Sunday, November 1, 2009

Pest of the Week: Tobacco and Tomato Hornworms

Figure 1 Tobacco hornworm larva
Courtesy of University of Kentucky

Figure 2 Parasitized larva
Courtesy Clemson University - USDA Cooperative
Extension Slide Series,

Figure 3 Tomato hornworm larva
Courtesy of Colorado State University

Common name: Tobacco and Tomato Hornworms

Latin Name: Manduca sexta (Linneaus), Manduca quinquemaculata

Life Cycle: Two or more generations per year in warmer climates, one generation per year in cooler climates (check local extension information for specifics on life cycles by region); adult moths lay eggs mostly on undersides of leaves, eggs hatch within about five days, larvae generally move through five instars to reach full size, overwinter as pupae in the soil and emerge in the spring as adults who then mate and begin the process again.

Plants effected: Tomatoes, peppers, tobacco, other Solonaceous crops and weed species.

Insect Habit: Adults emerge in spring (first generation) or summer (second and subsequent generations, depending upon climate) to mate and feed on the nectar of deep throated flowers; larvae feed upon foliage of Solonaceous crops and weeds. As larvae mature, large frass is produced and quite evident under and around effected plants even though the actual pest may not be observed. Tobacco hornworm has seven white lines on both sides and curved red horn on last body segment, tomato hornworm has v-shaped white lines on both sides and a straighter, blue-black horn.
Control: Remove larvae as they are found, till soil just after crops are finished for the season (very effective in ridding the soil of overwintering pupae), natural populations of paper wasps and yellowjackets will kill and feed larvae to their larvae, lady beetles and green lacewings will eat eggs1, larvae of the Cotesia congregatus wasp will parasitize hornworm larvae and, if found, should be left alone to complete their life cycle to build up natural enemy populations1 (Fig. 2), Bt products are effective against smaller larval stages.


Mary said...

We have a Black Lab who walks the tomato rows, smelling for hornworms, and then (yuck) pulls them off and eats them! Makes our job a little easier!

Carl said...

I love the last post about the black lab. The problem I have with the tomato hornworms is what a huge and beautiful moth they turn into. When I do find them I relocate them to "wild" tomato plants in my compost. I know not a great practice but I guess it balances out.

Anonymous said...

There's alot of nasty bugs I can deal with - Tomato worms no. I usually end up cutting off a huge chunk of plant and pitch them in the trash. EWWWW

Angela said...

We had them really bad last July - one of them was over 4 inches long and about an inch in diameter... uck. I still have a hard time eating tomatos after seeing these nasty beasties on my plants! Does anyone know of a way to "dust" for them safely? (I know, dust and safe are not usually used in the same sentence) but seriously, what is the point of growing tomatos if you can't eat them!!!

carl said...

You can use Dipel dust on them. I use this dust on my broccoli and cabbage for the cabbage worms.