The use of dormant oil
Q. What is the idea of dormant oil?
A. Dormant oil is an organic control that, when applied to the bark and branches of certain plants, suffocates the insects that are overwintering on or in the bark.
The most obvious target is scale insects on fruit trees, hollies, euonymus, sago palms, and other plants.
Recognize scale as small (pea size) circles of calcium attached to the bark. Scale is usually white and can resemble a fungus growth, but some are brown and relatively hard to see. Underneath the calcium cover is a small insect that makes its living by sucking the juices from the plant to which it is attached. The result is a weakened plant that expresses the insect’s attack by diminished and yellowish foliage.
Obtain dormant oil from your favorite source of pesticides and dilute it for application from a backpack or pump-up sprayer. Spray it on the bark and stems to the point it begins to drip off.
Dilution rates will be stated on the container label. They may be different if you are spraying evergreen plants, like citrus, or deciduous plants, such as peaches. The label will also state the necessity of waiting to spray until two days (48 hours) are forecast where temperatures are above 45 degrees Fahrenheit. If you are spraying deciduous fruit trees such as pears, peaches, plums, and apples, including some Kocide in the dormant oil spray will help control bacterial diseases as well.
Scale is an important target of dormant oil, but you will also obtain reasonable control of phylloxera and other aphids on pecan trees from dormant oil. Phylloxera is the insect that causes the deformed leaves on so many pecan trees. The problem can be so bad in some neighborhoods that a commercial sprayer is brought in so branches in the crown can also be sprayed.
Q. We have a newly constructed house and have decided to have a small lawn area with zoysia grass because it is attractive and traffic-tolerant, resists weeds, and can go dormant in a drought. Which variety of zoysia would you select and why? Do you have any other guidance?
A. Wow, you seem to have done your research. I like Jamur or El Toro, the thick-bladed zoysias, because they are easier to mow and seem to have more shade- and drought-tolerance than the thin-bladed selections. My best advice is to make sure there is 6 inches of soil beneath the new sod. If there is less, none of the good characteristics of zoysia can overcome the lack of a water reservoir in the soil.
Q. My live oak tree looks really scraggly right now; could it be oak wilt?
A. We have to stay alert to oak wilt, but the damage you see now is probably from the drought. It is also time for the live oaks to drop their leaves.
Q. I am going to grow tomatoes in containers again this year. Last year, I grew patio tomatoes. They were pretty, but the fruit was disappointing. Is there a better variety for containers?
A. My favorite tomatoes for containers are Surefire and Rodeo Surprise Cherry. Tycoon also works well. All are much more productive than patio tomatoes. They do need a container of at least 5 gallons. Ten gallons or 15 is better.
Calvin Finch is a horticulturist and the San Antonio Water System’s project director of regional initiatives and special projects. Hear him on “Gardening South Texas” on KLUP 930 AM radio Saturdays noon to 2 p.m., and 1-3 p.m. Sundays. Or, e-mail him at email@example.com.