen some very good control of bacteria and fungal leaf spots and powdery mildew. However, it is to be primarily used as a tank-mix partner with other bactericides or fungicides, according to the label.

Among the insecticides and miticides for production of certain vegetable transplants, TriStar 8.5SL, Safari, and Kontos are labeled. For greenhouse tomato (fruit) production, labeled products include miticides Pylon, Floramite, Akari, Onager, TetraSan, and Shuttle-O. Akari and Pylon labels include uses for some other pests. Malathion, Admire Pro, Distance, TriStar 8.5SL, and Talus are also labeled for other pests in greenhouse tomato production. Pylon, Distance, and Shuttle-O can be used on other greenhouse-grown fruiting vegetables, and Admire Pro, Beleaf, Akari, and Malathion have labeling for greenhouse cucumber.

A few products have very broad labeling for many greenhouse food crops, including M-Pede, azadirachtin products (AzaGuard, Azatin XL, Aza-Direct), horticultural oils (Suffoil-X, JMS Stylet Oil, Sunspray Ultra-Fine), Preferal, Bt products such as DiPel or Gnatrol, and pyrethrin-based materials (Pyrenone Crop Spray, Pyronyl Crop Spray, Pyreth-It, etc.).

Table 2 shows some insect- and mite-control products labeled for use on greenhouse food crops that might also meet organic certification criteria.

Preferal, BotaniGard, and Mycotrol will benefit from extended periods of high humidity following application (Preferal calls for 8 – 10 hrs. at 80-plus percent; the efficacy of BotaniGard may be improved if high humidity continues over two or more days). Of course, be aware of possible increased risks from diseases and judge accordingly.

The liquid formulation of BotaniGard has caused injury to tomatoes in our studies, so we suggest using the WP formulation on tomatoes instead. Observe label cautions with all products, and, as always, verify that both products and labels are approved for use in your particular state.

Use of introduced biological controls (such as Aphidius for aphids and Eretmocerus or Encarsia for whiteflies) is very popular in greenhouse vegetable production. Check for product compatibilities if using natural enemies. Some of the ‘conventional’ products noted above also work well with these beneficial insects and mites.

Ann Chase is a plant pathologist at Chase Agricultural Consulting, LLC. Dan Gilrein is an extension entomologist, Cornell University Cooperative Extension, Long Island Horticultural Research and Extension Center.