Sticky, shiny stuff on tree's leaves sure sign of aphids


: I happened to notice the leaves on my apricot tree were shiny. A closer look showed that they are full of what appears to be aphids or some similar bug. My question is since the leaves will fall soon anyway should I bother spraying for them. Enclosed are a few photographs. I hope they are clear enough to recognize.

A: Exactly right. The sticky, shiny sap you are seeing on the leaves results from their feeding. In the picture, you can see adults (larger and gray) and the younger ones (green) that were recently born. If you look closely at the insects, you will see these adults have wings. That is not always the case as aphids can develop with or without wings depending on the circumstances.

Aphids do not need wings for mating like so many other insects, but they need them to find a protected location that will provide them some food and safe harbor.

It makes little sense to control these insects this late in the year. The tree has little use for the leaves for the remainder of the year and they will be dropping soon. Aphids cause no damage to the tree other than to the leaves.

The overwintering insects will be killed during the winter if you apply a dormant oil in December after leaf drop and again in about mid-January. It also will be very helpful if you control any weeds in the area as aphids will overwinter on weeds where they can obtain both food and security.

If they make it through the winter, they will invade in the spring as soft leaves emerge. Then, they will multiply again like in your picture. This time, however, their feeding damage will cause the sticky sap along with curling as the leaves grow. This leaf curl gives added protection to the aphids from their natural larger enemies, such as birds, but lady bugs or ladybird beetles and green lacewings, which are so common at that time, will still have a smorgasbord with them.

The sticky and shiny stuff on the leaves is sugar, concentrated by aphids inside their bodies and excreted. This sugar attracts ants. They will climb trees and other plants with lots of aphids to collect the sugar for their own colonies. In fact, a good sign of aphids in a tree are the hordes of ants climbing in perfect rows along the trunk to the leaves and back down again.

Q: You recently advised watering trees once a week in winter for an hour. We are only supposed to use water for four minutes at a time, at most three times a day. How can we water anything for an hour?

A: You are looking at the recommendations for sprinkler irrigation. Usually my recommendations do not give specific times unless I know how much an hour's worth of water is delivering. Irrigations on trees need to deliver enough water to penetrate the soil down to a depth of 18 to 24 inches after each watering.

You should be looking at drip irrigation recommendations for watering if you are using drip irrigation. You also have to figure out how much water you are applying to know how much to water. Sprinkler and bubbler irrigation put out a lot more water faster than drip irrigation. In those cases, you are scheduling in minutes, and then they are telling you to water for three to four minutes, three times a day.

A bubbler can put out as much as 2 gallons per minute. If you run this for three minutes three times a day, that can be 18 gallons. Drip irrigation is in gallons per hour. If you use a 3 gallon per hour drip emitter, you would have to run it for six hours to get 18 gallons.

Q: I live in Pahrump. I have deer grass and butterfly iris plants that have grown huge. I want to cut them back. I asked for help at a nursery and was told to cut both back to 6 inches above the ground but that I should wait until January for the deer grass and after the last freeze for the iris. Is this accurate?

A: For a general recommendation, it is a good one.

Butterfly iris is not really an iris as we know an iris, so it is handled a bit differently than what you might read about if you researched information on iris. When individual leaves die, they must be clipped off rather than pulled in order to maintain neatness. Leaves will continue to store food as long as they are green. As they brown, clip them back.

Most of the butterfly iris will remain green through the winter if it is in a protected location out of cold winds and near a warm wall. It will be damaged at temperatures below 20 F. After about three or four years of good, healthy growth these clumps of iris will need to be dug up from the ground, separated into smaller clumps and then replanted.

As for the deer grass, you just want to make sure that you do not cut it back too far. These grasses grow from a point not at its base or from the growing tip. It is located somewhere in between and will vary from grass to grass.

To roughly determine where to cut, take a leaf blade and pull downward along the stem of the plant until you can't pull it any more. This will be the point at which you can safely cut; it should be quite low or deep inside the mound.

By the way, deer grass was used by Native Americans for making baskets. It is quite tough and fibrous.

Q: I have some plants in small containers that I will eventually plant outside, but they are very small right now. My concern is: I need to leave them outside to go dormant this winter but I am afraid that being in the small pots the roots will freeze. This goes for my other perennials as well, which are in larger pots. I did read somewhere that I should pack straw around the small pots and place them in larger pots. I have placed my smaller pots in larger ones throughout the summer to avoid direct sun on the smaller pots (no straw) but have a huge problem with cockroaches and other critters taking up residence in the larger pots.

A: Another method you could try is to bury the same sized container or the container itself in the ground. The soil will act as an insulator around the pot. Periodically turn the container in the soil without removing it to break any roots that might grow into the surrounding soil. Roots will grow as long as the soil temperature is above about 50 F. Then, I would cover the container with mulch, 2-3 inches deep.

You will have to water often because of the size of the container and the restricted roots inside the container. As soon as most of the cold winter is over, around mid-March, take them out of the ground or the roots will grow right through the holes in the bottom into the soil beneath the container. In fact, they may still do that even though it is cold.

If it were me, I would want to use the soil as a temperature and moisture buffer rather than leaving the container open to the outside air temperatures. The temperatures would widely fluctuate from day to night in a small container.

As far as your concerns over our Las Vegas water bugs or cockroaches, they like to hang out wherever there is water. Outside this is usually in irrigation valve boxes. Apply any treatment to these boxes and anywhere else there is a source of water to help with control. There are a lot of claims out there on organic control methods for these critters but I do not know of any surefire method.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.

 

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