This week I will continue to address the use of organic methods for controlling disease and insects in the garden. One of the most frequent questions I get from clients is about grub worms. They are the larvae of adult June bugs and can do some damage if present in large quantities. Quite often I find them in the soil when I am planting seeds or transplanting seedlings. There is no real reason to control them if there are fewer than 5-10 grubs per square foot, but if you simply detest the adults gathering around your outdoor lights, you can go ahead and treat the area. You can apply beneficial nematodes if the infestation is significant; youcan find these at The Natural Gardener in far southwest Austin, or perhaps at It’s About Thyme or Barton Springs Nursery, all south of the river. These three fairly local nurseries are (in my opinion) the best stocked with organic materials and native plants.
Our little city has been described to me by local resident and Pecan expert Jeff Hancock as coming close to being a “pecan orchard”. They are predominant street tree in town, and also planted in many residential gardens. Pecan webworms can be a problem, building nests high up in the branches. You can release Trichogramma wasps from May to early August when you first see the adult moths that will soon be laying their eggs. These small and harmless-to-us wasps will parasitize and kill the worms. If the webs are within reach, you can open up the webbed nest and spray Bacillus thurengis (B.t.) within.
Powdery mildew can be a problem on roses, Crepe Myrtles, grapes, and a number of other plants. The type of mildew is specific to that species of plant, but treatment is similar for all types. A spray of Potassium Bicarbonate or the organic preparation Serenade should help to control the problem. I have had trouble with mildew on roses in cooler and damp climates like the Bay Area, where I lived for ten years, and Seattle, my earlier home. It has not been a problem for me here, probably because it is too darn hot!
I just planted three types of summer squash today in my garden (zucchini, yellow squash, and the white patty-pan squash). Every year I struggle with the squash vine borers. The adult is an orange and yellow flying insect that resembles a wasp. In early summer the adults emerge from cocoons in the ground and soon thereafter begin laying eggs at the base of susceptible plants in the Cucurbit family. Summer and winter squash are usually the most affected, with cucumbers and melons slightly less so. I grow my cucumbers and melons on trellises, and they have not been affected in past years. About a week after the eggs are laid they hatch and burrow into the stems to feed. Usually the first sign of damage is wilting, and small areas of yellowish digested stem are visible.
There are several options to prevent damage. You can cover the plants with a lightweight row cover until they begin blooming. Then you can uncover and leave open, or hand pollinate and re-cover. You can also use yellow trap pans to detect squash vine borer adults. This can be any pan, pail, or bowl colored yellow and filled with water. Because squash vine borer adults are attracted to yellow, they will fly to the container and be trapped when they fall into the water. Place traps early, checking the traps at least once a day. When you notice squash vine borer adults in your traps you know they are active and it is time to take further action. Spraying the base of the plant weekly with B.t. may help, or once you see the damage on the stems, you can cut a slit in the stem, remove the borer, and cover the stem with soil.
All this may seem like a lot of work, but you could humor yourself and imagine that you are a big brave Texas bug hunter, and enjoy the process. I know you will enjoy the fruits of your labor in the garden once the vegetables are ripe and ready to eat.