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What to watch for with pests, disease in 2007 by Dr. Richard Lindquist, OHP Senior Technical Manager

As growers who produce greenhouse or nursery ornamental plants know, there never seems to be a shortage of problems to deal with. These problems include insects, mites and plant diseases. On many crops these pest problems are quite predictable, so growers can anticipate and develop plans to deal with them. However, there always seem to be additional “new”pest problems to confront. These can be in three categories:

1. Former bit players that suddenly assume a leading role. This may be due to pesticide resistance development, pesticide selection, production changes, use of biological controls, or some other factor. Leafminers have come and gone over the last several decades. They’re back again.
2. Common problems on some crops expand their range to attack crops that were previously left alone. This may be because of changes in cultivars, pesticide selection and availability, use of biological controls,or simply adaptation of pests to new host plants. Mites other than spider mites and downy mildews are examples.
3. Pests introduced from offshore. These pests normally arrive on imported plant material. Q biotype whiteflies and chilli thrips are two recent examples. Sometimes,a beneficial organism is also introduced from offshore. With the increasing worldwide transfer of plant material, expect more pest visitors, many of which will like it here and stay.

The following is a brief summary of some things to watch for in 2007 – and beyond. The list could be much longer, but this is a newsletter, not a book.

Thrips

Thrips are problems because they’re hard to detect, they may transmit plant pathogens, and there are few effective chemical or biological controls. We still have numerous problems managing the western flower thrips, Frankliniella occidentalis. The bad news is that the WFT is not alone. The new thrips kid on the block is the chilli thrips, Scirtothrips dorsalis. This thrips was detected in Florida in 2005. It also occurs in Australia, India, Indonesia,Taiwan and Japan. Chilli thrips have a wide host range that includes numerous ornamental and food crops. They are mainly foliage feeders, causing leaf distortion, bud abortion and plant stunting. They are not found in flowers or feeding on feeding on pollen. Chilli thrips apparently are able to transmit tomato spotted wilt virus (TSWV) and other plant viruses, so the potential problems from this species are serious.

Mites other than Spider Mites

Yes, Virginia, there are mites besides spider mites to be concerned about. We have seen more problems in recent years with tarsonemid mites (cyclamen and broad mites), and eriophyid mites (rust, gall and blister mites). These mites are microscopic in size and do not produce webbing. Eriophyid mites do not even look like“normal” mites. A hand lens is not powerful enough to see these tiny mites. The only good way to detect them is after they damage plants by producing galls, or stunting, distorting and bronzing leaves.

Downy Mildews

There are numerous downy mildews infecting a wide range of host plants, and the plant list continues to expand. Downy mildew on coleus seems to be the most recent problem. The downy mildew pathogens are related to those that cause Pythium and Phytophthora. There are currently eight different downy mildews that can infect different groups of plants, with little or no overlap. For example, the downy mildew that infects snapdragon is not the same as the downy mildew that attacks rose. Symptoms of downy mildew usually appear on upper leaf surfaces as a patchwork of purple, yellow or brown discoloration, often with leaf veins as borders. If the leaves are turned over, the tufts of gray or white fungal growth are visible.

Old World Hunter Fly

Not all introductions are potential problems. The so-called hunter fly, Coenosia attenuata,was first found in the United States in upstate New York in 1999. These flies are predators of many insects, including fungus gnat adults. They only go after their prey when it is flying. When it catches something, it punctures the victim with a dagger-like mouthpart and consumes the liquid inside. I mention this because after all the football is over and you’re tired of watching bowling,watching hunter flies do their thing could be entertaining.