Bacillus thuringiensis (Bt) and Bacillus species
Marijuana Horticulture
by Jorge Cervantes
Bacilus thuringiensis (Bt) is the best known of several bacteria that are fatal to caterpillars, larvae, and maggots. Caterpillars, larvae, and maggots all eat Bt bacteria, which can be applied as a spray, dust, or granules. Inject liquid Bt into stalks to kill borers. Shorty after they ingest it, their appetite is ruined, and they stop eating. Within a few days they shrivel up and die; cabbage loopers, cabbage worms, corn earworms, cutworms, gypsy moth larvae, and hornworms are controlled.
Commercial Bt products do not reproduce within insect bodies, so several applications may be necessary to control an infestation. Microbial Bt bacteria are nontoxic to animals (humans), beneficial insects, and plants; however, some people do develop an allergic reaction. Commercial Bt products do not contain living Bt bacteria, but the Bt toxin is extremely perishable. Keep within prescribed temperature range, and apply according to the directions. Most effective on young caterpillars, larvae, and maggots, so apply as son as they are spotted.
Get the most out of Bt applications by adding a UV inhibitor, spreader-sticker, and a feeding stimulant such as Entice, Konsume or Pheast. Bt is completely broken down by UV light in one to three days.
B. thuringiensis var. kurstaki (Btk) – introduced on the market in the early 1960s – is the most popular Bt. Toxic to many moth and caterpillar larvae including most f the species that feed on flowers and vegetables. Sold under many trade names, DiPel, BioBit, Javelin, etc, Btk is also available in a microencapsulated form, M-Trak, Mattch, etc. The encapsulation extends the effective life on foliage to more than a week.
B. thuringiensis var. israelensis (Bt-i) is effective against the larvae of mosquitoes, black flies, and fungus gnats. Look for Gnatrl, Vectobac, and Bacrimos. All are lethal to larvae. Adults do not feed on plants and are not affected. Fungus gnats can cause root problems including rot. Use Bti to get rid of them as soon as they are identified.
B. thuringiensis var. morrisoni is a new strain of Bt under development for insect larvae with high pH in their guts.
B. thuringiensis var. san diego (Btsd) targets the larvae of Colorado potato beetles and elm beetle adults and other leaf beetles.
B. thuringiensis var. tenebrionis (Btt) is lethal to Colorado potato beetle larvae.
B. cereus helps control damping off and rot-knot fungus. It flourishes in water-saturated mediums and promotes beneficial fungus that attacks the diseases.
B. subtilis is a soil dwelling bacterium that curbs Fusarium, Pythium, and Rhizoctonia that cause damping off. It is commercially available under the brand names Epic, Kodiac, Rhizo-Plus, Serenade, etc. Soak seeds and apply as a soil drench.