QUESTION:
Can you please give your thoughts towards some basic pest protection for home gardeners here in the Southwest? Between the fat finger-resembling green worms on tomatoes to the smaller caterpillars leaving black frass on the basil leaves, to thoughts on barrier treatments
(deltamethrin granules for soil around the beds & permethrin spray for the beds’ wooden
structural surfaces?), I am a little uncertain how to approach this. Also not sure, since the food is not commercial crop and will instead be consumed by homeowner and residents of the house, if that too opens up other viable treatment methods.
ANSWER:
Since you more or less specify pests on food-bearing plants it does dump this into a sensitive area. Even though this is a home garden and not a commercial crop you still would be considering applying insecticides to plants where something from that plant will later be consumed, so the first consideration is that a product labeled for these plants must be chosen. Then, the label needs to be read and adhered to VERY carefully with respect to the timing of the application. In particular there will be restrictions on how close to “harvest” the application can be made. You also should bring the customers into the decision making process to see if they have any strong thoughts on synthetic versus natural products.
Quite often, for caterpillars on food plants in this small of a garden, it may just be better to rely on a good visual inspection and hand removal of the caterpillars, and to be honest I suggest the customer be drawn into this. For the tomato hornworms you may only have 1 or 2 larvae on the plants, although that couple of big, fat, green larvae can quickly strip all the leaves off a single plant. Providing a “preventive” treatment to the tomatoes may not be feasible, but instead you may be better off waiting until the first damage is noted or the first large fecal pellets seen, and then apply a labeled product. Hand picking one or two sounds like an easy way to resolve it, but I have spent many hours visually checking for them on my own plants and their camouflage is fantastic, making it difficult to do.
So, given the difficulty of knowing exactly when these kinds of larvae are going to appear – or reappear – makes it difficult to do “protective” treatments of the vegetables. Your customer probably would prefer NOT to have a constant presence of insecticide on their plants, but instead prefer that the pests be killed quickly once they show up, and this relies on the customer having some involvement too. Since the caterpillars do not crawl to the plants from somewhere else, but instead come from eggs deposited directly on those plants by the adult moths, making treatments around the beds with residual insecticides will likely do very little to prevent the problem. This may be okay for eliminating some other kinds of crawling plant feeders, but not the caterpillars.
“Natural” insecticide choices when the first evidence of caterpillars is noted could include insecticidal soaps and bacteria, such as Dipel. These work well when applied directly onto the larvae or when eaten by the larvae shortly after the application, and work best on early instars rather than waiting for the caterpillars to get too large.
View past Ask Mr. Pest Control questions.
Pest QuestionsAugust 04, 2012
