by Xavier Martini, Austin N Fife, Gary Knox, and Mathews Paret
The eriophyid mite Phyllocoptes fructiphilus is the vector of Rose rosette virus (RRV), an emaravirus identified as the causal agent of the devastating Rose Rosette Disease (RRD). Incidence of RRD has grown exponentially, as the range of P. fructiphilus spread from the non-native, invasive wild rose, Rosa multiflora (Thunb) into other cultivated and uncultivated roses in the southeastern United States. In July 2019, P. fructiphilus was collected for the first time in Florida. Phyllocoptes fructiphilus is an established native pest of ornamental roses in the western United States and has become widely distributed in the eastern United States. However, the mite has never been previously found in Florida. RRV is currently not established in Florida. However, RRV infected plants have been identified on plants shipped for commercial production to Florida many times since 2013 and destroyed by UF-IFAS in collaboration with DPI-FDACS. Phyllocoptes fructiphilus were not present in any of these intercepted plants. This new confirmation of the presence of Phyllocoptes fructiphilus in the landscape is critical and warrants continued monitoring of the mite in Florida.
Description and biology
Eriophyid mites like Phyllocoptes fructiphilus are notable for their small size (140-170 µm long and 43 µm wide), carrot-shaped body and for having only four legs instead of the usual eight for other mites. P. fructiphilus lives on the new growth of buds and between stem and leaf petioles during the warm season. Mites overwinter under bark and old bud scales. Females begin laying eggs on shoots in the spring. Development from egg to adult takes 1 week. Adult females can live up to 26 days, and they can lay an egg each day. Therefore, these mites have the potential to build up to large numbers very quickly. P. fructiphilus lives and breeds on all cultivated roses, wild native roses and wild non-native roses such as multiflora roses.
Disease symptoms
It generally takes between 17 and 90 days for P. fructiphilus to transmit RRV to a rose. Symptoms appear 1 to 3 months after infection. As the mites are not visible to the naked eye, knowledge of how to recognize RRD symptoms is essential. Symptoms include: witches’ brooms (red small twisted leaves on elongated branches); severe thorn proliferation; leaf mosaic; distorted leaves and flower buds. Some of these symptoms can be misidentified and confused with herbicide damage or young leaf flush. In spring and fall, many healthy roses have reddened foliage; however, red pigmentation associated with RRD will persist for the life of the foliage. Plants usually die 1 to 2 years following infection.
Dispersal
Phyllocoptes fructiphilus dispersal is mostly aerial and the mite spreads via wind currents between plants. Therefore, the closer a rose is located to RRD roses the more likely it is to be infested, especially if the roses are situated downwind from the mite source. It is likely that humans also disperse these mites by moving infested plants or plant parts between different locations. Phoretic dispersal via insects and other animals is also possible but has not yet been demonstrated for P. fructiphilus. Another possible source of dispersion is by contaminated clothing and equipment.
Management
There is currently no cure for RRD. If a plant is infected, it is recommended to uproot (as the virus survives in the roots) and destroy the plant immediately. A new plant can be planted 7 days later in the same location, as mites do not survive more than 5 days without a rose host. To avoid spread of the disease, it is recommended to inspect roses for RRD symptoms before being purchased and avoiding entering areas with roses after coming back from an infested area. RRD can be transmitted by grafting but not by pruning.
Cultural control of mites
As dispersal of the mites is mostly aerial, walls and windbreaks may reduce P. fructiphilus dispersal and the spread of RRD. When planting roses, leave enough space between plants to prevent leaves from touching, which allows mites to crawl from one plant to another. Pruning will reduce mite populations, but prunings and fallen debris may contain mites. To prevent prunings from dispersing mites, it is critical to immediately bag prunings on-site and transport bagged materials for off-site disposal.
Chemical control of mites
Spirotetramat (e.g. Kontos®) and abamectin (e.g. Avid®)* based miticides include products labelled for eriophyid mite control in greenhouses and nurseries. Some studies indicate that carbaryl or bifenthrin based insecticides may effectively control P. fructiphilus. These chemicals can be found in some products labelled for use in landscapes and home gardens.
Scouting and collection
Due to their size, the mites are only visible under magnification. They can be found on leaf petiole bases and axillary buds, and are associated with fast-growing and soft tissues. There are a few different species of eriophyid mites that live on rose other than P. fructiphilus. Species identification can only be done under a microscope by a specialist. If the presence of either Phyllocoptes fructiphilus or RRD is suspected, please contact below before shipping. Collect the damaged/infested shoots and/or fruit and place them into a sealable polyethylene bag. Place paper towels into the bag (to reduce mold) and then carefully seal the bag before sending it to the following addresses:
Sam Bolton Division of Plant Industry/Entomology Florida Department of Agriculture and Consumer Services The Doyle Conner Building, 1911 SW 34th St, Gainesville, FL 32608 samuel.bolton@FreshFromFlorida.com 352-395-4679 or Dr. Xavier Martini University of Florida NFREC, 155 Research Road, Quincy, FL 32351 xmartini@ufl.edu 850-875-7160
Resources
For more information on RRD, please visit these sites: Rose Rosette Disease: A New Disease of Roses in Florida https://edis.ifas.ufl.edu/pp317
Roserosette.org
* Mentioning these pesticides does not signify endorsement or recommendation of any specific treatment option or chemical by the University of Florida.
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