Inserting an insecticide soak into a watering schedule

[BarryRice]

Hey Guys,

OK, I have mealybugs on my cactus collection (Ariocarpus, Astrophytum, Echinocereus, Gymnocalycium, Echinopsis, Mammillaria, Rebutia, Thelocactus, etc.) I grow the plants in a DG/pumice mix, and fertilize (50ppm of NPK) every watering, which is done on a weekly basis. Since my water is hard as rocks and quite basic, I acidify the water to pH=5.3.

I'm wondering what would be the optimal way to time an insecticidal soil drench (cyfluthrin, imidacloprid, via Bayer Advanced Insect Killer).

Options:

1)Incorporate the insecticide into my fertilizer mix, for a single watering this week.

2)Do a midweek insecticide soil drench.

3)Fertilize one day, insecticide the next day.

4)Skip the fertilization this week--just do the insecticidal treatment.

Opinions? Am I overthinking this?

Cheers

Barry

[CoronaCactus]

They aren't going to complain if they miss a feeding or 2. Use the drench w/o fert. as your weekly watering with one product, then do it again in another 4 weeks with another product with a different active ingredient. This keeps the bugs guessing so they don't get used to the same ingredient each time.

You may want to check ahead on the weather, if it's going to be as hot as it was today (100F+ for me) then you may want to wait until a slightly cooler spell comes through. If it's too hot the plants may take a quick nap and all is for nothing or very little will be absorbed. Although it's still early in the growing season, so they may just push through the heat.

[Peterthecactusguy]

I think that Darryl is correct. Do not fert and do the insecticide soak at the same time. I don't even think I would use the acid either. The rest is sound advice.

[BarryRice]

I intend to just apply insecticide, without fertilizer. I just have to wait for a few days that are below the 100F mark.

There is, potentially, a logic to applying insecticide with fertilizer. In some plants, applying the two together could increase plant growth and, consequently, insecticide uptake. At least, this logic works with herbicides--I'm thinking it might work with pesticides, but that's just hypothesizing.

The pest control specialist here at the UCDavis botanical conservatory tells me that acidifying the water should not have any harmful affects, and that most conflicts with pesticides and pH occur at high pH, not low pH.

Cheers

Barry

[Steve Johnson]

This is a quote from the section on scale in Daiv's pests & disease page:

"...you should treat your plant with a systemic insecticide. This is a poison that the plant will take in through the roots and into the plant tissue making the plant itself poisonous to the insect. For a systemic to work like this, the cactus must be growing and taking in water and nutrients at the time."

Although the section specifically applies to armored scale, mealies are also a type of scale insect. It therefore stands to reason that you should be fertilizing at the same time you're applying the insecticide soil soak. However, I can't tell you about whether it's essential or merely advisable.