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Q&A with Bob Polomski 19

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Extension Consumer Horticulturist, Clemson University

Every summer our tall fescue lawn is taken over by yellow nutsedge. We've tried handpulling and even replanting, but to no avail. Is there any solution?

—T.L. Bethpage, NY

Answer: Yellow nutsedge (Cyperus esculentus) has triangular stems with shiny, yellow-green leaves. Native to the Mediterranean but now spread worldwide, nutsedge thrives in full sun and, like other sedges, prefers low-lying areas where the soil is uniformly moist. This hardy perennial goes dormant in the fall but regrows in late spring and summer from small tubers, which it produces by the thousands. These tubers are edible, and have even been offered by vegetable seed catalogs under the name “chufa.” To paraphrase the plant explorer David Fairchild on running bamboo, one way to control yellow nutsedge is to eat more of it. Alas, the public's feeble appetite has so far been unable to prevent the plant from becoming a weed.

Small infestations can be controlled by patient handpulling, but this will have to be done faithfully until the supply is exhausted. The regrowth of nutsedge will be slowed by avoiding excessive irrigation and by ensuring that the lawn is well drained. Regular mowing, fertilizing, and a soil pH of 6.5 will favor the growth of your fescue turf.

In the case of a heavy infestation such as yours, herbicide applications are the most likely way to provide control. Herbicides, however, will need to be reapplied, because the tubers can remain dormant for an extended period of time. Homeowners can use an herbicide containing methanearsonate (Bayer Advanced Lawn All-in-One Weed Killer for Lawns). Other nutsedge herbicides must be applied by licensed commercial lawn applicators. These include bentazon (Basagran) and halosulfuron (Manage).

Ideally, any herbicide should be applied in late spring or early summer when the nutsedge is young, actively growing, and most sensitive to treatment. Mature plants, and plants growing in dry soil, are more difficult to kill.

I've seen claims that red plastic mulch will produce earlier and larger tomatoes. Is that true?

—CT., Cottonwood, UT

Answer: Red plastic mulch has indeed been shown to promote both earlier yields and increased size in tomatoes by as much as 20 percent. The benefit appears to come from two sources. First is the increase in soil temperature that any plastic mulch will provide. The second source of improvement is more complex, involving the ratio of far red to red light reflected upward to the foliage from the mulch. Greenhouse experiments have shown that the ratio of far red to red light hitting the leaves has an effect on the allocation of photosynthate. Specifically, a high ratio of far red to red light leads to improved shoot and fruit development. Not all red plastic will produce the desired effect, however; it must generate reflected light with a precise spectral composition. If you wish to experiment, be sure to use the specially designed red mulch called SRM-Red, which is manufactured by Ken-Bar ( Be advised that the growth of tomatoes in red mulch has not proven to be consistent, suggesting that local conditions also affect the outcome.

A neon-yellow, foamylooking blob just appeared one day on my mulch. It eventually turned black and powdery. How can I prevent it from coming back?

—M.T., Litchfield, NH

Answer: The colorful organism on your mulch is a slime mold, probably Fuligo septica, known colloquially as scrambled egg slime or the dog vomit fungus. Slime molds belong to an unusual class of organisms, the myxomycetes, that exhibit both animal and plantlike behavior. Cool, moist conditions prompt the invisible spores to germinate, releasing amoebalike cells. In time, these cells coalesce to create a multicellular plasmodium—the giant, frothy-looking mass you've seen. This colorful slime can flow over mulch, sidewalks, and even entire driveways in search of food (bacteria and other microorganisms). Scientists have discovered that the plasmodium can move as much as two feet or more per day. It poses no threat to your landscape. Eventually, the slime mold reaches the reproductive phase, when it dries and develops mushroomlike fruiting bodies. These release dustlike spores, which are spread by wind.

This curiosity warrants no control, since it will eventually dry up and disappear. However, if you're annoyed by its appearance, use a garden rake to break it apart, or spray it with a stream of water from the hose. Slime-mold outbreaks can be avoided by adjusting the irrigation system to prevent the mulch from becoming too wet. Also, periodically fluffing up the mulch with a rake will help aerate it and speed up drying.

I've been having problems with my fall lettuce crop. I sow the seed in late August, but I end up with a lot of skips. What am I doing wrong?

—T.L., Beekman, LA

Answer: Lettuce is a cool-weather crop. The optimum temperature range for growing it is between 55 and 70°F. The difficulty you are having is due to the lettuce's physiological response to warm weather, known as summer dormancy. When the soil temperature exceeds 85°F, lettuce seed experiences thermoinhibition and will not germinate.

Unless you can delay your sowing until the soil has cooled in the fall, you will have to take other steps to get your lettuce seed to sprout. One way to do this is to raise transplants by sowing the lettuce seed indoors, or in a shaded location outdoors, where the soil temperatures are cool. Allow three to four weeks for the seedlings to reach a size where they can be transplanted to the main garden.

Alternatively, you can sow seed directly in the garden under a temporary canopy of shade cloth or wooden lattice, or in the shadow of existing crops. Keeping the seed bed evenly moist will also help cool the soil through evaporation.

Successful seedling establishment is only half of the equation, however. It is also important to select varieties adapted to warm conditions. ‘Buttercrunch’ (Bibb type), ‘Ermosa’ (butterhead), ‘Red Sails’ (leaf), and ‘Apollo’ (romaine) are all heat-resistant varieties that should do well.