Downey Mildew problem for Impatiens

Starting in late 2011 the downey mildew disease of impatiens called Plasmopara obducens made its first appearance in Florida.  This disease has been known in other parts of the US for many years.  In Europe this disease has caused rapid destruction of impatiens.  There have been reports of the disease in Costa Rica, Guatemala, and Central America.  The potential for this disease to become widespread is enormous.

This disease likes cool moist conditions, so with summer here we may get a break until the cool weather returns.  Water and wind easily disperse the sporangia (a single celled or many celled structure in which spores are produced, as in fungi, algae, mosses, and ferns. Also called spore case.) produced on infected plants with younger tissue being more susceptible.

The symptoms are very subtle in the beginning.  First signs are faint chlorosis or stippling of the leaves that will become completely chlorotic.  Infected leaves fall off as the disease progresses, leaving bare stems.  If you inspect the underside of the leaves you will see downy white to light gray and masses of sporangia and sporangiophores.  Eventually the entire plant collapses.  The disease has spread considerably by the time more obvious signs have been noticed.

To help prevent this problem in your garden start with clean plants.  If you notice this in your landscape remove any debris from the plant immediately.  You should not compost infested material as it will contain lots of long lived spores that will get into the next generation of impatiens.  If you get this disease in your garden you may want to choose another plant for a while.

Most fungicides will be a used to protect not prevent.  If you need to use a fungicide the following are recommended by Cornell University;

Common Name of product          Active ingredient

Adorn                                                   *fluopicolide                      * follow resistance management guidelines

** FRAC Code 43

Presiio                                                  *fluopicolide                      * follow resistance management guidelines

** FRAC Code 43

Fenstop                                                 *fenamidone                    * this has a high risk of resistance

** FRAC Code 11

Subdue Maxx                                         *mefenoxam                    * some resistance

** FRAC Code 4

Heritage                                               *azoxystrobin                   * high resistance risk

** FRAC Code 11

Stature                                                 *dimethomorph                 * this has a low risk of resistance

** FRAC Code 40

You may need to use the services of a pest control company like Floridian Pest Management, Inc. and if you choose to try fixing this without a pest control company please read and follow all label directions.

To help avoid getting any resistant strains rotate the fungicides. Using a siloxane (any of a class organic or inorganic chemical compounds of silicon, oxygen, and usually carbon and hydrogen.) based adjuvant with the fungicide for foliar applications has been found to be beneficial.  Remember to always read and follow the label of the fungicide for direction of use.

Any questions you may email me;

Posted on by Dean Hall in Blog