Homegrown column Aug. 29, 2009

Our cucumber plants’ leaves have spots on them and they turn yellow. Is this a fungus? If so how do we treat this?

I can’t be sure without actually seeing the leaves, but I’d guess you have powdery mildew. We’re seeing a pretty good amount of it right now, mostly because of the wetter than normal June we had.

Unlike powdery mildew on roses, which a different fungus and really doesn’t do that much damage to the plant, mildew on cucurbits will cause defoliation and severe damage to your plants. The first step in dealing with it is to make sure that the leaves of the plant stay as dry as possible. Soak the plant from below to water it. If you cannot avoid overhead sprinklers from hitting it, water between 10 a.m. and noon.

There are several sprays I like to use for this. There are two organic choices. The first is called Season Long Spray Oil. You want to be sure to spray only early in the morning when it’s coolest and completely spray the plant — both the upper and lower leaf surfaces. It’s probably a good idea to give it a second spraying a week later. 

The second spray is called Remedy. It contains potassium bicarbonate, which is closely related to some our antacid tablets. Now, don’t assume you can use the Tums. The products are different. Follow the same directions as I’ve given for the oil. 

The last spray is a Fertilome product called Landscape and Garden Fungicide. Like the first two, you want to spray the plant thoroughly early in the morning and repeat the application again in a week or so.

You should start to see clean, new growth appear in a couple weeks.
I just bought a geisha mix plant (celosia). I was just wondering if it is a plant that comes back or if it is a one time thing?
— Amie

Celosia is an annual plant. It will die off this winter and you’ll have to replant it next year. The good part of the story is that annuals, which only live one year, will bloom pretty much all summer long. That’s the trade-off between annuals and perennials.

Perennials are loved because they come back year after year but they have a limited bloom season. 

I have three lilac bushes that are 10 years old and this is the first year they have been covered with blooms. Should I try to prune off all those seed pods? There are also a lot of sucker growths coming. Should I prune these out? 
— Tim

Pruning off the seed capsules will make the plant look better, and it may bloom a bit better next year because the plant isn’t wasting energy making seed. In all honesty, most people (including myself) don’t worry about pruning them off. If you want to cut them off, be careful. Just below that seed stalk there is a pair of buds. You don’t want to damage them because these top two buds are the only ones on that stem that will bloom next spring.

 As for the suckers, you actually want to encourage them to grow. In time, you’ll want to cut out a few of the biggest and thickest stems and allow those young sprouts to take their place. This will keep your plant fresh and vigorous with good dense foliage and abundant bloom.

Dennis Hill is the nursery manager at Bookcliff Gardens, online at http://www.bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or e-mail .(JavaScript must be enabled to view this email address).


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