Garden Plot: Beware of basil blight and how to curb mosquitoes with BTI

Choose your basil plants carefully. Some sweet varieties could suffer from basil blight. (Thinkstock)

Beware: A bad blight wants to bag your basil

Bad Basil Bulletin! Plant pathologists at Cornell have informed me that it seems that the same company that supplied tomato plants that were already infected with late blight to big box stores a few seasons ago has struck again — this time shipping diseased basil plants.

The most common, and popular, form of basil — known as Italian large leaf, or sweet, basil — has been affected. (“Genovese” is the most common variety name.) The disease — a specific type of downy mildew — will first appear as a powder on the undersides of the lowest leaves.

So keep an eye on your plants. If you see this powder down low, immediately harvest all the unaffected top leaves, which are safe to eat. Then destroy that plant.

Some good news: Specialty basils (such as Thai basil and other varieties with smallish leaves) are not affected — only sweet basil. And because the herb grows so fast, you still have time to start new plants and get a nice harvest of sweet basil for tomato sauce season.

To start those new plants, however, you really must start over. Use a brand-new container (do not plant your new basil in the ground), brand new organic potting soil (no garden soil!) and fresh seed. At this time of year, the seeds will germinate rapidly and the plants will grow fast.

Place the container outdoors in full sun in an area with great airflow. But be prepared to bring the container inside on wretchedly humid nights, which is when the risk is greatest. Do it right, and you’ll dodge the blight.

Control mosquitoes with BTI

Richard in Springfield, who apparently used to wire telegrams for a living, writes: “Please guide how to get rid of garden mosquitoes.”

Well, Rich, the first thing I want you to do is to inspect your gutters and clean them out if they’re clogged. Poorly maintained gutters are the No. 1 unseen source of mosquito breeding.

Next, dump out any standing water you can, and get a container of BTI granules. (One common national brand is Summit’s Mosquito Bits. They’re available at most hardware stores and garden centers. And Gardens Alive sells them mail-order as No- Squito.) Harmless to all other living things, BTI is a naturally occurring soil organism that prevents mosquito larvae from developing in the water they require to transform from the egg stage to biting adult.

Shake the granules into birdbaths, gutters that aren’t angled correctly and any areas of your landscape that don’t drain well, including wet spots in your lawn or puddles that persist.

And if you want to use a personal repellant while working in the garden, Bite Blocker, Garden’s Alive Sting Free and Repel’s Lemon Eucalyptus are as effective as DEET, without the toxicity.

Money doesn’t grow on trees and apples don’t grow in pots

Ed in Fredericksburg writes: “My roses are doing great since I made the switch from wood mulch to compost; great advice!” (You’re welcome, Ed. Thanks for listening!)

“Now, I have a dwarf apple and cherry tree on my back patio that are covered with Japanese beetles. The trees are in containers so we can bring them in over the winter. We planted them about a month ago with Miracle-Gro garden soil.”

Bad plan, Ed. Fruit trees must be planted in the ground during the winter so that they can get the required number of chilling hours. (And their roots would freeze if left outdoors in pots.) And the beetles were probably attracted by the chemical-laced soil you used. Chemical fertilizers make plants very attractive to these ravenous pests.

I would plan to replace the trees with ones you can plant in the ground this fall (not now; this is the worst time of year to plant a tree). Just be aware that cherry trees get very large, and that you’ll need more than one apple tree for good pollination. (You’ll also need to learn how to prune and thin them. They are very high-maintenance plants.)

‘Rope a Dope’ is the best plan for broadleaf weeds

Bill in Stephenson writes: “I’ve used corn gluten the last three years and my lawn looks fabulous with the exception of a few broadleaf weeds. Is there an organic broadleaf weed killer? Or is correct lawn care the answer?”

I love it when they answer their own question! Of course correct care is the answer, Bill — especially this time of year, when summer heat stress is moving in, and your desired grass is at its weakest. Time to make like The Champ: Lay back on the ropes, and let the weeds wear themselves out.

For cool-season grasses (such as bluegrass and fescue) that means cutting at 3 inches in sun, 3.5 in shade, but no lower. Always return the clippings to the turf. And if we’re ever going to need to add water this soggy season, do so deeply and only once a week — but only if it doesn’t rain at least an inch that week. (Wouldn’t that be nice?)

And don’t feed cool-season lawns between now and mid-August. Summer feedings create bare spots, as does spot killing of broadleaf weeds in warm weather, no matter what you use.

Giving the garden a season of rest

Bill in College Park wants to know the best way to rest his veggie garden this winter and next summer. He writes: “I have access to fresh horse manure (with sawdust and hay mixed in to keep the aroma in check) and was thinking of tilling it in, leveling it off and putting black plastic on next spring to sterilize the soil.”

No, no, and no, Bill! Just because you have access to something doesn’t make it a good idea. In fact, it’s a bad idea for at least five different reasons:

  1. Tilling causes weeds.
  2. You should never use any manure while it still has an odor.
  3. You never want to let sawdust anywhere near a garden.
  4. You especially don’t ever want to till saw dust into a garden.
  5. And solarization is an exact science that requires a specific thickness of clear plastic.

Your easiest option is to just cover the garden in shredded leaves this fall. If you want to be more adventurous, plant a cover crop late this summer that will die over winter. The resulting stubble will protect your soil against weedy invasion.

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