Vegetable Insect And Disease Issues You Need To Know

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Most flower growers are finished with their crops by the end of May or the beginning of June. Even if they plan to produce a fall crop, there is likely some down time, so many are looking at the potential for growing vegetables in those empty greenhouses between production cycles.

But vegetables can be a very different crop to grow all the way to fruit harvest, and that can present some unique challenges for growers used to working with ornamental crops. For example, growers who decide to produce tomatoes will find that this crop needs to stay at least 15 weeks in the greenhouses to harvest seven to eight trusses (or flower branches which set four to five fruit each). This is twice as much time in the greenhouse compared to many annual plants. That means twice as much time to develop unwanted populations of insect pests and diseases in the crop. And in this case, they’re starting a crop during summer where insects and diseases pressure from outside is high, which is very different from their experiences with an ornamental crop started in January.

Since these are edible crops, consumers will have higher quality expectations. Avoiding pest damage is even more important than with ornamentals, and many of the pest control solutions ornamental growers are familiar with may not be available for a vegetable crop. With this in mind, a grower must consider options in two different strategies to control insects: chemical or biological control.

Main Insect Pests. The three main insects found in greenhouse vegetable crops are whiteflies, two-spotted mites and aphids. Those are insects very well known to ornamental growers. While all three may be an issue in most vegetable and fruit crops, whiteflies can be a huge problem on tomatoes as are the two-spotted mites on cucumbers and aphids on peppers and leafy greens.

Biological Controls. Because of the limited number of effective insecticides for these pests on greenhouse vegetable crops, the use of biological control agents is often recommended. There are many beneficial insect suppliers in the market. They have strong skilled advisors that can guide you through the length of the crop. But more importantly, don’t forget vegetables are edible products. It is necessary to check the label closely to ensure the product you’re considering is labeled for greenhouse vegetable crops, and also has the least effect on beneficial insects.

Post-Harvest Interval. Considering that it is a food crop, the grower also has to know the minimum interval of time that must pass between the last pesticide application and the harvesting of the crop. Flower growers aren’t used to having to take this into account.

Disease Concerns. A greenhouse vegetable grower might have to deal with several disease problems as well. With tomato plants, for example, viruses that can be carried by whiteflies, bacterial diseases and fungal diseases such as grey mold, fusarium and powdery mildew are common. Powdery mildew can also be a big problem on peppers. The least number of diseases are with leafy greens and herbs; although one must be aware of pythium and other root diseases.

Another problem found in tomatoes in the last few years (particularly among some of the biggest greenhouse tomato operations) is bacterial canker. Growers need to know the first symptoms of bacterial canker and immediately quarantine these plants to avoid secondary spread.

Chemical Fungicides. Compared to ornamental crops, fewer chemical fungicides can be used but some are still very good and compatible with beneficial insects introduced. There are very good sources of information for growers who want to know more about fungicides’ side-effects on beneficial insects.

The maintenance of a crop health is essential. Growers need to follow the principles of IPM (Integrated Pest Management) and guidelines of good application practices. The first time a grower switches to a vegetable crop, he should start in a small area or in a minimum number of greenhouses and combine frequent visits from a pest control and/or beneficial insect advisor during the first season. This advisor can tell you what pesticides are compatible with beneficial insects and which are not. They can be of tremendous help in the diagnosis of insects and diseases in helping you with your pest control program as you venture into a whole new world of greenhouse vegetable production.

Régis Larouche (r.larouche@agrisys.ca) is an agronomist with Agrisys Consultants Inc. His specialties include crop protection, biological control and computerized climate control of the greenhouse environment.

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