It has been a busy week for gardeners. Here are a few questions that have crossed my desk:

Q: My rosebuds look rotten before opening. The petal tips are brownish. What is happening?

A: "It is a combination of wind and thrips," said Richard Jackson of the Las Vegas Rose Society. "You can't do much about wind except to water more. The petals were tarnished by a tiny insect called thrips. It gets down inside buds and feeds on petals just as they unfold.

"Notice they tarnish lighter colored roses than darker varieties," he said. "I used garlic spray I found at a nursery and it chased the thrips away. I, for the first time in a long time, entered white roses because of the spray. The garlic also comes in little packages to clip on branches and that drives them away, too."

Q: What is causing the sticky substance all over my rose trees?

A: These are aphids, which are small, soft-bodied, piercing, sucking insects that thrive in the cool weather we have experienced this past month in the valley. They disguise themselves in a variety of colors including green, yellow, and black or somewhat near the color of the plant they are attacking. You'll find them on the growing tips and buds of many annual plants and shrubs, where they suck plant sap. They cause wilting and leave a sticky residue. Nurturing beneficial insects -- which feed on aphids-- including ladybeetles, lacewings and tiny parasitic wasps, will get the aphids by not applying insecticides indiscriminately. Also, look for aphid mummies. Tiny parasitic wasps that lay their eggs within the aphid cause the mummies. The wasp egg hatches into a larva that feeds inside the living aphid. When the wasp has about completed its life cycle, it releases chemicals that cause the aphid to harden. Or wash aphids off with a strong blast of water and spray aphids with insecticidal soap.

Q: What is the white powdery stuff on my roses that I am now seeing some on my euonymus?

A: This is a very common disease called powdery mildew that creates a white, powdery substance on leaves and stems with these two favorites. It will also be a problem later on in cucurbits, vegetables and grapes and it even affects some of the weeds in our yards. It is abundant in our climate; the spores do not require moisture. It is an obligate parasite. It lands on the leaf of a plant and redirects nutrients to itself. In severe cases it covers the leaves, blocking out sun and inhibiting plants ability to photosynthesize. It often occurs when sun-loving plants are placed in the shade. The best control is to follow good management practices: Place plants in appropriate environment (adequate sun light and air circulation); After the new growth of affected plants reaches about six inches long and until temperatures reach into the 90s, apply dusting sulfur to foliage every 14 days and if necessary a fungicide. Fungicides work much better as a preventative measure, before the powdery mildew becomes a problem.

Q: What is eating holes in my cabbage leaves?

A: It is the cabbage looper feasting on leaves leaving those irregular-shaped holes. As they crawl, they arch their backs, making a "looping" movement from which they get their name. Some gardeners also call them inchworms, as they measure out about an inch with each move they make across a leaf. This insect eats irregular holes in beets, broccoli, Brussels sprouts, cauliflower, celery, collards, kale, lettuce, peas, potatoes, radishes, tomatoes and turnips. They also bore holes in lettuce and cabbage heads. You can remove them. Apply Bacillus thuringiensis, an organic pesticide, which disrupts their gut and they starve to death.

Q: What is scaring the skin on my new oranges?

A: Most likely, it is caused by a little bug called the citrus thrip. They start feeding on the new flush of citrus leaves, and small fruit, causing leaves to curl and scarring of fruit. Generally, you won't notice it until you find the damage already done, so don't worry too much about.

Q: How can I tell if my apples, pear, peach, cherry and apricot flowers suffered freeze damage?

A: Most of the fruit mentioned will freeze if in full bloom during temperatures from 23 to 28 degrees. To examine flowers or fruit, remove one from the tree. Make a horizontal cut with a knife through the base of the flower just beneath where the flower petals attach. If small fruits have formed, cut horizontally through them also. If the center of flower or fruitlet is brown in the center, then the flower or seeds are dead. If the flower or seed tissue is green they are alive. If the seeds die, then the hormonal stimulus that the seeds produce that signals fruit growth will not occur; therefore no fruit will be produced. Go around each tree and cut 10 or 20 flowers or fruitlets to determine the percent of survival. If only 10 to 20 percent, survived you will have a full crop. If more survived you will probably have to thin the fruit in a few weeks to produce large fruit. If thinning is not done either by man or Mother Nature's freezes, expect inferior fruit.

Q: I have a globe willow that has a dark-colored sap running down the bark. It seems to be coming from under the wood near the crotch of the tree. What is causing this? I also see some insects in this sap. The dark sap is dripping on my flagstones and discoloring them. What can I do?

A: Your tree is suffering from a disorder called slime flux or wet wood. It is thought to be a bacterial infection that is poorly understood. The water soaked, discolored appearance with constant bleeding of the sap at or below the branch crotches and trunk are the visual symptoms of this disease. Liquid may seep out of cracks or wounds and run down the bark. The liquid contains microorganisms that will cause the liquid to ferment and become dark in color, sticky and smelly, which attracts the insects and they feed on it. Pressure can build up under the bark from fermentation and cause splitting and cracking. Normally, the disease is not observed in young trees. Generally, trees that are at least 5 years old and have developed heartwood become infected. Wilting and die back of branches generally occurs. Younger trees may have leaves that yellow, wilt or curl, turn colors and then drop early. Susceptible trees grown in Nevada include: ash, elms; poplars, willows, mulberry, and mesquite. Slime flux infection can aggravate wounds and cause death of bark cambium.

Remove any dead or weak branches. Fertilize and water to keep the tree in a vigorous state. To keep it away from your flagstones, place a piece of cardboard or plastic to catch the dark liquid. If it stains the stones, bleach it.

Linn Mills writes a garden column each Thursday. You can reach him at linn@reviewjournal.com or at the Gardens at the Springs Preserve at 822-8325.