Mineral oil can control insects

: I just saw an article about a community farm in Pleasant Grove, Utah, that shows someone applying mineral oil to the corn cobs “to help keep bugs from getting in.” Do you know what this is about? Is this really about insect control? Is it something that I should consider?

A: If you are wondering why I am talking about corn now, I was encouraging you to plant corn late this summer for a fall harvest. Fall corn works well here, it is just a shorter season than when it is planted in the spring. This question refers to fall-harvested corn.

One of the biggest problems we have growing corn here is an insect called the corn earworm. Like its name suggests, this worm attacks the ear of corn. The adult female, a moth, lays her eggs on the freshly emerging silks of the corn. The silks are needed by the plant to wind-pollinate the kernels we so love to eat. If the kernels are not pollinated, they fail to form. The worm hatches from the moth’s eggs and journeys down the silk to the ear and the juicy kernels where it feeds.

This worm, or larva, is actually the immature form of the moth. It feeds on the corn kernels, usually near the tip of the ear, protected by the husk. When we shuck the ears is when we usually discover them feeding on the kernels.

The traditional way to get rid of this earworm on large commercial farms is to spray with pesticides. Another approach that can be used on a smaller scale is to substitute “softer” pesticides such as Bt for the more traditional “hard” pesticides. Still another option is to “suffocate” the small worm by using oil and applying it to their point of entry into the ear at the silk.

Some people use mineral oil for this purpose while others use vegetable oil. Mineral oil is not permitted legally unless it has a label for use as a pesticide. And still a third technique is to mix the Bt with the oil and apply the oil in the same manner. All three work. The mixture of Bt and the oil gives you a little longer protection and kills more mature earworms that the oil will not smother.

The key to getting control is proper timing of the application and applying it the right way. The oil is applied to the silks when the silks are turning brown. This timing is critical. It must be done two days after the silks have completely emerged. If it is applied too early, the kernels may not form well. Too late and you will miss your opportunity.

An easy applicator is an oil can. People who have combined the Bt with the oil have used 3 teaspoons of Bt per quart of oil. Not much oil is applied. Only about one-tenth of a teaspoon of oil is applied to the ear just at the point where the silk enters the ear.

Q: I was forced to heavily prune a large pomegranate tree but was able to salvage the fruit. The Internet provided conflicting advice. One site said the fruit would ripen if refrigerated, another said it would ripen in the sun, and still another said it would not ripen at all. Can you help?

A: Basically it does not ripen very much once harvested. Most scientists agree that there is little improvement in sugar content once harvested, regardless of methods used.

It seems (to the palate) to continue to sweeten somewhat if held in refrigeration but there is no change in the sugar content. I think it has to do more with the loss of acidity rather than a change in the amount of sugar.

If possible, put them in refrigeration for a couple of weeks. Keep the humidity up if you can to prevent shriveling. Otherwise keep them in the coolest place you possibly can. That will be the best and only thing you can do but I doubt it will improve much. The flavor of early-harvested pomegranates is usually tart and without much flavor.

Q: I have lived in my home in the northwest part of Vegas for over 20 years. I have about a dozen rose bushes of various types and colors in my yard. During the past few years I have had a problem with a “rambling rose” infiltrating my gardens. Now this plant has taken over the roses in the yard. I have a beautiful pink climbing rose that has been destroyed by this “parasite.” I have attached a photo of a branch (showing both types of rose) cut from the rose bush two weeks after pruning a clean bush. Is there anything I can do with this plant short of digging all of my roses out and starting anew? If I need to start anew, how do I prevent the same thing happening to future plants?

A: From the picture, this rose appears to be one of the rootstock roses used for grafting. (I am putting your picture in my newsletter for subscribers to see. Subscriptions are free by requesting copies by e-mail, morrisr@unce.unr.edu, or by phoning 257-5509.)

I am guessing the rootstock part of a grafted rose may have taken hold after some calamity destroyed the “good” part of the rose. If the rootstock, typically a more aggressive rose than the “good” rose, is allowed to grow beyond its rootstock then it can “take over” a rose plant.

In many cases for our climate the rose used for the rootstock can be this pink or red type. Be careful when pruning and don’t prune your roses too low or you can stimulate the rootstock to grow. If any shoots arise from below the graft, they must be removed totally. Remove them by cutting them off as close to the mother plant as possible and completely eliminate them.

Q: I put three small, dwarf almond trees in the ground when I moved here about a year ago. I live in the northwest part of Las Vegas. One tree apparently drowned due to a break in the irrigation system, but the other two bloomed last spring and I must have more than 100 almonds on each tree. About three or four weeks ago, just after a week of heavy rains, the almond pods started turning yellowish to purplish-brown and now the outer shell casings have started to crack open. None have fallen off of the trees, but I am wondering if this is natural and when I should start harvesting them.

A: Yes, it is the normal sequence for almonds to split as the nut matures. Some varieties will get a rose colored or purple coloration, particularly after a rain or unseasonably cold weather.

Leave them on the tree to dry or harvest them after they split open and dry them in the open air, protected from rain and varmints. Try a few fresh, even before they finish drying completely. They are delicious slightly immature and raw.

If you leave them on the tree and you have ground squirrels (some people call them chipmunks), they will harvest them for you. A few of those “cute” little varmints can clean out a mature tree in a day.

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.