Yellow Striped Armyworm Management
Posted: December 2, 2012
Larva of yellow striped armyworm damaging tomato, 2012. Photo by Steve Bogash, Penn State Extension.
1) Tomato growers reported a new insect pest this season, the Yellow Striped Armyworm. What is it, and what caused this pest to show up now?
The yellow striped armyworm, Spodoptera ornithogalli, is a close relative of a pest of sweet corn that you are more familiar with, the fall armyworm, Spodoptera frugiperda. Both of these species overwinter in southern areas and migrate northward each year. My best guess, and it is only a guess, is that the overwintering area was closer to us in the winter of 2011-2012, due to the very warm winter of that year, which enabled the northward migration to originate closer to us than what has typically occurred in the past. Migrants may have reached our area earlier than past years, and completed one or more generations.
It is not new to have yellow striped armyworm in our area. In fact, it is the most common non-target species we see in pheromone traps that are tracking another pest species that is moving into our area – the Western bean cutworm. It is also common in Iowa soybean fields, but not reaching pest status there. What is new is to see yellow striped armyworm reaching high enough numbers to be considered a pest. The geographic distribution of this species reaching pest status has historically been limited to southern states, the Caribbean, Mexico, and South America.
2) Can we expect this pest to over winter in our area?
It is unlikely at this time. Eggs, larva, and adults are killed by freezing temperatures. Pupa can withstand colder temperatures, and this species overwinters in North Carolina and Kentucky. But being able to overwinter is not the same as being very successful at it. Rates of overwintering probably increase as you move south.
Yellow striped armyworm is probably not overwintering in Pennsylvania. But it may be overwintering closer, or more successfully, at the northern edge of its overwintering range. I think that did happen in winter of 2011-2012, and it is more likely to happen again as the climate changes. The probability of having warm winters has increased due to the increasing greenhouse gasses in our atmosphere.
3) Which moth is the adult form of the Yellow Striped Armyworm?
Adults look very much like the adult form of fall armyworm. The wingspan is 1.3 to 1.6 inches. Front wings have a complex pattern of brown, tan and grey areas. A photo from Iowa State University shows the pattern.
The adults are difficult to distinguish from its relatives (such as the fall armyworm), but the larva are distinct. Larvae have a yellow stripe running longitudinally along their body. Less distinct stripes are below that, including a pink stripe above the prologs. Black triangles are positioned above the yellow stripe on most abdominal segments.
4) It seemed difficult to control. Is this pest a problem in Southern crops? Has it developed resistance to many commonly used Lepitopteran controls due to heavy exposure to insecticides?
It is a pest in many crops in the south. It has an extremely wide host range. A short list includes asparagus, bean, beet, crucifers, cucurbits, tomato, alfalfa, small fruit, peach, wheat… the literature includes many more. Important weed hosts include dock, horseweed, lambsquarters, plantain, and pigweed.
Resistance is very common in its relative, the fall armyworm. It may not be as severe in yellow striped armyworm. Insecticidal control can be expected to be more effective when targeting early instars.
5) Please explain the lifecycle of this pest.
Yellow striped armyworm overwinters as a pupa in the soil in southern states. In Kentucky, adults are active in April or May. Eggs are laid in clusters of 200-500 eggs per cluster, on the underside of leaves. Females are capable of depositing up to 3000 eggs. Young instars initially are gregarious, and later disperse, sometimes using silk strands carried by the wind, as they mature. There are typically 6 instars. Typical life cycles in Kentucky are 5-7 days in the egg stage, about 3 weeks as larvae, followed by pupation, and 3 to 4 generations per year.
6) Most growers did not find this pest until there was heavy feeding damage to tomatoes, are there any pheromone lures or other methods that can used to detect it earlier.
Pheromone lures might help. Great Lakes IPM carries a pheromone lure for yellow striped armyworm. Also, the lure currently used to trap the Western bean cutworm is capturing yellow striped armyworm adults. Field research should be conducted to determine if the lure is sufficiently selective – does it only, or mostly, attract yellow striped armyworms, or do we have a significant non-target capture in our area. Another option is to use blacklight traps, but you would need to sort through the captures of many species.
7) What cultural controls could work to reduce future infestations?
Scouting for early signs of infestation may help. In southern states, problems tend to start in the vegetative stage of plants. However, the larvae may move rapidly to fruit. In Florida tomatoes, the recommendation is to treat with an insecticide if there is one larva or more per six plants before bloom. After bloom, treat if one egg or larva is found per field.
8) What biological controls can be used to manage future infestations?
Even in more southern states, it is not always a pest. It has a very large number of predators, parasitoids, and fungal and viral pathogens. These mortality agents are present in the landscape, so conservation of natural enemies, by limiting insecticides as much as possible, may be the most effective biological control. When you move to protected-ag systems (high tunnels, greenhouses) you need to introduce biocontrols. Generalist predators may help. I don’t know if there are commercial sources of the specialist parasitoids. Microbial controls can be effective. These include Bt sprays, but they would need to reach the very young instars. There are several insecticides that are metabolites from fermentation culture of microbes that are effective, including Proclaim (emmamectin benzoate), and the various formulations of spinosyns (Radiant, or Entrust). Two of these options – Bt sprays and Entrust – are allowable in certified organic production.
9) What conventional insecticides are effective in managing this pest?
Materials that work for beet armyworm or fall armyworm should work against yellow striped armyworm. Use a current Commercial Vegetable Production Guide to see recommendations for beet armyworm or fall armyworm for the crop where the infestation is present. Check the label to see if it lists yellow striped armyworm, or the more general category of “armyworm”. If labeled for the pest, then options for tomato include Coragen, Proclaim, Synapse, Vetica, Avaunt, Volium Xpress, Lannate, Intrepid, Rimon, Radiant, Entrust, and Volium Flexi. If you are not finding these options for beet armyworm on tomatoes in your Veg Guide, then buy a current Guide.