Digging In: Treating Diseased Hollyhocks; Fighting Indoor Pests; Repelling Deer

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By Scott Aker
Special to The Washington Post
Thursday, May 28, 2009

Q Could you recommend a brand or two of fungicide to treat rust disease on hollyhocks?

A There are too many brand names to list here, but I can give you some details on active ingredients. My choice would be any fungicide containing myclobutanil, because the interval between sprays is longer than for most fungicides. There are fungicides with other active ingredients, namely copper, chlorthalonil, thiophanate-methyl, triadimefon and mancozeb. They are all effective against rust diseases of ornamentals. If you want an organic option, you could try a pesticide containing neem oil.

It is important to clean up and remove all traces of last year's diseased foliage. Given the amount of rain we have had this spring, spraying may be crucial to prevent rust outbreaks this season. You may also decide to replace your hollyhocks with another tall herbaceous plant with fewer chemical dependencies. Candidates include kniphofias, lilies, joe pye weed, acanthus and foxgloves.

When I brought my houseplants in last fall, they had accumulated insect pests from spending the summer outdoors. How can I prevent that this year?

One of the only downsides to a summer vacation outdoors for your houseplants is the insects that can hitch a ride indoors. The best line of defense is prevention. Don't neglect your plants during their time outdoors, and deal promptly with any major insect and mite problems that appear. When the time comes to bring them inside, plan ahead. Instead of working frantically the first night that frost is forecast, spray them before then with a 1 percent solution of horticultural oil. Bring them indoors when the spray has dried. Spray the plants thoroughly, and concentrate on the underside of the leaves.

Some insects may still find their way indoors. Pillbugs and millipedes always come indoors with my plants. They are not a major threat to the plants, and they seldom appear in sufficient numbers to cause any concern.

I have a lovely hydrangea, but over the past two summers a deer has eaten the top of the branches, resulting in few or no flowers the next year. What can I do?

One solution is to drive stakes around the hydrangea and cover the entire plant with netting, though this is not the most attractive solution. You could also try any one of the many deer repellents that are found on garden center shelves. These need to be applied frequently to work well, particularly when the plant is growing rapidly, to protect the new growth. The spray must also be renewed whenever rain washes it off.

Scott Aker is a horticulturist at the U.S. National Arboretum.


© 2009 The Washington Post Company

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