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Chapter 10DISEASES AND PLANT PESTS

Plants are considered diseased when their health or development is impairedenough that the adverse effects become visible to the eye. Disease may becaused by infectious microbes, such as bacteria or viruses, by pests suchas insects, or by nutritional deficiencies or imbalances. However, fordiseases that might affect your plants, there should be no need for a plantdoctor. You'll be able to diagnose the symptoms after careful observation.

Leaves naturally drop from plants during the course of their lives. Notevery leaf will develop perfectly or so. The small leaves that are formedduring the first few weeks of growth normally die within three months.Leaves at the bottom of healthy plants often die because they are shieldedby the upper instance, in a garden receiving only 80 watts of fluorescentlight, the plants may stay green only up to three or four feet away fromthe lights. Lower leaves may turn pale and yellow and then dry to gold orrust colours.

Microbial Diseases

Because Cannabis is not native to the Americas, most of the microbialdiseases that attack the plant are not found in this country. HomegrownCannabis is remarkably free of diseases caused by microbes, and there is

little chance of your plants suffering from these diseases. Fungal stem androot rots seem to be the only ones of consequence. These occur only becauseof improper care. Watering too often, coupled with a stagnant, humidatmosphere, encourages stem rot to develop. Stem rot appears as a brown orblack discolouration at the base of the stem and is soft or mushy to thetouch. Allow the soil to dry between waterings, and be sure to water aroundthe stem, not on it. Wipe as much of the fungus and soft tissue away aspossibly. If the rot doesn't disappear in a few weeks, treat it with afungicide.

Nutrient Diseases

Diseases due to nutrient deficiencies (see section 9), are common indoors,

and their symptoms usually worsen with time, affecting more and more of theplant. Whole leaves may be pale, or turn yellow or white; the condition mayfirst afflict the bottom, or top, or the entire plant at once. Deficiencysymptoms often appear as spots, splotches, or areas or chlorotic (lackinggreen) tissue. Sometimes necrotic (dead) tissue appears that is copper,brown, or gray. However, before you search to section 9, carefully inspectthe plants for any signs of plant pests.

Plant Pests

The indoor garden is an artificial habitat where the plants live inisolation from the natural world. For this reason, few of you will have anyproblems with plant pests. However, indoor plants are particularly

susceptible to pests once contaminated. In nature, the pest populations arekept in check by their natural enemies, as well as by wind, rain, andchanging temperatures. Without these natural checks, pests can run rampantthrough the indoor garden.

The most common and destructive pests are spider mites and whiteflies.Spider mites are barely visible to the naked eye; they are ovoid-shaped.Juvenile mites are transparent and change to green as they suck the plant'stissue. Adults are tan, black, or semitransparent. False spider mites arebright red. Mites are usually well-established before you discover them,

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because they are so difficult to see.

Whiteflies are white (obviously) but look like tiny moths rather thanflies. The adults are about 1/16 inch long, and you may not see one unlessif flutters by the corner of your eye. Then shake the plants. If the resultlooks like a small snowstorm, the plants are infested with whiteflies.{Figure 52. Left: Spider mite (x16). Right: A match head dwarfs tiny spidermites.}

The symptoms of infection by mites and whiteflies are similar. Symptomsusually appear on the lower leaves and gradually spread to the top of theplant. The first indications are that the plant loses vigour; lower leavesdroop and may look pale. Look closely at the upper surfaces of the leavesfor a white speckling against the green background. The speckles are due tothe pests sucking the plant's chlorophyll-rich tissue. With time, the leafloses all colour and dies.

Pests are easiest to find on the leaves that are beginning to show somedamage. You can usually see mites and whitefly larvae as tiny dots lookingup at the lights through the undersides of the leaves.

To find out which pest you have, remove some damaged leaves and inspect theundersides under bright daylight. With spider mites, if you discover themearly, a leaf may show only one or two tiny dots (adults) and a sprinkling

of white powder (eggs) along the veins. In advanced cases, the undersideslook dusty with the spider mites' webbing, or there may be webbing at theleaf nodes or where the leaflets meet the petioles. With whiteflies, youusually see the adults first. On the undersides of the leaves the whiteflylarvae look like mites, but there is no webbing, and there are tiny goldendroplets of "honeydew" excreted by the adult whiteflies. {Figure 53. Mitesappear as black specks when you look up to the lights from the undersidesof the leaves. Also see Plate 14.}

Take quick action once you discover plant pests. If the plants are lessthan a month old, you will probably be better off to clean out the garden,in order to eliminate the source of the pests, and start over. As long asthe plants are healthy they can withstand most attacks. The more mature the

plants are, the less they are affected by pests. Whiteflies and mitessometimes disappear from flowering plants, particularly the female flowers.Mites are difficult to eliminate completely. Often a holding action willsave a good crop.

If only a few plants in your garden are infected, remove them. Or else,remove any leaves that show damage. If the plants are three or more monthsold, you might consider forcing them to flower while they are stillhealthy. Plants that are good-sized and still vigorous will usually standup well to mites once they are flowering.

If you don't want to use insecticides, there are several alternative waysto keep the pests in check until flowering. Mix 1/8 to 1/4 pound of pure

soap (such as Ivory flakes) thoroughly in one gallon of lukewarm water.Then cover each pot with foil or newspaper, invert it, and dip and swishthe plant around several times in the soapy solution. Let is drip dry andrinse with clear water. Use the dunking procedure every week or two untilthe plants are larger. This is often enough to get the plants growing welland into flowering before the pest population can become a serious problem.

Two homemade sprays that can be effective are dormant oil sprays ((See"Insects and Pests" in the Outdoor Section.)) and hot pepper sprays.

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aphids.

Mealy bugs are white, about 3/16 of an inch long, and look like small, flatsowbugs. They don't seem to like marijuana and avoid it if other plants arepresent. Mealy bugs can be removed individually with cotton swabs andalcohol.

Gnats are attracted to moist soil that is rich in partially decayed organicmatter such as manures. To discourage gnats when using manures, cover thetop few inches in the pot with the soil mixture and no manure. Drench thesoil with malathion solution for gnats or any other soil pest. Flypaperwill also help against gnats as well as whiteflies.

Some people don't mind having a few pests on their plants. Whether you wantto eliminate the pests completely or simply keep them in check may comedown to whether you mind hearing the snap, crackle, and poop as theirlittle bug bodies heat and explode when the harvest is smoked. Commercialmarijuana, or any marijuana grown outdoors, will contain innumerable bugsand other small lifeforms.

Prevention

Whiteflies and spider mites are extremely contagious. Mites can be carriedto the plant on hands, clothing, or an animal's fur. Many houseplant pests

can fly or float to the garden through open windows. Mites crawl throughcracks in walls and foundations during autumn, seeking warmth.

Many houseplants are popular because they can withstand abuse andinfections by common plant pests. Your houseplants may harbor mites foryears without your knowledge. You can find out if your houseplants havemites by placing some marijuana seedlings among the houseplants. Mites seemto enjoy young marijuana plants so much that the plants show symptoms ofmites in a matter of weeks of any are nearby.

Hopefully, you'll never have to deal with pests. Prevention is the bestpolicy. Use soil that has been pasteurised or sterilised to avoid bringingpest eggs and larvae into the garden. Keep the garden isolated from other

plants. Use separate tools for the marijuana garden and for other plants.Screen windows in the garden with wire screen or mesh fabrics such asnylon.