Tomato hornworms find plants scrumptious

     By Bob Morris
     View columnist
      The following are typical items 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/.
     
      Now is a good time to be spending time outside. If you are outside at dusk you will see a strange, small "bird" flying near the flowers.
      It will appear like a hummingbird, hovering in midair and darting among the plants. These actually are large, fast-flying hawk moths sometimes mistaken for hummingbirds.
      They are large with a 4- to 5-inch wingspan. There are several types of hummingbird moths and one that is common here is the adult of the tomato hornworm.
      Tomato hornworms are those large plump caterpillars that you find eating voraciously on your tomato plants. If you look closely at the caterpillar you will find eight curved stripes on its body segments.
      One of the last body segments has a spine-like red or black horn that gives this insect its' name, "hornworm."
      Also sometimes called the tobacco hornworm in eastern parts of the U.S., this large caterpillar feeds on the leaves and sometimes fruits of tomato, pepper, potato and eggplant. Usually these caterpillars do not occur in sufficient enough numbers to cause severe problems.
      The tomato hornworm overwinters as a pupa in the soil. The adult moth emerges in late spring and deposits round green eggs on the undersides of the leaves.
      Eggs hatch in about a week. Larvae become fully developed in three or four weeks. The larva is the damaging stage and feeds on the leaves and stems of the tomato plant leaving behind dark green or black droppings. After three to four weeks the larva burrows three to four inches in the soil to pupate.
      You may have seen these cocoons or pupae if you work in the garden.
      They are hard to mistake. Those are the dark brown cocoons, about 3 inches long, shaped like a long seashell with an oblong loop at one end.
      In about three weeks the pupae transform into adult moths and another generation begins. Plants can tolerate some feeding, but if the larvae become a problem, remove them by hand.
      An effective organic control is the bacterium called Bt and marketed under the trade names Dipel or Thuricide. Cultivating the soil in late winter will reduce the number of overwintering pupae in the soil.
      The hornworm larva or caterpillar is attacked by a number of smaller insects. Small wasps, called Braconids, are an important natural enemy.
      Wasp eggs are laid on the body of the hornworm larva. Here the wasp larvae feed or cannibalize on the inside of the hornworm until the wasp is ready to pupate. The wasp cocoons appear as white "bumps" protruding from the hornworm's body.
      If such projections are seen, leave the hornworms in the garden. These wasp infants will kill the hornworms. When the wasp matures into the adult that can fly, they will seek out other hornworms to parasitise or cannibalize. Start looking for this insect to be feeding on your tomato plants in May sometime depending on the weather.
      I am seeing a lot of wind damage on plants with very tender leaves. The damage can look like insects or diseases but the leaf will have a more "tattered" appearance.
      Question: I have almond nuts oozing sap and the immature nuts are soft and rotting after splitting. What's the deal?
      Answer: This may be due to an attack of the young nuts by the leaffooted bug. The leaffooted bug is an infrequent pest in almonds.
      It is easily recognized by its small, leaflike enlargements on its hind legs. The narrow, brown body has a yellow zigzag line across its flattened back. It is about 1-inch long.
      The leaffooted bug overwinters around trees that it has infested the previous year. This could be in plant debris left on the ground in the growing area.
      Its presence is apparent in late spring when the immature nuts are still very small. Feeding on young nuts before the shell hardens can cause the young seed inside (the almond eventually) to wither and die. This causes the nut to drop from the tree early. It may cause the nut to gum internally, resulting in a bump or gumming on the shell.
      After the shell hardens, leaffooted bug feeding can still cause black spots or wrinkled, misshapen nutmeats. Because this insect is not a common pest in almonds it is recommended to apply a spray of sevin insecticide only when high numbers of the insect are present. Start looking for this insect now.
      Alternatives to sevin, a traditional pesticide, may be available. Contact our office for possible alternatives.
      Q: Why are the leaves on my ash tree all curled and twisted?
      A: This can be caused by a number of things such as cold or wind damage when the leaf was expanding from the leaf bud, damage due to weed killers drifting onto the leaves and aphids. The first thing to do is pull a few leaves apart and look for insects inside the curled part.
      Aphids have been quite active now and will use these convoluted leaves that they caused from feeding to act as a safe haven from the weather and predators like the ladybird beetles which most people call ladybugs. Since the aphids are inside the folds of the ash leaves they will be difficult to control with things such as plant-friendly soaps and horticultural oils.
      If you don't find any aphids then I would investigate the possibility of damage from drifting weed killers. Damage from weed killers such as the dandelion sprays will appear as distorted or misshapen leaves. Since these type of weed killers are synthetic plant hormones, this damage only appears on the leaves that are expanding or growing at the time the drift occurs.
      Leaves fully expanded and leaves that grow after the drift are not affected. So damage of this type is temporary and hits leaves all of the same age on the tree or plant. Usually this type of damage is heaviest on one side of the tree, the side facing the drift, or in one area such as the lower limbs.
      Damage is usually contained on the part showing damage and does not cause long term ill effects for the tree. So ignore it for now and try to find out where it came from so it can be prevented in the future.
      The tree takes care of wind damage by growing new foliage that compensates for the damaged foliage. If it is wind damage, new foliage will be unaffected.
      Q: I have palm trees growing close to pool deck. Will this cause problems by lifting the decking?
      A: I am going to hedge on this one. It is my impression that palm tree roots do not typically cause problems to walls and decking when grown close to them. However, I don't think we can make general statements about palms in this regard.
      Different palms have root systems that grow differently. I would not grow any large plant close to walls, foundations, decking, patios, sidewalks, driveways or any other surface where potential damage could occur. You are just asking for trouble.
      Many of the so-called fan palms have a lot of variability in their size and girth. Unless it's something like a windmill palm, which is truly a small palm tree, you will never know what that tree may be like in 10 to 20 years from now. Put smaller plants close to these types of structures and give large plants plenty of room to grow.
     
     Bob Morris is a horticulture specialist with Nevada Cooperative Extension.