New virus threatens cabbage crops

In the fall of 2000, several samples of cabbage and collard plants were received at the plant disease clinic in Tifton, Ga., that exhibited severely crinkled leaves and showed some mosaic patterns. These plants came from Brooks, Colquitt, Grady and Pierce counties.

Using PCR (polymerase chain reaction) techniques, it was determined that the affected plants tested positive for a whitefly-transmitted geminivirus.

The PCR product was sequenced and was found to be similar to cabbage leaf curl virus (CaLCuV) which was first reported in Florida in 1992.

This type of virus is spread by whiteflies and is the same type of virus as tomato yellow leaf curl virus (TYLCV) which we have had problems with in Georgia since 1999 due to high whitefly populations in the fall. We have observed CaLCuV again this fall in Colquitt, Echols, Grady, and Mitchell counties.

When CaLCuV was first reported in Florida, it was not very serious and currently is observed at low (sub-economic) incidence levels. However, outbreaks in Georgia have been quite serious and have caused up to 100 percent loss in some of the more severely affected fields.

As previously mentioned, the virus is spread by whiteflies very rapidly.

Once infected, the newest bud leaves of cabbage and collard plants become severely wrinkled and stunted which obviously results in unmarketable heads and leaves.

It is very difficult to recommend control measures for this disease because it has been only recently identified and its occurrence is so sporadic.

Controlling whitefly populations would seem logical but the best whitefly insecticides currently are not available for use on cabbage and collards.

Controlling TYLCV in tomatoes by spraying for whiteflies has not provided consistent suitable control.

The best methods for controlling this disease is to prevent virus-infected plants from being planted in the field and roguing out infected plants when they are identified. However, these methods require intensive scouting and plant screening and do not account for sources of inoculum outside of the field or in field borders.

Also, cabbage and collards in Georgia are grown adjacent to large plantings of cotton that harbor large populations of whiteflies, making insecticide sprays on these crops almost futile due to the influx of whiteflies from cotton. When cotton is defoliated, the whiteflies move out of the cotton and into surrounding vegetation, which in this case is primarily vegetable crops.

Farmers who grow both cotton and vegetables are advised to use insecticides to control whiteflies in cotton when it is grown adjacent to vegetables, especially collards and cabbage. There have been reports of come cabbage varieties being less affected by CaLCuV but side-by-side field evaluations have not been possible as yet.

The cabbage variety Bravo, which also happens to be one of our most popular cabbage varieties, is severely affected. In the coming years, we plan to use field trials to learn more about how to suppress losses to this disease. Until then, only the aforementioned tactics are available.

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