Tuesday, August 14, 2012
Does this look familiar? Besides a plague of powdery mildew and other diseases, our plants this year are suffering from a plague of hungry insects like this Japanese beetle. In part this is payback for our wonderfully warm winter. During that second week in February when we are asking ourselves why on earth we live in Chicago and dreaming of a home in Zone 7, we are not considering the advantages of a nice, cold winter.
Both fungal spores and insect larvae have to hide out somewhere during the winter. The Japanese beetle lays eggs in the soil, where they become grubs the following year. Eggs and spores that cannot survive a typical winter here mean that those species cannot plague us here.They plague our friends further south instead. But within our zone the harsher the winter the lower the survival rate for any organism exposed to it. From that point of view, our motto should be, "Let it freeze, let it freeze, let it freeze." There is no free lunch -- except for the beetles chewing on our roses.
So what to do about these unwelcome guests? Our options for getting rid of adult beetles are fairly limited. They are clumsy fliers and some people try to knock them off into a liquid. There are lots of beetle traps available, which I think are more trouble than they are worth. If you are feeling more adventurous than I, there is a wasp called Tiphia vernalis that preys on adult beetles. It is more available to the east of us than it is here, but it is effective. Otherwise you are stuck with some of the standard poisons like Malathion and Carbaryl. The plant based insecticide, Rotenone, can also be tried although it is rated less effective than the first two.
Prospects look much better when it comes to attacking the grubs. My lawn clients have been using Milky Spore -- a bacterium that eventually kills off the grubs that become Japanese beetles. Like most organic methods, however, it takes a while to become fully effective - in this case 2-4 years. For more immediate results you can use Bacillus thuringiensis (Bt).
Any of these methods will help you get your insects under control. but it will not get rid of them. Just like digging up all your dandelions will not prevent seeds from next door from drifting over, your efforts here will not stop Japanese beetles from flying in from the next block the following day and settling down again. Sigh. The real benefit of gardening is that it teaches us patience.
Sunday, August 5, 2012
We have experienced more plagues this summer than just drought. One of them has been an explosion of powdery mildew. A traditional enemy of common lilacs, this fungus attacks many shrubs, perennials, fruits and vegetables. The nursery industry has devoted many years to developing mildew-resistant strains of your favorite plants, and this has been a big help. Proper housekeeping and clean-up by home-owners, especially at the end of the season, also helps. For most people powdery mildew has been only an occasional problem on some plants.
Not this year. There is now powdery mildew in almost every yard. Peonies and phlox have been particularly hard-hit. The problem started, I believe, during the monsoons of last summer, when all our rainfall and humidity allowed the disease to gain new foot-holds. By the time we began to notice problems, the season was drawing to a close, so most of us did not do much about it. The mildew had a chance to create its spores, and they in turn had a wonderfully easy time surviving our mild winter. The result is the minor epidemic we see now. And all the recent watering we have done with sprinklers has spread the fungus even more. One of the first things you can do to resist powdery mildew is to replace your sprinklers with soaker hoses in your shrub and perennial beds.
Powdery mildew is easy to spot, as you can tell from the photograph. It harms fruit and vegetable production. For most plants it is disabling, but not fatal. It is, of course, disfiguring. Some of us have lived with our old mildewed lilacs for years, but other plants can be too ugly to look at.
The first step in controlling this pest is pruning. You should prune out as much diseased foliage as is practical, and, while you are at it, prune the area to thin and to increase air circulation as well. The leaves should not be composted. They are covered with spores that can spread the disease elsewhere. For badly infected perennials that have already bloomed (like peonies), it is probably better to cut the entire plant to the ground and wait for next year. Clean the ground around the plants thoroughly as well and remove any mulch you have in the immediate area. Again, remember those spores.
As for treatment, organic methods, are, as usual, more work and less effective than others, but still worth trying first. The easiest is to mix 1/2 tsp. of baking soda with a quart of water and spray regularly. This increases the leaves' PH and makes them more inhospitable to the fungus. Neets oil is also recommended by some. Sulfur is one of the most effective treatments for garden diseases. You can make your own sulfur solution with a garlic press, a strainer and a quart of water. Garlic has a high sulfur content.
If you are discouraged by this, you can always "nuke 'em" by using a commercial fungicide that contains sulfur or triforine. Read the label carefully. While toxic in liquid form, many are much less so once they have dried. It is worth mentioning that even these products don't "cure"what is already damaged; they just prevent new damage. And they are most effective when the fungus is first evident.
In short there are no miracles here. To have a better season next year you need first to clean up thoroughly this fall. Then look for disease resistant cultivars when you buy new plants next spring. Use soaker hoses. And thin your plants to get plenty of air circulating. After all, how much garlic do you want to crush when you can not even eat it?