Page 17 - Griffin Gazette Issue 3 - 2019

While hemp is a strong grower and generally establishes quickly, it does fall prey to a number of common
pests that can reduce crop quality and yield. Many of these pests are well known to ornamental growers,
including aphids, spider mites, thrips, fungus gnats, shoreflies and Botrytis. Some of these pests might become
problems, but it is possible to take action to control the infestation or infection.
However, there are a few other pests that are much more difficult to control: root aphids, hemp
russet mite and powdery mildew. Let’s look at best practices to control these three tough pests.

Root aphids Hemp russet mite (HRM) Powdery mildew (PM)

How to ID: Round bodies, often How to ID: White to clear, How to ID: White, powdery
olive-green, with cornicles on the cigar shaped mites. Requires coating on upper and lower
posterior. Visible to the naked eye. magnification to see. leaf surfaces.

Since root aphids feed on the roots, HRM presents, without question, the This fungal pathogen is an obligate
they can quickly impact nutrient biggest risk to hemp crops. This tiny, parasite and requires living tissue for
uptake and overall crop health. eriophyid mite causes distinctive leaf curl infection. The challenge with
Chemical control, where allowed, and bronzing and can lead to decreased PM is that the spores germinate on
can be a challenge due to difficulty production. The challenge is that once the leaf surface and then the pathogen
of achieving full media saturation established, it is very difficult to eliminate. quickly penetrate into the leaf
required for good contact. When In fact, serious infestations of HRM call tissue. The white spores that develop
infestations are heavy, the best course for disposal instead of treatment. on the leaf surface are actually a late
of action is to discard the infected Quarantine, scout and treat all sign of infection; surface
plants and avoid spread to the rest of incoming plant material. Avoid taking sprays may kill the spores, but often
the crop. don’t control the mycelium living
cuttings from mother plants infested within the leaf tissue. PM spores
Prevent root aphids by quarantining with HRM. When allowed, the are generally ubiquitous in the
and scouting all inbound plant horticultural and essential oil products environment and germinate best when
material. When allowed, drenches of (Suffoil-X, Ultra-Pure Oil, EcoTec Plus) humidity is high and leaf surfaces are
Ancora (Isaria fumosorosea Apopka are options for early intervention. The dry. PM is readily spread via cuttings;
Strain 97) are effective. Some growers best approach is to utilize beneficial be sure that moms are not infested.
report success with releases of Dalotia mites from the time of sticking or When allowed, use silicon products
coriaria. Note that the nematodes sowing through the end of the crop. for prevention (e.g. Sil-Matrix) or one
used against thrips and fungus Both Amblyseius andersoni and of the preventative standards for foliar
gnats are not effective A. californicus can be used to prevent fungal diseases: Cease, Regalia CG
against root aphids. HRM. Biological control agents are or Triathlon BA. Zero-Tol 2.0
not effective once HRM is widely sprays are also effective.
established on a crop.

It is the grower’s responsibility to understand federal, state and local regulations regarding pesticide use on hemp and cannabis
crops. Some pesticides are approved by some states and not by others. Applicators must read the entire pesticide label. It is the
responsibility of the applicator to read and follow all label directions. Labels do change without notice. Pesticides other than those
listed may be safe, legal and effective. The label is the law.

GRIFFIN GAZETTE 2019 | 17