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Sunday, June 12, 2011

Tobacco insect activity increasing

Yesterday, I visited Cross Creek Seed, Inc. in Raeford, NC to check on a research trial we treated last Friday. This trial is comparing Coragen, a newer insecticide from DuPont, applied through drip irrigation to an untreated control for tobacco budworm and tobacco hornworm management. We applied treatments last Friday, and this was our first post treatment count.

Drip applications of Coragen applied to 3 week old tobacco plants. Photo: HJB

It's too early to tell if there are any differences between treatments, but I lots of other noteworthy insects. Several green stink bugs were on plants, but I observed only one damaged leaf.  Stink bugs in tobacco feed on the mid ribs of leaves, sometimes causing the leaf in question to wilt.  Even in very high densities, stink bugs typically only damage one leaf per plant, and this damage is not economically significant.  Wilted leaves may recover or may be more susceptible sun scald and be unharvestable.  The most important consideration with respect to stink bug damage is to distinguish it from potential disease symptoms.  The early stages of several diseases in tobacco may cause wilting.  In order to confirm stink bug damage, stink bugs should be present in the field and damage should be recent (not sun burned).  If stink bugs cannot be confirmed in the field, and other causes of wilting, such as drowning, cannot be ruled out, disease samples should be collected to rule out soil borne pathogens.

Green stink bug present on a tobacco plant, Raeford, NC. Photo: HJB
Tobacco plant with leaf injured by stink bug feeding, Raeford, NC. Photo: HJB
Also moving around the tobacco plants were several snowy tree crickets (Oecanthus fultoni).  Crickets are another infrequent, non economic pest of tobacco.  I didn't see any cricket damage on the plants near Raeford.  When present, cricket injury to tobacco consists of ragged holes on medium to large leaves.

Snowy tree cricket on tobacco plant. Photo: HJB
Also present were fairly large numbers of the insects we are trying to control in this trial, tobacco budworms. Most of the larvae present were small (1st to 3rd larval instars), and adult budworm moths were also flying around.  While tobacco budworms are not necessarily an economically significant pest in tobacco leaf production, they can cause major losses in seed production.  Tobacco budworms preferentially feed on the reproductive parts of plants and can reduce seed set and consume developing seeds.  We have been studying methods to reduce pesticide use against tobacco budworms in seed production. Seed growers typically apply pesticides weekly for tobacco budworm, and we are comparing newer pesticides to reduce foliar application, both in foliar applied and soil forms.

Tobacco budworm (Heliothis virescens) moth present on tobacco plant. Photo: HJB
Last year was a banner year for caterpillars, referred to by some as the "year of the worm".  The 2011 growing season is still young, but signs point to this year being a similarly high pressure caterpillar year.  At Cross Creek, I saw the beginnings of tobacco/tomato hornworm activity--two eggs and one recently hatched larva.  
Tobacco or tomato hornworm eggs in tobacco near  Raeford, NC.  Photo: HJB
Tobacco hornworm larva. Tobacco hornworm larvae have a red caudal (rear) horn, while tomato hornworm larvae have a blue caudal horn. Photo: HJB
Last week, at a field in Harnett County near Lillington, I saw all ages of tobacco budworm larvae and tobacco hornworm larvae.  This is slightly earlier hornworm activity than typical, but it is not out of ordinary.  Growers should scout their fields at least once before topping to ensure that hornworms are not present.  Hornworms are common, but potentially devastating pests in tobacco and shouldn't be taken lightly.

First, second, and third instar tobacco budworm larvae, near Lillington, NC.  Photo: HJB

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