In spite of the recent stretch of 80 and 90 degree days, fall is definitely in play. The leaves are beginning to show their true colors and the asters and mums are blooming. Soon it will be time to put the gardens to bed, roll up the hoses and prepare for the colder months ahead. And just when we think all the threats to our gardens are under control we are alerted to a couple of new ones we can possibly look forward to next year. Here is brief introduction to two of the newest we can be on the lookout for next growing season.
Rose Rosette Disease (RRD) is a virus that is spreading throughout the country which deforms roses and kills infected plants in two to three years. RRD has been conformed or sighted in four Canadian provinces and more than two dozen states mostly in the South and Midwest.
It was discovered at the Minnesota Landscape Arboretum last year and the U of MN Plant disease Clinic in St. Paul has seen about 10 cases a year in the last few years. Over 550 rose cultivars are susceptible to the disease which turns the leaves red in irregular patterns, produces deformed clumps of rose buds, and an excessive number of thorns on thick red stems. The most alarming fact is that it is spread by a microscopic mite that is blown in by the wind; a single mite can destroy a rose plant. Once a cane is infected the virus can travel down to the roots and then through the other canes. Although a rose bush may not immediately die once infected it usually succumbs within a year or two depending on the age and size of the plant.
Alas there is no cure for RRD! Although researchers are working diligently to better understand RRD and perhaps find a cure or at least a treatment, there is very little you can do at this time if you should discover your roses infected. In this case your best recourse is to remove the plant. You can attempt to just cut the cane showing sign of infection, but since there is no way to tell if the virus has already traveled to the other canes you may just be delaying the inevitable. Pull out the plant cut it up and bag it. You can plant another non-rose plant in the site immediately but you should wait to plant another rose in the spot until you are sure that all of the rose roots are gone.
Spotted Wing Dropsophila (SWD) is a small fly no larger than 2-3 mm which was accidently imported from Asia in 2008. It first showed up in Minnesota in 2012. The SWD deposits it eggs in soft fruit, primarily raspberries, although it can use other fruit such as blackberries, strawberries or plums. The fly is most active between July and the first frost. Once they hatch, the tiny white larva feed on the fruit, leaving areas that appear sunken and rotted. Fruit that is soft on the vine is indicative of infection and if picked should be inspected for the tiny worms. The larva is not toxic but very unappealing in your fruit! The tiny eggs are not visible to the eye. If fruit is picked before the eggs hatch and left at room temperature they will hatch. Fruit that appeared perfectly normal when picked can deteriorate in hours.
SWD is difficult to control. You can spray for the adult fly with insecticides but this must be meticulous and carefully timed. You must follow all directions, especially those relating to the time interval required between application and harvest. You could cover your bushes with a fine netting to prevent the fly from getting to the fruit, but lifting the net to harvest the fruit can open a window of opportunity for the fly to reach the remaining fruit.
Your best bet if you discover that your fruit has been infested is to report it to the Minnesota Department of Agriculture and practice good sanitation. If your fruit is infested one year, it does not mean it has to be infested next. Clean up all the fruit on the ground. Pick the remaining fruit, dispose of all the infected fruit, by microwaving or cooking, to kill the larva, or place it in a plastic bag and put it in the trash — not the compost.
Good luck and I hope you do not encounter either of these newest threats in your garden next year.