Yellow loosestrife is a perennial flowering plant that produces tall spikes of yellow flowers in June, lasting through the end of July. Also known as creeping Jenny, it is the favorite meal of the grass sawfly's larvae. Light-colored worms with brown heads and large black eyes, the larvae measure just over 1 inch in length. Pest management experts at the University of Illinois claim that, because the grass sawfly larvae have more than five sets of legs, they are not considered caterpillars, so caterpillar controls are useless against this worm. Products containing Sevin, carbaryl or anything labeled as a “pyrethroid” will manage an infestation.
Fill the sprayer's tank with half the amount of water listed on the chemical's label.
Add the chemical to the tank, swirling as you pour it in. If the product is a powder or crystal, you may need to stir it until it is thoroughly dissolved.
Spray the yellow loosestrife's foliage until it drips, unless the label recommends otherwise. Swirl the tank as you spray, to keep the product mixed. Keep the spray away from the flowers to avoid damaging the bees that pollinate them.
Repeat the application per the label instructions.