Tobacco budworm is causing lack of petunia flowers

A: This is most likely tobacco budworm. The adult is a moth but the damage is done by the larval or caterpillar stage. In this stage the caterpillar feeds on flower buds and leaves.

The giveaways that it is tobacco budworm are the lack of flowers, holes in the leaves from feeding, the type of plant and the time of year. The flowers fail to open so lack of flowering is a pretty good indicator the pest is present. Small holes in the leaves are another good indicator.

Besides petunia, tobacco budworms like geraniums and nicotiana. Once in a while we might see damage on roses.

In the future, if you have these plants, look for holes in the leaves starting in April or May. That would be a pretty good time to start thinking about getting control because its population builds through the summer if not stopped.

Check your plants for these caterpillars as the sun is setting. This is the easiest time to find them and pick them off of the plants with your fingers. During the daytime they like to hide out close to the soil.

Tobacco budworm has become fairly resistant to a lot of insecticides so control is a little bit difficult. This is why you probably did not get control using the insecticide Sevin. Be really careful with that insecticide because it is pretty hard on bees.

You might try an insecticide with Spinosad on the label. Dipel or Thuricide might give you some control. Otherwise use insecticides that contain synthetic pyrethroids in the list of ingredients.

Regardless of the insecticide used, always spray either very early in the morning or at dusk when bees are no longer present.

Q: I have a neighbor concerned about his rosemary and boxwood hedges. The foliage has been falling off. Landscapers recommend he cut them to the ground to get them to recover but he opted to cut them back halfway instead. Now there is a lot of bare wood exposed with no leaves. What should he do to help them recover?

A: When plants are continuously pruned with hedge shears it causes them to get thick and bushy.

This increases their leaf density on the outer edges of the hedge, which, in turn, causes the interior of the hedge to become very dark and the stems on the inside of the hedge to drop their leaves.

They also drop their leaves because the wood on the inside is old. All the new growth occurs where the hedge is being cut over and over. So perhaps only an inch or two along the outer surface of the hedge has leaves.

If we cut the hedge back more than a couple of inches, we expose the older wood that has no leaves. The wood is alive, but without leaves. Once this interior wood begins to receive sunlight again, new growth will sprout from this older wood.

The rate of growth from this older wood depends on the plant. Rosemary grows faster than boxwood. If he is patient, your neighbor will eventually start to see new growth coming from the older wood. Boxwood will also have new growth but will fill in slower than rosemary.

If he is patient both hedges will eventually slowly fill back in but boxwood will be much slower. In cases like these, most people do not want to look at an ugly hedge for the next few years and would elect to replace the damaged plants.

Once plants are cut with hedge shears for a few years over and over they are very difficult to re-establish again as plants that are not shaped like a hedge.

Q: I have bamboo that was damaged last winter as you can see from my pictures. New growth is emerging from them but they are still yellow and brown. Should I fertilize them or give them iron?

A: If the plant is still brown from winter damage and the growth is yellow, the only way to really make them look good again is to cut them down and let them regrow from the base. This kind of damage is never going to recover from unsightliness without some regrowth.

I assume this is a running bamboo such as golden bamboo. They should come back if they are cut back to the ground but this is not the ideal time to do it. Prune cautiously this time of year.

It would be OK to cut back the largest ones now but leave younger ones until you see some good solid growth again from the base. Once you see healthy growth, go ahead and cut more back. Otherwise wait until next spring which would be ideal.

Fertilizer and iron will be helpful as it is growing back.

Q: We had a beautiful purple locust in our backyard that produced a profusion of purple flowers every spring until it was called to locust heaven. Before departing this world it sent off a runner which has sprouted into a lovely tree that is now 11 feet tall and producing white flowers. What’s with that?

A: I am making a lot of assumptions in answering this. I am assuming what you are seeing is a locust and not some other plant that happened to grow in that location. I am also assuming the flower looks exactly the same as the purple one, just that it is white.

If both of these are correct then you are seeing the rootstock suckering. The rootstock used for producing the locust with purple flowers is a black locust. Black locust has white flowers but otherwise looks identical to the purple locust.

Oftentimes the locust that has purple flowers is grafted onto a black locust rootstock. The purple part of the plant dies. Suckers grow from the roots of the black locust rootstock and have white flowers.

Q: I have an orange tree I planted nine years ago. It is about 4 feet high and only produced about two oranges a year. Last winter it did have some freeze damage. I trimmed and fertilized it with iron and nitrogen and watered it once a week with a hose instead of the drip system.

It is looking real good and has about 40 pea-sized oranges on it. Should I cull some of them as I don’t think the tree can handle that many?

A: Normally citrus fruit is not thinned. I wouldn’t take any off. At nine years of age it should be able to handle a lot of fruit. If you think the tree is abnormally small and can’t handle the fruit then remove some, but at nine years of age you should not need to.

Q: Last fall I planted five rose bushes and they appear to being doing well. Three of the bushes have one large stem growing from the middle of the bush. Should I cut the large stems back to make the bushes more symmetric?

A: Very strong growth from plants grafted to rootstocks is frequently a sign the rootstock has sent up a sucker. This type of growth must be removed or it will dominate the plant and squelch the growth from the good part of the plant.

Trace this growth back to its origin and identify where the union is located between the rootstock and the top of the plant that we value for the flowers. Remove this type of growth without leaving any stubs.

The union should be a swollen part of the plant that may resemble, in looks, like a gall or tumor but it is not. If this strong growth is coming from this spot or below it, remove it as close to the parent plant as possible.

The cut does not have to be sanitized but your pruning shears should be and be careful not to let your shears touch the soil before cutting.

You can transmit some problems from the soil to the plant on your shears through the open wound.

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