Insects/Mites that Feed on Hemp – Fluid Feeders

Beet Leafhopper and Beet
Curly Top Virus
Beet leafhopper, Neoalitursus(=Circulifer) tenellus)1 is an uncommon
insect found in hemp fields but cancause serious injury to the crop becauseof its ability to transmit the virus toplants that produces the disease beet
curly top2. In Colorado beet leafhopper
is most common in the West Slope
where outbreaks of this diseasefrequently appear on many crops (e.g.,tomato, bean, squash, beets, spinach).
Beet leafhopper and beet curly top isalso present in eastern Colorado, but isfar less common. In 2019, beet curly
top infections of hemp were foundacross the state, but were most severein the Tri-River counties.

Figure 1. Mild symptom of light yellowing of hemp
leaves produced by infection with beet curly top virus

Beet curly top has been observed toproduce an extremely wide range ofsymptoms in hemp. Leaf symptoms
may be quite mild, at least during earlystages of infection, producing only aslight yellowing/mottling, mostly at thebase of a leaf (Fig. 1). Symptoms areoften much more dramatic. In somecases whole plants will become paleyellow, often with some slight upwardleaf curling, and become generally
Figures 2a, 2b. Bright yellowing and stunting of thestunted; these are “classic” symptoms
whole plant are “classic” symptoms of beet curly top in
similar to what beet curly top produces
hemp.
in other susceptible crops (Figs. 2a, b).
Other hemp plants may show strong twisting of the new growth, which may remain green orturn yellow. Some stunting also occurs on plants with this symptom (Figs. 3, 4).
Hemp infected with beet curly top virus also has shown some very strange symptoms thatappear to be unique to the crop. In some cases, plants that show strong leaf curling appear toFigures 5a, b. A “bisymptomatic” hemp plant
infected with beet curly top virus. The original
main stem has tightly curled new growth (top).
Side branches that later develop on the plant arelargely symptom-free.

Figure 3. Hemp plant showing twisting of thenew growth from beet curly top virus.

Figure 4. Hemp showing a “trifecta” ofsymptoms, pale mottling of some leaves,twisting of new growth and yellowing.

be able to later outgrow most of thesesymptoms. Another peculiarity often observedis that plants may be “bisymptomatic” wheresome of the plant shows symptoms and otherparts do not (Figs. 5a, b). This most commonlyoccurs when the original stem develops leaf
twisting and becomes stunted. Side branches
developing off the main stem are thenstimulated to grow and these often appear
normal. Interestingly, in these plants, beet curly
top virus is detectable in both the original mainshoot and the side branches that do not showsymptoms.

Beet curly top in hemp is poorly studied and was
first described from the crop in 2019. The reason for this wide range in symptoms that canappear is unclear but may involve such things as genetic differences in plant response to thevirus or differences in the strains of the virus. There are several strains of beet curly top virus.

So far two of these have been detected in Colorado hemp, the Worland (BCTV-Wor) strain andthe Colorado (BCTV-CO) strain which have appeared alone and in combination in hemp plants
showing beet curly top symptoms in
2019. Future research on this situation in
the upcoming season should provide
more clarity as to whether there is morethan the two known strains (Worland,Colorado) of the beet curly top virus
producing these hemp disorders
Beet curly top virus has only one insect(vector) capable of allowing the virus tobe transmitted to plants, the beetleafhopper. All infections of hemp occur
when a beet leafhopper that is carrying
beet curly top virus (after previously
feeding on a BCTV-infected plant of somekind) feeds on a hemp plant. Both BCTVWor and BCTV-CO strains have been
confirmed in leafhoppers collected fromthe Western slope (Delta Co).
Beet leafhoppers are fairly similar in sizeand general coloration of some of themany other leafhoppers found in hemp
Figures 6a, b. Top and side views of adult beetand difficult to identify. Adults paleleafhopper. Top photo courtesy of G. Oldfield,
green/light yellow with some blotches,
USDA/Bugwood.org. Lower photo courtesy of A.C.
with and elongate slightly wedge-shaped
Magyorosky/Bugwood.org
body and about 1/8-1/6 inch in length(Figs. 6a, b). Adults are the only stage that would be found in hemp, this insect does not
reproduce on the crop.
(Over a dozen other species of leafhoppers have been found present in Colorado hemp fields.
Most are likely transients, as is beet leafhopper, and do not breed in hemp. Of the few that do
reproduce in hemp, most common is Ceratagallia uhleri (Fig. 7), which has some superficial
resemblance to beet leafhopper. No significant injury to hemp is produced by any of theseother leafhoppers and no other leafhoppers, other than beet leafhopper, are known to transmit
any viruses or other pathogens to hemp.)
The presence of beet leafhopper in Colorado during the growing season is largely, if notentirely, dependent on migrations entering the state in spring that originate from southernareas outside the state, particularly New Mexico. During winter the insect is able to survive on
various kinds of weedy plants that continue to grow through winter, particularly mustard-family

plants that grow as winter annuals. The abundance of winter host plants in the southern
breeding areas (in NM, maybe AZ) could be an important factor in the number of beetleafhoppers that appear in Colorado in spring; in winter 2019 moisture conditions were very
favorable in the southern breedingareas to support the plant on whichbeet leafhopper develops. Many ofthe migrant beet leafhoppers carrywith them beet curly top virus theyacquired when earlier feeding on beet
curly top infected plants.
Some beet leafhoppers also survive
through winter in western Colorado.
This could occur where winter annual
mustards, such as flixweed andpepperweed, are present and in goodcondition to support the insects. This
would happen most often when
Figure 7. Ceratagallia uhleri is the most common
winters were mild and moisture wasleafhopper found in hemp in Colorado and one ofgood. Severe, dry winters would
the only ones that reproduces on hemp. Although it
reduce the potential of beetfeeds on the plant this leafhopper produces noleafhopper to overwinter within thesignficant injuries nor transmits any pathogens tostate. However, whether any beetthe crop.
leafhoppers do ever survive within the state, it would happen in only localized areas, and their
numbers would be dwarfed by the vastly larger numbers of migrants originating from the main
winter breeding areas to the south.
During late spring and summer beet leafhopper can be found on a great many plants but will
reproduce on only some of these. Russian thistle is the best known weed host for summer
breeding by beet leafhopper and where but there are likely many others. Kochia is the plant on
which beet leafhopper is most easily found in western Colorado. Regular surveys of kochia
patches should allow one to detect when migrations have moved into the region and are thebest plant to survey to get a sense on the relative size of beet leafhopper populations fromseason to season.
In hemp, adults only will be present and these likely spend little time in the crop, feeding some
but then moving to more favored food plants. The detection of beet leafhopper is best done bysampling plants with a sweep net.
Beet curly top is a notoriously difficult disease to manage on any crop. Because of the mobilityof beet leafhopper and the rapid speed (a couple of hours) which the virus is transmitted,
insecticides are ineffective. Reflective surface mulches, which deter beet leafhopper and otherinsects (e.g., aphids) from landing on plants, may have some value in reducing beet curly top
virus spread in hemp.
1 Order, Hemiptera, Family Cicadellidae
2 Family, Geminiviridae; Genus Curtovirus

Credits: Dr. Punya Nachappa, and Judith Chiginsky, Colorado State University, did the analysesof hemp plants for beet curly top virus in 2019. Bob Hammon has provided exceptional
assistance regarding biology of the beet leafhopper and curly top virus in Western Colorado.