Q&A WITH BOB POLOMSKI 16

Extension Consumer Horticulturist, Clemson University

I have a number of evergreen azaleas whose leaves are turning yellow and falling off. Do they need to be fertilized? Could it be something more serious? –T.N., by e-mail

Answer: It could be normal leaf drop. Evergreen azaleas retain their leaves for three or four years before shedding them from the interior portions of their older branches. Some evergreen azalea varieties are prone to more frequent leaf-shedding than others, especially when on of the parents is a semideciduous azalea.

Although azaleas have relatively low nutritional requirements compared to other shrubs, a deficiency will cause leaves to turn yellow. A lack of nitrogen causes older leaves to turn yellow; inadequate levels of iron or magnesium cause the youngest leaves to develop interveinal chlorosis, which is characterized by yellow leaves with green veins.

Waterlogged soils or a high soil pH can reduce the availability of iron, as well as hamper roots’ absorption of it. Drought or injury from voles, insects, or diseases will cause leaf yellowing and leaf drop. These symptoms can also be caused by certain herbicides accidentally coming into contact with your azaleas.

I recommend that you submit a soil sample from the vicinity of the affected azaleas to your local extension agency and have it tested for pH and fertility levels. The soil test results and a visual inspection of the plants should help you diagnose the exact problem.

I live in southeast Wisconsin and my Kentucky bluegrass lawn is spotted with unsightly clumps of taller grass. How can I get rid of the invader without harming my bluegrass lawn? -S.Y., Kenosha, Wl

Answer: The clumps you describe are most likely a pasture-type of tall fescue (Festuca arundinacea), such as ‘Kentucky 31’. This grass has wide leaf blades, a lighter green color, and a pronounced clump habit that makes it look weedy in a fine-textured blue-grass lawn. Unfortunately, there is no cultural control that will assure you a pure blue-grass lawn, because both species are equally well-adapted to your site. The solution, therefore, is to physically or chemically remove the clumps of fescue. Handpull or dig out small pockets of tall fescue, removing as much of the root system as possible. Alternatively, spot spray or brush a nonselective herbicide, such as glyphosate, onto the individual clumps. The resulting bare areas will be filled in by Kentucky bluegrass, which spreads by underground stems or rhizomes. Where you have larger patches of tall fescue, spray a nonselective herbicide over a roughly rectangular area. Rake out the dead vegetation and then sow fresh b Laying down bluegrass sod will give you a quicker repair and will let you avoid the lengthy germination period for the seed. You might find that you can make and use your own sod, cutting it from out-of-the-way areas of your lawn.

There is a selective herbicide, chlorsulfuron (Corsair), that can be used to spot treat tall fescue in Ken tucky bluegrass lawns. Corsair will also control ryegrass, wild garlic, Virginia but-tonweed and a number of other lawn pest species. However, the product is expensive (about $100 for a two-ounce bottle, which is much more than you will need), so it is probably best to arrange for a commercial lawn service to make the application.

What is the best way to transplant palm trees?-A.F., Ojai, CA

Answer: Palms are best moved in late spring to early summer. They have a simple fibrous system of primary roots that emerge from a root initiation zone at the base of the trunk (below). Even on mature specimens, a majority of the roots are located within a foot of the trunk, so digging a root ball one foot deep and one foot from the trunk will be sufficient for most species. Pindo palm, Chinese fountain palm, and queen palm are exceptions. They should be moved with a larger root ball, one dug at least two feet deep.

Because palms are monocotyledonous trees, their vascular bundles are scattered throughout the stem. (As opposed to the ring of vascular and cork cambium on the outside of the trunk that dicotyledonous trees possess.) Therefore, there is not the danger of girdling the trunk when handling larger specimens. Still, gouges to the trunk will not repair themselves, so take care when moving your plants.

Once replanted, the severed roots of most palms will branch and regrow. New roots will also emerge from the root initiation zone. Palmetto palm (Sabal palmetto) is an exception. Nearly all severed roots die back to the trunk, necessitating the regeneration of an entirely new root system. With most palms it is enough–and wise– to remove dead and older fronds at transplanting, but with palmettos you should cut off all the fronds.

And finally, to prevent wind throw, temporary bracing of taller palms may be necessary until the plant s roothold is re-established. This is often done with simple board-bracing arrayed to support the trunk from three directions.

What is the scientific basis behind the requirement to isolate super-sweet varieties of corn from other types?-T.C, by e-mail

Answer: The sweetness of sweet com comes from the sugar (mainly sucrose) that is present in the endosperm of each kerne!. The union between the pollen and egg not only creates the embryo, but determines the characteristics of the endosperm as well. Endosperm makes up most of the volume of a corn kernel. It is the food-storage tissue that sustains the embryo during germination.

Sweet corn arose as mutations from field corn, which produces nonsweet kernels (the sugar being converted into starch). Traditional sweet corn has the normal sugary (su) gene that results in the accumulation of sugars in the endosperm of the kernels. The supersweet or extrasweet varieties have a gene called shrunken-2 (sh2). (Shrunken aptly describes the appearance of the dry, wrinkled kernels.) This recessive sh2 gene greatly enhances the sugar content, which is about 28 to 44 percent higher than traditional su types.

This shrunken gene was first reported in 1921 by C. B. Hutchison of Cornell University, who wrote that it originated from seed collected by Dr. M. R. Gilmore of the Nebraska Historical Society from the “gardens of the Ponka Indians on the Niobrara reservation in Nebraska.” In 1949 E. B. Main from the University of Michigan formally described the shrunken-2 gene. It is a recessive trait that can only be expressed when pollination occurs between supersweet types. Pollen from other sweet corn types possesses dominant genes that supplant the recessive gene, resuiting in kernels that have the toughness and starchiness of field corn. Not only will the supersweet corn be spoiled by cross-pollination, but so will the normal sweet corn and even sugary enhanced varieties.

The latter possess the so-called sugary enhanced (se) gene. While not as sweet as supersweets, these are sweeter than normal sweet corn. The advantage is these varieties do not require isolation from normal sweet corn. They do, however, need isolation from supersweet corn, field corn, and popcorn.

Future sweet corn varieties will include an assortment of su, sh2, and se genes stacked with their associated modifier genes. Growers will need to consult the specific catalog descriptions for each offering to be sure of the respective isolation requirements of each.

My strawberry plants look small and stunted and their leaves have half-moon notches in them. What is their problem? -C.R., Bend, OR

Answer: Your strawberries appear to be suffering from an infestation of weevils. The notched leaves are telltale signs of feeding by the adults, which also produce notches in the stems, especially near soil level. Examine your plantings at night. These nocturnal feeders climb up the plants at night to feed. During the day they seek refuge in the soil or in debris at the base of the plant.

Strawberries (as well as red raspberries, blueberries, and cranberries) in the Pacific Northwest are attacked by a complex of weevils, notably strawberry vine weevil (Otiorhynchus ovatus) and black vine weevils (O. sukatus).

Adult weevils only cause cosmetic injury to the foliage. However, the underground larvae cause significant damage as they feed on the roots and crowns of the strawberry plants. Feeding is most severe from late March to mid-May, before the larvae pupate and emerge as adults. There is only one generation per year.

The best way of managing weevils is to target the adults after they emerge and before they begin laying eggs. Insecticides containing neem or malathion should be applied after most of the adults have emerged from the soil but before egg-laying begins–typically between mid-June and early July. Apply the insecticide in the evening when the adults are active.

Adult weevils cannot fly, so barriers can be used to protect uninfested plants. Coat wooden boards with a sticky material such as Tack Trap or Tanglefoot and place them on the soil surface around the perimeter of uninfested beds. Crawling adults will be prevented from reaching the plants. Maintain this barrier regularly, keeping it clean and sticky. H

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