It can be confusing at this time of the year if the weather is causing some problems in our gardens or if the problem is caused by some other means. This year, lilies started out with many of them having yellow or yellowing leaves with as many plants not producing the normal amount of flowers that a gardener would typically see.
This occurred in many of the varying lilies, including the old fashioned orange or yellow colored lilies. You may see that some of them now look like they are on their last leg and you might be wondering if they will make it through this weather.
The basics behind this problem are many fold. It has been thought that the warm spring, followed by frost occurrences have left the door wide open soon after for these types of plants to be affected by a fungus. This is not written in stone that this is what is really going on but the early prognosis is pointing to a fungus and now drought causing the problem with our lilies. There isn't a whole lot that you can do but keep watering the plants and next year think about treating those plants as they emerge from dormancy, following the directions on the fungicide spray for application rates.
According to Michelle Grabowski, U of M Extension educator, many gardeners are noticing that their cone flowers (Echinacea spp.) are not so purple this year. In fact many flowers are partially to completely green and several have odd green growths sticking up from the center of the blossom. These are symptoms of the disease aster yellows.
Aster yellows are caused by tiny bacteria - like organism known as a phytoplasma. Phytoplasmas live with the phloem (nutrient conducting vascular system) of plants. The aster yellows group of phytoplasmas can infect over 60 families of plants including many common garden perennials, vegetables and weeds. Although many gardeners are noticing disease symptoms on coneflowers, infection of other plants such as cosmos, golden rod and carrot have also been reported.
Leaves of plants infected with aster yellows are often discolored yellow to red. The phytoplasma affects normal growth and development of the plant, resulting in clumps of weak shoots known as witches broom developing throughout the plant or on flower stalks. Flowers are often the most visibly affected part of the plant. Flowers often remain green and are distorted.
The aster yellows phytoplasmas are moved from plant to plant by aster leaf hoppers (Macrosteles spp.).
These insects have sucking mouth parts and they inadvertently suck up phytoplasmas with the plant sap they are feeding on. From then, the phytoplasmas actually live and reproduce within the aster leaf hopper.
Whenever the leaf hopper feeds, some phytoplasmas are released into the new plant, starting a new infection. Aster leaf hoppers do not overwinter in Minnesota.
Unfortunately, once a plant is infected with Aster Yellows, there is no way to cure it. Perennial plants may survive many years with the aster yellows phytoplasma and can serve as a source of the disease within the garden. The best way to deal with aster yellows is to remove infected plants.
Plants infected with aster yellows can be thrown on the compost pile or buried because the phytoplasma will not survive once the plant dies.
Unfortunately, removal of infected plants is no guarantee that the disease will not return to the same garden. Infected leaf hoppers and infected perennial weeds can both be a source of new infections in the garden.
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