Yes, Merit like most other insecticides is dangerous for fish. According to the Merit product label:" Do not apply directly to water, to areas where surface water is present or to intertidal areas below the mean high water mark. Do not contaminate water when disposing of equipment washwaters."
The best time to treat with Merit will depend on the type of insect that you are treating for and the region that you live in. We recommend contacting your local cooperative extension office to ask about insecticide timing for the pests in your region. These offices are an invaluable resource when dealing with pests and most have a master gardener and an entomologist on staff to answer pest insect questions. It is also a great idea to read through the Merit product label as the manufacturer may have provided information on the best time to treat for a particular insect.
Merit 75 WSP is labeled to treat grubs in turgrass and would be safe to use around ornamentals such as roses, but it will not kill the adult insects. Merit 75 WSP is diluted at a rate of one 1.6 oz packet per 300 gallons of water for ornamental treatment. If you only have a few plants, then you may want to consider using a product that is more specifically for roses, such as Bonide Systemic Rose and Flower. Monterey Rose and Flower Spray Plus can be used for adult insects on the plants.
As far as we know there are no known insecticides that will work on Ground Pearl. Ground Pearl is a type of hearty armored scale, and other than natural enemies like ants, no true solution is available. The best solution to try is to reduce plant stress by following recommended fertilizing and irrigation recommendations to enable turfgrass to tolerate the damage. You may also want to contact your local Cooperative Extension office to see if they have any recommendations.
Merit 75 WSP is not labeled for mites. You may be able to use something like Avid 0.15 EC instead.
We would recommend using Domnion 2L. It is labeled for use on trees for emerald ash borers as a preventative and a curative. This only needs to be done once a year. The mixing ratio is 0.1 to 0.2 fl oz per inch of the trunk diameter. This needs to be mixed in at least 5 gallons of water and poured around the roots of the tree.
Merit 75 WSP cannot be diluted in small volume applications. This is a very concentrated product, and it is designed to be used in large volumes of 300 gallons of water per packet for foliar sprays. This product also is not labeled for use on containerized plants, so we cannot recommend this application.
For mealybugs on cacti, you may consider a product containing dinotefuran, such as Safari 20SG. Safari can be used on in-ground plants and containerized plants, and it can be applied as a foliar spray or as a soil drench.
Merit 75 WSP is not labeled to used around citrus trees. We carry Bio Advanced Fruit, Citrus and Vegetable Insect Control which has the same active & can be used on listed citrus trees. We also carry Monterey Fruit Tree & Vegetable Systemic Soil Drench if a bigger size is needed
