Iron deficiency in plants grows as temperatures rise

I can tell it is getting hot by the many questions coming my way. Here are my responses to them.

Q: What is causing the leaves on my grapes to turn yellow between the green veins?

A: Your plants are expressing an iron deficiency. The books call it iron chlorosis and it is a problem across the valley. Chlorosis occurs throughout the year but becomes most severe as temperatures increase. You find it starting on newer leaves, with older leaves remaining green. As the deficiency increases, veins become yellow and leaves eventually turn brown and drop off. You will also find chlorosis in pears, pyracantha, roses peaches, nectarines, nandina, citrus trees and in many other plants.

Iron deficiency symptoms are similar in appearance to nitrogen, manganese and zinc deficiencies. Here is how you sort them out. Nitrogen symptoms appear on older leaves. Lack of zinc looks like iron chlorosis, but leaves are much smaller and appear in small tufts at the end of twigs. Manganese expresses itself similarly to iron chlorosis, but the greening spreads out along the veins to give it a Christmas tree effect.

If you have your soil analyzed, it will tell you there is iron in your soil but it is in a form unavailable to plants. Allow soil to dry out between irrigations to increase the oxygen levels. Iron absorption by roots requires active oxygen to make the transfer to plants. And our highly alkaline soil ties iron up, making it unavailable to plants.

Infrequent deep irrigation is the best management to correct the yellowing. Or select native plants adapted to our soil conditions. Or apply iron in a chelated form such as Kerex. You can apply Kerex to the leaves, but for long-lasting results, apply to the soil. Finally, incorporate organic matter before planting to lower the alkalinity so the iron remains available to plants.

Q: Is it OK to remove the seedpods now covering my valentine plants?

A: Yes, because it will improve their looks in the landscape. Many native plants such as the valentine plant are legumes and they produce their own nitrogen, so you don't need to fertilize them.

Q: Are the plums on my flowering plum tree edible?

A: Yes, but they are tart. Remember, nurseries specifically select flowering plums for their leaf color, not for quality of the fruit. Most of us harvest plums too soon and they can be tart.

Q: My zucchini fruit starts growing, but then does not develop and shrivels.

A: The initial flowers on vine crops are male, and this may be the reason for not developing, but females soon come along. In fact, the initial flowers on cucumber plants produce 15 male to one female, so don't worry when you see flowers laying on ground.

Sometimes female flowers don't open so bees can pollinate them, so you may have to play bee. Remove a male flower (the stem behind the flower is about the thickness of a pencil) and also the flower petals. Find a female blossom (miniature fruit behind the flower) and dab the male part on the female parts found in the center of the flower. For fun, have your children find the male and female flowers and transfer the pollen. In about five days, you'll have fruit.

Q: Please tell me what I can do to save my nectarine tree I planted this spring. The leaves are curling and have reddish spots at the edges and are falling off. It is getting enough water.

A: You may not be soaking up the root ball when you irrigate. If the root ball dries out, it repels water. That can cause leaves to shrivel and drop, so give it a deep soaking.

The reddish spots could be a disease called shot hole fungus. Reddish lesions appear on leaves and then drop out to give the look of someone shooting a shotgun through the leaves. To overcome this, apply a dormant spray immediately after leaves shed and again prior to bud break in spring.

Q: Why is the fruit on my citrus trees falling off? There are still lots of fruit hanging on.

A: Both fruit and citrus trees overset fruit, and then go through a natural thinning process and fruit drops. But don't worry, the remaining fruit will be bigger and you happier.

Q: What is causing the irregular holes in my kale leaves?

A: It is a cabbage looper. It gets its name by the way it crawls, arching its back making a "looping" movement. You'll find it feeding on beets, broccoli, brussels sprouts, cauliflower, collards, lettuce, potatoes, radishes, turnips and other vegetables. The larvae are pale green caterpillars up to 11/2 inches long with several white stripes down their backs. The adult has silver spots on its upper wings and likes to flutter over her kingdom.

The looper lays eggs on the undersides of older leaves, so look there for them. Control them either by hand picking or applying Bt, an organic pesticide that disrupts its gut process and starves them out.

Q: I am having a problem with my tomato plants. The veins on the new growth turn purple, and then the lower leaves curl. I have mulch on the ground.

A: It sounds like your plants need phosphorous. It also may be curly-top virus. It causes a purpling of the leaf veins and goes on to turn sickly yellow and eventually dies. The fruit also prematurely ripens and skins become very tough. This virus comes to your plants via a sugarbeet leafhopper while feeding on your plants. If you suspect this, remove infected plants.

Q: Do I need to strip the frond stubs off my palms, or is it OK to leave them on?

A: It all depends on what you like, because it doesn't matter. I like the design they create. If you do strip them off, stop stripping when the inner bark starts turning pinkish. Just above is the palms' growing point, and exposure will kill it.

Q: What do I do with the flowering stalks coming up in my rhubarb?

A: Pull the flowering stalks out as soon as they appear. This focuses the plant's energy on building a stronger plant in the future. Because of our heat, we don't get the quality of rhubarb found in cooler climates. If you plant some, place it on the northeast side of your home where it's cooler.

LANDSCAPE LIGHTING

When dramatically lit, your desert garden can take on a different character at night and become an additional room of your home. Learn how to use night lighting to emphasize the beauty of your landscape by illuminating the best features and hiding others. A class and lighting tour will be offered at 6 p.m. Wednesday at the Springs Preserve, 333 S. Valley View Blvd.

DRIP IRRIGATION

This free class equips you with skills to design and install a drip irrigation system. Learn the complete installation from the street to plants, including selecting and assembling components. Get involved by building a drip system right in the classroom and learn just how easy it is to save water and have great looking plants. Experts from the Southern Nevada Water Authority Conservation Water Waste program at the Las Vegas Valley Water District will teach you at 6 p.m. June 25 at the Springs Preserve.

Linn Mills writs a gardening column each Sunday. You can reach him at linn.mills@springspreserve.org or call him at 822-7754.