Use Plant Covers for Insect, Disease Protection

This season, you may want to try a technique which will not only enable you to have early production, but may be the difference between whether you produce an abundant crop or no crop at all. This technique will also enable you to grow a pest-free crop without applying pesticides.

Gardeners blame everything from vengeful neighbors to dishonest nurserymen for stunted, nonproductive plants which are infected with a virus. No person is to blame - thousands of insects, such as thrips, feed on a plant which already has a virus and then transmit the virus to another plant. Not all insects spread viruses. Insects which have been known to cause problems include aphids, thrips, white flies and leaf-feeding beetles. Aphid mouth parts puncture an infected plant and draw the virus particles and cell contents into their body.

Some aphid-borne viruses are carried only on mouth parts, but others are taken into the gut, circulatory system and eventually the salivary glands. All the aphid has to do is "slobber" on a healthy plant to cause infection. This is why virus prevention is so difficult - 100 percent insect control is both impossible and impractical. Even if you could grow a plant full of pesticide which would immediately kill any insect that damaged the foliage, the virus is delivered the instant the plant tissue is penetrated. Insect sprays are not the answer!

The remedy for insect damage and contamination is a physical barrier. Transplant tomatoes and peppers into the garden. Immediately install concrete reinforcing wire cages. Cages are nothing more than cylinders made of reinforcing wire, hog wire or similar material to support the plant and keep the fruit off the ground.

Make the cylinder 18 to 20 inches in diameter and 2 1/2 (called half cages) to 5 feet tall (the length of the roll of wire becomes the height of the cage). Concrete reinforcing wire, generally considered to be the best, is available in rolls of varying lengths. A 5-foot length makes a tomato cage 18 to 20 inches in diameter. Cages are held together by bending and crimping the wire ends around one of the vertical wires.

To keep the cage supported and standing, snip off the bottom ring of the cage and push the remaining prongs into the ground. Install cages around young transplants
and anchor all sides well with wire stakes in the soil. For a barrier, cover the cages to the ground with clear plastic or a translucent, fabric-like material known as spunweb (Grow-web). Adequate anchorage is essential for cages covered with plastic or spunweb during windy periods.

Covered transplants will be protected from virus-carrying thrips and aphids until the plant touches the sides of the cage and plastic has to be removed. Plants covered with spunweb never have to be uncovered. Plastic covering must be removed when foliage begins to touch the edges and bunch against the sides of plastic. This will usually be about the time the plant has marble-sized fruit. Because of excessive heat build-up, the plastic covering must be removed when temperatures regularly begin to reach the high 80s.

Spunweb will never overheat plants since the temperature inside the fabric-like material will not exceed 15°F above the daytime high temperature. Spunweb can also be used for the fall crop, planted in July, since it will not overheat plants and seems to act as a shading cloth. Plastic-covered cages need to be closely monitored since temperatures will be 30°F warmer inside the plastic. Ventilation from the bottom, by raising the plastic 4 to 6 inches, as well as opening the top, may be necessary when daytime temperatures above 75°F occur.

The tops of these miniature greenhouses which are covered with plastic will have to be left open during warm days to avoid excessive heat build up, but most insects do not enter from the top. Most insects are blown in by the wind. The covered plants are "hidden" from contaminating insects and not as attractive to them as unprotected plants. Leave tops open when daytime temperatures get above 75°F. On cold nights, tops should be closed to provide extra protection. One of the advantages of the spunweb is that it never requires ventilation. However, this web-like material does not provide as much cold protection as plastic; each web-covered cage will have to be artificially heated (with Christmas lights, etc.) if temperatures fall below freezing.

One of the greatest benefits of this system will be protection from wind. Findings indicate that winds as low as 15 mph can significantly slow plant growth, delay harvest and decrease yields of vegetable crops. You may wonder if plants will set fruit when covered with plastic or spunweb since no bees or insects are able to enter. Tomatoes, peppers and eggplants are 85 percent self-pollinated; that is, they don't need movement of pollen by insects. If you want to insure adequate pollination, vigorously shake the covered cages every day after bloom begins or thump bloom clusters daily with your finger. You can also artificially set early blooms by spraying bloom clusters with Blossom-Set, a plant hormone spray. Resulting fruit will have fewer seeds.

Protect tender transplants as soon as possible from virus-carrying insects and environmental adversities with the covered cages. The larger a plant is before infection occurs, the more productive it will be, and conversely. To protect seedlings from birds or other varmints and vine crops (such as broccoli and cole crops) from leaf-eating caterpillars, cover them with spunweb. You can also use spunweb to "vine ripen" fruit. Spunweb products can be found in local nurseries or ordered directly from the manufacturer through the mail. One address is:
Indeco Products Incorporated, P.O. Box 865, San Marcos, Texas 78666 Telephone: 512-396-5814 or 1-888-246-3326; email ¶