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Jeff Lowenfels: powdery mildew, lawn repair and banana slugs

Jeff Lowenfels
A banana slug, which isn't native to Southcentral Alaska. If you find one of these, let me know! Inklein photo / CC via Wikimedia

I am often asked to write a column about a specific subject. This is not always easy, as the timing may not be right, the issue may not be one of general interest or there isn’t enough to say about at the subject to fill a whole column. Still, most are good subjects that present questions that need answering.

Take the issue of what to do about powdery mildew. This is the name given to a number of fungi, all of which form a white, powdery substance on the tops and, less often, the undersides of leaves. They are hosted in particular by two popular shrubs, caragana and lilacs. Roses get powdery mildew, as do impatiens, begonias and tall lawn grasses. So do cottonwoods, which, along with caragana, seem to be a vector for the stuff. Many would argue you should get rid of any caragana (not to mention the cottonwoods).

It’s a bit late now to deal with these fungi. However, there are some general rules to follow to prevent it. First and foremost is air circulation. Prune out the bottoms of shrubs so air can move through them. And thin out older growth, again so air can move through the leaves of the shrub. Good sunlight helps plants dry off, so that is needed for susceptible plants as well. Spraying with some of the remedies noted below, as a preventative measure, should also help.

Once you see powdery mildews, it is almost impossible to get rid of them but it is always worth a try provided you go organic. Some folks regularly spray their plants with homemade concoctions to keep the stuff at bay in the first place. Compost tea is one. Milk is another favorite spray ingredient, with recipes using a mixture somewhere between equal parts water and milk and a 3-to-1 ratio. This is sprayed on plants once a week or after rain or when infections are noted.

The other remedy, actually one that the Cooperative Extension Service suggests, is one teaspoon of bicarbonate soda mixed in a quart of water. Don’t overuse this stuff, as it may burn the leaves if you do so. And make sure to clean all cutting and other tools that come into contact with it.

Next is when to repair the lawn. Sure, this is a great topic but right now we are on the edge of the period when you can safely spread seed and have it all germinate before a killing frost. It takes about 21 days. Do we have three more weeks left? It’s a gamble but if you act this weekend, you probably will make it. Any later than that and you are really taking your chances.

In any case, this is a simple one. Buy the seed that has the least amount of weeds in it. It's on the labels. Roll the seeds in endomycorrhizal fungi. Once they're on the ground, make sure the soil is damp for the entire 21 days. Keep animals, including humans, off it.

Here is another good one: how to grow one of those really, really, big dahlias like the ones at the State Fair this year. The trick is to plant “dinner plate” varieties. That is really all there is to it. These are the ones that have been bred to produce the biggest flowers. It also helps to let just one bud develop, which means pulling off any competitive buds and hence sacrificing a lot of flowers. It’s up to you.

Finally, here’s one that just won’t fit an entire column … yet. Is it possible to have seen one of those huge, yellow, Seattle-size banana slugs up here? At least one reader, the questioner, has seen and photographed one, so the answer is an unfortunate yes. All sorts of things hitchhike up here on plants and in soils. Tiny snails are now almost common, whereas they were unheard of 15 years ago. Banana slugs? Oh, no. Get the traps going. And please, send pictures if you spot a banana slug yourself.

 

Jeff’s Alaska Garden Calendar for the week of Aug. 29

Alaska State Fair: Go. Enjoy. Vow to enter your veggies and flowers next year.

Alaska Botanical Garden: Visit. It looks terrific. Walk the Lowenfels Family Nature Trail while you are there. That is what it is for.

Fungi: They are all over this time of year. Get a good identification book. 

Harvesting: Do it. 

Greenhouse tomatoes: Unless you are going to heat into the fall or move plants indoors, the new flowers you see won’t produce. 

Potatoes: Wait until after frost to harvest.

Sweet peas: Keep picking the flowers to keep plants flowering.