Nematodes

Marijuana Horticulture

by Jorge Cervantes

Identify

Of the hundreds and thousand of species of microscopic nematodes – sometimes, big ones are called eelworms – a few are destructive to plants. Most often nematodes attack roots and are found in the soil; however, a few nematodes attack stems and foliage. Root nematodes can often be seen in and around roots with the help of a 30X microscope. Often growers just diagnose the damage caused by destructive nematodes rather than actually seeing them.

Damage

Slow growth, leaf chlorosis, wilting several hours during daylight hours from lack of fluid flow – symptoms can be difficult to discern from nitrogen deficiency. Root damage is often severe by the time they are examined. Rot knot nematodes are some of the worst. They cause roots to swell with galls. Other nematodes scrape and cut roots, compounded by fungal attacks. Roots turn soft and mushy.

Cultural and physical control

Cleanliness! Use new, sterilized potting soil or soilless mix to exclude nematodes’ entrance. Nematodes rarely cause problems indoors in clean grow rooms.

Biological

French marigolds, Tagetes patula, repels soil nematodes, fungus (Myrothecium verrucaria, trade name DeTera ES).

Sprays

Neem is used as a soil-drench.