Plume Moth – Cool-looking Pest, Not Cool to Your Lisianthus’ Health

Few flowers have the versatility and appeal of lisianthus. Lisianthus has established itself as a flower with strong consumer appeal and is produced by the majority of specialty cut flower growers. We have several growers in southern and central Maryland growing lisianthus as a perennial in overwintering greenhouses.  Besides being easy to grow and market the really nice thing is lisianthus has also been relatively pest free. Keep in mind that whenever something is planted in greater quantities by lots of growers you can expect a pest problem to show up to show up sooner or later.                    

On the first day of spring a grower alerted us to an interesting moth that was found in a greenhouse producing cut flowers. He noticed a small insect that looked a little like a mosquito flying around inside a greenhouse in which lisianthus was growing for the winter.                                 

This odd-looking insect is a plume moth, Platyptilia  sp.  The plume moth holds its narrow wings out at right angles to the body, and moves them up and down erratically.  They are pretty weak fliers.  When disturbed they fly erratically, and relatively short distances. The body is slender and the legs are long. Both the fore and hind wings are divided into lobes, giving the appearance of several pairs of wings. The body is buff to brownish. The hind legs are alternating black and white and there are pairs of spines projecting at the joints in the leg.  The moths are most active just before sunset.                    

The grower commented that he noticed small caterpillars feeding on the flower buds of lisianthus in the fall. Those caterpillars must have pupated in his overwintering greenhouse. The pupae are light green, long and slender and slightly angular.  Adults usually overwinter but pupae can also overwinter.        

There are over 40 species of plume moth found in North America. Two of economic importance are the geranium plume moth, Platyptilia pica and snapdragon plume moth, Platyptilia antirrhina.                     

In the nice warm environment of the March greenhouse the adults were out and flitting about the greenhouse in March. The overwintering lisianthus were just starting to put up new growth. Adult plume moths will find a mate and the females should start to lay eggs singly on foliage or newly forming flower buds
        
Biology                                    

The females will lay eggs on foliage and flower buds and the larvae hatch in 14- 21 days and start feeding. The green, tapered larvae feed for 3 -5 weeks.  They can be recognized by slender, stalk-like prolegs and setae (hairs) with swollen tips.  We found larvae feeding on the outer surface of the foliage but the larvae also bore into leaf tissue and feed as a leafminer, making a splotch-type of dead area on the leaf.  I found several larvae in the center of the plant where leaves overlap protect the caterpillars.  Later instar larvae will tunnel into leaves and flower buds, making them unmarketable. Some will web tip leaves together and feed between the leaf surfaces.  Occasionally larvae will bore into new shoots and in some cases into the base of the plant, causing the plant to collapse.                    

After the grower had made the first insecticide application the larvae on open leaf surfaces were dead but the ones that had webbed the tip growth together survived and were feeding. This might mean that you will need multiple applications to control this pest.
            
Monitoring
    
Look for the presence of the small green larvae. You may notice small, dark fecal pellets excreted by the caterpillars as they feed on the foliage (See photo on page 19). Look for leaves being damaged. Finally, look for the small moth early in the morning when temperatures are cool. The moth does not fly readily when it is cool and this is a good time of the day to look for the adults on foliage or plants.                        

Lisianthus has been pretty much pest free, except for thrips problems, up to now. This plume moth may be a potential problem that growers need to watch for.   Many of you plant out your lisianthus in April. You may want check your plant in May and June. If you’re growing lisianthus outdoors check the foliage for clusters of small caterpillar. Look for them on new, soft succulent leaves. If you are growing geraniums and snapdragons check for adult plume moths in your greenhouse. You do not want this pest to get established.
                      
Control
    
Bacillus thuringiensis (Bt) or Conserve should provide excellent control. If the caterpillars are feeding in a greenhouse, Pylon, a translaminar material, has a label for caterpillar control in greenhouses. This material should get the larvae feeding in leaf folds. It is very important to control the early instar larvae. If the larvae bore into the buds or into the crown of the plant the pesticide will have little impact.                 

The good news is we have materials to deal with this pest. Lisianthus is still a great plant, we just need to keep alert and watch for pest such as the plume moth and control it early before it becomes a major problem.