Cutting back tomato plants during fall has benefits

     By Bob Morris
     View columnist
      The following are typical questions our Master Gardeners deal with daily at the Nevada Cooperative Extension. If you have gardening questions, call the Master Gardeners' hot line at 257-5555 between 9 a.m. and 4 p.m. Monday through Friday. There is also a gardening Web site at http://www. intermind.net/mgarden/.
     
      Question: Does cutting back tomato plants back in the fall work?
      Answer: Yes it can, or you can leave the plant the way it is and it will respond to the more favorable fall weather and begin to set fruit. You can take the tomato plants that you already have and cut them back at this time of year or you can purchase new ones.
      The advantage in cutting back existing tomato plants is that their top growth will be phenomenal because they already have a huge root system. Cut the tops back, leaving some lower leaves. While it is still hot, have some leaves left after you prune so that water is being pulled up the stems. If it's too hot and all the leaves are removed with bare stems remaining, you may kill the plant.
      Fertilize once with a good garden fertilizer for top growth. I would shade the plant from direct sun until you see new growth. Don't fertilize again until you see blossoms.
      Q: I want to kill a cottonwood tree that is lifting my driveway. When can I do this?
      A: Now is the best time to kill plants that may sucker after they have been cut down. In the spring, in our climate, most of the flow of a plant is from the root system to the top. This is when new growth begins and leaves unfold.
      This flow is filled with sugar stored in the roots the previous fall. Maple syrup tapped from sugar maples in the spring is a good example. In the fall, as temperatures drop and the days become shorter, the major flow inside the tree is from the top to the root system.
      If poisons enter a plant's sap flow in the fall, the poison has a much better chance of getting deeper into the root system. This is very important when trying to kill plants that sucker from their roots like cottonwood or elm. This is not quite so important when trying to kill plants that don't sucker.
      Q: When do you harvest pumpkins and watermelon?
      A: In colder climates, we would tell you to harvest pumpkins after the first light frost. This is because the sugar content increases with colder weather.
      In our climate, this might not be until November.
      Pumpkins are harvested when fully mature. You can tell when they are mature by pressing your thumbnail into the skin. The rind should be hard and difficult to scratch with your nails.
      You can speed up the process by cutting back on the water to the vine or damaging it by stepping on it but not killing it. This sends a signal to the plant that it might die, so it starts the pumpkin maturation process.
      The pumpkin begins to mature at whatever size it might be at the time. If the plant is going to die, it wants to perpetuate itself by making sure the seeds will survive.
      Watermelon can be checked by "thumping" or observing the rind color on the bottom of the melon. When thumping the melon, the sound created when you tap hard should be resonant and deep. While resting your other hand on the melon, tap the melon hard.
      You should feel the vibrations and hear a deep "thud," not a pinging thud. Turn the melon over and look at the bottom that was resting on the ground. The color should be a yellow-cream color, not white.
      Q: I have holes in the leaves of my peach tree. They are brown at first, then drop out and leave holes. What can I do?
      A: This is most likely shot hole fungus attacking weak, chlorotic or yellow leaves. If there isn't substantial damage to the leaves, I would leave it alone. In other words, if the leaves are staying on the tree and don't die, then don't spray. If the disease is causing substantial leaf drop then I would spray with a fungicide that is labeled for coryneum blight, or shot hole fungus, on peach.
      Make sure you clean up the area of old peach leaves after they drop this fall. Sanitation is critical for disease control. Or you can use your mulching mower and mulch the leaves into the lawn.
      Q: I have willow and plum trees that are oozing sap. My friends have told me that I have borers in the trees but I can't find any holes in the trunks of the trees. What's the deal?
      A: There are many reasons why trees may have sap oozing from the trunk. The reasons why trees may be oozing sap include borers, heat stress, certain diseases and injury to the trunk. Some oozing can be natural.
      Willow and plum trees are both susceptible to borers. Likewise they are both also susceptible to heat stress.
      Willows will commonly get a disease called slime flux, or wetwood. If the willow is a weeping willow type, it will get sunscald in the upper branches.
      This will commonly spread into the main branches or trunks. Did you ever notice that there aren't any real old weeping willows in town?
      They just don't do well after about 10 years in this climate. However, the globe willows will last much longer, but both are not typically long-lived trees.
      Don't plant ornamental plums in hot locations in the landscape. Avoid desert landscapes with both of these plants as well as hot walls or buildings. Limbs and leaves of these plants should shade the trunk from the hot summer sun.
      In the first few years after transplanting, allow small limbs to grow along the trunk to shade and protect the young, thin bark. Remove these limbs when they reach pencil size in diameter.
      Be careful of tree wraps. Some of them can actually cause damage to the trunk. Energy from the sun's light on trunk wraps can cause excess heat that damages thin-barked trees. Pesticide sprays applied to the trunk are preventative only.
      They are usually not effective once borers have caused extensive damage. Injections of pesticides into the tree are usually not effective as well.
      Q: Someone told me that now is the time to control spurge in my lawn. When should I put a preemergent herbicide on my lawn?
      A: Apply spurge control products in the early spring. Spurge is a low-growing weed with reddish stems and small, roundish leaves. Some of the plants may have a dark spot in the middle of the leaf, while other plants may not.
      Spurge is a what we call a euphorbia. Euphorbia all have milky sap, so when you break the stem of spurge or tear off a leaf you will see a white latex-looking sap ooze. That makes it easy to identify.
      Spurge is a very poor competitor with properly maintained lawns. The best control of spurge is the combination of proper mowing height and proper fertilizer levels.
      This means that the sprinkler heads must not be weed-whacked so that there is a bowl of short grass around each head. This combination of short grass and plenty of water is a perfect environment for spurge and crabgrass.
      Apply preemergent herbicides in late February, mow high and keep the lawn well fed to prevent spurge problems.
     
     Bob Morris is a horticulture specialist with Nevada Cooperative Extension.