Wet spring weather causes havoc to tomatoes, grapes

Q: What’s causing the leaves of my tomatoes to turn brown and die? The soil is fresh. I added all new soil with some compost. They are being kept uniformly damp. I’m watering with a slow soaker system from the ground. Over half of the tomato plants have very brown leaves. They are producing well. I’m afraid that the whole plant will turn brown and die.

A: I think it is a disease problem but also check for spider mites. Disease-wise it may be a late blight of tomato. Follow the label directions for disease control of tomatoes.

Any fungicide should work as long as it is labeled to control tomato diseases. Wet spring weather is still causing havoc on tomatoes (now) and grapes (as we enter July and August).

Diseases on tomato plants are controlled with a commercial fungicide and organically with 2 to 3 teaspoons of baking soda, combined with a teaspoon of vegetable oil and a small amount of mild soap added to a gallon of water. This is directly from the USDA blog. I would emulsify this concoction.

Then spray the tomato plants with this solution. Organic sprays should be reapplied weekly to 10 days apart to maintain their efficiency. Frequently, a commercial fungicide spray is applied less often.

I know you didn’t ask but there is not much you can do at this time of year for most grape diseases. These “bunch diseases” are controlled in early spring when they are flowering, way before the disease is seen on grapes.

As we enter the hot weather of summer, spider mites come alive. Slap brown (but not dead) leaves against a white paper two or three times. Keep the white paper in the light, hold it very still so you can see them crawling. Spider mites (the bad guys) are the size of a period and crawl very slowly to our eyes. (There are good spider mites too, but they are usually larger.)

Use a miticide spray (it is actually an insecticide) if they are seen. Miticides or any spray that controls insect-like creatures, unlike fungicides, are not preventive but kill on contact. If you prefer organics, then use soap and water sprays weekly until no mites are noticed using the same white paper test.

Q: What’s this sticky stuff that is on a few of the branches of a kumquat tree in our community garden? I saw it on just one of the trees.

A: I think it is sap from the tree. The tree may have produced it because of damage to twiggy growth. It is not from insects. Don’t get out your arsenal and spray it.

The only insect I have seen here causing this type of early damage (and may be confused with it) are aphids. You can usually spot aphid problems because of curled and sticky leaves and experience.

Q: One of my apricot trees that I have at home (and three apricot trees in our community garden) has plenty of fruit but very few leaves. Do you know why?

A: I think it’s because of the cool weather earlier. As it starts to warm more, you should see more growth, leaves and stems, and it will start to fill out. The filling-out kind of growth happens before August.

Temperate fruit trees like apricots slow their growth in preparation for winter. Depending on the spring freezes (off and on), you may also see larger than normal fruit because of the weather-related thinning of the fruit.

Q: Why are just some leaves on my African sumac tree turning yellow while the rest are lush green?

A: It may be from a lack of nitrogen fertilizer. Try fertilizing the tree with straight nitrogen (such as 21-0-0 or ammonium sulfate) to push new growth and stop the trees from developing yellow leaves from green.

A second thing to try is controlling the salt (or salinity) of the soil. Because African sumac has few or no listed varieties, the tree is started from seed and not grafted. It is usually propagated in the nursery from seed.

Seedlings, as they are called, have a lot of variability compared to varieties. This includes sensitivity to salt.

The only thing that controls salt sensitivity is water and drainage. Your tree may need additions of compost (to amend or modify the soil and improve drainage) and water.

Make sure you water the tree with enough water to wet the soil to a depth of 18 to 24 inches deep on mature African sumac. Make sure the water applied wets the soil to at least half the area under the tree’s canopy and to the appropriate depth.

Q: A neighbor was told to leave three main branches when she cuts back a newly bought peach tree from a nearby box store. I decided to investigate this idea. While I have found some online commentators provide a similar rule-of-thumb, there are some differences. However, in general, I think I would want to try this idea out.

A: I have found, in the desert, to protect the trunk from sun damage when it is young is very important for its long-term health and vigor. In nondesert areas, shading is not as important.

Controlling damage from the sun helps to control damage from borers. As it gets about 6 or 7 years old, natural shade from the tree’s lowest limbs helps to control borers.

To do this, pick a tree from the nursery that has lower limbs as low on the trunk as possible. I like trees that have limbs so low that I must remove them to get the right height. Ideally, you want limbs on the tree lower than knee height to get enough to remove.

Usually, this means selecting a smaller tree as nursery practices remove lower limbs and favor a clean trunk and then up to a canopy of limbs and leaves. Avoid choosing trees with a clean trunk.

Once planted, remove limbs that will touch the ground when bearing fruit. The idea is to have productive limbs as low on the trunk (to prevent sun damage) as you can get them. Fruit touching the ground oftentimes rot.

The reason for keeping lower limbs is to shade the trunk and harvest fruit that is as low on the tree as possible. Fruit easiest to pick without using a ladder is favored.

Q: I had “white fuzzies” on my prickly pear cactus and got tired of treating it with many different healthy solutions that would not damage the cactus. But it wouldn’t disappear. Instead, these critters were infecting other cactuses that were nearby. I sprayed this solution that I use to mop my floors and it contained bleach, lots of bleach. As soon as I sprayed it on, a red color started to run. It cleaned up pretty good and never came back again!

A: Thanks for the tip. The insect causing this red dye color is probably the cochineal scale. It is a problem with many cactuses and succulents during the summer.

For organic control, I would hose the cochineal scale with a strong burst of water from a hose. This would last about one week during the summer, and the cochineal scale would be back. I would have to hose it again in a week.

Perhaps the chlorine in the bleach got rid of this problem.

Q: We bought our home five years ago in Summerlin. We had six beautiful Italian cypresses at least 30 feet in height. Two of them died very rapidly after we moved in. I hired a well-known local tree company to fertilize and apply borer treatments (on a schedule). I asked them how much I should be watering them, and they said every day up to 4 feet from the trunk. When I followed their advice, they looked worse! I am very confused about how often to water them and watering on a slope.

A: Most Italian cypresses don’t have borer problems. It is rare.

Italian cypress is from the Mediterranean region (think Italy and Greece) with wet winters and dry summers. Southern California (west of the mountains) also has a Mediterranean climate. To the east of the mountains, it is drier.

Watering these trees depends on the soil but most of our soil will tolerate watering three days a week or less often during the summer. How much water to give them is enough to wet the roots of this tree to a depth of 24 inches at that height and then wait.

These trees will grow to a height of 60 feet, so they were not intended for single-story homes. Flopping of branches is usually a sign of watering too often.

When watering on a slope, put the water above the tree and let the water wet the soil containing the roots. In the desert, roots will are attracted to applied water. In higher rainfall areas, the roots are confused about irrigation.

There are tighter, more upright varieties such as Stricta and those with a bluish cast such as Glauca and Wichita Blue, and even with a golden cast such as Swayne’s Golden as well as smaller varieties. But you have to buy these from the web.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.